Papers for Wednesday, Jul 30 2025

The globular cluster Palomar 5 (Pal 5) is in the process of being tidally shredded as it orbits the Milky Way. Its core is currently at a heliocentric distance of ~21 kpc, near apogalacticon (~18 kpc), and it reaches ~5-7 kpc at perigalacticon. Pal 5's leading and trailing arms stretch over 20 degrees on the sky, making them sensitive probes of the Milky Way's mass distribution. In this work, we search for red giant members of Pal 5 using spectroscopic data from APOGEE DR17 and photometric and astrometric data from Gaia DR3. Based on position and proper motion, we identify eight members of Pal 5: six in the core and two in the stream. The clustering algorithm HDBSCAN finds these same eight. We then use chemical tagging with APOGEE abundances to search for additional members across five APOGEE fields overlapping Pal 5. While several dozen candidates are identified, most deviate (some significantly) from known kinematic and color-magnitude trends, suggesting that they are less likely to be true members. We estimate the expected number of giants in the APOGEE pointings based on the area and stellar mass of the streams. Given APOGEE's limiting magnitude, we find that few, if any, new giants are expected, especially if the stream is more diffuse at these locations. Our results support the presence of density variations in Pal 5's tidal streams, consistent with earlier studies attributing such features to baryonic perturbers in the Milky Way, dark matter subhaloes, or interactions with passing globular clusters.

We report the first CO detection in Leo T, representing the most extreme observation of carbon monoxide molecules in the lowest stellar mass gas-rich dwarf galaxy ($M_{\star}$$\sim$10$^5$ M$_{\odot}$) known to date. We acquired and present new Atacama Compact Array (ACA) $^{12}$CO($J$=1-0) data within our CHIMERA Survey project for the central region of Leo~T, a metal-poor ([M/H]$\sim$-1.7) dwarf in the Milky Way (MW) outskirts. We identified three compact molecular clouds ($<13$ pc) with estimated upper limit virial masses of $M_{\rm mol}$$\sim$5$\times10^{3}$ M$_{\odot}$ each and a total of 1.4$\pm$0.4$\times$10$^{4}$ M$_{\odot}$, corresponding to $\sim\!3\%$ of the total gas mass. We obtained CO-to-H$_2$ conversion factors ($\alpha_{\rm CO}$) as high as $\sim$155 M$_{\odot}$ $({\rm K\, km\, s^{-1}\, pc^2})^{-1}$ and mean molecular gas surface densities of $\Sigma_{\rm mol}$$\sim$9 M$_\odot$ pc$^{-2}$ that are consistent with values found in dwarf galaxies with extremely low metal content. All CO clouds are shifted ($\sim$60 pc) from the stellar population centers, and only one cloud appears within the densest \hi region. Two clouds have velocity offsets with the \hi of $\Delta v_{\rm los}\sim\!+13$ km s$^{-1}$ being within twice the velocity dispersion ($\Delta v_{\rm los}/\sigma_{\rm HI,los}\sim2$) and probably bound. However, the northern cloud is faster ($\Delta v_{\rm los}\sim\!+57$ km s$^{-1}$); our models with low halo masses ($M_{\rm h}\! \lesssim \!10^9$ M$_{\odot}$) result in unbound orbits, suggesting that this material is likely being expelled from the dwarf, providing evidence for molecular gas depletion. These properties reveal a perturbed dynamics intertwined with star formation processes in low-mass dwarf galaxies, supporting a scenario of episodic bursts until they are fully quenched by the MW environment.

The ejection of planets by the instability of planetary systems is a potential source of free-floating planets. We numerically simulate multi-planet systems to study the evolution process, the properties of surviving systems, and the statistics of ejected planets. For systems with only super-Earth planets, we find that the time (in units of the orbital period $P_{1}$ of the innermost planet) for the system to lose the first planet by collision or ejection increases with the semimajor axis of the innermost planet. In contrast, the time (in units of $P_{1}$) for the first close encounter between two planets is identical. These two timescales also depend differently on the orbital spacing between the planets. Most systems with only super-Earths do not have planets ejected. In systems with super-Earths and a cold Jupiter, we discover that a cold Jupiter significantly increases the probability of ejection of the super-Earths by close encounters. Of 38\% of ejected super-Earths, most velocities relative to their parent stars are smaller than $6\ \mathrm{km\ s^{-1}}$. We conservatively estimate that more than 86\% of the surviving two-planet systems in the super-Earths plus cold Jupiter sample are long-term stable by using empirical criteria. Most super-Earths in the remaining two-planet systems are on highly elliptical but stable orbits and have migrated inwards compared with their initial states.

The Neutron Star X-ray binary Sco X-1 is one of the brightest Z-type sources in our Galaxy, showing frequent periods of flaring activity and different types of relativistic outflows. Observations with RXTE have shown that the strongest X-ray variability appears in the transition from/to the flaring state. During this transition, it has been proposed that two particular types of quasi-periodic oscillations might be connected with the ejection of the so-called ultra-relativistic flows. In this paper, we present an analysis of the first NICER observations of Sco X-1 obtained during a multi-wavelenght campaign conducted in February 2019, in order to characterise the properties of QPOs as the system evolves through its various accretion states. We compute a light-curve and a Hardness-Intensity diagram to track the evolution of the source spectral properties, while we investigate the X-ray time variability with a Dynamical Power Density Spectrum. To trace the temporal evolution of QPOs, we segment the dataset into shorter, continuous intervals, and compute and fit the averaged PDS for each interval. Our analysis shows that the overall behaviour of the source is consistent with the literature; strong QPOs around 6 Hz are detected on the normal branch, while transitions to/from the flaring branch -- occurring over timescales of a few hundreds of seconds -- are characterised by rapid, weaker quasi-periodic variability reaching frequencies up to 15 Hz. Despite limited statistical significance, we also identify faint, transient timing features above 20 Hz, occasionally coexisting with the prominent 6 Hz QPOs. Although tentative, the existence of these features in the NICER data is crucial for interpreting the simultaneous radio observations from the same multi-wavelength campaign, potentially reinforcing the connection between the ejection of relativistic outflows and the accretion states in Sco X-1.

Ultra-hot Jupiters showcase extreme atmospheric conditions, including molecular dissociation, ionisation, and significant day-to-night temperature contrasts. Their close proximity to host stars subjects them to intense stellar irradiation, driving high temperatures where hydride ions (H$^-$) significantly contribute to opacity, potentially obscuring metal features in near-infrared transmission spectra. We investigate the atmosphere of WASP-189b, targeting atomic, ionic, and molecular species (H, He, Fe, Ti, V, Mn, Na, Mg, Ca, Cr, Ni, Y, Ba, Sc, Fe$^+$, Ti$^+$, TiO, H$_2$O, CO, and OH), focusing on (i) the role of H$^-$ as a source of continuum opacity, and (ii) the relative hydride-to-Fe abundance using joint optical and near-infrared data. We present two transits of WASP-189b gathered simultaneously in the optical with HARPS and near-infrared with NIRPS, supported by photometric light curves from EulerCam and ExTrA. Transmission spectra were analysed via cross-correlation to detect absorption features and enhance the signal-to-noise ratio. Atmospheric retrievals quantified relative abundances by fitting overall metallicity and proxies for TiO, H$^-$, and e$^-$. Only atomic iron is detected in HARPS data (S/N ~5.5), but not in NIRPS, likely due to H$^-$ continuum dampening. Retrievals on HARPS-only and HARPS+NIRPS suggest the hydride-to-Fe ratio exceeds equilibrium predictions by about 0.5 dex, hinting at strong hydrogen ionisation. Including NIRPS data helps constrain H$^-$ abundance and set an upper limit on free electron density, unconstrained in HARPS-only data. These results emphasise H$^-$ as a significant continuum opacity source impeding detection of planetary absorption features in WASP-189b's near-infrared transmission spectrum.

The Experiment to Detect the Global Epoch of Reionization 21 cm Signal (EDGES) has reported evidence for an absorption feature in the sky-averaged radio background near 78 MHz. A cosmological interpretation of this signal corresponds to absorption of 21 cm photons by neutral hydrogen at $z \sim 17$. The large depth of the signal has been shown to require an excess radio background above the CMB and/or non-standard cooling processes in the IGM. Here, we explore the plausibility of a scenario in which the EDGES signal is back-lit by an excess radio background sourced from a population of radio-loud AGN at high redshift. These AGN could also explain the unexpected abundance of UV-bright objects observed at $z > 10$ by JWST. We find that producing enough radio photons to explain the EDGES depth requires that nearly all high-$z$ UV-bright objects down to $M_{\mathrm{UV}} \gtrsim -15$ are radio-loud AGN and that the UV density of such objects declines by at most 1.5 orders of magnitude between $z = $10 and 20. In addition, the fraction of X-ray photons escaping these objects must be $\lesssim 1\%$ of their expected intrinsic production rate to prevent the absorption signal being washed out by early IGM pre-heating. Reproducing the sharp boundaries of the absorption trough and its flat bottom requires that the UV luminosity function, the fraction of UV light produced by AGN, and the X-ray escape fraction have fine-tuned redshift dependence. We conclude that radio-loud AGN are an unlikely (although physically possible) candidate to explain EDGES because of the extreme physical properties required for them to do so.

We use the Romulus25 cosmological simulation volume to study a large sample of late-type gas-rich galaxies with low central surface brightnesses known as classical low surface brightness (LSB) galaxies and compare them to a mass-matched sample of high surface brightness (HSB) galaxies. We find that classical LSB galaxies make up a substantial fraction of the galaxy population, accounting for ~60% of all central galaxies with 8$\leq$log$_\mathrm{10}$(M$_\star$/M$_\odot$)$\leq$10. In Romulus25, classical LSB galaxies are predominantly formed through major mergers in which the secondary galaxy is co-rotating and aligned with the primary galaxy's gas disk and/or has above average orbital angular momentum at infall. The merger product is a high spin galaxy in which star formation is spread out and inefficient, allowing the galaxy to build up a large supply of relatively unenriched gas. The star formation rates of LSB galaxies are nearly constant over time, leading to stellar populations that are, on average, slightly older and therefore optically redder than those of similar HSB galaxies. However, because LSB galaxies are diffuse and metal-poor, they have very little internal reddening, causing them to appear bluer than HSB galaxies. We also find that, when compared to the bulges of HSB galaxies, the bulges of LSB galaxies are similar in mass, but are lower surface brightness, redder, and more diffuse on average. Despite these differences, classical LSB galaxies are part of the continuum of the galaxy population in Romulus25, constituting one of many evolutionary paths.

Over the last few years, an increasing number of gamma-ray bursts (GRB) have been detected with very high energy (VHE) emission in excess of 100 GeV, with a few cases above 1 TeV. In several instances, synchrotron seed photons do not fully explain the emission observed, suggesting the presence of other seed photon sources to up-scatter. In this work, we consider the kilonova as a source of seed photons for up-scattering in the afterglow. We model the kilonova as a thermal source injecting into the back of a GRB fireball, evolved using a shell model, and with the electron and photon populations updated via a kinetic solver. We find that VHE emission from weaker afterglows, such as those found in short GRBs, can be affected by such seed photons, with the kilonova seed photons mitigating the loss of synchrotron photons on the VHE emission when afterglow parameters are varied. We also find that VHE emission in structured jets, due to weaker synchrotron emission at their wings, can also benefit from this supply of seed photons, especially when viewed off-axis. We apply this model to GRB 170817A, and show that its VHE emission is higher than expected in previous models for the first 100 days, though still below the detection threshold.

mcdust is a parallel simulation code for dust evolution in protoplanetary disks. The code is written in FORTRAN90 and parallelised with OpenMP. The code models dust collisional evolution and transport in the vertical and radial directions. The currently included collisional outcomes are dust growth by sticking, fragmentation of dust particles and erosion, where a small particle chips a portion of the large particle. We employ a representative particle approach to track a limited number of particles instead of tracking every particle, saving computational time. We have a static power-law gas disk with temperature assumed to be vertically isothermal. Dust coagulation depends on the local gas properties, and therefore, we bin particles into grids and perform collisions. We make use of an adaptive grid approach where we make sure that each cell has an equal number of representative particles. This guarantees that there are always sufficient particles to resolve the physics of collisions. The code resolves dust coagulation in 2D(r-z). To access the documentation of the code, see this https URL .

Recent advancements in high-resolution Very Long Baseline Interferometry (VLBI) have significantly improved our understanding of jet collimation near supermassive black holes in active galactic nuclei (AGNs), particularly in high-power systems. However, the collimation properties of jets in low-luminosity AGNs (LLAGNs) remain poorly explored. In this study, we investigate the jet structure of M84, a nearby radio galaxy and a representative LLAGN, to probe jet collimation properties in a low-accretion regime. Utilizing astrometric phase-referencing observations from the Very Long Baseline Array (VLBA), supplemented by archival Very Large Array (VLA) data, we trace the jet geometry of M84 over a broad range of scales, from approximately 10^2 to 10^7 Schwarzschild radii (rs). Our analysis reveals a well-defined transition from a semi-parabolic profile, W(r) proportional to r^0.71, to a conical shape, W(r) proportional to r^1.16, occurring at approximately 1.67 x 10^4 rs. This indicates that the M84 jet is notably less collimated than those in other known LLAGN sources. Our findings provide new insights into the relationship between jet collimation and accretion rate, offering crucial constraints for jet formation models in LLAGNs.

While stellar metallicity has long been known to correlate with planetary properties, the galactic metallicity gradient alone does not account for the trend. It is therefore possible that there exists some time-dependent component to planet occurrence in the Milky Way over Gyr timescales, driven by something other than the metal enrichment of the ISM. In this paper, we investigate the observable effect of a time-dependent planet occurrence rate upon a Kepler-like sample of stars. Using a novel planetary system population synthesis code, psps, we impose several prescriptions for time-variable planet occurrence upon our sample. For this study, we employ a simplistic step function fiducial model for Milky Way planet occurrence, where we vary the time of the step and the planet occurrence rate before and after. We then forward model the expected yield for a synthetic Kepler mission as a function of galactic height, employing the mission's footprint and sensitivity to transits. Finally, we compare the modeled trends to the observed result from the mission itself. We find that, broadly speaking, models in which planet occurrence increased by a factor of several within the past few Gyr can reproduce the occurrence-galactic height trend as-observed; this timing is broadly consistent with the galactic kinematic heating timescale. We consider how varying the functional form of our planet occurrence prescription affects our conclusions. Finally, we consider the physical implications of a seemingly recent increase in planet occurrence on Gyr timescales, as part of a broader conversation about the galactic context for planet formation.

Context. Secular resonances can control the dynamical evolution of near-Earth asteroids (NEAs) and, in some cases, lead to increased orbital stability. Asteroid 622577 Miorita (2014 LU14 ) was the first NEA found by the Isaac Newton Telescope (INT) and exhibits unusual dynamical traits although it approaches Venus, Earth, and Mars at relatively close range. Aims. Here, we investigate the orbital context of Miorita and search for possible dynamical analogs within the NEA population. Methods. We studied the orbital evolution of Miorita using direct N-body calculations. We used the NEOMOD 3 orbital distribution model to verify our conclusions. Observational data were obtained with INT's Wide Field Camera. Results. Miorita is subjected to a von Zeipel-Lidov-Kozai secular resonance, but it is also in a near apsidal resonance, both controlled by Jupiter. We identified a group of dynamical analogs of Miorita that includes 387668 (2002 SZ), 2004 US1 , 299582 (2006 GQ2), and 2018 AC4. Miorita-like orbits can evolve into metastable, low-perihelion trajectories driven by apsidal and von Zeipel-Lidov-Kozai secular resonances like those of 504181 (2006 TC) and 482798 (2013 QK48). Objects in such paths may end up drawn into the Sun. Conclusions. Concurrent secular resonances tend to stabilize the orbits of these asteroids as they are protected against collision with Earth and other inner planets by the resonances. This group signals the existence of an active dynamical pathway capable of inserting NEAs in comet-like orbits. NEOMOD 3 gives a low probability for the existence of NEAs like Miorita, 504181 or 482798.

Triaxial pulsators are a recently discovered group of oscillating stars in close binary systems that show pulsations around three axes at the same time. It has recently been theoretically shown that new types of pulsation modes, the Tidally Tilted Standing (TTS) modes, can arise in such stars. Here, we report the first detection of a quadrupole TTS oscillation mode in the pulsating component of the binary system EL CMi following an analysis of TESS space photometry. Two dipole oscillations around different axes in the orbital plane are present as well. In addition, the binary system is characterized using new radial velocity measurements, phoebe as well as simultaneous spectral energy distribution and light curve modeling. The pulsating primary component has properties typical of a Delta Scuti star but has accreted and is still accreting mass from its Roche Lobe filling companion. The donor star is predicted to evolve into a low-mass helium white dwarf. EL CMi demonstrates the potential of asteroseismic inferences of the structure of stars in close binaries before and after mass transfer and in three spatial dimensions.

Stellar activity variability is one of the main obstacles to the detection of Earth-like planets using the RV method. The aim of this work is to measure the effect of activity in the spectra of M dwarfs and detect activity-sensitive lines in the NIR. We took advantage of the simultaneous observations of HARPS and the newly commissioned NIRPS spectrograph to carry out a blind search of the most activity-sensitive spectral lines in the NIR using NIRPS spectra and known activity indicators in the optical from HARPS as a reference. We analysed the spectra of Proxima (M5.5V) and Gl 581 (M3V), two M dwarfs with different activity levels and internal structures. Spectral lines were identified for both stars and their profiles were fitted using different models. We found hundreds of lines sensitive to activity for both stars; the Proxima spectra were more affected. For Proxima, 32% of the identified lines can be used to measure the rotation period of the star, while for Gl 581 the numbers drops to 1%. The fraction of lines sensitive to activity increases with increasing line depth. A list of 17 lines with rotation period detection for both stars is provided. Stellar activity is able to affect a significant number of spectral lines in the NIR, and methods should be developed to mitigate those effects at the spectral level. The line distortions detected here are expected to come mainly from the flux effect due to temperature contrasts between active regions and the quiet photosphere; however, we cannot rule out the possibility that core-emission from chromospheric activity or Zeeman splitting are also affecting some lines. The new line lists presented here can be used to improve the RV extraction and the detection of RV variability due to stellar activity signals, and to help false positive detection and the modelling of activity variability, thereby enhancing exoplanet detection in the NIR.

With the rise of large radio interferometric telescopes, particularly the SKA, there is a growing demand for computationally efficient image reconstruction techniques. Existing reconstruction methods, such as the CLEAN algorithm or proximal optimisation approaches, are iterative in nature, necessitating a large amount of compute. These methods either provide no uncertainty quantification or require large computational overhead to do so. Learned reconstruction methods have shown promise in providing efficient and high quality reconstruction. In this article we explore the use of generative neural networks that enable efficient approximate sampling of the posterior distribution for high quality reconstructions with uncertainty quantification. Our RI-GAN framework, builds on the regularised conditional generative adversarial network (rcGAN) framework by integrating a gradient U-Net (GU-Net) architecture - a hybrid reconstruction model that embeds the measurement operator directly into the network. This framework uses Wasserstein GANs to improve training stability in combination with regularisation terms that combat mode collapse, which are typical problems for conditional GANs. This approach takes as input the dirty image and the point spread function (PSF) of the observation and provides efficient, high-quality image reconstructions that are robust to varying visibility coverages, generalises to images with an increased dynamic range, and provides informative uncertainty quantification. Our methods provide a significant step toward computationally efficient, scalable, and uncertainty-aware imaging for next-generation radio telescopes.

The Compton Spectrometer and Imager (COSI) is an upcoming NASA Small Explorer satellite mission, designed for all-sky observations in the soft gamma-ray domain with the use of germanium detectors (GeDs). An active Anticoincidence System (ACS) of BGO scintillators surrounds the GeDs to reduce the background and contribute to the detection of transient events. Accurately modeling the ACS performance requires simulating the intricate scintillation processes within the shields, which significantly increases the computational cost. We have encoded these effects into a correction matrix derived from dedicated Geant4 simulations with the inclusion of the optical physics. For this purpose, we use laboratory measurements for the energy and spatial response of the ACS lateral wall to benchmark the simulation and define instrument parameters, including the BGO absorption length and the electronic noise. We demonstrate that the simulations replicate the experimental energy resolution and light collection uniformity along the BGO crystal, with maximum discrepancies of 20% and 10%, respectively. The validated simulations are then used to develop the correction matrix for the lateral wall, accounting for the light collection efficiency and energy resolution based on the position within the crystal. The gamma-ray quantum detection efficiency is also position-dependent via the inclusion of the optical physics. It is enhanced by $\sim$8% close to the SiPMs and suppressed by $\sim$2% in the adjacent corners with respect to the average value. Finally, we explore the energy threshold and resolution of the bottom ACS, considering the impact of its smaller crystals compared with the lateral walls.

Planned and ongoing campaigns for the acquisition of high-quality local measurements of the Galactic magnetic field (GMF) at interstellar cloud locations have generated intense interest in the use of such measurements to accurately backtrack Ultra High-Energy Cosmic Rays (UHECR) through the Milky Way, a crucial aspect of charged-particle astronomy. However, the inherent sparsity of these measurements raises concerns regarding the feasibility of this approach. We assessed the achievable accuracy of UHECR backtracking using mock sparse local GMF data derived from the Jansson & Farrar 2012 (JF12) GMF model and mock UHECR events. We created mock UHECR datasets that trace back within a 3 degree angular range from the galaxy M82 (a hypothesized UHECR source), and we investigated the impact on such backtracking attempts of varying GMF measurement sparsity and of varying GMF strength, which we emulated by rescaling the strength of the ordered components of the JF12 model. We found that: (a) for an average GMF strength of $1\mu G$, satisfactory backtracking results for magnetic rigidities of $10^{20}$ eV can be obtained even with very sparse measurements ($ \sim 1600$ pc); (b) when the average GMF strength is significantly increased ($\sim$ factor of 10) the accuracy of backtracking breaks down at measurement spacings of 400 pc. These findings emphasize on one hand that sparsity is not an automatic deal-breaker for the utility of local GMF measurements in UHECR backtracking. On the other hand, we also confirm that important challenges remain on the path from sparse local GMF measurements to precise charge-particle astronomy, especially in directions of high-strength ordered magnetic fields. This underscores the importance of using all available complementary magnetic field measurements and sophisticated reconstruction techniques to enable accurate backtracking of UHECR.

In arXiv:2505.18900 it was claimed that an apparent evolution of the dark energy equation of state occurs within the standard $\Lambda$CDM cosmological model. I point out that this erroneous conclusion is due to a mathematical error.

Near-infrared high-resolution echelle spectrographs unlock access to fundamental properties of exoplanets, from their atmospheric escape and composition to their orbital architecture, which can all be studied simultaneously from transit observations. We present the first results of the newly commissioned ESO near-infrared spectrograph, NIRPS, from three transits of WASP-69b. We used the RM Revolutions technique to better constrain the orbital architecture of the system. We extracted the high-resolution helium absorption profile to study its spectral shape and temporal variations. Then, we made 3D simulations from the EVE code to fit the helium absorption time series. We measure a slightly misaligned orbit for WASP-69b (psi of 28.7+/-5.7 deg). We confirm the detection of helium with an average excess absorption of 3.17+/-0.05%. The helium absorption is spectrally and temporally resolved, extends to high altitudes and has a strong velocity shift up to -29.5+/-2.5 km/s 50 minutes after egress. EVE simulations put constraints on the mass loss of 2.25 10^11 g/s and hint at reactive chemistry within the cometary-like tail and interaction with the stellar winds that allow the metastable helium to survive longer than expected. Our results suggest that WASP-69b is undergoing a transformative phase in its history, losing mass while evolving on a misaligned orbit. This work shows how combining multiple observational tracers such as orbital architecture, atmospheric escape, and composition, is critical to understand exoplanet demographics and their formation and evolution. We demonstrate that NIRPS can reach precisions similar to HARPS for RM studies, and the high data quality of NIRPS leads to unprecedented atmospheric characterization. The high stability of NIRPS combined with the large GTO available for its consortium, enables in-depth studies of exoplanets as well as large population surveys.

With more than a dozen significant detections, the helium triplet has emerged as a key tracer of evaporating exoplanet atmospheres. This near-infrared feature can be observed from the ground and holds great promise, especially with upcoming observations provided by new-generation instruments such as the Near Infrared Planet Searcher (NIRPS). However, as the helium triplet is also present in stellar spectra, careful removal of the average stellar contribution is necessary to accurately characterize the atmospheres of transiting exoplanets. In this study, we analyze multi-epoch observations of the Sun obtained with NIRPS to investigate the temporal variability of the helium triplet. Our findings reveal significant variability across different timescales, ranging from minutes to days. We identify telluric contamination and stellar activity as likely sources for the short-term and long-term variability, respectively. Importantly, we demonstrate that this variability has minimal impact on the retrieval of planetary parameters crucial to the study of atmospheric escape.

We study the bolometric evolution of the exceptional Type Ic Supernova (SN) 2022jli, aiming to understand the underlying mechanisms responsible for its distinctive double-peaked light curve morphology, extended timescales, and the rapid, steep decline in luminosity observed at around 270 days after the SN discovery. We present a quantitative assessment of two leading models through hydrodynamic radiative simulations: two shells enriched with nickel and a combination of nickel and magnetar power. We explore the parameter space of a model in which the SN is powered by radioactive decay assuming a bimodal nickel distribution. While this setup can reproduce the early light curve properties, it faces problems to explain the prominent second peak. We therefore consider a hybrid scenario with a rapidly rotating magnetar as additional energy source. We find that the observed light curve morphology can be well reproduced by a model combining a magnetar engine and a double-layer $^{56}$Ni distribution. The best-fitting case consist of a magnetar with a spin period of $P\simeq 22$ ms and a bipolar magnetic field strength of $B\simeq 5\times 10^{14}$ G and a radioactive content with total nickel mass of 0.15 M$_\odot$, distributed across two distinct shells within a pre-SN structure of 11 M$_\odot$. To reproduce the abrupt drop in luminosity at $\sim 270$ d, the energy deposition from the magnetar must be rapidly and effectively switched off.

Pulsational pair-instability supernovae (PPISNe) are transient events occurring in progenitor stars with helium cores of approximately 32-65 solar masses, where rapid electron-positron pair production induces pressure loss, collapse, and pulsations driving episodic mass loss. The number, strength, and duration of these pulses can lead to shell collisions that produce shock-powered transients, potentially explaining some of the most luminous events, such as superluminous supernovae, and other rare transients. Rapid progenitor rotation lowers the PPISN mass threshold and influences the dynamics, energetics, and chemical composition of PPISN-driven pulses. In this study, we computed 1D evolutionary models of massive, rotating PPISN progenitor stars with zero-age main-sequence masses of 85-140 solar masses and solar metallicity and 10% solar metallicity. Our analysis reveals strong correlations between PPISN ejected mass and total energy as well as between ejected mass and peak ejected shell velocity. Additionally, moderate correlations indicate that higher initial PPISN progenitor mass leads to greater mass ejection and energy release, while negative correlations show that rapid rotation appears to reduce mass ejection and kinetic energy of the shells. Subsequent pulses lead to hydrogen-poor, carbon- and oxygen-enriched ejected shells, indicating the effect of rotationally-induced chemical mixing in PPISN-driven episodic mass loss with implications for their transients. We model the light curve and synthetic spectra that arise from the collision of two H-poor shells for one of our models using the radiation transport code SuperLite. We find that shock-heated H-poor PPISN shell collisions from rapidly rotating progenitors can lead to moderately luminous H-poor transients that share some similarities with observed SLSN-I events.

Special orientations of the orbital planes may be reminiscent of the specific conditions that triggered and drove the star formation processes and how these are related to local and global Galactic kinematics. For a special sample of 66 extrasolar planets discovered with the microlensing method it is possible to determine the position angle of the planets in the sky relative to their hosts. We test the hypothesis that such orientations are randomly distributed against the possibility that the orbital planes follow some preferential alignment. We find that planets in the Scutum-Centaurus arm show a significant alignment with the Galactic plane, with an isotropic distribution disfavored by a factor of 10. Bulge planets and disk planets outside this major arm are instead compatible with isotropic distributions or show weak alternative preferences at most. Using the method proposed here, the future Roman microlensing survey will be able to identify and quantify preferential orientations in all structures from the Sun to the bulge with high confidence and accuracy.

We report the discovery of activity emanating from (18916) 2000 OG44 (alternately designated 1977 SD), a minor planet previously reported to be both an extinct comet or an asteroid on a cometary orbit. We observed 2000 OG44 with a thin tail oriented towards the coincident anti-solar and anti-motion vectors (as projected on the sky) in images we acquired on UT 2023 July 24 and 26 with the Apache Point Observatory 3.5-meter Astrophysical Research Consortium telescope (New Mexico, USA). We also include observations made in Arizona with the Vatican Advanced Technology Telescope at the Mount Graham International Observatory and the Lowell Observatory Lowell Discovery Telescope near Happy Jack. We performed dynamical simulations that reveal 2000 OG44 most likely originated in the Oort cloud, arriving within the last 4 Myr. We find 2000 OG44, which crosses the orbits of both Jupiter and Mars, is at present on an orbit consistent with a Jupiter-family comet (JFC). We carried out thermodynamical modeling that informed our broader diagnosis that the observed activity is most likely due to volatile sublimation.

The standard approach to searching for gravitational wave signatures in pulsar timing array (PTA) data has been to compare the theoretical Hellings and Downs (HD) curve with the observed correlations in pulsar timing residuals as a function of angular separation on the sky between pulsar pairs. While this approach has successfully produced evidence for the presence of nanohertz-wavelength gravitational waves, it does not, on its own, produce any directional information. It is also insensitive to the polarization of the gravitational waves. An alternative approach is to construct maps of the gravitational wave distribution on the sky. In this paper, we present a simple quadratic estimator of the gravitational wave power as a function of direction on the sky that is sensitive to the polarization state of the wave. In this way, we describe the full, $S_2 \times S_2$, state-space of a polarized gravitational wave background across the sky and the Poincaré sphere describing polarization. A natural question arises from this perspective: what is the resolution of a polarized sky-map, i.e. effectively how many independent pixels can a such a map contain? In other words, how many distinct gravitational waves can a PTA, in principle, distinguish? It turns out the answer is finite, and is approximately $N_{\rm res} = 16 \times 2 = 32$, where 16 is the number of resolvable sky-positions and 2 is the number of distinct polarization states. This corresponds to an angular resolution of $58^\circ$, which can be achieved by a PTA with more than $N_{\rm pulsar} \gtrsim 20$ pulsars. We demonstrate that the variance of the map is equivalent to the HD significance, while for a single point source, a 3-$\sigma$ HD signal corresponds to a 5.2-$\sigma$ map significance.

We have initiated a large project on identifying the requirements for developing a realistic and ground-up approach to simulating the formation of terrestrial planets in our solar system. As the first phase of this project, we present here the criteria that any model of planetesimal growth needs to fulfill in order to be self-consistent and produce reliable results. We demonstrate how these criteria emerge by revisiting runaway growth and carrying out a thorough analysis of its results. As our goal is to identify the pathway to a realistic model, we focus analysis on simulations where at the beginning, planetesimals are not artificially enlarged. We show how using uninflated planetesimals, as the first requirement for a realistic model, will result in a set of criteria naturally emerging from the evolution of the system. For instance, the growth times in simulations with uninflated planetesimals become comparable to the time of giant planet formation implying that any realistic simulation of planetesimal growth, in addition to using real-size planetesimals, needs to include the perturbation of the growing giant planets as well. Our analysis also points to a strong connection between the initial distribution of planetesimals and the final outcome. For instance, due to their natural expansion, initially isolated distributions, or a collection of initially isolated distributions, such as rings of planetesimals, do not produce reliable results. In a self-consistent and realistic model, where the initial conditions are supported by basic principles and do not include simplifying, ad hoc assumptions, the entire disk of planetesimals has to be simulated at once. We present the results of our analyses and discuss their implied criteria.

The interstellar object 3I/ATLAS is expected to arrive at a distance of $53.56(\pm 0.45)$ million ${\rm km}$ ($0.358\pm 0.003$~au) from Jupiter on March 16, 2026. We show that applying a total thrust $\Delta$V of $2.6755{\rm km~s^{-1}}$ to lower perijove on September 9, 2025 and then execute a Jupiter Oberth Maneuver, can bring the Juno spacecraft from its orbit around Jupiter to intercept the path of 3I/ATLAS on March 14, 2026. A close fly-by might be able to probe the nature of 3I/ATLAS far better than telescopes on Earth.

The James Webb Space Telescope has discovered high luminosity galaxies that appear to be "too many" and "too massive" compared to predictions of the Standard LCDM cosmology, suggesting that star formation in the early universe is more rapid than previously anticipated. In this paper we examine in detail the following three effects which can instead provide alternative explanations for these observations: (1) a "top heavy" initial mass function (IMF) for the stars, (2) a variety of star formation histories (constant, exponentially decreasing, and peaked star formation rates), and (3) a variety of initial metallicities. Due to any of these three effects, galaxies of a given luminosity in JWST may be interpreted as having a larger stellar mass than they actually do. Our results are obtained using the Pegase stellar population code, and are presented as the ratio of the modified star formation efficiency relative to the fiducial one (which uses a Salpeter IMF and constant star formation rate). As an example, if the high-mass end of the IMF goes as $M^{-1.35}$, the star formation efficiency and inferred stellar galactic mass could be lower by a factor of $\sim 10$ than in the fiducial case. Our examination (keeping the star formation rate constant) of a top-heavy IMF with slope $\alpha$ leads to a simple relation that is a good approximation to the numerical results, $\epsilon(\alpha) \approx \epsilon_{\rm fid}e^{2.66(\alpha -2.35)}$. Since there are more low mass galaxies than high mass galaxies, these effects may result in a large number of seemingly overly massive galaxies compared to the expectations. Thus, the effects studied in this paper may explain both puzzling observations regarding high luminosity galaxies in JWST: the apparently overly massive galaxies as well as the profusion of apparently high mass galaxies.

We determine optimal requirements for the joint detection of habitable-zone planets and cold giant planets with the Habitable Worlds Observatory (HWO). Analysis of 164 nearby stars shows that a coronagraph outer working angle (OWA) of 1440 milliarcseconds (mas) is necessary to achieve 80-90% visibility of cold giants. Approximately 40 precursor radial velocity measurements with 1 m/s precision are required to adequately constrain orbital parameters before HWO observations. We demonstrate that 6-8 astrometric measurements distributed across the mission timeline, compared to radial velocity constraints alone and to astrometry constraints alone, significantly improve orbital parameter precision, enabling direct determination of orbital inclination with uncertainties of 0.8-3 degrees. For habitable-zone planet characterization, 4-5 epochs provide moderate confidence, while high-confidence (95%) confirmation requires 8+ observations. These specifications are essential for the comprehensive characterization of planetary system architectures and understanding the potential habitability of terrestrial exoplanets.

The physical origins of double-peaked narrow emission-line spaxels (DPSs) in barred galaxies are explored through the analysis of a sample of 72 barred double-peaked emission-line galaxies (DPGs) extracted from the MaNGA dataset. In this study, we examine two potential scenarios: the gas inflow along the bar and the formation of a bar-induced gaseous nuclear ring. By applying a classical galactic dynamics model, we calculate the radii and rotational velocities of the nuclear rings for all barred DPGs, and compare them with the observed properties of their DPSs. Our analysis reveals a significant correlation between the predicted radii of the nuclear rings and the maximum centric distances of the DPSs, as well as a marginal correlation between the predicted rotational velocities of the nuclear rings and the observed maximum velocity differences of the DPSs. These findings provide strong evidence to support the hypothesis that the DPSs of a barred DPG in MaNGA primarily originate from the convolution of the PSF effect with its bar-induced fast-rotating gaseous nuclear ring.

We present maps of the mean metallicity distributions on the Galactocentric $R$--$Z$ plane at different azimuthal angles using red clump stars selected from the LAMOST and APOGEE surveys. In the inner disk ($R < $ 11\,kpc), the metallicity distribution is symmetric between the upper and lower disk. However, we find a North-South metallicity asymmetry in the outer disk ($R > 11$\,kpc), especially towards the anti-Galactic center ($-5^\circ < \Phi < 15^\circ$) direction. By further dissecting the map in age space, we detect this asymmetry across all mono-age stellar populations. However, the asymmetry is less pronounced in older populations ($\tau > 8$ Gyr) compared to younger ones ($\tau < 6$\,Gyr). This reduced significance likely stems from three factors: larger age uncertainties, fewer stars in the outer disk, and the kinematically hotter nature of older populations. The observed metallicity asymmetry may be the consequence of the purturbation of the recent pericentric passage through the Galactic disk and tidal force of the well-known Sagittarius dwarf galaxy.

Although the debate about the systematic errors of DESI DR1 is still open, recent DESI DR2 is consistent with DESI DR1 and further strengthens the results of DESI DR1. In this analysis, we present a $\sim 2.38 \sigma$ discrepancy between Planck $\Lambda$ CDM cosmology and the DESI DR2 Luminous Red Galaxy (LRG1) data at $z_{\text{eff}} = 0.51$, which predicts an unexpectedly large value for $\Omega_m$, $\Omega_m = 0.471^{+0.119}_{-0.065}$. We find that the $w_0 w_a$CDM model, using DESI DR2 data, suggests $w_0 > 1$, indicating a deviation from the standard $\Lambda$CDM paradigm, where is strictly $w_0 = -1$. Additionally, the DESI DR2 data reveals that the value of $\Omega_m$ fluctuates at the 2.97 $\sigma$ level as redshift bin increases, particularly within the $\Lambda$CDM paradigm. The DESI DR2 LRG1 data at $z_{\text{eff}} = 0.51$ seem to contradict the results from Type Ia supernovae in the same redshift range. However, it is expected that this discrepancy will become less significant with future DESI data releases, and the trend for $\Omega_m$ is expected to continue to increase as higher redshifts are considered. The statistical significance of this trend was approximately $1.8 \sigma$ when only the DESI DR1 data was considered, but, in the light of DESI DR2 data, the significance has decreased to about $0.52 \sigma$. Despite this reduction, the trend showing an increase in $\Omega_m$ with higher redshifts remains, though with less statistical confidence. This highlights the importance of understanding why the DESI LRG1 data at $z_{\text{eff}} = 0.51$ appear to be an outlier in the determination of $\Omega_m$.

The Quintuplet cluster, located in the Galactic centre, is one of the few young massive clusters in the Milky Way. It allows us to study dozens of massive, post main sequence stars individually, providing unique insights into the properties of the most massive stars. Our goal is to study the radio continuum emission of the most massive stars in the cluster. We carried out a total of nine observations (three in the C- and six in the X-band) of the Quintuplet cluster with the Karl G. Jansky Very Large Array in A-configuration. We cross-matched the detected sources with infrared stellar catalogues to ensure cluster membership, calculated their spectral indices, quantified variability, and inferred clumping-scaled mass-loss rates We present the most complete catalogue of radio stars in the Quintuplet cluster to date, with a total of 41 detections, and the deepest images of the cluster in the 4 to 12 GHz range (reaching an rms noise level of $2.3\, \mu\mathrm{Jy/beam}$ in the X-band). The six year baseline of our observations allowed us to perform a robust variability assessment, finding that around $60\%$ of the Quintuplet radio-stars are variable on timescales of months to years. We derived the spectral indices of 28 out of the 41 sources. Based on their spectral indices and variability, we classify 11 of them as colliding-wind binaries, seven as strictly thermal sources, and ten as ambiguous. Including the ambiguous sources, we estimate a multiplicity fraction of ($75\pm22\%$). We also computed upper limits for the mass-loss rates of the thermal radio-stars, finding them in agreement with typical values for WNh and WC stars. Finally, we compare these results to the ones obtained from our analogous study of the Arches cluster.

AstroPix is a novel high-voltage CMOS active pixel sensor being developed for a next generation gamma-ray space telescope, AMEGO-X. To meet AMEGO-X instrument requirements, AstroPix must achieve full depletion of its $500~\rm{\mu m}$ thick, $500~\rm{\mu m}$-pitch pixels. It must be sensitive to gamma rays in the range of $25-700$ keV, with the energy resolution at 122 keV of $<10$%. Furthermore, given the space-based nature of AMEGO-X, the power consumption of AstroPix needs to be lower than $1.5~\rm{mW/{cm}^2}$. We report the gamma-ray response of the latest version of AstroPix, AstroPix4. The chip contains $16\times 13$ array of $500~\rm{\mu m}$-pitch pixels. The power consumption is estimated to be about $2~\rm{mW/{cm}^2}$, which is approximately half the power of the previous AstroPix version. The input capacitance is reduced, allowing for the detection of the 14 keV photopeak from $\rm{^{57}Co}$ and a moderate energy resolution of 14% at 122 keV. The dynamic range is estimated to be in the range from 14 keV to $\sim250$ keV. We found that the sensor depletion layer expands as expected and the measured depletion depth is approximately $90~\rm{\mu m}$ when biased at $-240$ V.

We present and discuss optical emission line properties obtained from the analysis of Sloan Digital Sky Survey (SDSS) spectra for an X-ray selected sample of 3684 galaxies (0.002 < z < 0.55), drawn from the eRASS1 catalog. We modeled SDSS-V DR19 spectra using the NBursts full spectrum fitting technique with E-MILES simple stellar populations (SSP) models and emission line templates to decompose broad and narrow emission line components for correlation with X-ray properties. We place the galaxies on the Baldwin-Phillips-Terlevich (BPT) diagram to diagnose their dominant excitation mechanism. We show that the consistent use of the narrow component fluxes shifts most galaxies systematically and significantly upward to the active galactic nuclei (AGN) region on the BPT diagram. On this basis, we confirm the dependence between a galaxys position on the BPT diagram and its (0.2-2.3 keV) X-ray/H$\alpha$ flux ratio. We also verified the correlation between X-ray luminosity and emission line luminosities of the narrow [O\iii]$\lambda 5007$ and broad H$\alpha$ component; as well as the relations between the Supermassive Black Hole (SMBH) mass, the X-ray luminosity, and the velocity dispersion of the stellar component ($\sigma_{*}$) on the base on the unique sample of optical spectroscopic follow-up of X-ray sources detected by eROSITA. These results highlight the importance of emission line decomposition in AGN classification and refine the connection between X-ray emission and optical emission line properties in galaxies.

We investigate the polycyclic aromatic hydrocarbon (PAH) emission features of T Cha, a G8-type T Tauri star that has exhibited "seesaw"-type mid-infrared continuum variability over nearly two decades due to the destruction of the disk's inner wall, using JWST/MIRI and Spitzer observations. We report the first detection of weak PAH emission at 6.2, 7.7, and 8.6 microns in the Spitzer/IRS spectrum from 2005. The inner wall destruction in the 2022 JWST epoch allowed more ultraviolet photons to reach the outer disk, increasing the flux levels of PAH bands and enabling their detection well above the continuum. The 11.2 micron PAH flux increases by a factor of three, yet its profile shape remains remarkably stable. The 6.2/11.2 micron flux ratio has increased, but the charge state of the PAH population remains 75% neutral. The PAH features exhibit a "class C" spectral profile, with redshifted peaks and broadened wings consistent with emission from low-mass T Tauri disks. A weak 12.7/11.2 micron ratio points to a lower abundance of duo- and trio-hydrogen modes, implying a predominantly zigzag carbon structure. A faint "class A" sub-component in the 6.2 and 7.7 micron bands may indicate additional PAH processing by ultraviolet radiation from accretion hotspots. Placement on PAH charge-size grids locates T Cha in the low-ionisation, small-size regime (NC <= 30), signifying a largely neutral PAH population across multiple epochs spanning 18 years. Through multi-epoch, high-resolution data from JWST and Spitzer, we identify T Cha as a benchmark source for probing disk evolution and PAH processing, emphasizing the potential of temporal monitoring with JWST.

Coronal holes (CHs) are widely considered as the main sources of high-speed solar wind streams. We validate this thesis comparing the smoothed time series of solar wind speed measured by Advanced Composition Explorer (ACE) and various indices of CH areas constructed from the CH catalog compiled at the Kislovodsk Mountain Astronomical Station for the period 2010-2025. The main result is that we find specific indices of CH areas that give a strong correlation with smoothed solar wind speed variations. As an example, 1-year averaged areas of CHs located within 30 degrees of the solar equator yield a correlation of 0.9 with 1-year averaged solar wind speed. This strong correlation is a feature of the particular CH catalog, and considering an alternative CH catalog obtained using the Spatial Possibilistic Clustering Algorithm (SPoCA) from the Heliophysics Event Knowledgebase (HEK), the same index provides a correlation of only 0.3. Although the fact that the correlation significantly depends on the catalog requires a separate discussion, we conclude that if some of the catalogs can be used to construct a reliable indicator of solar wind speed variations, then this methodology should be maintained further. Additionally, we present time-latitude diagrams of rolling correlation between CHs areas and solar wind speed, which, in our opinion, can be used to reveal source CHs for high-speed solar wind streams.

We investigate the evolution of spectral energy distribution (SED) and underlying electron energy distribution (EED) by modeling the nearly simultaneous broadband spectra of selected bright 4FGL blazars, in the context of a combined cooling and stochastic acceleration scenario. We find that one-zone leptonic model with log-parabolic (LP) EED can successfully fit the GeV-TeV emission of blazars. The synchrotron frequency $\nu_s$ of blazars mainly evolves due to variation of electron peak energy $\gamma_{3p}$. The BL Lac objects (BL Lacs) show a negative trend in the $\nu_s- \nu_s L_s$ SED plane, known as blazar sequence, that does not seem to be an artifact of Doppler boosting, but driven by the equipartition constraints. A positive correlation is found between the derived magnetic field $B$ and electron density $n_e$, whereas $n_e$ and $\gamma_{3p}$ negatively relate, as expected in an equipartition scenario. The flat spectrum radio quasars (FSRQs) deviate significantly from such a scenario, indicating their jet parameters should be varying independently. The synchrotron peak frequency $\nu_s$ and its spectral curvature $b_s$ negatively correlate for all blazars, confirming the stochastic particle acceleration in blazar jets. However, blazars do not show the signature of hard-sphere acceleration, indicating that magnetic turbulence in the jets might be soft and physical conditions might be near to steady state, consistent with equipartition. Furthermore, for BL Lacs, the SED curvature $b_s$ and the EED curvature $r$ and nearly meet the theoretical relationship $r=5b_s$, whereas the FSRQs show large deviation due to poor constrain on $b_s$ due to presence of thermal component.

Colliding wind binaries (CWBs) are promising sources of high-energy gamma-ray emission driven by shock acceleration of particles at wind interaction zones. The nearby CWB system $\gamma^2$ Velorum (WR 11), composed of a Wolf-Rayet (WR) and an O-star, has been recently associated with GeV gamma-ray emission observed by Fermi-LAT, including evidence of orbital variability. This offers a valuable opportunity to test models of phase-dependent hadronic emission and absorption in CWBs. We aim to explain both the spectral energy distribution (SED) and orbital variability of gamma-ray emission from $\gamma^2$ Velorum using a physically motivated phase-dependent hadronic model. We consider the injection of accelerated relativistic protons based on the WR wind's kinetic energy intercepted at the wind collision region (WCR), and calculate the resulting phase-dependent hadronic gamma-ray emission assuming a proton conversion efficiency $\eta_p$ and accounting for energy-dependent diffusion, advection, conical shock interception and the evolution of the effective acceleration volume, assumed to scale with the WCR, with the orbital phase. Gamma-ray emission from hadronic interactions is attenuated by $\gamma$ - $\gamma$ absorption, calculated via full angular integration over both stellar photon fields. Our model successfully reproduces the observed SED and is consistent with the apastron-to-periastron flux ratio, resulting in a dip in emission at periastron passage and an increase during apastron. Our findings support the conclusion that the observed orbital modulation is primarily driven by geometric variations of the WCR. This underscores the significant influence of evolving orbital geometry on the high-energy gamma-ray light curves of $\gamma^2$ Velorum.

It has remained challenging to reliably identify sub-parsec supermassive black hole binaries (SMBHBs), despite them being expected to be ubiquitous. We propose a new method using multi-band continuum reverberation mapping to identify low-mass-ratio SMBHBs in active galactic nuclei. The basic principle is that, due to the presence of a low-density cavity between the mini-disks and the circumbinary disk, the continuum emissions show a deficit at certain wavelengths, leading to a distinguishing feature in the relation between the inter-band time lag and wavelengths $\tau(\lambda)$. Specifically, the relation appears flat at short wavelengths because of the truncated sizes of the mini-disks and transits to a power law $\lambda^{4/3}$ at long wavelength stemming from the circumbinary disk. This transition feature is distinct from the uniform relation $\lambda^{4/3}$ of the standard accretion disk around a single black hole. Using the lamp-post scenario and assuming that only the secondary black hole is active in a low-mass-ratio SMBHB, we design a simple continuum reverberation model to calculate the transfer function of the accretion disks and the resulting $\tau(\lambda)$ relations for various SMBHB orbital parameters. The transition wavelength typically can lie at UV/optical bands, mainly depending on the total mass and orbital separation of the SMBHB. We apply our SMBHB model to the intensive multiwavelength monitoring data of the SMBHB candidate PG1302-102 and find that the SMBHB model can reproduce the inter-band time lags. Remarkably, the inferred total mass and orbital period from the SMBHB fitting are consistent with values derived from other independent methods.

We explore the possibility of retrieving cosmological information from 21-cm tomographic data at intermediate redshift. The first step in our approach consists of training an encoder, composed of several three dimensional convolutional layers, to cast the neutral hydrogen 3D data into a lower dimension latent space. Once pre-trained, the featurizer is able to generate 3D grid representations which, in turn, will be mapped onto cosmology ($\Omega_{\rm m}$, $\sigma_{8}$) via likelihood-free inference. For the latter, which is framed as a density estimation problem, we consider a Bayesian approximation method which exploits the capacity of Masked Autoregressive Flow to estimate the posterior. It is found that the representations learned by the deep encoder are separable in latent space. Results show that the neural density estimator, trained on the latent codes, is able to constrain cosmology with a precision of $R^2 \ge 0.91$ on all parameters and that most of the ground truth of the instances in the test set fall within $1\sigma$ uncertainty. It is established that the posterior uncertainty from the density estimator is reasonably calibrated. We also investigate the robustness of the feature extractor by using it to compress out-of-distribution dataset, that is either from a different simulation or from the same simulation but at different redshift. We find that, while trained on the latent codes corresponding to different types of out-of-distribution dataset, the probabilistic model is still reasonably capable of constraining cosmology, with $R^2 \ge 0.80$ in general. This highlights both the predictive power of the density estimator considered in this work and the meaningfulness of the latent codes retrieved by the encoder. We believe that the approach prescribed in this proof of concept will be of great use when analyzing 21-cm data from various surveys in the near future.

Comet C/2020 F3 (NEOWISE) was the brightest comet in the northern hemisphere since C/1995 O1 (Hale-Bopp), providing a unique opportunity to study its composition and spatial distribution of emissions. We conducted narrow-band photometry and long-slit low-resolution spectroscopy to monitor the comet's activity and compositional evolution over several weeks post-perihelion. Narrow-band images (OH, NH, CN, C$_2$, C$_3$, BC, GC, RC) and broad-band images (B, V, Rc, Ic) were acquired with TRAPPIST-North between 22 July and 10 September 2020 to derive production rates, mixing ratios, and dust proxy (Af$\rho$). A long-slit spectrum obtained on 24 July 2020 with HFOSC on the 2-m HCT was used to analyse emission profiles along the sunward and anti-sunward directions. We report production rates and mixing ratios of OH, NH, CN, C$_2$, C$_3$, and NH$_2$, and derive the water production rate using forbidden oxygen line flux. Ionic emissions from N$_2^+$, CO$^+$, CO$_2^+$, and H$_2$O$^+$ were detected at 4$\times$10$^4$ to 1$\times$10$^5$ km from the nucleus in the tailward direction. The average N$_2^+$/CO$^+$ ratio was found to be (3.0 $\pm$ 1.0)$\times$10$^{-2}$, refined to (4.8 $\pm$ 2.4)$\times$10$^{-2}$ using fluorescence modeling. The CO$_2^+$/CO$^+$ ratio was measured to be 1.34 $\pm$ 0.21. These results suggest the comet likely formed in the cold mid-to-outer solar nebula (approx. 50-70 K). Additionally, the average rotation period was estimated as 7.28 $\pm$ 0.79 hours, with a CN outflow velocity of 2.40 $\pm$ 0.25 km/s

Cygnus X-3 is the only known Galactic high-mass X-ray binary with a Wolf-Rayet companion. Recent X-ray polarimetry results with the Imaging X-ray Polarimetry Explorer have revealed it as a concealed ultraluminous X-ray source. It is also the first source where pronounced orbital variability of X-ray polarization has been detected -- notably with only one polarization maximum per orbit. Polarization caused by scattering of the source X-rays can only be orbitally variable if the scattering angles change throughout the orbit. Since this requires an asymmetrically distributed medium around the compact object, the observed variability traces the intrabinary structures. The single-peaked profile further imposes constraints on the possible geometry of the surrounding medium. Therefore, the X-ray polarization of Cygnus X-3 is the first opportunity to study the wind structures of high-mass X-ray binaries in detail. We aim to uncover the underlying geometry through analytical modeling of the polarized variability. Knowledge of these structures could be extended to other sources with similar wind-binary interactions. We study the variability caused by single scattering in the intrabinary bow shock, exploring both the optically thin and optically thick limits. We consider two geometries of the reflecting medium, the axisymmetric parabolic bow shock and the parabolic cylinder shock, and determine the geometry that best matches the X-ray polarimetric data. We find that the peculiar properties of the data can only be replicated with a cylindrical bow shock with asymmetry across the shock centerline and significant optical depth. This geometry is comparable to shocks formed by the jet-wind or outflow-wind interactions. The position angle of the orbital axis is slightly misaligned from the orientation of the radio jet in all our model fits.

This paper presents a novel method for real-time nighttime cloud detection, tracking, and prediction using all-sky cameras, aimed at enhancing the efficiency of ground-based robotic telescopes. Ground-based telescopes are vulnerable to adverse weather conditions, particularly cloud cover, which can lead to the loss of valuable observation time and potential damage to the telescope. Existing methods for cloud detection have limitations in accuracy, particularly under varying illumination conditions such as gibbous moon phases. To address these challenges, we developed an algorithm that uses the temporal incoherence of image sequences from all-sky cameras. The method computes difference images to highlight moving cloud structures, applies Otsu thresholding to generate binary cloud maps, and uses mathematical morphology techniques to reduce noise from bright stars and other artifacts. Segmented cloud regions are then tracked across successive frames, allowing estimation of a velocity vector and enabling short-term predictions of cloud movement. Our approach achieves reliable cloud detection and tracking, providing predictions up to 15 minutes into the future - a capability critical for robotic telescopes that rely on look-ahead scheduling. The system was validated against extensive historical data from the Liverpool Telescope's Skycam A and T systems, achieving a false positive rate of approximately 1% and a similar false negative rate, depending on cloud thickness and speed. By improving cloud forecasting and observational scheduling, the system offers a valuable tool for enhancing the operational reliability of robotic telescopes.

This paper presents constraints on the cosmological density of baryons from a systematic search for O VII and O VIII absorption lines in the XMM-Newton and Chandra X-ray spectra of 51 background sources. The search is based on far ultra-violet redshift priors from HST and FUSE, and it has resulted in the identification of 34 possible O VII and O VIII absorption-line systems at the 99% confidence level, out of a search in 1,224 systems with fixed redshift priors. Of these, 7 O VII and 8 O VIII systems pass additional screening criteria and are deemed to be associated with the warm-hot intergalactic medium (WHIM). We find that the cosmological baryon density associated with these possible detections is consistent with the value required to solve the missing baryons problem. Specifically, we find that $\Omega_{WHIM,X} /\Omega_b = 0.83\pm^{3.99}_{0.62}$ from the O VII lines, at the 68% level of confidence (assuming 20% Solar abundances and 100% ionization fraction), or separately $\Omega_{WHIM,X} /\Omega_b = 0.79\pm^{3.08}_{0.50}$ from the O VIII lines (assuming 20% Solar abundances 50% ionization fraction). We also conducted an extensive analysis of systematic errors affecting these estimates, and provided evidence of the association between the detected X-ray absorption line systems with known filaments of SDSS galaxies. The results of this analysis therefore contributes to the characterization of the missing baryons and it indicates that they are in fact associated with the high-temperature portion of the warm-hot intergalactic medium, and possibly with large-scale WHIM filaments traced by galaxies, as consistently predicted by numerical simulations and by other independent probes.

We obtained 420 high-resolution spectra of Proxima, over 159 nights, using the Near Infra Red Planet Searcher (NIRPS). We derived 149 nightly binned radial velocity measurements with a standard deviation of 1.69 m/s and a median uncertainty of 55 cm/s, and performed a joint analysis combining radial velocities, spectroscopic activity indicators, and ground-based photometry, to model the planetary and stellar signals present in the data, applying multi-dimensional Gaussian process regression to model the activity signals. We detect the radial velocity signal of Proxima b in the NIRPS data. All planetary characteristics are consistent with those previously derived using visible light spectrographs. In addition, we find evidence of the presence of the sub-Earth Proxima d in the NIRPS data. When combining the data with the HARPS observations taken simultaneous to NIRPS, we obtain a tentative detection of Proxima d and parameters consistent with those measured with ESPRESSO. By combining the NIRPS data with simultaneously obtained HARPS observations and archival data, we confirm the existence of Proxima d, and demonstrate that its parameters are stable over time and against change of instrument. We refine the planetary parameters of Proxima b and d, and find inconclusive evidence of the signal attributed to Proxima c (P = 1900 d) being present in the data. We measure Proxima b and d to have minimum masses of 1.055 $\pm$ 0.055 Me, and 0.260 $\pm$ 0.038 Me, respectively. Our results show that, in the case of Proxima, NIRPS provides more precise radial velocity data than HARPS, and a more significant detection of the planetary signals. The standard deviation of the residuals of NIRPS after the fit is 80 cm/s, showcasing the potential of NIRPS to measure precise radial velocities in the near-infrared.

The first stars, the chemically pristine Population III, likely played an important role in heating the intergalactic medium during the epoch of cosmic dawn. The very high effective temperatures ($\sim 10^5$ K) predicted for the most massive Population III stars could also give rise to tell-tale signatures in the emission-line spectra of early star clusters or small galaxies dominated by such stars. Important quantities in modelling their observational signatures include their photon production rates at ultraviolet energies at which photons are able to ionize hydrogen and helium, dissociate molecular hydrogen and cause Lyman-$\alpha$ heating. Here, we model the spectral energy distributions of Population III stars to explore how these key quantities are affected by the initial mass and rotation of Population III stars given a wide range of models for the evolution of these stars. Our results indicate that rotating Population III stars that evolve to effective temperatures $\sim 2\times 10^5$ K could potentially give rise to a very strong HeII 1640 emission line in the spectra from primordial star clusters, without requiring stellar masses of $\gtrsim 100\ \mathrm{M}_\odot$ indicated by previous models for non-rotating Population III stars. At the same time, the observable impact on 21-cm signatures from cosmic dawn and epoch of reionization from our set of rotating stars that evolve to $\sim 2\times 10^5$ K are modest, and produce potentially detectable features in the global 21-cm signal and 21-cm power spectrum for high Population III star formation efficiencies only.

The Near-InfraRed Planet Searcher (NIRPS) is a high-resolution, high-stability near-infrared (NIR) spectrograph equipped with an AO system. Installed on the ESO 3.6-m telescope, it was developed to enable radial velocity (RV) measurements of low-mass exoplanets around M dwarfs and to characterise exoplanet atmospheres in the NIR. This paper provides a comprehensive design overview and characterisation of the NIRPS instrument, reporting on its on-sky performance, and presenting its GTO programme. The instrument started its operations on 1 Apr 2023 after intensive on-sky testing phases. The spectral range continuously covers the Y, J, and H bands from 972.4 to 1919.6 nm. The thermal control system maintains 1 mK stability over several months. The NIRPS AO-assisted fibre link improves coupling efficiency and offers a unique high-angular resolution capability with a fibre acceptance of only 0.4 arcsec. A high spectral resolving power of 90 000 and 75 000 is provided in HA and HE modes, respectively. The overall throughput from the top of the atmosphere to the detector peaks at 13 percent. The RV precision, measured on the bright star Proxima with a known exoplanetary system, is 77 cm/s. NIRPS and HARPS can be used simultaneously, offering unprecedented spectral coverage for spectroscopic characterisation and stellar activity mitigation. Modal noise can be aptly mitigated by the implementation of fibre stretchers and AO scanning mode. Initial results confirm that NIRPS opens new possibilities for RV measurements, stellar characterisation, and exoplanet atmosphere studies with high precision and high spectral fidelity. NIRPS demonstrated stable RV precision at the level of 1 m/s over several weeks. The instrument high throughput offers a notable improvement over previous spectrographs, enhancing our ability to detect small exoplanets.

AR Aur is a detached eclipsing binary containing two late-B stars which are chemically peculiar, on a circular orbit of period 4.135 d. The primary is a HgMn star which shows temporal changes in its chemical abundances and spectral line profiles, whilst the secondary is a likely weak Am star. Published analyses of the system have used spectroscopic light ratios to constrain the eclipse models and found that the secondary star is larger than the primary. This unexpected outcome has been taken as an indication that the system is young and the secondary has yet to reach the main sequence. In this work we present the first analysis of the light curve of the system obtained by the Transiting Exoplanet Survey Satellite (TESS), whose quality allows us to avoid using a spectroscopic light ratio to constrain the solution. When combined with literature spectroscopic results we obtain highly precise masses of 2.544 +/- 0.009 Msun and 2.358 +/- 0.009 Msun, and radii of 1.843 +/- 0.002 Rsun and 1.766 +/- 0.003 Rsun. The light ratio is inconsistent with spectroscopic determinations, confirming the suggestion of Takeda (2025) that spectroscopic light ratios of the system are unreliable due the chemical peculiarity of the stars. The properties of the system are matched by theoretical predictions for a slightly super-solar metallicity and an age of 33 +/- 3 Myr: both components are young main-sequence stars.

Short--period ($P<$1 hr orbits) detached double white dwarf binary (DWDB) components identified with transient surveys (e.g. SDSS, ZTF) have hot surface temperatures ($>$10,000 K) and observed radii a factor two larger than completely degenerate white dwarfs. We formulate tidal heating in helium composition extremely low mass white dwarf (ELM WD) components of detached DWDBs which reach mass transfer within a Hubble time. We combine a mass radius relation which varies with surface temperature and the tidal friction model of Hut 1981, where the additional orbital energy loss from tidal friction is accounted for by increases in the primary surface temperature, and hence increasing radius. Applying this heating model to the current sample of binaries with ZTF, we predict temperature increases from the present day of up to $\sim$40\% before the onset of mass transfer. We find that helium white dwarfs are generically hot and large at the onset of mass transfer, even for the oldest DWDBs whose components can cool to be degenerate by the present day. In the population of Galactic DWDBs, we find that the onset of mass transfer should occur at orbital periods as long as 1000s (17 minutes), or binary gravitational wave frequency of 2 mHz. This is over three times longer than periods expected for degenerate WD (5 minutes). Since mass transferring DWDBs are progenitors for a variety of transients and stellar populations e.g. RCrB stars, AM CVn binaries, type .Ia supernova, the finite temperature of donor white dwarfs should be taken into account.

Stellar flares and coronal mass ejections (CMEs) can strip planetary atmospheres, reducing the potential habitability of terrestrial planets. While flares have been observed for decades, stellar CMEs remain elusive. Extreme ultraviolet (EUV) emissions are sensitive to both flares and CME-induced coronal dimming. We assess the detectability of stellar CME-induced EUV dimming events by adapting a known "Sun-as-a-star" dimming technique -- validated by the Solar Dynamics Observatory's EUV Variability Experiment (EVE) -- to stellar conditions. We adapt the solar data to reflect a range of stellar intensities, accounting for intrinsic brightness, distance, and interstellar medium (ISM) attenuation. We generate synthetic light curves for two different missions: the legacy EUV Explorer (EUVE) and the proposed ESCAPE mission. Our results indicate that dimming detections are well within reach. EUVE's broadband imager was capable of detecting stellar CMEs -- albeit with limited spectral (temperature) resolution -- but that was not part of the observing plan. EUVE's spectroscopic survey lacked sufficient sensitivity for CME detections. Optimizing modern instrument design for this task would make the observation fully feasible. In this work, we present a tool to explore the stellar-CME detection parameter space. Our tool shows that an instrument with performance similar to ESCAPE, setting a 600-second integration period, and integrating the spectra into bands, any star with an X-ray flux $\geq 2.51 \times 10^{-12}$ergs$^{-1}$~cm$^{-2}$ should have a $\geq 3\sigma$ detection even for a modest few-percent dimming profile, regardless of ISM attenuation. Such measurements would be crucial for understanding the space weather environments of exoplanet host stars and, ultimately, for evaluating planetary habitability.

We present the first observations of magnetic fields in pre-planetary nebulae (PPNe) made with the POL-2 polarimeter on the James Clerk Maxwell Telescope (JCMT). We observed the PPNe CRL 618 and OH231.8+4.2 in 850 $\mu$m polarized light. In both cases, we observe ordered magnetic fields that appear to arise from dusty circumstellar material that has been swept up by the passage of outflows driven by the central post-Asymptotic Giant Branch (post-AGB) star. CRL 618 shows a magnetic field aligned with one of the most extreme position angles of the outflowing bullets ejected from the central source. We hypothesize that polarized emission in CRL 618 may preferentially arise from material in the walls of the dust cavity opened by the ejected bullets. Conversely, OH231.8+4.2 shows a magnetic field that is aligned approximately perpendicular to the outflow direction, which may preferentially arise from an infrared-bright dense clump embedded near the base of the outflow. Despite CRL 618 being carbon-rich and OH231.8+4.2 being oxygen-rich, there is no significant difference in the polarization fractions of the two sources. This suggests that at linear resolutions $\sim 10^{4}$ au, the complexity of the magnetic field geometry on scales smaller than the beam, rather than grain composition, sets the measured polarization fraction of these sources.

Turbulence and magnetic fields are components of the interstellar medium and are interconnected through plasma processes. In particular, the magnetic flux transport in the presence of magneto-hydrodynamic (MHD) turbulence is an essential factor for understanding star formation. The theory of Reconnection Diffusion (RD), based on statistics of Alfvénic turbulence, predicts a dependence of the diffusion coefficient of the magnetic field on the Alfvénic Mach number $M_A$. However, this theory does not consider the effects of compressibility which are important in the regime of supersonic MHD turbulence. In this work, we measure the diffusion coefficient of magnetic fields in sub-Alfvénic MHD turbulence, with different sonic Mach numbers $M_S$. We perform numerical simulations of forced turbulence in periodic domains from the incompressible limit to the supersonic regime. We introduce two methods to extract the diffusion coefficient, based on the analysis of tracer particles. Our results confirm the RD assumption regarding the correspondence between the diffusion of magnetic field and that of fluid Lagrangian particles. The measured diffusion rate provided by incompressible turbulence agrees with the suppression predicted by the RD theory in the presence of strong magnetic fields: $D \propto M_A^3$. Our simulations also indicate an increase in RD efficiency when the turbulence is compressible. The dependency on $M_A$ and $M_S$ from the simulations can be described by the relation $D \propto M_A^\alpha$, where $\alpha(M_S) \approx 3/(1 + M_S)$. This quantitative characterization of $D$ is critical for modeling star formation in turbulent molecular clouds and evaluating the efficiency of this transport compared to other mechanisms.

Outflows and jets launched from the nuclei of galaxies emit radio synchrotron emission that can be used to study the impact of accretion energy on the host galaxy. The decades-long baseline now enabled by large radio surveys allows us to identify cases where new outflows or jets have been launched. Here, we present the results of a targeted VLA program observing four post-starburst galaxies that have brightened significantly in radio emission over the past ~20 years. We obtain quasi-simultaneous observations in five bands (1-18 GHz) for each source. We find peaked spectral energy distributions, indicative of self-absorbed synchrotron emission. While all four sources have risen significantly over the past ~20 years in the 1-2 GHz band, two also show clear recent flares in the 2-4 GHz band. These sources are less luminous than typical peaked spectrum radio AGN. It remains unclear whether these sources are low luminosity analogs of the peaked radio AGN from accreted gas, or driven by tidal disruption events with missed optical flares. Regardless of the source of the accreted material, these newly-launched outflows contain sufficient energy to drive the molecular gas outflows observed in post-starburst galaxies and to drive turbulence suppressing star formation.

The Lyman-$\alpha$ (Ly$\alpha$) forest is a key tracer of large-scale structure at redshifts z > 2, traditionally studied using spectra of quasars. Here, we explore the viability Lyman Break Galaxies (LBGs) as alternative background sources for Ly$\alpha$ forest studies. We analyze 4,151 Ly$\alpha$ forest skewers extracted from LBG spectra obtained in the DESI pilot surveys in the COSMOS and XMM-LSS fields. We present the first measurement of the Ly$\alpha$ forest auto-correlation function derived exclusively from LBG spectra, probing comoving separations up to 48 $h^{-1}$Mpc at an effective redshift of $z_\mathrm{eff}$ = 2.70. The measured signal is consistent with that from DESI DR2 quasar Ly$\alpha$ forest spectra at a comparable redshift, validating LBGs as reliable background sources. We also measure the cross-correlation between the LBG Ly$\alpha$ forest and 13,362 galaxy positions, showing that this observable serves as a sensitive diagnostic for galaxy redshift uncertainties and systematic offsets. Finally, using synthetic LBG spectra and Fisher forecasts, we show that a future wide-area survey over 5000 deg$^2$, targeting 1000 LBGs per deg$^2$ at similar signal-to-noise than our dataset, could enable Ly$\alpha$ forest baryon acoustic oscillation (BAO) measurements with 0.4% precision on the isotropic BAO scale and 1.3% on the anisotropic (Alcock-Paczynski) scale. Combining BAO with a Ly$\alpha$ forest full-shape analysis improves the AP constraint to 0.6%. These results open a new path for precision cosmology at high redshift using dense LBG samples.

Solar active regions are where sunspots are located and photospheric magnetic fluxes are concentrated, therefore being the sources of energetic eruptions in the solar atmosphere. The detection and statistics of solar active regions have been forefront topics in solar physics. In this study, we developed a solar active region detector (SARD) based on the advanced object detection model YOLOv8. First, we applied image processing techniques including thresholding and morphological operations to 6975 line-of-sight magnetograms from 2010 to 2019 at a cadence of 12~h, obtained by the Helioseismic and Magnetic Imager onboard the Solar Dynamic Observatory. With manual refinement, we labeled 26531 active regions in the dataset for further training and test with the detection model. Without any overlap between the training and test sets, the superior performance of SARD is demonstrated by an average precision rate as high as 94\%. We then performed a statistical analysis on the area and magnetic flux of the detected active regions, both of which yield log-normal distributions. This result sheds light on the underlying complexity and multi-scale nature of solar active regions.

High center-of-mass electromagnetic~(EM) interactions could produce decaying heavy leptons and hadrons, leading to neutrino generation. These processes might occur in the most extreme astrophysical scenarios, potentially altering the expected gamma-ray and neutrino fluxes in both the hadronic and the leptonic pictures. For instance, neutrinos could arise from high-redshift EM cascades, triggered by gamma rays beyond $10^{18} \; \text{eV}$ scattering background photons, from radio to ultraviolet energy bands. Such energetic gamma rays are predicted in cosmogenic models and in scenarios involving non-standard physics. On astrophysical scales, leptonic production of neutrinos could take place in active galactic nuclei cores, where several-TeV gamma rays interact with the X-ray photons from the hot corona. We explore these scenarios within the CRPropa Monte Carlo code framework, developing dedicated tools to account for leptonic production and decay of heavy leptons and hadrons. In particular, the latter are performed by interfacing with the PYTHIA event generator. With these novel tools, we characterise the spectrum and flavour composition of neutrinos emerging from cosmological EM cascades and from leptonic processes in the core of active galactic nuclei. Finally, we investigate the leptonic production of neutrinos in the context of the IceCube detection of NGC~1068.

We compare an autoencoder convolutional neural network (AE-CNN) with a conventional maximum-likelihood estimator (MLE) for inferring cluster virial masses, $M_v$, directly from the galaxy distribution around clusters, without identifying members or interlopers. The AE-CNN is trained on mock galaxy catalogues, whereas the MLE assumes that clusters of similar mass share the same phase-space galaxy profile. Conceptually, the MLE returns an unbiased estimate of $\log M_v$ at fixed true mass, whereas the AE-CNN approximates the posterior mean, so the true $\log M_v$ is unbiased at fixed estimate. Using MDPL2 mock clusters with redshift space number density as input, the AE-CNN attains an rms scatter of $0.10\,\textrm{dex}$ between predicted and true $\log M_v$, compared with $0.16\,\textrm{dex}$ for the MLE. With inputs based on mean peculiar velocities, binned in redshift space or observed distance, the AE-CNN achieves scatters of $0.12\,\textrm{dex}$ and $0.16\,\textrm{dex}$, respectively, despite strong inhomogeneous Malmquist bias.

We have reprocessed the data archived from the Parkes 70-cm pulsar (PKS70) survey with an expanded DM search range and an acceleration search. Our goal was to detect pulsars that might have been missed in the original survey processing. Of the original 43842 pointings, 34869 pointings were archived, along with 440 additional pointings for confirmation or timing. We processed all of these archived data and detected 359 known pulsars: 265 of these were detected in the original survey, while an additional 94 currently known pulsars were detected in our reprocessing. A few among those 94 pulsars are highly accelerated binary pulsars. Furthermore, we detected 5 more pulsars with DMs higher than the original survey thresholds, as well as 6 more pulsars below the nominal survey sensitivity threshold (from the original survey beams with longer integrations). We missed detection of 33 (of the 298) pulsars detected in the original survey, in part because portions of the survey data were missing in the archive and our early stage candidate sifting method. We discovered one new pulsar in the re-analysis, PSR J0540$-$69 which has a spin period of 0.909 s and resides in the Large Magellanic Cloud (LMC). This new pulsar appeared in three PKS70 beams and one additional L-band observation that targeted the LMC pulsar PSR B0540$-$69. The numerous pulsar detections found in our re-analysis and the discovery of a new pulsar in the LMC highlight the value of conducting multiple searches through pulsar datasets.

3I/ATLAS is the third macroscopic interstellar object detected traversing the Solar System. Since its initial discovery on UT 01 July 2025, hundreds of hours on a range of observational facilities have been dedicated to measure the physical properties of this object. These observations have provided astrometry to refine the orbital solution, photometry to measure the color, a rotation period and secular light curve, and spectroscopy to characterize the composition of the coma. Here, we report precovery photometry of 3I/ATLAS as observed with NASA's Transiting Exoplanet Survey Satellite (TESS). 3I/ATLAS was observed nearly continuously by TESS from UT 07 May 2025 to 02 June 2025. We use the shift-stack method to create deep stack images to recover the object. These composite images reveal that 3I/ATLAS has an average TESS magnitude of $T_\textrm{mag} = 19.6 \pm 0.1$ and an absolute visual magnitude of $H_V = 12.5 \pm 0.3$, consistent with magnitudes reported in July 2025, suggesting that 3I/ATLAS may have been active out at $\sim 6.4$ au. Additionally, we extract a $\sim 20$ day light curve and find no statistically significant evidence of a nucleus rotation period. Nevertheless, the data presented here are some of the earliest precovery images of 3I/ATLAS and may be used in conjunction with future observations to constrain the properties of our third interstellar interloper.

PDS 70c is a source of Ha emission and variable sub-mm signal. Understanding its emission mechanisms may enable observations of accretion rates and physical conditions in the circum-planetary environment. We report ALMA observations of PDS 70 at 145 GHz (Band 4), 343.5 GHz (Band 7) and 671 GHz (Band 9) and compare with data at 97.5 GHz (Band 3), taken within two months. The radio spectrum (SED) is analyzed with analytic circumplanetary disk (CPD). In a novel approach we include the free-free continuum from HI, metals (e.g. KI) and H-. New detections in Bands 3 (tentative at 2.6sigma), 4 (5sigma), and 7 (re-detected at 9sigma) are consistent with optically thick thermal emission from PDS 70c (spectral index alpha 2+-0.2). However, a Band 9 non-detection lies 2.6sigma below an optically thick extrapolation. A viscous dusty disk is inconsistent with the data, even with the inclusion of ionised jets. Interestingly, the central temperatures in such CPD models are high enough to ionise HI, with huge emission measures and an optically thick spectrum that marginally accounts for the SED (within 3sigma of Band 9). By contrast, uniform-slab models suggest much lower emission measures to account for the Band 9 drop, with ionisation fractions ~1E-7 , and an outer radius of ~0.1au. Such conditions are recovered if the CPD interacts with a planetary magnetic field, leading to a radially variable viscosity alpha(R)<~1 and central temperatures ~1E3K that regulate metal ionisation. However, the H- opacity still results in an optically thick SED, overshooting Band 9. We find that the optically thin turnover at ~600GHz is only recovered if a thin shocked layer is present at the CPD surface, as suggested by simulations. A photospheric shock or accretion funnels are ruled out as radio emission sources because their small solid angles require T~1e6K, which are unrealistic planetary shock accretion.

Quasar microlensing can be used to constrain important astrophysical properties, such as the accretion disk size and the amount of stars in the lensing galaxy. The associated brightness variations over time, in particular high magnification events (HMEs) and caustic crossings, can yield precise constraints due to their strong dependence on the relative projected velocities of the components and accretion disk size. The next generation of large sky area surveys, such as The Vera Rubin Observatory (LSST) and Euclid, are expected to find and follow-up thousands of lensed quasars from which such events could be identified and observed. In this work we present a characterization and estimation of all HMEs that could potentially be observed, focusing on systems that could be identified by ground based telescopes. From systems whose minimum image separation is at least 1 arcsec, and their second dimmest image is at least 21.5 magnitudes in the i-band ($\sim560$ in the southern or northern sky), we estimate $\sim60$ HMEs with amplitudes $>0.3$ [mag] in the r-band per year. We find that on average, saddle images are approximately four times more likely to host events than minima, and $\sim10\%$ ($\sim50\%$) of events are caustic crossings for saddles (minima). We also find that HMEs in saddle images can have amplitudes $\sim1-2$ [mag] larger than minima.

The nature of dark matter remains one of the most pressing open questions in modern cosmology. Despite extensive experimental efforts, no direct or indirect detection of dark matter particles has been confirmed. This has motivated alternative approaches, including modifications to the underlying theory of gravity. In this work, we investigate the implications of a specific non-local gravity (NLG) theory, which modifies General Relativity by introducing non-local effects that manifest as an effective dark matter component. We analyze the velocity dispersion profiles of eight classical dwarf spheroidal (dSph) galaxies - Carina, Draco, Fornax, Leo I, Leo II, Sculptor, Sextans, and Ursa Minor - to test the predictions of NLG. Using the Jeans equation, we model the kinematics of these galaxies and perform a Bayesian Markov Chain Monte Carlo analysis to constrain the parameters of the NLG kernel chosen for our analysis. Our results indicate that NLG might successfully reproduce the observed kinematics of dSph galaxies without requiring particle dark matter, providing constraints on the scale-dependent modifications to gravity that are compatible with previous studies in the literature. However, a parameter inconsistency remains in the cases of Fornax and Sextans galaxies that requires further attention.

The age determination of symbiotic stars is essential to put further constraints on models explaining these binary systems. In the Galactic field, this is especially problematic because of several limitations due to reddening estimations, for example. We searched for symbiotic stars as members of Galactic open clusters for which the age and overall metallicity can be determined in a statistical sense. The most recent lists of well-established and candidate symbiotic stars and open clusters were matched, and we found seven good candidates from which the well-established symbiotic star CQ Dra seems to be a true member of the old open cluster HSC 1224. The colour-magnitude diagrams for the other candidates raise some doubts about membership.

Axion-like particles (ALPs) provide a compelling avenue for exploring physics beyond the Standard Model. In astrophysical magnetized plasmas an ALP-photon coupling $g_{a\gamma}$ induces energy-dependent oscillations in the photon survival probability that imprint modulations on emission spectra. X-ray observations of bright spectrally-smooth sources can provide particularly sensitive probes of ultralight ALPs with masses $m_a \lesssim 10^{-11}$ eV due to long propagation distances, strong magnetic fields and high photon statistics. We present a comprehensive forecast of ALP-photon conversion in three representative systems: (i) background active galactic nuclei (AGNs) observed through foreground intracluster magnetic fields, (ii) central AGNs within their host cluster halos and (iii) Galactic X-ray binaries viewed through the Milky Way field. Using detailed simulations we assess the prospective sensitivity of high-resolution X-ray missions including XRISM, Athena, and Arcus. For typical magnetic field configurations a 5 Ms XRISM observation of the Perseus Cluster AGN NGC 1275 can reach down to $g_{a\gamma} \sim 3 \times 10^{-13}$ GeV$^{-1}$ at $m_a \lesssim 10^{-12}$ eV, while Athena's superior energy resolution improves this reach by a factor of $\sim 3$. We quantify the impact of magnetic field modeling, photon statistics, and spectral binning strategies. Our results demonstrate the scientific potential of high-resolution X-ray observations to probe photon-ALP coupling in previously inaccessible parameter space, offering a powerful window into physics beyond the Standard Model.

We propose an alternative physical interpretation and formation pathway for the recently discovered "little red dots" (LRDs). We model LRDs as super-massive stars (SMSs) surrounded by massive self-gravitating accretion discs (SMDs) that form as a consequence of gas-rich major galaxy mergers. The model provides an excellent match for numerous spectral features of LRDs, where the V-shape arises from the superposition of two black bodies, and Balmer line broadening is sourced by the intrinsic rotation of the SMD. No additional AGN, stellar wind, dust obscuration or galactic component is required. This results in a model with uniquely few, physically motivated free parameters that are robust to variations in observed LRD properties. We perform MCMC fits for two representative LRD spectra, for which the full parameter posterior distributions are determined. Allowing for a compressed SMS mass-radius relation, the recovered parameters are compatible with sub-Eddington accretion in self-gravitating discs, and the recovered SMS masses of few $ 10^6$ M$_{\odot}$ imply the subsequent formation of massive black holes (BH) that squarely follow the expected BH mass--galaxy mass relation. In addition, the model implies a redshift distribution for LRDs that accurately matches with observations.

Star-forming regions are essential for studying very young stellar objects of various masses. They still contain a significant amount of dust and gas. We present a study of light curves of stars in the field of the Chamaeleon I association. We use automatic spectral classification with MKCLASS to identify the spectral types of the stars in the field with a light curve from the NEOWISE and Gaia surveys. The light curves are analysed using the software Peranso and astropy. We also used VSX to identify the variability type. Based on astrometry, we have identified 92 stars, 73 of which are members of the association. We received light curves for 55 stars from the Gaia survey and for 69 stars from the ALLWISE/NEOWISE survey. For 28 of them, it was possible to determine the types of variables, mostly T Tauri and Orion variables. The spectral types of the members are mostly cooler M-type stars, with one being a possible chemically peculiar (CP) star. The non-members associated with light curve measurements include spectral types A-G with one CP candidate.

Strange quark stars (SQSs), namely compact stars entirely composed of deconfined quark matter, are characterized by similar masses and compactness to neutron stars (NSs) and have been theoretically proposed to exist in the Universe since the 1970s. However, multiwavelength observations of compact stars in the last 50 years have not yet led to an unambiguous SQS identification. This article explores whether SQSs could form in the supernova (SN) explosion of an evolved star (e.g., carbon-oxygen, or Wolf-Rayet) occurring in a binary with the companion being a neutron star (NS). The collapse of the iron core of the evolved star generates a newborn NS and the SN explosion. Part of the ejected matter accretes onto the NS companion as well as onto the newborn NS via matter fallback. The accretion occurs at hypercritical (highly super-Eddington) rates, transferring mass and angular momentum to the stars. We present numerical simulations of this scenario and demonstrate that the density increase in the NS interiors during the accretion process may induce quark matter deconfinement, suggesting the possibility of SQS formation. We discuss the astrophysical conditions under which such a transformation may occur and possible consequences.

The hydrogenation of polycyclic aromatic hydrocarbons (PAHs) is crucial to understanding molecular hydrogenation formation in the interstellar medium. This process also helps to elucidate the weakening of the aromatic bonds in PAHs, which may function as a carbon reservoir. Tunneling can significantly promote the hydrogenation process in a low to moderate temperature range. We present the hydrogenation sequence of the newly observed PAH molecule, indene, and clarify the tunneling rule at temperature in photodissociation region (PDR) and dark molecular cloud conditions. In addition, we report fit parameters to be utilized in astronomical modeling. The hydrogenation sequence was studied using simple hydrogenation rules and confirmed by barriers from density functional theory (DFT). To make our kinetic studies useful to modelers, we implemented a Monte Carlo method based program to generate and optimize random initial fit parameters (alpha, beta, gamma, and T0) to achieve the statistically best fit. We find that indene hydrogenation follows rules similar to those of other PAHs, such as pentacene, coronene, and corannulene, with binding energies for odd numbered hydrogenation steps ranging from 0.5 to 2 eV and barriers around 0.13 eV for the first, fifth, and seventh hydrogenation steps. The third hydrogenation step is the rate limiting step, similar to what is found for other PAHs. Even numbered hydrogenation steps have lower barriers and lead to more stable intermediates as a result of radical recombinations. The hydrogenation sequence follows a scheme that strongly depends on the PAH's shape, the number of aromatic rings, and the presence of five membered rings. Furthermore, we observe that tunneling plays an important role in the hydrogenation of indene at temperatures between 30 and 75 K, which corresponds to the temperatures of dust in PDRs.

We analysed the cooling of white dwarfs in the globular cluster 47 Tucanae using deep observations from the Hubble Space Telescope that resolve the white dwarf cooling sequence to late enough cooling times that the white dwarf core has begun to crystallise and the envelope has become convectively coupled to the core. At such late cooling times, both the state of matter assumed for ions in the treatment of element diffusion and the thickness of the outer H envelope become important considerations for modelling white dwarf cooling. Using the stellar evolution software Modules for Experiments in Stellar Astrophysics (MESA), we created a suite of white dwarf cooling models for different treatments of element diffusion, as well as different values of the white dwarf mass and H envelope thickness parameters. Three different diffusion scenarios were considered: i) the standard MESA implementation, which implicitly uses an ideal gas approximation for the ions, ii) a custom modified implementation that accounts for non-ideal gas effects, and iii) no diffusion. An unbinned likelihood analysis was performed to compare these cooling models to the observations. This work both constrains the values of parameters important for modelling white dwarf cooling and tests the implementation of element diffusion in MESA to late cooling times. We find that models with thicker H envelopes are preferred and that the standard MESA diffusion treatment produces a best-fitting model that well reproduces the cumulative white dwarf luminosity functions of the observations.

Theories with radiative symmetry breaking (RSB) lead to first-order phase transitions and the production of gravitational waves as well as primordial black holes if the supercooling period lasted long enough. Here we explain how to efficiently reheat the universe after such period in the above-mentioned class of theories. Two cases are possible, depending on whether the RSB scale is much larger than the electroweak (EW) symmetry breaking scale or not. When it is, the dominant reheating mechanism can be the decays of the field responsible for RSB in the Standard Model (SM) sector. We point out that in a similar way dark matter (DM) can be produced and we analyze in some detail the case of a sterile-neutrino, finding that the full DM abundance is reproduced when this particle is at the $10^2$ MeV scale in a well-motivated SM completion. When the RSB scale is not much larger than the EW symmetry breaking scale, we find that efficient reheating always occurs when the energy density of the false vacuum is first entirely transferred to a dark photon and then to SM fermions via dark-photon decays.

We show that, in a consistent model of a stabilized extra-dimensional theory, the radion can serve as a natural portal between ordinary matter and WIMP dark matter. With an effective coupling scale of the Kaluza-Klein theory of 20-100 TeV, the radion portal can produce the observed relic abundance through resonant annihilation for dark matter masses up to a TeV. Existing and planned direct dark matter detection experiments cannot constrain this model. However, indirect detection limits exclude dark matter masses between 5 and 80 GeV, where the radion mediator primarily decays into b-quarks.

In the current study, we present the observational data constraints on the parameters space for an anisotropic cosmological model of Bianchi I type spacetime in general relativity (GR). For the analysis, we consider observational datasets of Cosmic Chronometers (CC), Baryon Acoustic Oscillation (BAO), and Cosmic Microwave Background Radiation (CMBR) peak parameters. The Markov chain Monte Carlo (MCMC) technique is utilized to constrain the bestfit values of the model parameters. For this purpose, we use the publicly available Python code from CosmoMC and have developed the contour plots with different constraint limits. For the joint dataset of CC, BAO, and CMBR, the parameter's best-fit values for the derived model are estimated as H_0 = 69.9\pm 1.4 km/s/Mpc, \Omega_{m0}=0.277^{+0.017}_{-0.015}, \Omega_{\Lambda 0} = 0.722^{+0.015}_{-0.017}, and \Omega_{\sigma 0} = 0.0009\pm0.0001. To estimate H(z), we explore machine learning (ML) techniques like linear regression, Artificial Neural Network (ANN), and polynomial regression and thereafter analyze the results with the theoretically developed H(z) for the proposed model. Among these ML techniques, the polynomial regression exceeds the performance compared to other techniques. Further, we also note that larger dataset provides a better understanding of the cosmological scenario in terms of ML view point.

A well-established result in quantum field theory in four-dimensional de Sitter space is that the vacuum state of a massless scalar field breaks the de Sitter isometry group, leading to time-dependent (secular) growth in correlation functions computed in inflationary coordinates. This behavior is widely believed to extend to more general theories involving light scalar fields with weak non-derivative interactions. In such cases, secular growth is thought to be further amplified by loop corrections, and the stochastic formalism is often regarded as the appropriate framework to resum these infrared effects. In this article we challenge this prevailing view. A crucial distinction must be made between two cases: a massless scalar field protected by a shift symmetry, and a light scalar without such a symmetry. In the former, the shift symmetry enforces derivative interactions, yielding observables in which secular growth plays no physical role. In the latter, although correlation functions develop infrared divergences in the massless limit, they remain fully invariant under the de Sitter isometry group. We analyze the structure of these divergences arising from loop integrals and show that, in the soft-momentum limit, they do not alter the time dependence of tree-level correlators. In fact, using a de Sitter-invariant renormalization scheme based on Wilson's axioms for integration, these divergences can be systematically removed order by order. We therefore conclude that neither massless nor light scalar fields in de Sitter space exhibit genuine secular growth. We further discuss the implications of these findings for the validity and scope of the stochastic approach to inflation.

Primordial black holes (PBHs) are well-motivated candidates for cold dark matter and may also account for a fraction of the binary black hole mergers observed by the LIGO-Virgo-KAGRA Collaboration. In this study, we investigate the gravitational-wave signatures of PBHs, with a particular focus on evaluating their integrated contribution to the stochastic gravitational-wave background arising from binary mergers over a broad range of redshifts. We perform a Bayesian analysis of gravitational-wave events following all Gravitational-Wave Transient Catalog data, assuming a log-normal PBH mass function. We compute the merger rate distribution of PBH binaries by accounting for gravitational torques from the surrounding PBH. To constrain this rate, we employ the latest limits from the third observing run of LIGO/Virgo. Owing to their primordial origin, PBHs exhibit enhanced merger activity at high redshifts, prior to the onset of stellar formation. Our analysis yields a relatively weak inference on the redshift evolution index of the PBH merger rate, with $\alpha = 2.19^{+0.16}_{-0.16}$ at 68\% confidence level. The local merger rate of PBH binaries is found with posterior estimates lying in the range $23.5-30.3~\mathrm{Gpc}^{-3}\,\mathrm{yr}^{-1}$, reflecting a high degree of statistical precision in the inferred distribution. Additionally, we emphasize the potential of stochastic gravitational-wave background observations to probe the cumulative history of PBH mergers across cosmic time.

We explore dark matter phenomenology in Myrzakulov $F(R,T)$ gravity, formulated via the vielbein approach in Weitzenböck spacetime. In this torsion-based extension of gravity, dark matter emerges as a geometric effect rather than a particle species, with curvature and torsion contributing dynamically to the field equations. Using recent data -- including SPARC galaxy rotation curves, Planck CMB observations, and weak lensing from DES and KiDS -- we constrain the model through MCMC analysis. Our results show that, under specific parameter choices, the theory replicates key cosmological features without introducing additional dark sector matter. This framework offers a testable alternative to $\Lambda$CDM, providing new insight into structure formation, gravitational lensing, and cosmic acceleration -- all rooted in the geometry of spacetime.

As space exploration extends into cislunar space and further towards Mars, understanding the relativistic effects on clocks on Mars, particularly in relation to multibody gravitational influences, becomes increasingly important for accurate clock synchronization. This study estimates clock rates on Mars and compares them to those on the Moon and Earth. We find that, on average, clocks on Mars tick faster than those on the Earth's geoid by 477 microseconds per day, with a variation of 226 microseconds per day over a Martian year. Additionally, there is an amplitude modulation of approximately 40 microseconds per day over seven synodic cycles. We also introduce a formalism for addressing the effects of solar tides on the Earth-Moon system for predicting clock rates on the Moon and Mars more accurately when compared to using only Keplerian orbit approximations. Our analysis quantifies the relativistic proper time offsets among Martian, lunar, and terrestrial clocks, highlighting important implications for mission planning and the implementation of timekeeping systems on Mars.

Scalar fields in the early Universe are mostly discussed in two limits: either in equilibrium or completely decoupled. In this work we discuss scenarios where there are scalar fields that are not in equilibrium, but for which the coupling to thermal bath leads to interesting non-trivial dynamics. For example, in theories where scalar fields control the effective couplings of the theory, such out-of-equilibrium behavior can lead to cases where the couplings vary during cosmological evolution. We systematically examine the generic features governing the evolution of these couplings, and as an application we highlight a novel effect where the scalar quartic coupling of an Abelian Higgs model is modified, leading to stronger cosmological phase transitions than would be obtained for static non-evolving quartics.

The KM3NeT Collaboration recently reported the detection of an ultra-high-energy neutrino event KM3-230213A with a reconstructed energy of $220^{+110}_{-60}$ PeV, the most energetic astrophysical neutrino ever detected. The absence of convincing electromagnetic counterparts motivates exploration of exotic origins beyond standard astrophysical processes. We present a vector dark matter model based on a new $U(1)_X$ gauge symmetry to interpret this event through superheavy dark matter decay. Our analysis demonstrates that dark matter lifetimes in the range $7.3 \times 10^{28}$ to $2.9 \times 10^{30}$ s can successfully account for the KM3-230213A event while satisfying stringent constraints from gamma-ray observations. Moreover, the spontaneous breaking of $U(1)_X$ in our model naturally predicts cosmic string formation, generating a stochastic gravitational wave background with string tension $4.5 \times 10^{-11} \lesssim G\mu \lesssim 1.2 \times 10^{-10}$, consistent with recent pulsar timing array observations. This multi-messenger consistency across neutrinos, gamma-rays, and gravitational waves validates our vector dark matter interpretation of the KM3-230213A event while providing testable predictions for upcoming multi-wavelength experiments.

Attitude sensors determine the spacecraft attitude through the sensing of an astronomical object, field or other phenomena. The Sun and fixed stars are the two primary astronomical sensing objects. Attitude sensors are critical components for the survival and knowledge improvement of spacecraft. Of these, sun sensors are the most common and important sensor for spacecraft attitude determination. The sun sensor measures the Sun vector in spacecraft coordinates. The sun sensor calibration process is particularly difficult due to the complex nature of the uncertainties involved. The uncertainties are small, difficult to observe, and vary spatio-temporally over the lifecycle of the sensor. In addition, the sensors are affected by numerous sources of uncertainties, including manufacturing, electrical, environmental, and interference sources. This motivates the development of advanced calibration algorithms to minimize uncertainty over the sensor lifecycle and improve accuracy. Although modeling and calibration techniques for sun sensors have been explored extensively in the literature over the past two decades, there is currently no resource that consolidates and systematically reviews this body of work. The present review proposes a systematic mapping of sun sensor modeling and calibration algorithms across a breadth of sensor configurations. It specifically provides a comprehensive survey of each methodology, along with an analysis of research gaps and recommendations for future directions in sun sensor modeling and calibration techniques.

The orbital evolution of binary black hole (BBH) systems is determined by the component masses and spins of the black holes and the governing gravity theory. Gravitational wave (GW) signals from the evolution of BBH orbits offer an unparalleled opportunity for examining the predictions of General Relativity (GR) and for searching for missing physics in the current waveform models. We present a method of stacking up the time-frequency pixel energies through the orbital frequency evolution with the flexibility of gradually shifting the orbital frequency curve along the frequency axis. We observe a distinct energy peak corresponding to the GW signal's quadrupole mode. If an alternative theory of gravity is considered and the analysis of the BBH orbital evolution is executed following GR, the energy distribution on the time-frequency plane will be significantly different. We propose a new consistency test to check whether our theoretical waveform explains the BBH orbital evolution. Through the numerical simulation of beyond-GR theory of gravity and utilizing the framework of second-generation interferometers, we demonstrate the efficiency of this new method in detecting any possible departure from GR. Finally, when applied to an eccentric BBH system and GW190814, which shows the signatures of higher-order multipoles, our method provides an exquisite probe of missing physics in the GR waveform models.

We investigate relativistic Bondi accretion in the Simpson-Visser spacetime, which, via a single parameter $\ell$, interpolates between the Schwarzschild, regular black hole, extremal and wormhole regimes. First, we analyze the neutral Simpson-Visser geometry, recovering Schwarzschild at $\ell=0$, and then its charged extension of the Reissner-Nordström metric. In both these cases, we derive the conservation equations and analyze two representative fluid models: a barotropic perfect fluid and a constituent with an exponential density profile. By varying the parameters across regimes, we locate critical (sonic) points and integrate velocity, density and pressure profiles. While near-horizon inflow velocities are similar across the different solutions, we find that the critical radius and the resulting accretion rates and luminosities severely change, depending on the value of the parameter and type of fluid. Remarkably, the barotropic and exponential cases exhibit different trends in the outer regions. Moreover, by extending the analysis to the charged SV spacetime, we find that the presence of a central charge $Q$ produces additional, albeit modest, shifts in the sonic radius which, in combination with those induced by the regularization parameter $\ell$, could provide a double observational marker. In particular, while $\ell$ acts predominantly on the position of the critical point, in the barotropic fluid case, the electromagnetic contribution of $Q$ slightly dampens the inflow velocity near the horizon.

Gravitational wave observations have recently revealed with high significance, and high precision, the existence of $\mathcal{O}(100) \, M_\odot$ rapidly rotating black holes, allowing gravitational wave events to be used for the first time to probe unexplored axion parameter space using the phenomenon known as black hole superradiance. Here, we present new limits on axions using the binary black hole merger event GW231123, whose constituent black holes are among the fastest spinning observed with gravitational waves to date. We demonstrate that the most viable binary formation channels lead to conservative constraints on axion masses $\mu \sim [0.6-5] \times \, 10^{-13}$ eV and decay constants $f_\Phi \gtrsim 10^{14}$ GeV, extending existing superradiance constraints derived using x-ray observations to yet lower axion masses.

This paper presents properties and approximations of a random variable based on the zero-order modified Bessel function that results from the compounding of a zero-mean Gaussian with a $\chi^2_1$-distributed variance. This family of distributions is a special case of the McKay family of Bessel distributions and of a family of generalized Laplace distributions. It is found that the Bessel distribution can be approximated with a null-location Laplace distribution, which corresponds to the compounding of a zero-mean Gaussian with a $\chi^2_2$-distributed variance. Other useful properties and representations of the Bessel distribution are discussed, including a closed form for the cumulative distribution function that makes use of the modified Struve functions. Another approximation of the Bessel distribution that is based on an empirical power-series approximation is also presented. The approximations are tested with the application to the typical problem of statistical hypothesis testing. It is found that a Laplace distribution of suitable scale parameter can approximate quantiles of the Bessel distribution with better than 10% accuracy, with the computational advantage associated with the use of simple elementary functions instead of special functions. It is expected that the approximations proposed in this paper be useful for a variety of data science applications where analytic simplicity and computational efficiency are of paramount importance.

Neutrinos, being massive, can decay. A heavier neutrino could decay into a lighter one and a massless scalar or pseudoscalar boson, such as the Majoron. Two-body non-radiative decay could occur in dense matter, such as in the inner dense regions of a core-collapse supernova. We first derive novel bounds on neutrino-Majoron couplings using the spectral distortions induced by neutrino non-radiative two-body decay in matter, and two-dimensional likelihood analyses of the 24 $\bar{\nu}_e$ events from SN1987A. We then explore the prospects of neutrino-Majoron couplings from a future galactic core-collapse supernova, leaving either a neutron star or a black-hole. To this aim, we use information from detailed one-dimensional supernova simulations. We consider the supernova neutrino signal associated with inverse-beta decay in the upcoming JUNO and Hyper-Kamiokande detectors, with neutrino-argon scattering in DUNE, or with coherent neutrino-nucleus scattering in the DARWIN experiment. In a full 3$\nu$ framework, based on the spectral distortions induced by neutrino decay in matter, we perform two-dimensional likelihood analyses and provide prospects for the limits on neutrino-Majoron couplings. Our results show that the observation of a future supernova will significantly improve on the current bounds, in particular from SN1987A and neutrinoless double-beta decay. Finally, we explore the impact of neutrino decay in matter on the diffuse supernova neutrino background formed by past supernova explosions. We show for the first time that the effects on black-hole contributions are important and modify the DSNB number of events by several tens of percent in Hyper-Kamiokande.

Simulations of hadronic and nuclear interactions are essential in both collider and astroparticle physics. The Chromo package provides a unified Python interface to multiple widely used hadronic event generators, including EPOS, DPMJet, Sibyll, QGSJet, and Pythia. Built on top of their original Fortran and C++ implementations, Chromo offers a zero-overhead abstraction layer suitable for use in Python scripts, Jupyter notebooks, or from the command line, while preserving the performance of direct calls to the generators. It is easy to install via precompiled binary wheels distributed through PyPI, and it integrates well with the Scientific Python ecosystem. Chromo supports event export in HepMC, ROOT, and SVG formats and provides a consistent interface for inspecting, filtering, and modifying particle collision events. This paper describes the architecture, typical use cases, and performance characteristics of Chromo and its role in contemporary astroparticle simulations, such as in the MCEq cascade solver.

We investigate the spherical accretion of various types of fluids onto a Schwarzschild-like black hole solution modified by a Kalb-Ramond field implementing spontaneous Lorentz symmetry violation (LV). The system is analyzed for isothermal fluids characterized by the equation of state $p=\omega\rho$, including ultra-stiff, ultra-relativistic, and radiation fluids. We investigate the effect of the LV parameter $l$ on the fluid density $\rho(r)$, radial velocity $u(r)$, and accretion rate $\dot{M}$. Using a Hamiltonian dynamical systems approach, we examine the behavior near critical points and identify the sonic transitions in each scenario. Our results show that the LV parameter influences the location of critical points, the flow structure, and the accretion rate, with $l>0$ ($l<0$) enhancing (suppressing) the latter. For ultra-stiff fluids, no critical points are found, and the flow remains entirely subsonic. For ultra-relativistic and radiation fluids, transonic solutions exist, with the position of the sonic point depending on the sign of $l$. We also analyze polytropic fluids $p=\mathcal{K} \rho^{\Gamma}$ with $\Gamma=5/3$ and $\Gamma=4/3$, observing similar qualitative behavior, where the sonic transition is affected by both the equation of state and the LV parameter. These findings suggest that Lorentz symmetry breaking can significantly alter accretion dynamics in black hole spacetimes.