Papers for Friday, Dec 22 2023

We identify a horseshoe-shaped ring (HSR) of diffuse emission in J1407+0453 from the Faint Images of Radio Sky at Twenty-cm (FIRST) survey using the Very Large Array telescope. An optical galaxy SDSSJ140709.01+045302.1 is present near the limb of the HSR of J1407+0453, with a spectroscopic redshift of $z=0.13360$. The total extent of the source, including the diffuse emission of J1407+0453, is 65 arcsec (with a physical extent of 160 kpc), whereas the diameter of the HSR is approximately 10 arcsec (25 kpc). The flux density of HSR is $\sim$47 mJy at 1400 MHz whereas the flux densities of whole diffuse emission of J1407+0453 at 1400 MHz and 150 MHz are 172 mJy and 763 mJy, respectively. We measure the radio luminosity of HSR J1407+0453 as 1.94 $\times 10^{24}$ W Hz$^{-1}$ with a spectral index $\alpha_{150}^{1400}=-0.67$. The black hole mass of J1407+0453 is 5.8$\times10^8$ M$_{\odot}$. We compare the HSR of diffuse emission of J1407+0453 with other discovered diffused circular sources. The possible formation scenarios for J1407+0453 are discussed to understand the nature of the source. We present a spectral index map of 147+0453 to study the spectral properties of the source.

Perturbations to stellar systems can reflect the gravitational influence of dark matter substructures. Whereas perturbations to cold stellar systems are the most commonly studied, the sources of perturbations to dynamically hot systems are less ambiguous because such systems cannot support persistent inhomogeneity on small scales. We point out a simple algebraic relationship between the two-point statistics of a hot stellar system and those of the perturbing matter. The density and velocity power spectra of the stars are proportional to the density power spectrum of the perturbers, scaled by $k^{-4}$. This relationship allows easy evaluation of the suitability of a stellar system for detecting dark substructure. As examples, we show that the Galactic stellar halo is expected to be sensitive to cold dark matter substructure at wave numbers $k\lesssim 0.4$ kpc$^{-1}$, and the Galactic disk might be sensitive to substructure at wave numbers $k\sim 4$ kpc$^{-1}$. These systems could provide direct measurements of the nonlinear matter power spectrum at these wave numbers.

The stellar initial mass function (IMF) in the early universe is essential to understand the formation of ancient galaxies. To this end, we conduct a series of long-term radiation hydrodynamic simulations following star cluster formation, varying the metallicity from $Z/Z_\odot = 10^{-4}$ to $1$. We particularly consider the effects of protostellar radiative feedback, which modify the exact shape of the IMF and determine the star formation efficiency (SFE), i.e. the ratio between the mass in stars and the initial gas mass in the parental cloud. Our results show that the IMF changes from a Salpeter-type to a top-heavy function as the metallicity decreases. When $Z/Z_\odot \lesssim 10^{-2}$, the IMF becomes log-flat and distinct from a Salpeter-like IMF. Stellar feedback is effective in shaping both the low- and high-mass ends of the IMF. Heating of dust grains by stellar radiation suppresses small-scale fragmentation and reduces the number of low-mass stars with $M_* \lesssim 1~M_\odot$ at all metallicities. The ionizing radiation hinders the growth of massive stars, steepening the slope of the IMF at the high-mass end. The resulting feedback is more effective at lower metallicity, and star formation is regulated by stellar radiative feedback, with the SFE decreasing with decreasing metallicity. We suggest that the unexpectedly large number of UV-bright galaxies at $z>10$ reported by JWST observations can be explained by considering star cluster formation at $Z/Z_\odot \sim 10^{-2}$ or $10^{-3}$, where the IMF is top-heavy, but the SFE is not too low due to stellar feedback.

The physics of stellar rotation plays a crucial role in the evolution of stars, their final fate and the properties of compact remnants. Diverse approaches have been adopted to incorporate the effects of rotation in stellar evolution models. This study seeks to explore the consequences of these various prescriptions for rotation on essential outputs of massive star models. We compute a grid of 15 and 60 M$_{\odot}$ stellar evolution models with the Geneva Stellar Evolution Code (GENEC), accounting for both hydrodynamical and magnetic instabilities induced by rotation. In both the 15 and 60 M$_{\odot}$ models, the choice of the vertical and horizontal diffusion coefficients for the non magnetic models strongly impacts the evolution of the chemical structure, but has a weak impact on the angular momentum transport and the rotational velocity of the core. In the 15 M$_{\odot}$ models, the choice of diffusion coefficient impacts the convective core size during the core H-burning phase, whether the model begins core He-burning as a blue or red supergiant and the core mass at the end of He-burning. In the 60 M$_{\odot}$ models, the evolution is dominated by mass loss and is less affected by the choice of diffusion coefficient. In the magnetic models, magnetic instability dominates the angular momentum transport and such models are found to be less mixed when compared to their rotating non-magnetic counterparts. Stellar models with the same initial mass, chemical composition, and rotation may exhibit diverse characteristics depending on the physics applied. By conducting thorough comparisons with observational features, we can ascertain which method(s) produce the most accurate results in different cases.

We present the first results from a dark matter search using six Skipper-CCDs in the SENSEI detector operating at SNOLAB. With an exposure of 534.9 gram-days from well-performing sensors, we select events containing 2 to 10 electron-hole pairs. After aggressively masking images to remove backgrounds, we observe 55 two-electron events, 4 three-electron events, and no events containing 4 to 10 electrons. The two-electron events are consistent with pileup from one-electron events. Among the 4 three-electron events, 2 appear in pixels that are likely impacted by detector defects, although not strongly enough to trigger our "hot-pixel" mask. We use these data to set world-leading constraints on sub-GeV dark matter interacting with electrons and nuclei.

We present new 1.5-8.5 GHz Very Long Baseline Array (VLBA) observations and 0.32-1.26 GHz Giant Meterwave Radio Telescope (GMRT) observations of J0354-1340, which is the only known radio-quiet (RQ) or radio-intermediate (RI) narrow-line Seyfert 1 galaxy with a 100-kpc two-sided radio jet. A pc-scale one-sided jet in the southeast direction from the core emission is found in the VLBA observations, while the kpc-scale jet observed with Karl G. Jansky Very Large Array (VLA) and GMRT is in the south-north direction. The core spectra on pc and kpc scales are presented in combination with the archival VLASS observations at 3.0 GHz and the VLA C configuration observations at 5.5 GHz. The pc-scale emission dominates the kpc-scale emission above ~ 5 GHz, and the spectrum is inverted due to synchrotron self-absorption. This indicates a compact synchrotron source with a size of ~ 0.04 pc, which is associated with either the jet base or the corona. A sub-kpc scale jet, which is unresolved on scales of ~ 3 arcsec, probably dominates the emission below ~ 5 GHz. Future radio observations can explore the jet structure between the pc and 100 kpc scales, the origin of their direction mismatch, and the pc-scale jet proper motion. It remains to be explored how common such large-scale jets are in RQ or RI AGN.

The debate about the universality of the stellar initial mass function (IMF) revolves around two competing lines of evidence. While measurements in the Milky Way, an archetypal spiral galaxy, seem to support an invariant IMF, the observed properties of massive early-type galaxies (ETGs) favor an IMF somehow sensitive to the local star formation conditions. The fundamental methodological and physical differences between both approaches have hampered, however, a comprehensive understanding of IMF variations. We describe here an improved modelling scheme that allows for the first time consistent IMF measurements across stellar populations with different ages and complex star formation histories. Making use of the exquisite MUSE optical data from the TIMER survey and powered by the MILES stellar population models, we show the age, metallicity, [Mg/Fe], and IMF slope maps of the inner regions of NGC 3351, a spiral galaxy with a mass similar to that of the Milky Way. The measured IMF values in NGC3351 follow the expectations from a Milky Way-like IMF, although they simultaneously show systematic and spatially coherent variations, particularly for low-mass stars. In addition, our stellar population analysis reveals the presence of metal-poor and Mg-enhanced star-forming regions that appear to be predominantly enriched by the stellar ejecta of core-collapse supernovae. Our findings showcase therefore the potential of detailed studies of young stellar populations to better understand the early stages of galaxy evolution and, in particular, the origin of the observed IMF variations beyond and within the Milky Way.

Morphology and color patterns hold fundamental insights into the early formation history of high-z galaxies. However, 2D reconstruction of rest-frame (RF) color maps of such systems from imaging data is a non-trivial task. This is mainly because the spectral energy distribution (SED) of high-sSFR (starburst) galaxies near and far is spatially inhomogeneous and thus the common practice of applying a spatially constant "morphological" k-correction can lead to serious observational biases. In this study we use the nearby blue compact galaxy Haro11 to illustrate how the spatial inhomogeneity of the SED impacts the morphology and color maps in the observer's frame (ObsF) visual and NIR, and potentially affects the physical characterization of distant starburst galaxies with the JWST and Euclid. Based on MUSE spectroscopy and spectral modeling, we first examine the elements shaping the spatially varying optical SED of Haro11, namely intrinsic stellar age gradients, strong nebular emission and its spatial decoupling from the ionizing stellar background, and differing extinction patterns in the stellar and nebular component both spatially and in their amount. Our simulations show, inter alia, that an optically bright yet dusty star-forming (SF) region may evade detection whereas a gas-evacuated (thus, potentially Lyman continuum photon-leaking) region with weaker SF activity can dominate the ObsF (RF UV) morphology of a high-z galaxy. We also show that ObsF color maps are affected by strong emission lines moving in and out of filter passbands depending on z, and, if taken at face value, can lead to erroneous conclusions about the nature, evolutionary status and dust content of a galaxy. A significant additional problem stems from the uncertain prominence of the 2175 {\AA} extinction bump that translates to appreciable inherent uncertainties in RF color maps of high-z galaxies. (abridged)

We present the AM$^3$ (``Astrophysical Multi-Messenger Modeling'') software, which has been successfully used in the past to simulate the multi-messenger emission, including neutrinos, from active galactic nuclei, including the blazar sub-class, gamma-ray bursts, and tidal disruption events. AM$^3$ is a documented state-of-the-art open source software that efficiently solves the coupled integro-differential equations for the spectral and temporal evolution of the relevant particle densities (photons, electrons, positrons, protons, neutrons, pions, muons, and neutrinos). AM$^3$ includes all relevant non-thermal processes (synchrotron, inverse Compton scattering, photon-photon annihilation, proton-proton and proton-photon pion production, and photo-pair production). The software self-consistently calculates the full cascade of primary and secondary particles, outperforming simple test-particle approaches, and allows for non-linear feedback and predictions in the time domain. It also allows to track separately the contributions of different radiative processes to the overall photon and neutrino spectra, including the different hadronic interaction channels. With its efficient hybrid solver combining analytical and numerical techniques, AM$^3$ combines efficiency and accuracy at a user-adjustable level. We describe the technical details of the numerical framework and present examples of applications to various astrophysical environments.

The detection of gravitational waves (GWs) has led to a deeper understanding of binaries of ordinary astrophysical objects, including neutron stars and black holes. In this work, we point out that binary systems may also exist in a dark sector with astrophysical-mass macroscopic dark matter. These "dark binaries," when coupled to an additional attractive long-range dark force, may generate a stochastic gravitational wave background (SGWB) with a characteristic spectrum different from ordinary binaries. We find that the SGWB from planet-mass dark binaries is detectable by space- and ground-based GW observatories. The contribution to the SGWB today is smaller from binaries that merge before recombination than after, avoiding constraints on extra radiation degrees of freedom while potentially leaving a detectable GW signal at high frequencies up to tens of GHz.

The direct imaging of an Earth-like exoplanet will require sub-nanometric wavefront control across large light-collecting apertures, to reject host starlight and detect the faint planetary signal. Current adaptive optics (AO) systems, which use wavefront sensors that reimage the telescope pupil, face two challenges that prevent this level of control: non-common-path aberrations (NCPAs), caused by differences between the sensing and science arms of the instrument; and petaling modes: discontinuous phase aberrations caused by pupil fragmentation, especially relevant for the upcoming 30-m class telescopes. Such aberrations drastically impact the capabilities of high-contrast instruments. To address these issues, we can add a second-stage wavefront sensor to the science focal plane. One promising architecture uses the photonic lantern (PL): a waveguide that efficiently couples aberrated light into single-mode fibers (SMFs). In turn, SMF-confined light can be stably injected into high-resolution spectrographs, enabling direct exoplanet characterization and precision radial velocity measurements; simultaneously, the PL can be used for focal-plane wavefront sensing. We present a real-time experimental demonstration of the PL wavefront sensor on the Subaru/SCExAO testbed. Our system is stable out to around ~400 nm of low-order Zernike wavefront error, and can correct petaling modes. When injecting ~30 nm RMS of low order time-varying error, we achieve ~10x rejection at 1 s timescales; further refinements to the control law and lantern fabrication process should make sub-nanometric wavefront control possible. In the future, novel sensors like the PLWFS may prove to be critical in resolving the wavefront control challenges posed by exoplanet direct imaging.

X-ray continuum emission of active galactic nuclei (AGNs) may be reflected by circumnuclear dusty tori, producing prominent fluorescence iron lines at X-ray frequencies. Here we discuss the broad-band emission of three radio-loud AGN belonging to the class of compact symmetric objects (CSOs), with detected narrow Fe\,K$\alpha$ lines. CSOs have newly-born radio jets, forming compact radio lobes with projected linear sizes of the order of a few to hundreds of parsecs. We model the radio--to--$\gamma$-ray spectra of compact lobes in J1511+0518, OQ+208, and 2021+614, which are among the nearest and the youngest CSOs known to date, and are characterized by an intrinsic X-ray absorbing column density of $N_{\rm H} > 10^{23}$\,cm$^{-2}$. In addition to the archival data, we analyze the newly acquired {\it Chandra} X-ray Observatory and Sub-Millimeter Array (SMA) observations, and also refine the $\gamma$-ray upper limits from the {\it Fermi} Large Area Telescope (LAT) monitoring. The new {\it Chandra} data exclude the presence of the extended X-ray emission components on scales larger than $1.5^{\prime \prime}$. The SMA data unveil a correlation of the spectral index of the electron distribution in the lobes and $N_{\rm H}$, which can explain the $\gamma$-ray quietness of heavily obscured CSOs. Based on our modeling, we argue that the inverse-Compton emission of compact radio lobes may account for the intrinsic X-ray continuum in all these sources. Furthermore, we propose that the observed iron lines may be produced by a reflection of the lobes' continuum from the surrounding cold dust.

Using high-resolution simulations of black hole formation from the direct collapse of massive stars undergoing pulsational pair-instability supernovae (PPISN), we find a new phenomenon which significantly affects the explosion and leads to two peaks in the resulting black hole mass function (BHMF). Lighter stars experiencing the pair-instability can form a narrow shell in which alpha ladder reactions take place, exacerbating the effect of the PPISN. The shell temperature in higher mass stars ($>62 {\rm M}_\odot $ at the onset of helium burning for population-III stars with metallicity $Z=10^{-5}$) is too low for this to occur. As a result, the spectrum of black holes $M_{\rm BH} (M_i)$ exhibits a shoulder feature whereby a large range of initial masses result in near-identical black hole masses. PPISN therefore predict two peaks in the mass function of astrophysical black holes -- one corresponding to the location of the upper black hole mass gap and a second corresponding to the location of the shoulder. This shoulder effect may explain the peak at $35_{-2.9}^{+1.7}{\rm M}_\odot$ in the LIGO/Virgo/KAGRA GWTC-3 catalog of merging binary black holes.

We tested a new model of CMOS detector manufactured by the Gpixel Inc, for potential space astronomical application. In laboratory, we obtain some bias images under the typical application environment. In these bias images, clear random row noise pattern is observed. The row noise also contains some characteristic spatial frequencies. We quantitatively estimated the impact of this feature to photometric measurements, by making simulated images. We compared different bias noise types under strict parameter control. The result shows the row noise will significantly deteriorate the photometric accuracy. It effectively increases the readout noise by a factor of 2 to 10. However, if it is properly removed, the image quality and photometric accuracy will be significantly improved.

The tidal disruption of a star around a supermassive black hole (SMBH) offers a unique opportunity to study accretion onto a SMBH on a human-timescale. We present results from our 1000+ days NICER, Swift and Chandra monitoring campaign of AT 2019avd, a nuclear transient with TDE-like properties. Our primary finding is that approximately 225 days following the peak of X-ray emission, there is a rapid drop in luminosity exceeding two orders of magnitude. This X-ray drop-off is accompanied by X-ray spectral hardening, followed by a 740-day plateau phase. During this phase, the spectral index decreases from 6.2+-1.1 to 2.3+-0.4, while the disk temperature remains constant. Additionally, we detect pronounced X-ray variability, with an average fractional root mean squared amplitude of 47%, manifesting over timescales of a few dozen minutes. We propose that this phenomenon may be attributed to intervening clumpy outflows. The overall properties of AT 2019avd suggest that the accretion disk evolves from a super-Eddington to a sub-Eddington luminosity state, possibly associated with a compact jet. This evolution follows a pattern in the hardness-intensity diagram similar to that observed in stellar-mass black holes, supporting the mass invariance of accretion-ejection processes around black holes.

This molecular orbital analysis predicts that pure carbon graphene molecules would play an important role on astronomically observed Diffuse Interstellar Bands (DIB), rather than fullerene. Laboratory experiments precisely coincided with observed DIB bands as studied by E. Cambell et al., which were considered to originate from mono-cation fullerene-(C$_{60}$)$^{1+}$. To check theoretically a molecular orbital excitation of (C$_{60}$)$^{1+}$ was calculated by the Time-Dependent DFT. Calculated two bands were close to observed DIBs, but there were two problems, that the oscillator strength was zero, and that other three DIBs could not be reproduced. Laboratory experiments was the mass spectroscopic one filtering m/e=724, to suggest fullerene-(C$_{60}$)$^{1+}$ combined with He. However, there were other capabilities, as like He-atom intercalated 3D-graphite, [graphene(C$_{53}$)$^{1+}$--He--(C$_7$)], [graphene(C$_{51}$)$^{1+}$--He--(C$_9$)] and so on. A family of graphene (C$_{53}$), (C$_{52}$) and (C$_{51}$) was calculated. Results show that an astronomically observed 957.74nm band was reproduced well by calculated 957.74nm, also confirmed by laboratory experiment of 957.75nm. Other observed 963.26, 936.57 and 934.85nm bands were calculated to be 963.08, 935.89 and 933.72nm. Moreover, experimental 922.27nm band was calculated to be 922.02nm, which is not yet astronomically observed. Similarly, experimental 925.96, 912.80, 909.71 and 908.40nm bands were calculated to 926.01, 912.52, 910.32 and 908.55nm. It should be emphasized that graphene molecules may be ubiquitously floating in interstellar space.

We report new measurements of the position angle and separation of the double star WDS 03245+5938 STI 450, based on our observations, Gaia EDR3, and historical data. We find that the position angle and separation are 209.7{\deg} and 7.68", respectively, showing slight changes from the previous values of 210{\deg} and 7.742". We also find that the distances between the two stars are far apart, suggesting that the system is an optical double, and therefore not gravitationally bound together. Furthermore, we find that the ratio of proper motion (rPM) metric of the system is distinct, indicating that the system is a chance alignment of two unrelated stars that are at different distances.

We present a statistical characterization of circumstellar disk orientations toward 12 protostellar multiple systems in the Perseus molecular cloud using the Atacama Large Millimeter/submillimeter Array at Band 6 (1.3 mm) with a resolution of 25 mas (8 au). This exquisite resolution enabled us to resolve the compact inner disk structures surrounding the components of each multiple system and to determine the projected 3-D orientation of the disks (position angle and inclination) to high precision. We performed a statistical analysis on the relative alignment of disk pairs to determine whether the disks are preferentially aligned or randomly distributed. We considered three subsamples of the observations selected by the companion separations, a <100 au, a >500 au, and a < 10,000 au. We found for the compact (< 100 au) subsample, the distribution of orientation angles is best described by an underlying distribution of preferentially aligned sources (within 30deg) but does not rule out distributions with 40% misaligned sources. The wide companion (>500 au) subsample appears to be consistent with a distribution of 40%-80% preferentially aligned sources. Similarly, the full sample of systems with companions (a< 10, 000 au) is most consistent with a fractional ratio of at most 80% preferentially aligned source and rules out purely randomly aligned distributions. Thus our results imply the compact sources (<100 au) and the wide companions (>500 au) are statistically different.

We present the Atacama Large Millimeter/submillimeter Array (ALMA) observations of linearly polarized 1.1 mm continuum emission at $\sim$0.14" (55 au) resolution and CO ($J$=2$-$1) emission at $\sim$1.5" (590 au) resolution towards one prestellar (MMS 4), four Class 0 (MMS$\,$1, MMS$\,$3, MMS$\,$5, and MMS$\,$6), one Class I (MMS$\,$7), and one flat-spectrum (MMS$\,$2) sources in the Orion Molecular Cloud$\,$3 region. The dust disk-like structures and clear CO outflows are detected towards all sources except for MMS$\,$4. The diameters of these disk-like structures, ranging from 16 au to 97 au, are estimated based on the deconvolved full width half maximum (FWHM) values obtained from the multi-Gaussian fitting. Polarized emissions are detected towards MMS$\,$2, MMS$\,$5, MMS$\,$6, and MMS$\,$7, while no polarized emission is detected towards MMS$\,$1, MMS$\,$3, and MMS$\,$4. MMS$\,$2, MMS$\,$5, and MMS$\,$7 show organized polarization vectors aligned with the minor axes of the disk-like structures, with mean polarization fractions ranging from 0.6$\%$ to 1.2$\%$. The strongest millimeter source, MMS$\,$6, exhibits complex polarization orientations and a remarkably high polarization fraction of $\sim$10$\%$ around the Stokes $I$ peak, and 15$-$20$\%$ on the arm-like structure, as reported by Takahashi et al. (2019). The origins of the polarized emission, such as self-scattering and dust alignment due to the magnetic field or radiative torque, are discussed for individual sources. Some disk-like sources exhibit a polarized intensity peak shift towards the nearside of the disk, which supports that the polarized emission originates from self-scattering.

FRIPON is an efficient ground-based network for the detection and characterization of fireballs, which was initiated in France in 2016 with over one hundred cameras and which has been very successfully extended to Europe and Canada with one hundred more stations. After seven successful years of operation in the northern hemisphere, it seems necessary to extend this network towards the southern hemisphere - where the lack of detection is evident - to obtain an exhaustive view of fireball activity. The task of extending the network to any region outside the northern hemisphere presents the challenge of a new installation process, where the recommended and tested version of the several sub-systems that compose a station had to be replaced due to regional availability and compatibility considerations, as well as due to constant software and hardware obsolescence and updates. In Chile, we have a unique geography, with a vast extension in latitude, as well as desert regions, which have generated the need to evaluate the scientific and technical performance of the network under special conditions, prioritizing the optimization of a set of factors related to the deployment process, as well as the feasible and achievable versions of the required components, the geographical location of the stations, and their respective operational, maintenance, safety, and communication conditions. In this talk, we will present the current status of this effort, including a brief report on the obstacles and difficulties encountered and how we have solved them, the current operational status of the network in Northern Chile, as well as the challenges and prospects for the densification of the network over South America.

We study an open cluster NGC 6940 using \textit{AstroSat}/UVIT data and other archival data. This is an intermediate age cluster ($\sim$ 1 Gyr), located at about 770 pc distance, harboring several exotic populations apart from normal single and binary stars. We identify members of this cluster using a machine learning algorithm, ML-MOC and identify 492 members, including 1 blue straggler star (BSS), 2 yellow straggler stars (YSS), 11 blue lurker (BL) candidates, and 2 red clump (RC) stars. The cluster shows the effect of mass segregation, with massive stars segregated the most into the cluster, followed by the equal-mass binary members and the single low mass stars. We report the presence of an extended main-sequence turn-off (eMSTO) feature in this cluster and suggest that the age spread may be a contributing factor behind it. However, the effect of stellar rotation, and the dust absorption needs to be examined more comprehensively with a larger fraction of MSTO stars. All the sixteen sources mentioned above have a counterpart in the UVIT/F169M filter. In order to characterize them, we construct multi-wavelength spectral energy distributions (SEDs) of 14 of these objects having no nearby sources within 3". The BSS is successfully fitted with a single-component SED. We find that three BLs, two YSS, and one RC star have UV excess greater than 50$\%$ and successfully fit two-component SEDs having hot companions. The parameters derived from the SEDs imply that the hot companions of BLs and the RC star are low-mass and normal-mass white dwarfs, whereas the hot companions of YSS are likely to be subdwarf B (sdB) stars. We suggest that at least 6 out of 14 stars ($\sim$42 $\%$) are formed via mass transfer and/or merger pathways.

Electromagnetic radiation at higher harmonics of the plasma frequency ($\omega \sim n\omega_{pe}, n > 2$) has been occasionally observed in type II and type III solar radio bursts, yet the underlying mechanism remains undetermined. Here we present two-dimensional fully kinetic electromagnetic particle-in-cell simulations with high spectral resolution to investigate the beam-driven plasma emission process in weakly magnetized plasmas of typical coronal conditions. We focused on the generation mechanisms of high-harmonic emission. We found that a larger beam velocity ($u_d$) favors the generation of the higher-harmonic emission. The emissions grow later for higher harmonics and decrease in intensity by $\sim$2 orders of magnitude for each jump of the harmonic number. The second and third harmonic ($\rm H_2$ and $\rm H_3$) emissions get closer in intensity with larger $u_d$. We also show that (1) the $\rm H_3$ emission is mainly generated via the coalescence of the $\rm H_2$ emission with the Langmuir waves, i.e., $\rm H_2 + L \rightarrow H_3$, wherein the coalescence with the forward-propagating beam-Langmuir wave leads to the forward-propagating $\rm H_3$, and coalescence with the backward-propagating Langmuir wave leads to the backward-propagating $\rm H_3$; and (2) the $\rm H_4$ emission mainly arises from the coalescence of the $\rm H_3$ emission with the forward- (backward-) propagating Langmuir wave, in terms of $\rm H_3 + L \rightarrow H_4$.

It is known from archival TESS data that the semi-detached Algol system XZ UMa is one of the candidate binary stars exhibiting short-period oscillations. We secured new high-resolution spectroscopic observations for the program target to better understand its binary and pulsation properties. From the echelle spectra, the radial velocities (RVs) of the eclipsing pair were derived, and the atmosphere parameters of the primary component were measured to be $v_{\rm A}\sin$$i = 80\pm7$ km s$^{-1}$, $T_{\rm eff,A}$ = $7940\pm120$ K, and [M/H] = $-0.15\pm0.20$. The combined solution of our double-lined RVs and the TESS data provides robust physical parameters for XZ UMa with mass and radius measurement precision of better than 2 \%. The outside-eclipse residuals from a mean light curve in the 0.002 phase bin were used for multifrequency analyses, and we extracted 32 significant frequencies (22 in $<$ 5.0 day$^{-1}$ and 10 in 39$-$52 day$^{-1}$). The low frequencies may be mostly aliasing sidelobes, while six of the high frequencies may be pulsation signals arising from the detached primary located inside the $\delta$ Sct domain. Their periods, pulsation constants, and pulsational-orbital-period ratios indicate that the mass-accretion primary star is a $\delta$ Sct pulsator and, hence, XZ UMa is an oscillating eclipsing Algol.

With an X-ray stacking analysis of ~ 12, 000 Lyman-break galaxies (LBGs) using the Chandra Legacy Survey image, we investigate average supermassive black hole (SMBH) accretion properties of star-forming galaxies (SFGs) at 4 <~ z <~ 7. Although no X-ray signal is detected in any stacked image, we obtain strong 3 sigma upper limits for the average black hole accretion rate (BHAR) as a function of star formation rate (SFR). At z ~ 4 (5) where the stacked image is deeper, the 3 sigma BHAR upper limits per SFR are ~ 1.5 (1.0) dex lower than the local black hole-to-stellar mass ratio, indicating that the SMBHs of SFGs in the inactive (BHAR <~1M_sun yr^{-1}) phase are growing much more slowly than expected from simultaneous evolution. We obtain a similar result for BHAR per dark halo accretion rate. QSOs from the literature are found to have ~ 1 dex higher SFRs and >~ 2 dex higher BHARs than LBGs with the same dark halo mass. We also make a similar comparison for dusty starburst galaxies and quiescent galaxies from the literature. A duty-cycle corrected analysis shows that for a given dark halo, the SMBH mass increase in the QSO phase dominates over that in the much longer inactive phase. Finally, a comparison with the TNG300, TNG100, SIMBA100, and EAGLE100 simulations finds that they overshoot our BHAR upper limits by <~ 1.5 dex, possibly implying that simulated SMBHs are too massive.

We measure the bolometric luminosity of a complete and unbiased 12 micron-selected sample of active galactic nuclei (AGN) in the local Universe. For each galaxy we used a 10-band radio-to-X-ray Spectral Energy Distribution (SED) to isolate the genuine AGN continuum in each band, including sub-arcsecond measurements where available, and correcting those contaminated by the host galaxy. We derive the median SED of Seyfert type 1 AGN, Seyferts with hidden broad-lines (HBL), Seyferts of type 2, and LINER nuclei in our sample. The median Seyfert 1 SED shows the characteristic blue bump feature in the UV, but nevertheless the largest contribution to the bolometric luminosity comes from the IR and X-ray continua. The median SEDs of both HBL and type 2 AGN are affected by starlight contamination in the optical/UV. The median SED of HBL AGN is consistent with that of Seyfert 1's, when an extinction of Av = 1.2 mag is applied. The comprehensive SEDs allowed us to measure accurate bolometric luminosities and derive robust bolometric corrections for the different tracers. The 12 micron and the K-band nuclear luminosities have good linear correlations with the bolometric luminosity, similar to those in the X-rays. We derive bolometric corrections for either continuum bands (K-band, 12 micron, 2-10 keV and 14-195 keV) and narrow emission lines (mid-IR high ionization lines of [OIV] and [NeV] and optical [OIII]5007A) as well as for combinations of IR continuum and line emission. A combination of continuum plus line emission accurately predicts the bolometric luminosity up to quasar luminosities.

We present the kinematics of the parsec-scale jet in 3C 84 from 2003 November to 2022 June observed with the Very Long Baseline Array (VLBA) at 43 GHz. We find that the C3 component, a bright feature at the termination region of the most recent jet, has maintained a nearly constant apparent velocity of 0.259 +/- 0.003c over the period covered by observations. We observe the emergence of four new subcomponents from C3, each exhibiting apparent speeds higher than that of C3. Notably, the last two subcomponents exhibit apparent superluminal motion, with the fastest component showing an apparent speed of 1.41 +/- 0.08c. Our analysis suggests that a change in viewing angle alone cannot account for the fast apparent speeds of the new subcomponents, indicating that they are intrinsically faster than C3. We identify jet precession (or reorientation), a jet-cloud collision, and magnetic reconnection as possible physical mechanisms responsible for the ejection of the new subcomponents.

We propose that the merger rate of primordial black hole (PBH) binaries can be a probe of Hubble parameter by constraining PBH mass function in the redshifted mass distribution of PBH binaries. In next-generation gravitational wave (GW) detectors, the GWs from PBH binaries would be detected at high redshifts, which gives their redshifted mass and luminosity distances. From a number of detected events, the redshifted mass distribution of PBH binaries can be statistically obtained, and it depends on PBH mass function and redshift distribution of detected PBH binaries. The PBH mass function can be inversely solved by applying the gradient descent method in the relation between redshifted mass distribution and redshift distribution. However, the construction of redshift distribution requires an assumed Hubble parameter in a background cosmology to extract redshift from luminosity distances, which causes solved PBH mass function also depends on assumed Hubble parameter. To determine the Hubble parameter, the merger rate of PBH binaries constrains on this Hubble parameter-dependent PBH mass function by comparing calculated merger rate distribution with observed one, and the best-fit result produces an approximate mass distribution of the physical PBH mass function and pins down the Hubble parameter.

Multi-wavelength properties of the nearby Supernova(SN)-associated low-luminosity GRB 171205A are investigated in depth to constrain its physicalan origin synthetically. The pulse width is found to be correlated with energy with a power-law index of $-0.24\pm0.07 $, which is consistent with the indices of other SN/GRBs but larger than those of long GRBs. By analyzing the overall light curve of its prompt gamma-rays and X-ray plateaus simultaneously, we infer that the early X-rays together with the gamma-rays should reflect the activities of central engine while the late X-rays may be dominated by the interaction of external shocks with circumburst material. In addition, we find that the host radio flux and offset of GRB 171205A are similar to those of other nearby low-luminosity GRBs. We adopt 9 SN/GRBs with measured offset to build a relation between peak luminosity ($L_{\gamma,p}$) and spectral lag ($\tau$) as $L_{\gamma,p}\propto\tau^{-1.91\pm0.33}$. The peak luminosity and the projected physical offset of both 12 SN/GRBs and 10 KN/GRBs are found to be moderately correlated, suggesting their different progenitors. The multi-wavelength afterglow fitted with a top-hat jet model indicates that the jet half-opening angle and the viewing angle of GRB 171205A are $\thicksim$ 34.4 and 41.8 degrees, respectively, which implies that the off-axis emissions are dominated by the peripheral cocoon rather than the jet core.

We investigate the accretion flow around a giant planet using two-dimensional hydrodynamical simulations by studying the local region of accretion disk around the planet. The results show that, when the initial orbit of the planet embedded in protoplanetary disk is eccentric, the accretion disk formed around the planet is retrograde during the evolution and may be a possible origin of the retrograde ring around eccentric extrasolar giant planet.

We study the local environmental properties of 418 supernovae (SNe) of all types using data from the Javalambre Photometric Local Universe Survey (J-PLUS), which includes 5 broad- and 7 narrow-band imaging filters, using two independent analyses: 1) the Normalized Cumulative Rank (NCR) method, utilizing all 12 single bands along with five continuum-subtracted narrow-band emission and absorption bands, and 2) simple stellar population (SSP) synthesis, where we build spectral energy distributions (SED) of the surrounding SN environment using the 12 filters. Improvements over previous works include: (i) the extension of the NCR technique to other filters using a set of homogeneous data; (ii) a correction for extinction to all bands based on the relation between the g-i color and the color excess; and (iii) a correction for the [NII] line contamination that falls within the H$\alpha$ filter. All NCR distributions in the broad-band filters, tracing the overall light distribution in each galaxy, are similar to each other, being type Ia, II and IIb SNe are preferably located in redder environments than the other SN types. The radial distribution of the SNe shows that type IIb SNe seem to have a preference for occurring in the inner regions of galaxies. All core-collapse SN (CC) types are strongly correlated to the [OII] emission, which traces SFR. The NCR distributions of the Ca II triplet show a clear division between II/IIb/Ia and Ib/Ic/IIn subtypes, which is interpreted as a difference in the environmental metallicity. Regarding the SSP synthesis, we found that including the 7 J-PLUS narrow filters in the fitting process has a more significant effect for the CC SN environmental parameters than for SNe Ia, shifting their values towards more extinct, younger, and more star-forming environments, due to the presence of strong emission-lines and stellar absorptions in those narrow-bands.

The James Webb Space Telescope (JWST) has recently uncovered a new record-breaking quasar, UHZ1, at a redshift of $z\sim10$. This discovery continues JWST's trend of confronting the expectations from the standard $\Lambda$CDM model of cosmology with challenges. Namely, too many very massive galaxies and quasars have been observed at very high redshifts, when the universe was only a few hundred million years old. We have previously shown that Supermassive Dark Stars (SMDSs) may offer a solution to this puzzle. These fascinating objects would be the first stars in the universe, growing to be $\sim 10^5-10^7 M_{\odot}$ and shining as bright as $10^9$ suns. Unlike Population III stars (the major alternative proposed model for the first stars in the universe, which would also have zero metallicity and would be powered by nuclear fusion), SMDSs would be powered by dark matter heating (e.g. dark matter annihilation) and would be comparatively cooler. At the ends of their lives (when they run out of dark matter fuel), SMDSs would directly collapse into black holes, thus providing possible seeds for the first quasars. Previous papers have shown that to form at $z\sim10$, UHZ1 would require an incredibly massive seed ($\sim 10^4 -10^5 M_{\odot}$), which was assumed to be a Direct Collapse Black Hole (DCBH). In this paper, we demonstrate that Supermassive Dark Stars (SMDSs) offer an equally valid solution to the mystery of the first quasars, by examining the four most distant known quasars: UHZ1, J0313-1806, J1342+0928, and J1007+2115, with particular emphasis on UHZ1.

We present an improved study of the relation between supermassive black hole growth and their host galaxy properties in the local Universe (z < 0.33). To this end, we build an extensive sample combining spectroscopic measurements of star-formation rate (SFR) and stellar mass from Sloan Digital Sky Survey, with specific Black Hole accretion rate (sBHAR, $\lambda_{\mathrm{sBHAR}} \propto L_{\mathrm{X}}/\mathcal{M}_{\ast}$) derived from the XMM-Newton Serendipitous Source Catalogue (3XMM-DR8) and the Chandra Source Catalogue (CSC 2.0). We find that the sBHAR probability distribution for both star-forming and quiescent galaxies has a power-law shape peaking at $\log\lambda_{\mathrm{sBHAR}}\sim -3.5$ and declining toward lower sBHAR in all stellar mass ranges. This finding confirms the decrease of AGN activity in the local Universe compared to higher redshifts. We observe a significant correlation between $\log\,\lambda_{\mathrm{sBHAR}}$ and $\log\,{\mathrm{SFR}}$ in almost all stellar mass ranges, but the relation is shallower compared to higher redshifts, indicating a reduced availability of accreting material in the local Universe. At the same time, the BHAR-to-SFR ratio for star-forming galaxies strongly correlates with stellar mass, supporting the scenario where both AGN activity and stellar formation primarily depend on the stellar mass via fuelling by a common gas reservoir. Conversely, this ratio remains constant for quiescent galaxies, possibly indicating the existence of the different physical mechanisms responsible for AGN fuelling or different accretion mode in quiescent galaxies.

The cosmological constant term can be seen as a constant potential for a (scalar) field. In this viewpoint, at late times, the field is stopped rolling and behaves as a cosmological constant ($w=-1$). While at the early universe, its kinetic term can be dominant and behaves as a stiff fluid ($w=+1$). This new phase lowers the cosmological sound horizon by increasing the Hubble parameter for very high redshifts. Consequently, the lower cosmological sound horizon results in the higher Hubble constant at the present time. This early phase ends before the photon decoupling, so we do not expect any new physics after the last scattering surface. We checked this model in the presence of (reduced) CMB, BAO's and $H_0$ datasets and could show the Hubble tension is fully relieved.

Context. Relative field line helicity (RFLH) is a recently developed quantity which can approximate the density of relative magnetic helicity. Aims. This paper aims to determine whether RFLH can be used as an indicator of solar eruptivity. Methods. Starting from magnetographic observations from the Helioseismic and Magnetic Imager instrument onboard the Solar Dynamic Observatory of a sample of seven solar active regions (ARs), which comprises over 2000 individual snapshots, we reconstruct the AR's coronal magnetic field with a widely-used non-linear force-free method. This enables us to compute RFLH using two independent gauge conditions for the vector potentials. We focus our study around the times of strong flares in the ARs, above the M class, and in regions around the polarity inversion lines (PILs) of the magnetic field, and of RFLH. Results. We find that the temporal profiles of the relative helicity that is contained in the magnetic PIL follow those of the relative helicity that is computed by the accurate volume method for the whole AR. Additionally, the PIL relative helicity can be used to define a parameter similar to the well-known parameter R (Schrijver 2007), whose high values are related with increased flaring probability. This helicity-based R-parameter correlates well with the original one, showing in some cases even higher values, and additionally, it experiences more pronounced decreases during flares. This means that there exists at least one parameter deduced from RFLH, that has important value as a solar eruptivity indicator.

In this work we demonstrate that Dark Matter (DM) evaporation severely hinders the effectiveness of exoplanets and Brown Dwarfs as sub-GeV DM probes. Moreover, we find useful analytic closed form approximations for DM capture rates for arbitrary astrophysical objects, valid in four disticnt regions in the $\sigma-m_X$ parameter space. As expected, in one of those regions the Dark Matter capture saturates to its geometric limit, i.e. the entire flux crossing an object. As a consequence of this region, which for many objects falls within the parameter space not excluded by direct detection experiments, we point out the existence of a DM parameter dependent critical temperature ($T_{crit}$), above which astrophysical objects lose any sensitivity as Dark Matter probes. For instance, Jupiters at the Galactic Center have a $T_{crit}$ ranging from $700$ K (for a $3 M_J$ Jupiter) to $950$ K (for $14 M_J$). This limitation is rarely (if ever) considered in the previous literature of indirect Dark Matter detection based on observable signatures of captured Dark Matter inside celestial bodies.

Volatile elements play a crucial role in the formation of planetary systems. Their abundance and distribution in protoplanetary disks provide vital insights into the connection between formation processes and the atmospheric composition of individual planets. Sulfur, being one of the most abundant elements in planet-forming environments, is of great significance, and now observable in exoplanets with JWST. However, planetary formation models currently lack vital knowledge regarding sulfur chemistry in protoplanetary disks. Developing a deeper understanding of the major volatile sulfur carriers in disks is essential to building models that can meaningfully predict planetary atmospheric composition, and reconstruct planetary formation pathways. In this work, we combine archival observations with new data from ALMA and APEX, covering a range of sulfur-bearing species/isotopologs. We interpret this data using the DALI thermo-chemical code, for which our model is highly refined and disk-specific. We find that volatile sulfur is heavily depleted from the cosmic value by a factor of 1000, with a disk-averaged abundance of S/H = 1e-8. We show that the gas-phase sulfur abundance varies radially by 3 orders of magnitude, with the highest abundances inside the inner dust ring and coincident with the outer dust ring at 150 to 230 au. Extracting chemical abundances from our models, we find OCS, H2CS, and CS to be the dominant molecular carriers in the gas phase. We also infer the presence of a substantial OCS ice reservoir. We relate our results to the potential atmospheric composition of planets in HD 100546, and the wider exoplanet population

Abridged. Eclipsing spectroscopic double-lined binaries are the prime source of precise and accurate measurements of masses and radii of stars. These measurements provide a stringent test of models of stellar evolution that are persistently reported to contain major shortcomings. The mass discrepancy observed for the eclipsing spectroscopic double-lined binaries is one of the manifestations of shortcomings in stellar evolution models. Our ultimate goal is to provide an observational mapping of the mass discrepancy and propose a recipe for its solution. We initiate a spectroscopic monitoring campaign of 573 candidate eclipsing binaries of which 83 are analysed in this work with the methods of least-squares deconvolution and spectral disentangling. TESS light curves are used to provide photometric classification of the systems according to the type of their intrinsic variability. We confirm 69 systems as either spectroscopic binaries or higher-order multiple systems. Twelve stars are classified as single and two more objects are found at the interface of their line profile variability being interpreted as due to binarity and intrinsic variability of the star. Moreover, 20 eclipsing binaries are found to contain at least one component that exhibits stellar oscillations. The sample presented in this work contains both detached and semi-detached systems and covers a range in the effective temperature and mass of the star of Teff = [7000,30000] K and M = [1.5,15] M_Sun, respectively. We conclude an appreciable capability of the spectral disentangling method to deliver precise and accurate spectroscopic orbital elements from as few as 6-8 orbital phase-resolved spectroscopic observations. Orbital solutions obtained this way are accurate enough to deliver age estimates with accuracy of 10% or better, an important resource for calibration of stellar evolution models.

Dwarf barred galaxies are the perfect candidates for hosting slowly-rotating bars. They are common in dense environments and they have a relatively shallow potential well, making them prone to heating by interactions. When an interaction induces bar formation, the bar should rotate slowly. They reside in massive and centrally-concentrated dark matter halos, which slow down the bar rotation through dynamical friction. While predictions suggest that slow bars should be common, measurements of bar pattern speed, using the Tremaine-Weinberg method, show that bars are mostly fast in the local Universe. We present a photometric and kinematic characterisation of bars hosted by two dwarf galaxies in the Virgo Cluster, NGC 4483 and NGC 4516. We derive the bar length and strength using the Next Generation Virgo Survey imaging and the circular velocity, bar pattern speed, and rotation rate using spectroscopy from the Multi Unit Spectroscopic Explorer. Including the previously studied galaxy IC 3167, we compare the bar properties of the three dwarf galaxies with those of their massive counterparts from literature. Bars in the dwarf galaxies are shorter and weaker, and rotate slightly slower with respect to those in massive galaxies. This could be due to a different bar formation mechanism and/or to a large dark matter fraction in the centre of dwarf galaxies. We show that it is possible to push the application of the Tremaine-Weinberg method to the galaxy low mass regime.

We present a study of the influence of solar UV anisotropy on the heliospheric backscatter helioglow generated by resonant scattering of solar Lyman-alpha photons on interstellar hydrogen atoms around the Sun. Simulations based on the WawHelioGlow model suggest that the response of the helioglow pole-to-ecliptic ratio to the anisotropy is linear, but 15% of the anisotropy (polar darkening) generates 30-40% change in the ratio in the solar minimum and 15-20% in the solar maximum. We attribute this difference to an interplay between the solar UV anisotropy and the latitudinal structure of the solar wind in solar minima. The solar UV anisotropy also increases the helioglow intensity from the downwind direction by 5-10%, due to the influence of the anisotropy on the ionization losses and trajectories of atoms passing by the Sun in polar regions. Consequently, mid-latitude regions (in the heliographic and ecliptic coordinates) are least affected by the UV anisotropy. By comparison of the simulation results with observations of the SOHO/SWAN satellite instrument, we derive the day-by-day time evolution of the solar Lyman-alpha anisotropy for the north and south poles over two solar cycles from 1996 to 2022. The inferred anisotropy is ~5-10% in solar minima and ~15-25% in solar maxima, the northern anisotropy being stronger than the southern. Our study suggests that in solar minima a highly structured solar wind is associated with relatively small solar UV anisotropy, while in solar maxima the solar wind is more isotropic but a substantial solar UV anisotropy appears.

Ground-based high-contrast instruments have yielded reflected light images of protoplanetary disks. Quantitative measurements of the reflected radiation provide strong constraints on the scattering dust which can clarify the dust particle evolution in these disks and the composition of the forming planets. This study aimed to derive the wavelength dependence of polarized reflectivity $(\hat{Q}_{\varphi}/I_\star)_\lambda$ for 11 disks, constraining dust properties and identifying systematic differences. Using ESO archive data from SPHERE/ZIMPOL and SPHERE/IRDIS instruments, we obtained accurate intrinsic polarized reflectivity $\hat{Q}_\varphi/I_\star$ values at wavelengths from 0.62$\mu$m to 2.2$\mu$m. Polarized reflectivities ranged from $Q_\varphi/I_\star\approx 0.1\%$ to 1.0$\%$, with PSF-corrected values averaging 1.6 times higher than observed. Accurate PSF calibrations reduced systematic errors to $\Delta\hat{Q}_\varphi/\hat{Q}_\varphi\approx 10\%$ or less. For each disk, we derived a polarized reflectivity color $\eta_{V/IR}$ between a visible band $\lambda<1~\mu$m and a near-IR band $\lambda>1~\mu$m and other wavelength combinations. Wavelength gradients $\eta$ varied significantly among objects. Disks around Herbig stars (HD 169142, HD 135334B, HD 100453, MWC 758, and HD 142527) showed a red color $\eta_{\rm V/IR}>0.5$, suggesting rather compact dust grains. T-Tauri star disks (PDS 70, TW Hya, RX J1615, and PDS 66) were predominantly gray $-0.5<\eta_{\rm V/IR}<0.5$, with an absence of blue colors incompatible with porous aggregates. Exceptional red colors for LkCa15 and MWC758 were attributed to potential extra reddening from hot dust near the star. Future studies incorporating parameters like fractional polarization $\langle p_\varphi \rangle$ hold promise for advancing our understanding of dust properties within protoplanetary disks.

Observations of the high-frequency gravitational waves (GWs) emitted by the hot and massive remnant of a binary neutron star merger will provide new probes of the dense-matter equation of state (EoS). We show that current uncertainties in the thermal physics can cause the emergent GW spectum to differ by a degree comparable to changing the cold EoS by $\pm\sim120$ m in the characteristic radius of a neutron star. Unless a very close binary neutron star merger takes place, these effects are unlikely to be measurable with current GW detectors. However, with proposed next-generation detectors such as Cosmic Explorer or Einstein Telescope, the effects can be measured for events at distances of up to ~80-200 Mpc, if the cold EoS is sufficiently well constrained.

Water is a key ingredient for the emergence of life as we know it. Yet, its destruction and reformation in space remains unprobed in warm gas. Here, we detect the hydroxyl radical (OH) emission from a planet-forming disk exposed to external far-ultraviolet (FUV) radiation with the James Webb Space Telescope. The observations are confronted with the results of quantum dynamical calculations. The highly excited OH infrared rotational lines are the tell-tale signs of H2O destruction by FUV. The OH infrared ro-vibrational lines are attributed to chemical excitation via the key reaction O+H=OH+H which seeds the formation of water in the gas-phase. We infer that the equivalent of the Earth ocean's worth of water is destroyed per month and replenished. These results show that under warm and irradiated conditions water is destroyed and efficiently reformed via gas-phase reactions. This process, assisted by diffusive transport, could reduce the HDO/H2O ratio in the warm regions of planet-forming disks.

We investigate the linear axisymmetric viscous overstability in dense planetary rings with typical values of the dynamical optical depth $\tau\gtrsim 0.5$. We develop a granular flow model which accounts for the particulate nature of a planetary ring subjected to dissipative particle collisions. The model captures the dynamical evolution of the disc's vertical thickness, temperature, and effects related to a finite volume filling factor of the ring fluid. We compute equilibrium states of self-gravitating and non-self-gravitating rings, which compare well with existing results from kinetic models and N-Body simulations. Subsequently, we conduct a linear stability analysis of our model. We briefly discuss the different linear eigenmodes of the system and compare with existing literature by applying corresponding limiting approximations. We then focus on the viscous overstability, analysing the effect of temperature variations, radial and vertical self-gravity, and for the first time the effects of vertical motions on the instability. In addition, we perform local N-body simulations incorporating radial and vertical self-gravity. Critical values for the optical depth and the filling factor for the onset of instability resulting from our N-body simulations compare well with our model predictions under the neglect of radial self-gravity. When radial self-gravity is included, agreement with N-body simulations can be achieved by adopting enhanced values of the bulk viscous stress.

Observations have shown a clear association of filament/prominence eruptions with the emergence of magnetic flux in or near filament channels. Magnetohydrodynamic (MHD) simulations have been employed to systematically study the conditions under which such eruptions occur. These simulations to date have modeled filament channels as two-dimensional (2D) flux ropes or 3D uniformly sheared arcades. Here we present MHD simulations of flux emergence into a more realistic configuration consisting of a bipolar active region containing a line-tied 3D flux rope. We use the coronal flux-rope model of Titov et al. (2014) as the initial condition and drive our simulations by imposing boundary conditions extracted from a flux-emergence simulation by Leake et al. (2013). We identify three mechanisms that determine the evolution of the system: (i) reconnection displacing foot points of field lines overlying the coronal flux rope, (ii) changes of the ambient field due to the intrusion of new flux at the boundary, and (iii) interaction of the (axial) electric currents in the pre-existing and newly emerging flux systems. The relative contributions and effects of these mechanisms depend on the properties of the pre-existing and emerging flux systems. Here we focus on the location and orientation of the emerging flux relative to the coronal flux rope. Varying these parameters, we investigate under which conditions an eruption of the latter is triggered.

The large number of exoplanets discovered with the Transiting Exoplanet Survey Satellite (TESS) means that any observational biases from TESS could influence the derived stellar multiplicity statistics of exoplanet host stars. To investigate this problem, we obtained speckle interferometry of 207 control stars whose properties in the TESS Input Catalog (TIC) closely match those of an exoplanetary host star in the TESS Object of Interest (TOI) catalog, with the objective of measuring the fraction of these stars that have companions within $\sim1.2"$. Our main result is the identification of a bias in the creation of the control sample that prevents the selection of binaries with $0.1" \lesssim \rho \lesssim 1.2"$ and $\Delta$mag $\lesssim3$. This bias is the result of large astrometric residuals that cause binaries with these parameters to fail the quality checks used to create the TIC, which in turn causes them to have incomplete stellar parameters (and uncertainties) in the TIC. Any stellar multiplicity study that relies exclusively upon TIC stellar parameters to identify its targets will struggle to select unresolved binaries in this parameter space. Left uncorrected, this selection bias disproportionately excludes high-mass-ratio binaries, causing the mass-ratio distribution of the companions to deviate significantly from the uniform distribution expected of FGK-type field binaries. After accounting for this bias, the companion rate of the FGK control stars is consistent with the canonical $46\pm2\%$ rate from Raghavan et al. 2010, and the mass-ratio distribution agrees with that of binary TOI host stars. There is marginal evidence that the control-star companions have smaller projected orbital separations than TOI host stars from previous studies.

Throughout the cosmic history, PBHs may experience an efficient phase of baryonic mass accretion from the surrounding medium. Its main consequences on their cosmological evolution are characteristic growths of the PBH masses and spins, as well as the emission of radiation, which is ultimately responsible for feedback effects that could weaken the efficiency of the process. In this chapter we review the basic formalism to describe the accretion rate, luminosity function and feedback effects, in order to provide distinctive predictions for the evolution of the PBH mass and spin parameters.

The black hole mass MBH is crucial in constraining the growth of supermassive BHs within their host galaxies. Since direct measurements of MBH with dynamical methods are restricted to a limited number of nearly quiescent nearby galaxies and a small minority of active galactic nuclei (AGN), we must rely on indirect methods. In this work, we utilize an unbiased, volume-limited, hard X-ray selected sample of AGN to compare the reliability of some commonly used indirect methods, emphasising those that can be applied to obscured AGN. Based on a subsample of AGN with MBH determined via dynamical methods, our study suggests that X-ray based techniques, such as the scaling method and the one based on the variability measured through the excess variance, are in good agreement with the dynamical methods. On the other hand, the M-sigma correlation based on inactive galaxies tends to systematically overestimate MBH, regardless of the level of obscuration. We provide a correcting factor that produces an acceptable agreement with dynamical values and can be used to quickly correct the MBH computed with this method. We also derive an alternative M-sigma correlation based on this unbiased sample of AGN with a slope considerably shallower than the ones obtained using inactive galaxies, suggesting that the latter correlation may not be appropriate to compute the MBH in AGN. Finally, we find that no quick fix can be applied to correct the MBH obtained from the fundamental plane of black hole activity, casting doubts on the reliability of this method.

The large-scale structure of the universe is distributed in a cosmic web. Studying the distribution and clustering of dark matter particles and halos may open up a new horizon for studying the physics of the dark universe. In this work, we investigate the nearest neighbour statistics and spherical contact function in cosmological models with massive neutrinos. For this task, we use the relativistic N-body code, gevolution and study particle snapshots at three different redshifts. In each snapshot, we find the halos and evaluate the letter functions for them. We show that a generic behaviour can be found in the nearest neighbour, $G(r)$, and spherical contact functions, $F(r)$, which makes these statistics promising tools to constrain the total neutrino mass.

We analyse three interacting vacuum dark energy models with the aim of exploring whether the $H_0$ and $\sigma_8$ tensions can be simultaneously resolved in such models. We present the first ever derivation of the covariant gauge-invariant perturbation formalism for the interacting vacuum scenario, and, for the sub-class of geodesic cold dark matter models, connect the evolution of perturbation variables in this approach to the familiar cosmological observables. We show how $H_0$ and $\sigma_8$ evolve in three interacting vacuum models: firstly, a simple linear coupling between the vacuum and cold dark matter; secondly, a coupling which mimics the behaviour of a Chaplygin gas; and finally a coupling which mimics the Shan--Chen fluid dark energy model. We identify, if any, the regions of parameter space which would correspond to a simultaneous resolution of both tensions in these models. When constraints from observational data are added, we show how all the models described are constrained to be close to their $\Lambda$CDM limits.

We present the discovery of twelve thus far non-repeating fast radio burst (FRB) sources, detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These sources were selected from a database comprising of order $10^3$ CHIME/FRB full-array raw voltage data recordings, based on their exceptionally high brightness and complex morphology. Our study examines the time-frequency characteristics of these bursts, including drifting, microstructure, and periodicities. The events in this sample display a variety of unique drifting phenomenologies that deviate from the linear negative drifting phenomenon seen in many repeating FRBs, and motivate a possible new framework for classifying drifting archetypes. Additionally, we detect microstructure features of duration $\lesssim$ 50 $\mu s$ in seven events, with some as narrow as $\approx$ 7 $\mu s$. We find no evidence of significant periodicities. Furthermore, we report the polarization characteristics of seven events, including their polarization fractions and Faraday rotation measures (RMs). The observed $|\mathrm{RM}|$ values span a wide range of $17.24(2)$ - $328.06(2) \mathrm{~rad~m}^{-2}$, with linear polarization fractions between $0.340(1)$ - $0.946(3)$. The morphological properties of the bursts in our sample appear broadly consistent with predictions from both relativistic shock and magnetospheric models of FRB emission, as well as propagation through discrete ionized plasma structures. We address these models and discuss how they can be tested using our improved understanding of morphological archetypes.

We report the time series analysis of TESS light curves of three blazars, BL Lacertae, 1RXS J111741.0+254858, and 1RXS J004519.6+212735, obtained using a customized approach for extracting AGN light curves. We find tentative evidence for quasi-periodic oscillations (QPOs) in these light curves that range from 2 to 6 days. Two methods of analysis are used for assessing their significance: generalized Lomb-Scargle periodograms and weighted wavelet Z-transforms. The different approaches of these methods together ensure a robust measurement of the significance of the claimed periodicities. We can attribute the apparent QPOs to the kink instability model which postulates that the observed QPOs are related to the temporal growth of kinks in the magnetized relativistic jet. We confirm the application of this model to BL Lacertae and extend the kink instability model to the other two BL Lac objects.

Due to the importance of satellites for society and the exponential increase in the number of objects in orbit, it is important to accurately determine the state (e.g., position and velocity) of these Resident Space Objects (RSOs) at any time and in a timely manner. State-of-the-art methodologies for initial orbit determination consist of Kalman-type filters that process sequential data over time and return the state and associated uncertainty of the object, as is the case of the Extended Kalman Filter (EKF). However, these methodologies are dependent on a good initial guess for the state vector and usually simplify the physical dynamical model, due to the difficulty of precisely modeling perturbative forces, such as atmospheric drag and solar radiation pressure. Other approaches do not require assumptions about the dynamical system, such as the trilateration method, and require simultaneous measurements, such as three measurements of range and range-rate for the particular case of trilateration. We consider the same setting of simultaneous measurements (one-shot), resorting to time delay and Doppler shift measurements. Based on recent advancements in the problem of moving target localization for sonar multistatic systems, we are able to formulate the problem of initial orbit determination as a Weighted Least Squares. With this approach, we are able to directly obtain the state of the object (position and velocity) and the associated covariance matrix from the Fisher's Information Matrix (FIM). We demonstrate that, for small noise, our estimator is able to attain the Cram\'er-Rao Lower Bound accuracy, i.e., the accuracy attained by the unbiased estimator with minimum variance. We also numerically demonstrate that our estimator is able to attain better accuracy on the state estimation than the trilateration method and returns a smaller uncertainty associated with the estimation.

Metastable `false' vacuum states are an important feature of the Standard Model of particle physics and many theories beyond it. Describing the dynamics of a phase transition out of a false vacuum via the nucleation of bubbles is essential for understanding the cosmology of vacuum decay and the full spectrum of observables. In this paper, we study vacuum decay by numerically evolving ensembles of field theories in 1+1 dimensions from a metastable state. We demonstrate that for an initial Bose-Einstein distribution of fluctuations, bubbles form with a Gaussian spread of center-of-mass velocities and that bubble nucleation events are preceded by an oscillon - a long-lived, time-dependent, pseudo-stable configuration of the field. Defining an effective temperature from the long-wavelength amplitude of fluctuations in the ensemble of simulations, we find good agreement between theoretical finite temperature predictions and empirical measurements of the decay rate, velocity distribution and critical bubble solution. We comment on the generalization of our results and the implications for cosmological observables.

We report on the results of a survey we conducted on the Japanese public's attitudes toward astronomy. This survey was conducted via an online questionnaire, with 2,000 responses received. Based on this data, we present what kind of interest the general public in Japan has in astronomy. We also conducted a questionnaire survey of those involved in astronomy communication to examine how they differ from the general public. The results suggest that while there are clear differences between them in terms of their engagement in astronomy, there is also continuity between them by looking at their attributes in more detail. The data presented in this paper could help us to promote communicating astronomy to the public.

We consider inflationary models with multiple spectator axions coupled to dark gauge sectors via Chern-Simons (CS) terms. The energy injection into Abelian gauge fields from the axions engenders a multi-peak profile for scalar and tensor spectra. We highlight the constraining power of CMB spectral distortions on the scalar signal and discuss the conditions under which spectator sectors can account for the recently observed stochastic gravitational wave (GW) background in the nHz range. Given the tantalizing prospect of a multi-peak ``GW forest'' spanning several decades in frequency, we elaborate on possible ultraviolet origins of the spectator models from Type IIB orientifolds. String compactifications generically produce a multitude of axions, the ``Axiverse'', from dimensional reduction of p-form gauge fields. The CS coupling of such axions to dark gauge fields in the worldvolume theory of D7-branes can be tuned via multiple brane wrappings and/or quantized gauge field strengths. If string axions coupled to Abelian gauge fields undergo slow-roll during inflation, they produce GW signals with peaked frequency distribution whose magnitude depends on the details of the compactification. We discuss the restrictions on spectator models from consistency and control requirements of the string compactification and thereby motivate models that may live in the string landscape as opposed to the swampland.

Two moons of Saturn, Janus and Epimetheus, are in co-orbital motion, exchanging orbits approximately every four Earth years as the inner moon approaches the outer moon and they gravitationally interact. The orbital radii of these moons differ by only 50 km (less than the moons' mean physical radii), and it is this slight difference in their orbits that enables their periodic exchanges. Numerical n-body simulations can accurately model these exchanges using only Newtonian physics acting upon three objects: Saturn, Janus, and Epimetheus. Here we present analytical approaches and solutions, and corresponding computer simulations, designed to explore the effects of the initial orbital radius difference on otherwise similar co-orbital systems. Comparison with our simulation results illustrates that our analytic expressions provide very accurate predictions for the moon separations at closest approach and simulated post-exchange orbital radii. Our analytic estimates of the exchange period also match the simulated value for Janus and Epimetheus to within a few percent, although systems with smaller differences in their orbital radii are less well-modeled by our simple approach, suggesting that either full simulations or more sophisticated analytic approaches would be required to estimate exchange periods in those cases.

We propose a general procedure for evaluating, directly from microphysics, the constitutive relations of heat-conducting fluids in regimes of large fluxes of heat. Our choice of hydrodynamic formalism is Carter's two-fluid theory, which happens to coincide with \"{O}ttinger's GENERIC theory for relativistic heat conduction. This is a natural framework, as it should correctly describe the relativistic ``inertia of heat'' as well as the subtle interplay between reversible and irreversible couplings. We provide two concrete applications of our procedure, where the constitutive relations are evaluated respectively from maximum entropy hydrodynamics and Chapman-Enskog theory.

In spirit of the recently proposed four-parameter generalized entropy of apparent horizon, we investigate inflationary cosmology where the matter field inside of the horizon is dominated by a scalar field with a power law potential (i.e., the form of $\phi^n$ where $\phi$ is the scalar field under consideration). Actually without any matter inside of the horizon, the entropic cosmology leads to a de-Sitter spacetime, or equivalently, an eternal inflation with no exit. Thus in order to achieve a viable inflation, we consider a minimally coupled scalar field inside the horizon, and moreover, with the simplest quadratic potential. It is well known that the $\phi^2$ potential in standard scalar field cosmology is ruled out from inflationary perspective as it is not consistent with the recent Planck 2018 data; (here it may be mentioned that in the realm of ``apparent horizon thermodynamics'', the standard scalar field cosmology is analogous to the case where the entropy of the apparent horizon is given by the Bekenstein--Hawking entropy). However, the story becomes different if the horizon entropy is of generalized entropic form, in which case, the effective energy density coming from the horizon entropy plays a significant role during the evolution of the universe. In particular, it turns out that in the context of generalized entropic cosmology, the $\phi^2$ potential indeed leads to a viable inflation (according to the Planck data) with a graceful exit, and thus the potential can be made back in the scene.

Light hypothetical particles with masses up to $\mathcal{O}(100)\ {\rm MeV}$ can be produced in the core of supernovae. Their subsequent decays to neutrinos can produce a flux component with higher energies than the standard flux. We study the impact of heavy neutral leptons, $Z'$ bosons, in particular ${\rm U(1)}_{L_\mu-L_\tau}$ and ${\rm U(1)}_{B-L}$ gauge bosons, and majorons coupled to neutrinos flavor-dependently. We obtain new strong limits on these particles from no events of high-energy SN 1987A neutrinos and their future sensitivities from observations of galactic supernova neutrinos.

Modified $f(R)$ theories of gravity have been investigated for quite a long time in the literature as a possible explanation for the inflationary period of the universe. The correspondence to General Relativity with an extra scalar field $\tilde\phi$ in the so-called Einstein Frame via a conformal transformation is a major tool in this class of theories. Here, we assume three different potentials $V(\tilde\phi)$ and a parametric-resonance coupling between $\tilde\phi$ and a secondary scalar field $\tilde\psi$ such that one can have both inflation and preheating in the Einstein frame. We study the instability resonance band structure for our models. Further, we determine the correspondent mechanism -- and the function $f(R)$ itself -- in the Jordan frame, that is possibly related to the so-called vacuum awakening mechanism.

We devise and demonstrate a method to search for non-gravitational couplings of ultralight dark matter to standard model particles using space-time separated atomic clocks and cavity-stabilized lasers. By making use of space-time separated sensors, which probe different values of an oscillating dark matter field, we can search for couplings that cancel in typical local experiments. We demonstrate this method using existing data from a frequency comparison of lasers stabilized to two optical cavities connected via a 2220 km fiber link [Nat. Commun. 13, 212 (2022)]. The absence of significant oscillations in the data results in constraints on the coupling of scalar dark matter to electrons, d_me, for masses between 1e-19 eV and 2e-15 eV. These are the first constraints on d_me alone in this mass range, and improve the dark matter constraints on any scalar-Fermion coupling by up to two orders of magnitude.

Axion-like particles with a coupling to non-Abelian gauge fields at finite temperature can experience dissipation due to sphaleron heating. This could play an important role for warm inflation or dynamical dark energy. We investigate to what degree the efficiency of this non-perturbative mechanism depends on the details of the underlying particle physics model. For a wide range of scenarios and energy scales, we find that a previously discussed suppression of sphaleron heating by light fermions can be alleviated. As an outlook, we point out that fermionic effects may provide a new mechanism for ending warm inflation.

Assuming axions are potential dark matter (DM) candidate that make up all of the DM abundance, we discuss production of axions via (i) standard misalignment mechanism during the period of reheating and (ii) graviton-mediated 2-to-2 scattering of the inflaton and bath particles, where the inflaton $\phi$ oscillates in a monomial potential $V(\phi)\propto\phi^k$ with a general equation of state. Considering reheating takes place purely gravitationally, mediated by massless gravitons, we explore the viable region of the parameter space that agrees with the observed DM relic abundance, satisfying bounds from big bang nucleosynthesis (BBN) and cosmic microwave background radiation (CMB). We also discuss complementarity between dedicated axion search experiments and futuristic gravitational wave search facilities in probing the viable parameter space.

Hot viscous plasmas unavoidably emit a gravitational wave background, similar to the electromagnetic black body radiation. We study the contribution from hidden particles to the diffuse background emitted by the primordial plasma in the early universe. While this contribution can easily dominate over that from Standard Model particles, we find that both are capped by a generic upper bound that makes them difficult to detect with interferometers in the foreseeable future. However, resonant cavity experiments could potentially observe backgrounds that saturate the upper bound. We illustrate our results for axions and heavy neutral leptons. Finally, our results suggest that previous works overestimated the gravitational wave background from particle decays out of thermal equilibrium.

The exploration of the parameter space of axion and axion-like particle dark matter is a major aim of the future program of astroparticle physics investigations. In this context, we present a possible strategy that focuses on detecting radio emissions arising from the conversion of dark matter axions in the Sun's magnetic field, including conversion in sunspots. We demonstrate that near-future low-frequency radio telescopes, such as the SKA Low, may access regions of unexplored parameter space for masses $m_a\lesssim 10^{-6}$ eV.

Recent detections of a low-frequency gravitational wave background (GWB) from various pulsar-timing-array (PTA) observations have renewed the interest in the inspiraling supermassive black hole binaries (SMBHBs), whose population is believed to be the most promising candidate of but disfavored by the observed GWB spectrum naively fitted with purely GW-driven circular binaries. Including either orbital eccentricity or dark matter (DM) spike can improve the fit to the current data, but the inclusion of both can further display distinctive features detectable in future PTA observations. With a typical initial eccentricity $e_0\sim\mathcal{O}(0.1)$ for the inspiraling SMBHBs, the DM spike can easily drive the orbital eccentricity close to unity, leaving behind a large turnover eccentricity when GWs begin to dominate the orbital circularization. In particular, the DM spike index $\gamma_\mathrm{sp}$ universally flattens the characteristic strain $h_c\sim f^{7/6-\gamma_\mathrm{sp}/3}$ in the infrared and produces a novel structure with an oscillating turnover followed by a flat dip and a bump-like peak at low, intermediate, and high frequencies, respectively. Future PTA detection of such characteristics would necessarily provide the smoking gun for the DM spike and even reveal the nature of DM.

In this review article, we revisit the topic of baryogenesis, which is the physical process that generated the observed baryon asymmetry during the first stages of the primordial Universe. A viable theoretical explanation to understand and investigate the mechanisms underlying baryogenesis must always ensure that the Sakharov criteria are fulfilled. These essentially state the following: (i) baryon number violation; (ii) the violation of both C (charge conjugation symmetry) and CP (the composition of parity and C); (iii) and the departure from equilibrium. Throughout the years, various mechanisms have been proposed to address this issue, and here we review two of the most important, namely, electroweak baryogenesis (EWB) and Grand Unification Theories (GUTs) baryogenesis. Furthermore, we briefly explore how a change in the theory of gravity affects the EWB and GUT baryogenesis by considering Scalar--Tensor Theories (STT), where the inclusion of a scalar field mediates the gravitational interaction, in addition to the metric tensor field. We consider specific STT toy models and show that a modification of the underlying gravitational theory implies a change in the time--temperature relation of the evolving cosmological model, thus altering the conditions that govern the interplay between the rates of the interactions generating baryon asymmetry, and the expansion rate of the Universe. Therefore, the equilibrium of the former does not exactly occur as in the general relativistic standard model, and there are consequences for the baryogenesis mechanisms that have been devised. This is representative of the type of modifications of the baryogenesis processes that are to be found when considering extended theories of gravity.

The evidence for a non-vanishing isotropic cosmic birefringence in recent analyses of the CMB data provides a tantalizing hint for new physics. Domain wall (DW) networks have recently been shown to generate an isotropic birefringence signal in the ballpark of the measured value when coupled to photons. In this work, we explore the axionic defects hypothesis in more detail and extending previous results to annihilating and late-forming networks, and by pointing out other smoking-gun signatures of the network in the CMB spectrum such as the anisotropic birefringent spectrum and B-modes. We also argue that the presence of cosmic strings in the network does not hinder a large isotropic birefringence signal because of an intrinsic environmental contribution coming from low redshifts thus leaving open the possibility that axionic defects can explain the signal. Regarding the remaining CMB signatures, with the help of dedicated 3D numerical simulations of DW networks, that we took as a proxy for the axionic defects, we show how the anisotropic birefringence spectrum combined with a tomographic approach can be used to infer the formation and annihilation time of the network. From the numerical simulations, we also computed the spectrum of gravitational waves (GWs) generated by the network in the post-recombination epoch and use previous searches for stochastic GW backgrounds in the CMB to derive for the first time a bound on the tension and abundance of networks with DWs that annihilate after recombination. Our bounds extend to the case where the network survives until the present time and improve over previous bounds by roughly one order of magnitude. Finally, we show the interesting prospects for detecting B-modes of DW origin with future CMB experiments.

The IceCube collaboration pioneered the detection of $\mathcal{O}{(\text{PeV})}$ neutrino events and the identification of astrophysical sources of high-energy neutrinos. In this study, we explore scenarios in which high-energy neutrinos are produced in the vicinity of astrophysical objects with strong magnetic field, such as magnetars. While propagating through such magnetic field, neutrinos experience helicity precession induced by their magnetic moments, and this impacts their flux and flavour composition at Earth. Considering both flavor composition of high-energy neutrinos and Glashow resonance events we find that detectable signatures may arise at neutrino telescopes, such as IceCube, for presently unconstrained neutrino magnetic moments in the range between $\mathcal{O}(10^{-15})~\mu_B$ and $\mathcal{O}(10^{-12})~\mu_B$.

Tests of the no-hair theorem using astrophysical black holes involve the detection of at least two quasi-normal modes (QNMs) in the gravitational wave emitted by a perturbed black hole. A detection of two modes -- the dominant, $(\ell, m, n) = (2,2,0)$, mode and its first overtone, the $(2,2,1)$ mode -- in the post-merger signal of the binary black hole merger GW150914 was claimed in Isi et al. [arXiv:1905.00869], with further evidence provided in Isi \& Farr [arXiv:2202.02941]. However, Cotesta et al. [arXiv:2201.00822] disputed this claim, finding that evidence for the overtone only appeared if the signal was analyzed before merger, when a QNM description of the signal is not valid. Due to technical challenges, both of these analyses fixed the merger time and sky location of GW150914 when estimating the evidence for the overtone. At least some of the contention can be attributed to fixing these parameters. Here, we surmount this difficulty and fully marginalize over merger time and sky location uncertainty while doing a QNM analysis of GW150914. We also simultaneously and independently fit the pre-merger inspiral signal. We find that marginalizing over all parameters yields low evidence for the presence of the overtone, with a Bayes factor of $2.3\pm 0.1$ in favor of a QNM model with the overtone versus one without. The arrival time uncertainty of GW150914 is too large to definitively claim detection of the $(2,2,1)$ mode.

We explore the consequences of imposing robust thermodynamic constraints arising from perturbative Quantum Chromodynamics (QCD) when inferring the dense-matter equation-of-state (EOS). We find that the termination density, up to which the EOS modeling is performed in an inference setup, strongly affects the constraining power of the QCD input. This sensitivity in the constraining power arises from EOSs that have a specific form, with drastic softening immediately above the termination density followed by a strong stiffening. We also perform explicit modeling of the EOS down from perturbative-QCD densities to construct a new QCD likelihood function that incorporates additional perturbative-QCD calculations of the sound speed and is insensitive to the termination density, which we make publicly available.

We derive new constraints on axion-like particles (ALPs) using precision $X$-ray polarization studies of magnetars. Specifically, we use the first detection of polarized $X$-rays from the magnetars 4U 0142+61 and 1RXS J170849.0-400910 by the Imaging $X$-ray Polarimetry Explorer (IXPE) to place bounds on the product of the ALP-photon and ALP-nucleon couplings, $g_{a\gamma}g_{aN}$, with $g_{aN}$ being responsible for ALP production in the core of the magnetar and $g_{a\gamma}$ controlling the ALP-photon conversion probability in the magnetosphere. These bounds are most sensitive to the magnetar core temperature, and we use two benchmark values of $1\times 10^8$ K and $5\times 10^8$ K to derive our constraints. For the latter choice, our bounds are competitive with the existing bounds on the coupling product coming from a combination of CAST (for $g_{a\gamma}$) and SN1987A (for $g_{aN}$). We advocate for more precise and extensive observational campaigns in the higher end of the $2~-~8~$keV spectral window, where ALP-induced polarization is the strongest. We further advocate for hard $X$-ray polarization studies of young, hot, near-Earth magnetars with strong magnetic fields.