Papers for Friday, Aug 25 2023

Eccentric orbits can be decomposed into a series of sine curves which affects how the false alarm probability is computed when using traditional periodograms on radial-velocity data. Here we show that a candidate exoplanet orbiting the M dwarf GJ 9404, identified by the HADES survey using data from the HARPS-N spectrograph, is in fact a bona-fide planet on a highly eccentric orbit. Far from a candidate, GJ 9404 b is detected with a high confidence. We reach our conclusion using two methods that assume Keplerian functions rather than sines to compute a detection probability, a Bayes Factor, and the FIP periodogram. We compute these using nested sampling with {\tt kima}.

Gravitational-wave searches for cosmic strings are currently hindered by the presence of detector glitches, some classes of which strongly resemble cosmic string signals. This confusion greatly reduces the efficiency of searches. A deep-learning model is proposed for the task of distinguishing between gravitational wave signals from cosmic string cusps and simulated blip glitches in design sensitivity data from the future Einstein Telescope. The model is an ensemble consisting of three convolutional neural networks, achieving an accuracy of 79%, a true positive rate of 76%, and a false positive rate of 18%. This marks the first time convolutional neural networks have been trained on a realistic population of Einstein Telescope glitches. On a dataset consisting of signals and glitches, the model is shown to outperform matched filtering, specifically being better at rejecting glitches. The behaviour of the model is interpreted through the application of several methods, including a novel technique called waveform surgery, used to quantify the importance of waveform sections to a classification model. In addition, a method to visualise convolutional neural network activations for one-dimensional time series is proposed and used. These analyses help further the understanding of the morphological differences between cosmic string cusp signals and blip glitches. Because of its classification speed in the order of magnitude of milliseconds, the deep-learning model is suitable for future use as part of a real-time detection pipeline. The deep-learning model is transverse and can therefore potentially be applied to other transient searches.

Small-scale dark matter structures lighter than a billion solar masses are an important probe of primordial density fluctuations and dark matter microphysics. Due to their lack of starlight emission, their only guaranteed signatures are gravitational in nature. We report on results of a search for astrometric weak lensing by compact dark matter subhalos in the Milky Way with Gaia DR3 data. Using a matched-filter analysis to look for correlated imprints of time-domain lensing on the proper motions of background stars in the Magellanic Clouds, we exclude order-unity substructure fractions in halos with masses $M_{l}$ between $10^{7} \, M_{\odot}$ and $10^{9} \, M_{\odot}$ and sizes of one parsec or smaller. We forecast that a similar approach based on proper accelerations across the entire sky with data from Gaia DR4 may be sensitive to substructure fractions of $f_{l} \gtrsim 10^{-3}$ in the much lower mass range of $10 \, M_{\odot} \lesssim M_{l} \lesssim 3 \times 10^{3} \, M_{\odot}$. We further propose an analogous technique for stacked star-star lensing events in the regime of large impact parameters. Our first implementation is not yet sufficiently sensitive but serves as a useful diagnostic and calibration tool; future data releases should enable average stellar mass measurements using this stacking method.

JWST is revolutionizing our understanding of the high-z Universe by expanding the black hole horizon, looking farther and to smaller masses, and revealing the stellar light of their hosts. New detections of high-z systems offer unprecedented insights into the formation of the first black holes and their early co-evolution with galaxies. By examining JWST galaxies at z=4-7 that host H$\alpha$-detected black holes, we investigate (i) the high-z $M_\bullet-M_\star$ relation and (ii) the black hole mass distribution, especially in its low-mass range ($M_\bullet\lesssim10^{6.5} M_\odot$). With a detailed statistical analysis, our findings conclusively reveal a high-z $M_\bullet-M_\star$ relation that deviates at $>3\sigma$ confidence level from the local relation: $\log(M_\bullet/M_\odot) = -2.38^{+0.82}_{-0.83}+1.06^{+0.09}_{-0.09}\log(M_\star/M_\odot)$. Black holes are overmassive by $\sim10-100\times$ compared to their local counterparts in similar galactic hosts. This fact is not due to a selection effect in surveys. Moreover, our analysis predicts the possibility of detecting in high-z JWST surveys $5-18\times$ more black holes with $M_\bullet\lesssim10^{6.5} M_\odot$, and $10-30\times$ more with $M_\bullet \lesssim 10^{8.5} M_\odot$, compared to local relation's predictions. The lighter black holes preferentially occupy galaxies with a stellar mass of $\sim 10^{7.5}-10^8 M_\odot$. We have yet to detect these sources because (i) they may be inactive (duty cycles 1%-10%), (ii) the host overshines the AGN, or (iii) the AGN is obscured and not immediately recognizable by line diagnostics. A search of low-mass black holes in existing JWST surveys will further test the $M_\bullet-M_\star$ relation. Current JWST fields represent a treasure trove of black hole systems at z=4-7; their detection will provide crucial insights into their early evolution and co-evolution with their galactic hosts.

We use the IllustrisTNG50 cosmological hydrodynamical simulation, complemented by a catalog of tagged globular clusters, to investigate the properties and build up of two extended luminous components: the intra-cluster light (ICL) and the intra-cluster globular clusters (ICGC). We select the 39 most massive groups and clusters in the box, spanning the range of virial masses $5 \times 10^{12} < \rm M_{200}/\rm M_{\odot} < 2 \times 10^{14}$. We find good agreement between predictions from the simulations and current observational estimates of the fraction of mass in the ICL and its radial extension. The stellar mass of the ICL is only $\sim10\%-20\%$ of the stellar mass in the central galaxy but encodes useful information on the assembly history of the group or cluster. About half the ICL in all our systems is brought in by galaxies in a narrow stellar mass range, $M_*=10^{10}-10^{11}$ $\rm M_{\odot}$. However, the contribution of low-mass galaxies ($M_*<10^{10}$ $\rm M_{\odot}$) to the build-up of the ICL varies broadly from system to system, $\sim 5\%-45\%$, a feature that might be recovered from the observable properties of the ICL at $z=0$. At fixed virial mass, systems where the accretion of dwarf galaxies plays an important role have shallower metallicity profiles, less metal content and a lower stellar mass in the ICL than systems where the main contributors are more massive galaxies. We show that intra-cluster GCs are also good tracers of this history, representing a valuable alternative when diffuse light is not detectable.

We present VLT/MUSE Narrow Field Mode (NFM) observations of a pair of disc-bearing young stellar objects towards the Orion Bar: 203-504 and 203-506. Both of these discs are subject to external photoevaporation, where winds are launched from their outer regions due to environmental irradiation. Intriguingly, despite having projected separation from one another of only 1.65{\arcsec} (660au at 400pc), 203-504 has a classic teardrop shaped ``proplyd'' morphology pointing towards $\theta^2$Ori A (indicating irradiation by the EUV of that star, rather than $\theta^1$ Ori C) but 203-506 has no ionisation front, indicating it is not irradiated by stellar EUV at all. However, 203-506 does show [CI] 8727{\AA} and [OI] 6300{\AA} in emission, indicating irradiation by stellar FUV. This explicitly demonstrates the importance of FUV irradiation in driving mass loss from discs. We conclude that shielding of 203-506 from EUV is most likely due to its position on the observers side of an ionized layer lying in the foreground of the Huygens Region. We demonstrate that the outflow HH 519, previously thought to be emanating from 203-504 is actually an irradiated cloud edge and identify a new compact outflow from that object approximately along our line of sight with a velocity $\sim130$\,km\,s$^{-1}$.

In order to address fundamental questions related to the expansion history of the Universe and its primordial nature with the next generation of galaxy experiments, we need to model reliably large-scale structure observables such as the correlation function and the power spectrum. Cosmological $N$-body simulations provide a reference through which we can test our models, but their output suffers from sample variance on large scales. Fortunately, this is the regime where accurate analytic approximations exist. To reduce the variance, which is key to making optimal use of these simulations, we can leverage the accuracy and precision of such analytic descriptions using Control Variates (CV). We apply two control variate formulations to mock catalogs generated in anticipation of upcoming data from the Dark Energy Spectroscopic Instrument (DESI) to test the robustness of its analysis pipeline. Our CV-reduced measurements, of the power spectrum and correlation function, both pre- and post-reconstruction, offer a factor of 5-10 improvement in the measurement error compared with the raw measurements from the DESI mock catalogs. We explore the relevant properties of the galaxy samples that dictate this reduction and comment on the improvements we find on some of the derived quantities relevant to Baryon Acoustic Oscillation (BAO) analysis. We also provide an optimized package for computing the power spectra and other two-point statistics of an arbitrary galaxy catalog as well as a pipeline for obtaining CV-reduced measurements on any of the AbacusSummit cubic box outputs. We make our scripts, notebooks, and benchmark tests against existing software publicly available and report a speed improvement of a factor of $\sim$10 for a grid size of $N_{\rm mesh} = 256^3$ compared with $\texttt{nbodykit}$.

We study the 10 Myr evolution of parsec-scale stellar disks with initial masses of $M_{\mathrm{disk}} = 1.0$ - $7.5 \times 10^4 M_\odot$ and eccentricities $e_\mathrm{init}=0.1$-$0.9$ around supermassive black holes (SMBHs). Our disk models are embedded in a spherical background potential and have top-heavy single and binary star initial mass functions (IMF) with slopes of $0.25$-$1.7$. The systems are evolved with the N-body code $\texttt{BIFROST}$ including post-Newtonian (PN) equations of motion and simplified stellar evolution. All disks are unstable and evolve on Myr timescales towards similar eccentricity distributions peaking at $e_\star \sim 0.3$-$0.4$. Models with high $e_\mathrm{init}$ also develop a very eccentric $(e_\star\gtrsim0.9)$ stellar population. For higher disk masses $M_\mathrm{disk} \gtrsim3 \times10^4\;\mathrm{M_\odot}$, the disk disruption dynamics is more complex than the standard secular eccentric disk instability with opposite precession directions at different disk radii - a precession direction instability. We present an analytical model describing this behavior. A milliparsec population of $N\sim10$-$100$ stars forms around the SMBH in all models. For low $e_\mathrm{init}$ stars migrate inward while for $e_\mathrm{init}\gtrsim0.6$ stars are captured by the Hills mechanism. Without PN, after $6$ Myr the captured stars have a sub-thermal eccentricity distribution. We show that including PN effects prevents this thermalization by suppressing resonant relaxation effects and cannot be ignored. The number of tidally disrupted stars is similar or larger than the number of milliparsec stars. None of the simulated models can simultaneously reproduce the kinematic and stellar population properties of the Milky Way center clockwise disk and the S-cluster.

We consider a model of early modified gravity (EMG) that was recently proposed as a candidate to resolve the Hubble tension. The model consists in a scalar field $\sigma$ with a non-minimal coupling (NMC) to the Ricci curvature of the form $F(\sigma) = M_{\mathrm{pl}}^2+\xi\sigma^2$ and an effective mass induced by a quartic potential $V(\sigma) = \lambda \sigma^4/4$. We present the first analyses of the EMG model in light of the latest ACT DR4 and SPT-3G data in combination with full Planck data, and find a $\gtrsim 2\sigma$ preference for a non-zero EMG contribution from a combination of primary CMB data alone, mostly driven by ACT DR4 data. This is different from popular 'Early Dark Energy' models, which are detected only when the high-$\ell$ information from Planck temperature is removed. We find that the NMC plays a key role in controlling the evolution of density perturbations that is favored by the data over the minimally coupled case. Including measurements of supernovae luminosity distance from Pantheon+, baryonic acoustic oscillations and growth factor from BOSS, and CMB lensing of Planck leaves the preference unaffected. In the EMG model, the tension with S$H_0$ES is alleviated from $\sim 6\sigma$ to $\sim 3\sigma$. Further adding S$H_0$ES data rise the detection of the EMG model above $5\sigma$.

The MeerKAT Absorption Line Survey (MALS) has observed 391 telescope pointings at L-band (900 - 1670 MHz) at $\delta\lesssim$ $+20\deg$. We present radio continuum images and a catalog of 495,325 (240,321) radio sources detected at a signal-to-noise ratio (SNR) $>$5 over an area of 2289 deg$^2$ (1132 deg$^2$) at 1006 MHz (1381 MHz). Every MALS pointing contains a central bright radio source ($S_{1\,\mathrm{GHz}} \gtrsim 0.2$ Jy). The median spatial resolution is $12^{\prime\prime}$ ($8^{\prime\prime}$). The median rms noise away from the pointing center is 25 $\mu$Jy beam$^{-1}$ (22 $\mu$Jy beam$^{-1}$) and is within $\sim$ 15% of the achievable theoretical sensitivity. The flux density scale ratio and astrometric accuracy deduced from multiply observed sources in MALS are less than 1% (8% scatter) and $1^{\prime\prime}$, respectively. Through comparisons with NVSS and FIRST at 1.4 GHz, we establish the catalog's accuracy in the flux density scale and astrometry to be better than 6% (15% scatter) and $0.8^{\prime\prime}$, respectively. The median flux density offset is higher (9%) for an alternate beam model based on holographic measurements. The MALS radio source counts at 1.4 GHz are in agreement with literature. We estimate spectral indices ($\alpha$) of a subset of 125,621 sources (SNR$>$8), confirm the flattening of spectral indices with decreasing flux density and identify 140 ultra steep-spectrum ($\alpha<-1.3$) sources as prospective high-$z$ radio galaxies ($z>2$). We have identified 1308 variable and 122 transient radio sources comprising primarily of AGN that demonstrate long-term (26 years) variability in their observed flux densities. The MALS catalogs and images are publicly available at https://mals.iucaa.in.

GWSkyNet-Multi is a machine learning model developed for classification of candidate gravitational-wave events detected by the LIGO and Virgo observatories. The model uses limited information released in the low-latency Open Public Alerts to produce prediction scores indicating whether an event is a merger of two black holes, a merger involving a neutron star, or a non-astrophysical glitch. This facilitates time sensitive decisions about whether to perform electromagnetic follow-up of candidate events during LIGO-Virgo-KAGRA (LVK) observing runs. However, it is not well understood how the model is leveraging the limited information available to make its predictions. As a deep learning neural network, the inner workings of the model can be difficult to interpret, impacting our trust in its validity and robustness. We tackle this issue by systematically perturbing the model and its inputs to explain what underlying features and correlations it has learned for distinguishing the sources. We show that the localization area of the 2D sky maps and the computed coherence versus incoherence Bayes factors are used as strong predictors for distinguishing between real events and glitches. The estimated distance to the source is further used to discriminate between binary black hole mergers and mergers involving neutron stars. We leverage these findings to show that events misclassified by GWSkyNet-Multi in LVK's third observing run have distinct sky area, coherence factor, and distance values that influence the predictions and explain these misclassifications. The results help identify the model's limitations and inform potential avenues for further optimization.

The Compton Spectrometer and Imager (COSI) is a NASA Small Explorer (SMEX) satellite mission in development with a planned launch in 2027. COSI is a wide-field gamma-ray telescope designed to survey the entire sky at 0.2-5 MeV. It provides imaging, spectroscopy, and polarimetry of astrophysical sources, and its germanium detectors provide excellent energy resolution for emission line measurements. Science goals for COSI include studies of 0.511 MeV emission from antimatter annihilation in the Galaxy, mapping radioactive elements from nucleosynthesis, determining emission mechanisms and source geometries with polarization measurements, and detecting and localizing multimessenger sources. The instantaneous field of view for the germanium detectors is >25% of the sky, and they are surrounded on the sides and bottom by active shields, providing background rejection as well as allowing for detection of gamma-ray bursts and other gamma-ray flares over most of the sky. In the following, we provide an overview of the COSI mission, including the science, the technical design, and the project status.

The star cluster initial mass function is observed to have an inverse power law exponent around 2, yet there is no consensus on what determines this distribution, and why some variation is observed in different galaxies. Furthermore, the cluster formation efficiency covers a range of values, particularly when considering different environments. These clusters are often used to empirically constrain star formation and as fundamental units for stellar feedback models. Detailed galaxy models must therefore accurately capture the basic properties of observed clusters to be considered predictive. We use hydrodynamical simulations of a dwarf galaxy as a laboratory to study star cluster formation. We test different combinations of stellar feedback mechanisms, including stellar winds, ionizing radiation, and supernovae. Each feedback mechanism affects the cluster formation efficiency and cluster mass function. Increasing the feedback budget by combining the different types of feedback decreases the cluster formation efficiency by reducing the number of massive clusters. Ionizing radiation is found to be especially influential. This effect depends on the timing of feedback initiation, as shown by comparing early and late feedback. Early feedback occurs from ionizing radiation and stellar winds with onset immediately after a massive star is formed. Late feedback occurs when energy injection only starts after the main-sequence lifetime of the most massive SN progenitor, a timing that is further influenced by the choice of the most massive SN progenitor. Late feedback alone results in a broad, flat mass function, approaching a log-normal shape in the complete absence of feedback. Early feedback, on the other hand, produces a power-law cluster mass function with lower formation efficiency, albeit with a steeper slope than that usually observed.

The ratio of the Lowes spectrum and the secular variation spectrum measured at the Earth's surface provides a time scale $\tau_{\rm sv}(l)$ as a function of spherical harmonic degree $l$. $\tau_{\rm sv}$ is often assumed to be representative of time scales related to the dynamo inside the outer core and its scaling with $l$ is debated. To assess the validity of this surmise and to study the time variation of the geomagnetic field $\boldsymbol{\dot B}$ inside the outer core, we introduce a magnetic time-scale spectrum $\tau(l,r)$ that is valid for all radius $r$ above the inner core and reduces to the usual $\tau_{\rm sv}$ at and above the core-mantle boundary (CMB). We study $\tau$ in a numerical geodynamo model. Focusing on the large scales, we find that $\tau \sim l^{-1}$ at the CMB. Just below the CMB, $\tau$ undergo a sharp transition such that the scaling becomes shallower than $l^{-1}$. This transition stems from the magnetic boundary condition at the CMB that ties all three components of $\boldsymbol{\dot B}$ together. In the interior of the outer core, the time variation of the horizontal magnetic field, which dominates $\boldsymbol{\dot B}$, has no such constraint. The upshot is $\tau_{\rm sv}$ becomes unreliable in estimating time scales inside the outer core. Another question concerning $\tau$ is whether a scaling argument based on the frozen-flux hypothesis can be used to explain its scaling. To investigate this, we analyse the induction equation in the spectral space. We find that away from both boundaries, the magnetic diffusion term is negligible in the power spectrum of $\boldsymbol{\dot B}$. However, $\boldsymbol{\dot B}$ is controlled by the radial derivative in the induction term, thus invalidating the frozen-flux argument. Near the CMB, magnetic diffusion starts to affect $\boldsymbol{\dot B}$ rendering the frozen-flux hypothesis inapplicable.

We conduct 3D magnetohydrodynamic (MHD) simulations of decaying turbulence in the solar wind context. To account for the spherical expansion of the solar wind, we implement the expanding box model. The initial turbulence comprises uncorrelated counter-propagating Alfv\'en waves and exhibits an isotropic power spectrum. Our findings reveal the consistent generation of negative residual energy whenever nonlinear interactions are present, independent of the normalized cross helicity $\sigma_c$. The spherical expansion facilitates this process. The resulting residual energy is primarily distributed in the perpendicular direction, with $[S_2(\mathbf{b})-S_2(\mathbf{u})] \propto l_\perp$ or equivalently $-E_r \propto k_\perp^{-2}$. Here $S_2(\mathbf{b})$ and $S_2(\mathbf{u})$ are second-order structure functions of magnetic field and velocity respectively. In most runs, $S_2(\mathbf{b})$ develops a scaling relation $S_2(\mathbf{b}) \propto l_\perp^{1/2}$ ($E_b \propto k_\perp^{-3/2}$). In contrast, $S_2(\mathbf{u})$ is consistently shallower than $S_2(\mathbf{b})$, which aligns with in-situ observations of the solar wind. We observe that the higher-order statistics of the turbulence, which act as a proxy for intermittency, are strongly affected by the expansion effect but have weak dependence on the initial $\sigma_c$. Generally, the intermittency is more pronounced when the expansion effect is present. Finally, we find that in our simulations although the negative residual energy and intermittency grow simultaneously as the turbulence evolves, there is no obvious causal relation between them because they are generated on different scales.

Interstellar ices are largely composed of frozen water. It is important to derive fundamental parameters for H$_2$O ice such as absorption and scattering opacities for which accurate complex refractive indexes are needed. The primary goal of this work is to derive ice-grain opacities based on accurate H$_2$O ice complex refractive indexes and to assess their impact on the derivation of ice column densities and porosity in space. We use the \texttt{optool} code to derive ice-grain opacities values based on new mid-IR complex refractive index measurements of H$_2$O ice. Next, we use those opacities in the \texttt{RADMC-3D} code to run a radiative transfer simulation of a protostellar envelope containing H$_2$O ice. This is used to calculate water ice column densities. We find that the real refractive index in the mid-IR of H$_2$O ice at 30~K is $\sim$14\% lower than previously reported in the literature. This has a direct impact on the ice column densities derived from the simulations of embedded protostars. We find that ice porosity plays a significant role in the opacity of icy grains and that the H$_2$O libration mode can be used as a diagnostic tool to constrain the porosity level. Finally, the refractive indexes presented here allow us to estimate a grain size detection limit of 18~$\mu$m based on the 3~$\mu$m band whereas the 6~$\mu$m band allows tracing grain sizes larger than 20~$\mu$m. Based on radiative transfer simulations using new mid-IR refractive indexes, we conclude that H$_2$O ice leads to more absorption of infrared light than previously estimated. This implies that the 3 and 6~$\mu$m bands remain detectable in icy grains with sizes larger than 10~$\mu$m. Finally, we propose that also the H$_2$O ice libration band can be a diagnostic tool to constrain the porosity level of the interstellar ice, in addition to the OH dangling bond, which is routinely used for this purpose.

Magnetars are slowly-rotating neutron stars with extremely strong magnetic fields that rarely produce extremely bright, energetic giant flares. Magnetar Giant Flares (MGFs) begin with a short (200 ms) intense flash, followed by fainter emission lasting several minutes that is modulated by the magnetar spin period (typically 2-12 s). Over the last 40 years, only three MGFs have been observed within our Galaxy and the Magellanic Clouds, which all suffered from instrumental saturation due to their extreme intensity. It has been proposed, that extragalactic MGFs masquerade as a small subset of short Gamma-ray Bursts (GRBs), noting that the sensitivity of current instrumentation prevents us from detecting the pulsating tail to distances slightly beyond the Magellanic Clouds. However, their initial bright flash is readily observable out to distances of < 25 Mpc. In this presentation, we will evaluate the spectral and temporal behaviors of MGFs using recent observations from events such as GRB200415A, to differentiate them from other progenitors, such as short GRBs. We then present an overview of the Moon Burst Energetics All-sky Monitor (MoonBEAM), which will attempt to discover more of these events, providing highly sensitive data that will help unravel the nature of these phenomena further in an attempt to better understand their emission mechanisms comparatively with GRBs. In doing so, MoonBEAM will help provide a comprehensive picture of energetic astrophysical phenomena, a key goal of the Astro2020 decadal survey.

Transient radio sources, such as fast radio bursts, intermittent pulsars, and rotating radio transients, can offer a wealth of information regarding extreme emission physics as well as the intervening interstellar and/or intergalactic medium. Vital steps towards understanding these objects include characterizing their source populations and estimating their event rates across observing frequencies. However, previous efforts have been undertaken mostly by individual survey teams at disparate observing frequencies and telescopes, and with non-uniform algorithms for searching and characterization. The Petabyte Project (TPP) aims to address these issues by uniformly reprocessing data from several petabytes of radio transient surveys covering two decades of observing frequency (300 MHz-20 GHz). The TPP will provide robust event rate analyses, in-depth assessment of survey and pipeline completeness, as well as revealing discoveries from archival and ongoing radio surveys. We present an overview of TPP's processing pipeline, scope, and our potential to make new discoveries.

The Laser Interferometer Space Antenna (LISA) is expected to detect a wide variety of gravitational wave sources in the mHz band. Some of these signals will elude individual detection, instead contributing as confusion noise to one of several stochastic gravitational-wave backgrounds (SGWBs) -- notably including the `Galactic foreground', a loud signal resulting from the superposition of millions of unresolved double white dwarf binaries (DWDs) in the Milky Way. It is possible that similar, weaker SGWBs will be detectable from other DWD populations in the local universe, including the Large Magellanic Cloud (LMC). We use the Bayesian LISA Inference Package ($\tt{BLIP}$) to evaluate the detectability by LISA of an anisotropic SGWB generated by unresolved DWDs in the LMC. To do so, we simulate the LMC SGWB from a realistic DWD population generated via binary population synthesis, simulate four years of time-domain data with $\tt{BLIP}$ comprised of stochastic contributions from the LMC SGWB and the LISA detector noise, and analyze this data with $\tt{BLIP}$'s spherical harmonic anisotropic SGWB search. We present results of this analysis and show that the SGWB from DWDs in the LMC is potentially detectable by LISA.

The Compton Pair (ComPair) telescope is a prototype that aims to develop the necessary technologies for future medium energy gamma-ray missions and to design, build, and test the prototype in a gamma-ray beam and balloon flight. The ComPair team has built an instrument that consists of 4 detector subsystems: a double-sided silicon strip detector Tracker, a novel high-resolution virtual Frisch-grid cadmium zinc telluride Calorimeter, and a high-energy hodoscopic cesium iodide Calorimeter, all of which are surrounded by a plastic scintillator anti-coincidence detector. These subsystems together detect and characterize photons via Compton scattering and pair production, enable a veto of cosmic rays, and are a proof-of-concept for a space telescope with the same architecture. A future medium-energy gamma-ray mission enabled through ComPair will address many questions posed in the Astro2020 Decadal survey in both the New Messengers and New Physics and the Cosmic Ecosystems themes. In this contribution, we will give an overview of the ComPair project and steps forward to the balloon flight.

Radiation feedback from massive population III stars may have given rise to low mass star formation from primordial or nearly primordial material. If early universe low mass stars did form, some should remain locally as white dwarfs, sub-giants, or main sequence stars. In this paper, we present model calculations for the evolution of single 0.8 Msun to 3.0 Msun stars with primordial metallicity from pre-main sequence to the white dwarf cooling track, and calculations for the evolution of single 4.0 Msun to 7.0 Msun stars which conclude in the giant phase. One goal of this work is to identify potential observable markers for potential observed progenitors of first or nearly first stars. We uncover a number of seemingly peculiar evolutionary differences between that of pop III low mass stars compared with younger higher Z stars, as well as compared to other primordial evolution models. We also present an initial-final mass relationship and identify the minimum mass of a single white dwarf that could have had a population III progenitor.

Using young open clusters and O--B2-type stars in~\emph{Gaia}~DR3, we investigate the kinematics of the local spiral structure. In general, the young sources in the outer spiral arms may present larger peculiar motions than those in the inner spiral arms. The young open clusters appear to have smaller peculiar motions than the O--B2-type stars, and the sources in both the Perseus and Local Arms may show an inward motion toward the Galactic center and rotate slower than Galactic rotation. Meanwhile, the sources in the Carina Arm may move in the opposite direction from the Sun to the Galactic center and rotate marginally faster than Galactic rotation. In addition, using young open clusters and O--B2-type stars, we have improved the distance estimations of kinematic methods for several regions near the Sun.

We present the first set of broadband spectral and timing studies of two transient X-ray pulsars, MXB 0656-072 and MAXI J1409-619 using NuSTAR observations conducted during quiescence. Despite being captured at one of their lowest luminosity states, both these targets show signs of ongoing low-level accretion. Results from the time-averaged spectral analysis indicate for the first time, the presence of a strong soft power law component along with thermal emission from the neutron star hot spots. For both targets, the quiescent thermal X-ray emission is consistent with the deep crustal heating model. In MXB 0656-072, we do not detect any pulsations or indications of a cyclotron line during quiescence. However, in MAXI J1409-619 we detect strong pulsations at 502 s with a pulsed fraction of $\sim$66%, which adds this pulsar to the list of a handful of quiescent-state pulsating systems.

Massive black hole binaries (MBHBs) are the loudest gravitational-wave (GW) sources in milli-Hertz (mHz) GW band, but their dynamical evolution may stall when the black holes reach the innermost parsec of a galaxy. Such a ``final-parsec problem'' could be solved if MBHB forms in a gas-rich environment, such as an active galactic nucleus (AGN), but other solutions not involving AGNs also exist. Testing the correlation between MBHBs and AGNs is difficult in real observation because AGNs are ubiquitous. To overcome this difficult, we use a statistical method, first designed to constrain the host galaxies of stellar-mass binary black holes, to search for the MBHB-AGN correlation in different scenarios. We find that by detecting only one MBHB at $z\lesssim0.5$, a mHz GW detector, such as the Laser Interferometer Space Antenna (LISA), can already distinguish different merger scenarios thanks to its ability of precisely localizing the source. Moreover, future detector networks and deeper AGNs surveys will allow us to testify the MBHB-AGN correlation up to a redshift of $z\sim 3$ even if only a small fraction of $20\%$ of MBHBs actually merge in AGNs. These constraints will help settle the long-standing debate on the possible solutions to the final-parsec problem.

To understand the formation and growth of supermassive black holes (SMBHs) and their co-evolution with host galaxies, it is essential to know the impact of environment on the activity of active galactic nuclei (AGN). We present new Chandra X-ray observations of nuclear emission from member galaxies in the Antlia cluster, the nearest non-cool core and the nearest merging galaxy cluster, residing at D = 35.2 Mpc. Its inner region, centered on two dominant galaxies NGC 3268 and NGC 3258, has been mapped with three deep Chandra ACIS-I pointings. Nuclear X-ray sources are detected in 7/84 (8.3%) early-type galaxies (ETG) and 2/8 (25%) late-type galaxies with a median detection limit of 8x10^38 erg/s. All nuclear X-ray sources but one have a corresponding radio continuum source detected by MeerKAT at the L-band. Nuclear X-ray sources detected in early-type galaxies are considered as the genuine X-ray counterpart of low-luminosity AGN. When restricted to a detection limit of logLx(erg/s) > 38.9 and a stellar mass of 10 < log Ms(Msun) <11.6, 6/11 (54.5%) ETG are found to contain an X-ray AGN in Antlia, exceeding the AGN occupation fraction of 7/39 (18.0%) and 2/12 (16.7%) in the more relaxed, cool core clusters, Virgo and Fornax, respectively, and rivaling that of the AMUSE-Field ETG of 27/49 (55.1%). Furthermore, more than half of the X-ray AGN in Antlia are hosted by its younger subcluster, centered on NGC 3258. We believe that this is because SMBH activity is enhanced in a dynamically young cluster compared to relatively relaxed clusters.

Dust particles in protoplanetary disks experience various chemical reactions under different physicochemical conditions through their accretion and diffusion, which results in the radial chemical gradient of dust. We performed three-dimensional Monte Carlo simulations to evaluate the dust trajectories and the progress of fictitious irreversible reactions, of which kinetics is expressed by the Johnson-Mehl-Avrami equation. The distribution of the highest temperature that each particle experiences before the degree of reaction exceeds a certain level shows the log-normal distribution, and its mode temperature was used as the effective reaction temperature. Semi-analytical prediction formulas of the effective reaction temperature and its dispersion were derived by comparing a reaction timescale with a diffusive transport timescale of dust as a function of the reaction parameters and the disk parameters. The formulas reproduce the numerical results of the effective reaction temperatures and their dispersions within 5.5 and 24 %, respectively, in a wide temperature range (200-1400 K). We applied the formulas for the crystallization of amorphous silicate dust and its oxygen isotope exchange with the H2O vapor based on the experimentally determined kinetics. For sub-micron sized amorphous forsterite dust, the predicted effective reaction temperature for the oxygen isotope exchange was lower than that of crystallization without overlap even considering their dispersions. This suggests that the amorphous silicate dust in the protosolar disk could exchange their oxygen isotopes efficiently with the 16O-poor H2O vapor, resulting in the distinct oxygen isotope compositions from the Sun.

This paper explores a possible linkage between solar motion about the solar system center of mass and the quasi-periodicity evident in the pressure and temperature of planet atmospheres. We establish that dominant mid frequency range periodicity in planet atmospheres corresponds closely to the harmonic series 39.5/n = TA/n years where n = 2, 3, 4, etc. We establish that the period TA = 39.5 years is the interval between acceleration impulses experienced by the Sun as it passes close to the solar system center of mass and that the time sequence of impulses generates the spectral harmonic series TA/n that is observed in the periodicity of climate indices like the North Atlantic Oscillation and the Quasi Biennial Oscillation. We develop a model of a simple harmonic oscillator responding to periodic acceleration impulses and show that the response duplicates several features of the Quasi Biennial Oscillation. We conclude that oscillatory phenomena observed in solar activity and in planet atmosphere variability could be due to the response of the various natural oscillatory modes to impulsive Sun acceleration associated with planetary motion.

The solar inner corona is a region that plays a critical role in energizing the solar wind and propelling it to supersonic and supra-Alfvenic velocities. Despite its importance, this region remains poorly understood because of being least explored due to observational limitations. The coronal radio sounding technique in this context becomes useful as it helps in providing information in parts of this least explored region. To shed light on the dynamics of the solar wind in the inner corona, we conducted a study using data obtained from coronal radio-sounding experiments carried out by the Akatsuki spacecraft during the 2021 Venus-solar conjunction event. By analyzing X-band radio signals recorded at two ground stations (IDSN in Bangalore and UDSC in Japan), we investigated plasma turbulence characteristics and estimated flow speed measurements based on isotropic quasi-static turbulence models. Our analysis revealed that the speed of the solar wind in the inner corona (at heliocentric distances from 5 to 13 solar radii), ranging from 220-550 km/sec, was higher than the expected average flow speeds in this region. By integrating our radio-sounding results with EUV images of the solar disk, we gained a unique perspective on the properties and energization of high-velocity plasma streams originating from coronal holes. We tracked the evolution of fast solar wind streams emanating from an extended coronal hole as they propagated to increasing heliocentric distances. Our study provides unique insights into the least-explored inner coronal region by corroborating radio sounding results with EUV observations of the corona.

Precipitable water vapor (PWV) strongly affects the quality of data obtained from millimeter- and submillimeter-wave astronomical observations, such as those for cosmic microwave background (CMB) measurements. Some of these observatories have used radiometers to monitor PWV. In this study, PWV was measured from April 2021 to April 2022 using Global Navigation Satellite System (GNSS) instruments in the Atacama Desert, Chile, where several millimeter and submillimeter-wave telescopes are located. We evaluated the accuracy of these measurements by comparing them to radiometer measurements. We calculated the PWV from GNSS data using Canadian Spatial Reference System Precise Point Positioning (CSRS-PPP), an online software package. When using GNSS data alone, the estimated PWV showed a systematic offset of +1.08 mm. When combining GNSS data with data from a barometer which was co-located with the GNSS receiver, the estimated PWV showed a lower systematic offset of -0.14 mm. The GNSS PWV showed a statistical error of 0.52 mm with an averaging time of an hour. Compared to other PWV measurement methods, GNSS instruments are robust in bad weather conditions, have sufficient time resolution, and are less expensive. By demonstrating good accuracy and precision in low PWV conditions, this paper shows that GNSS instruments are valuable tools for PWV measurements for observing site evaluation and data analysis for ground-based telescopes.

While Gamma-Ray Burst (GRBs) are clear and distinct observed events, every individual GRB is unique. In fact, GRBs are known for their variable behaviour, and BATSE was already able to discover two categories of GRB from the T90 distribution; the short and long GRBs. These two categories match up with the expected two types of GRB progenitors. Nowadays, more features have been found to be able to further distinguish them, such as the hardness ratio or the presence of supernovae. However, that does not mean that it is by any means simple to categorise individual GRBs. Furthermore, more GRB categories have been theorised as well, such as low-luminosity or X-ray-rich GRBs. These different types of GRBs also could indicate a different neutrino spectrum, with different types of GRBs more likely to emit higher amounts of neutrinos. We present an ongoing effort to use machine learning to categorise and classify GRBs, searching for subpopulations that could yield a larger neutrino flux. We specifically use unsupervised learning, as it allows hidden patterns and correlations to come to light. With the help of features such as the T90, hardness, fluence, SNR, spectral index and even the full light curve and spectra, different structures and categories of Gamma-Ray bursts can be found.

Optical spectroscopy offers the most direct view of the stellar properties and the accretion indicators. Standard accretion tracers, such as $H\beta$, $H\alpha$, and, Ca II triplet lines, and most photospheric features, fall in the optical wavelengths. However, these tracers are not readily observable from deeply embedded protostars because of the large line of sight extinction (Av $\sim$ 50-100 mag) toward them. In some cases, however, it is possible to observe protostars at optical wavelengths if the outflow cavity is aligned along the line-of-sight that allows observations of the photosphere, or the envelope is very tenuous and thin such that the extinction is low. In such cases, we can not only detect these protostars at optical wavelengths but also follow up spectroscopically. We have used the HOPS catalog (Furlan et al. 2016) of protostars in Orion to search for optical counterparts for protostars in the Gaia DR3 survey. Out of the 330 protostars in the HOPS sample, an optical counterpart within 2" is detected for 62 of the protostars. For 17 out of 62 optically detected protostars, we obtained optical spectra { (between 5500 to 8900 $\AA$) using the Aries-Devasthal Faint Object Spectrograph \& Camera (ADFOSC) on the 3.6-m Devasthal Optical Telescope (DOT) and Hanle Faint Object Spectrograph Camera (HFOSC) on 2-m Himalayan Chandra Telescope (HCT)}. We detect strong photospheric features, such as the TiO bands in the spectra {(of 4 protostars)}, hinting that photospheres can form early on in the star formation process. We further determined the spectral types of protostars, which show photospheres similar to a late M-type. Mass accretion rates derived for the protostars are similar to those found for T-Tauri stars, in the range of 10$^{-7}$ to 10$^{-8}$ $M_\odot$/yr.

By means of the data sets of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), we investigate the relationship between the variability amplitude and luminosity at 5100 \AA, black hole mass, Eddington ratio, $ R_{\rm Fe \, II}$ ( the ratio of the flux of Fe II line within 4435-4685 \AA ~to the broad proportion of $\rm H\beta$ line) as well as $ R_{5007}$ (the ratio of the flux [O III] line to the total $\rm H\beta$ line) of the broad line Seyfert 1 (BLS1) and narrow line Seyfert 1 (NLS1) galaxies sample in g,r,i,z and y bands, respectively. We also analyze the similarities and differences of the variability characteristics between the BLS1 galaxies and NLS1 galaxies. The results are listed as follows. (1). The cumulative probability distribution of the variability amplitude shows that NLS1 galaxies are lower than that in BLS1 galaxies. (2). We analyze the dependence of the variability amplitude with the luminosity at 5100 \AA, black hole mass, Eddington ratio, $ R_{\rm Fe \,II}$ and $ R_{5007}$, respectively. We find significantly negative correlations between the variability amplitude and Eddington ratio, insignificant correlations with the luminosity at 5100 \AA. The results also show significantly positive correlations with the black hole mass and $ R_{5007}$, significantly negative correlations with $ R_{\rm Fe\, II}$ which are consistent with Rakshit and Stalin(2017) in low redshift bins (z<0.4) and Ai et al.(2010). (3). The relationship between the variability amplitude and the radio loudness is investigated for 155 BLS1 galaxies and 188 NLS1 galaxies. No significant correlations are found in our results.

Aims. We carry out the self-consistent dynamic evolution of the orbital structure of Milky Way globular clusters. This allows us to estimate possible and probable close passages and even collisions of the clusters with each other. Methods. We reproduced the orbits of 147 globular clusters in 10 Gyr lookback time using our own high-order N-body parallel dynamic phi-GPU code. The initial conditions (three coordinates and three velocities for the present time) were derived from the Gaia DR3 catalogue. The galaxy is represented by five external potentials from the IllustrisTNG-100, whose masses and sizes of the disk and halo components are similar to the physical values of the Milky Way at present. Results. We present a statistical analysis of the cumulative close passages rate: About ten close passages with relative distances shorter than 50 pc for every billion years for each of the five external potentials. We present the 22 most reliable collision pairs with a good probability. As an example: Terzan 4 versus Terzan 2 (49%), Terzan 4 versus NGC 6624 (44%), Terzan 4 versus Terzan 5 (40%), Terzan 4 versus NGC 6440 (40%), and Terzan 4 versus Liller 1 (42%). The most active globular cluster in the collision sense is Terzan 4, which has 5.65 collision events on average (averaged over all individual 1000 initial condition realisations). Most collisions are located inside the Galactic disk and form two ring-like structures. The first ring-like structure has the highest collision number density at 1 kpc, and the second sturcture has a maximum at 2 kpc. Conclusions. Based on our numerical simulations, we can conclude that the few dozen Milky Way globular clusters probably undergo some close encounters and even possible collisions during their lifetimes, which can significantly affect their individual dynamical evolution and possibly even their stellar content.

Slow-roll of the inflaton field defines the standard dynamics of the inflationary epoch. However, the inflationary system deviates from slow-roll when it encounters an extremely flat region of the inflaton potential, and enters a phase dubbed Ultra slow roll. In this article, we explore the possibility of realizing an Ultra slow-roll phase in a particularly interesting inflationary scenario, called Warm Inflation. In the Warm inflationary scenario a thermalized, sub-dominant radiation bath coexists with the inflaton energy density as an effect of dissipative dynamics. We show in this article that though the background dynamics indicate Ultra slow-roll when the potential becomes extremely flat, in Warm Inflation models, where the dissipation coefficient is a sole function of the temperature of the radiation bath, the system fails to maintain the thermal equilibrium as soon as it enters the Ultra slow-roll phase. As thermal equilibrium is a key feature of Warm Inflation, and as it is not yet known how to deal with Warm Inflation without thermal equilibrium, we could not analyze such systems any further in this article. However, we demonstrate that brief periods of Ultra slow-roll phase, which smoothly ends into standard slow-roll, can be accommodated in WI models where the dissipation coefficient is not only a function of the temperature of the radiation bath but also depends on the amplitude of the inflaton field. We theoretically determine the criteria of successfully embedding Ultra slow-roll in WI while the system remain in thermal equilibrium, and also demonstrate numerically that such short Ultra slow-roll phases can indeed be embedded in specific Warm Inflation models which comply with the theoretically determined criteria.

For over 15 years the Fermi Large Area Telescope (Fermi-LAT) has been monitoring the entire high-energy gamma-ray sky, providing the best sampled 0.1 -- $>1$ TeV photons to this day. As a result, the Fermi-LAT has been serving the time-domain and multi-messenger community as the main source of gamma-ray activity alerts. All of this makes the Fermi-LAT a key instrument towards understanding the underlying physics behind the most extreme objects in the universe. However, generating mission-long LAT light curves can be very computationally expensive. The Fermi-LAT light curve repository (LCR) tackles this issue. The LCR is a public library of gamma-ray light curves for 1525 Fermi-LAT sources deemed variable in the 4FGL-DR2 catalog. The repository consists of light curves on timescales of days, weeks, and months, generated through a full-likelihood unbinned analysis of the source and surrounding region, providing flux and photon index measurements for each time interval. Hosted at NASA's FSSC, the library provides users with access to this continually updated light curve data, further serving as a resource to the time-domain and multi-messenger communities.

Astrophysical shocks create cosmic rays by accelerating charged particles to relativistic speeds. However, the relative contribution of various types of shocks to the cosmic ray spectrum is still the subject of ongoing debate. Numerical studies have shown that in the non-relativistic regime, oblique shocks are capable of accelerating cosmic rays, depending on the Alfv\'enic Mach number of the shock. We now seek to extend this study into the mildly relativistic regime. In this case, dependence of the ion reflection rate on the shock obliquity is different compared to the nonrelativistic regime. Faster relativistic shocks are perpendicular for the majority of shock obliquity angles therefore their ability to initialize efficient DSA is limited. We define the ion injection rate using fully kinetic PIC simulation where we follow the formation of the shock and determine the fraction of ions that gets involved into formation of the shock precursor in the mildly relativistic regime covering a Lorentz factor range from 1 to 3. Then, with this result, we use a combined PIC-MHD method to model the large-scale evolution of the shock with the ion injection recipe dependent on the local shock obliquity. This methodology accounts for the influence of the self-generated or pre-existing upstream turbulence on the shock obliquity which allows study substantially larger and longer simulations compared to classical hybrid techniques.

Asteroseismology of solar-like oscillations in giant stars allow the derivation of their masses and radii. For members of open clusters this allows an age estimate of the cluster which should be identical to the age estimate from the colour-magnitude diagram, but independent of the uncertainties that are present for that type of analysis. Thus, a more precise and accurate age estimate can be obtained. We aim to measure asteroseismic properties of oscillating giant members of the open cluster NGC 6866 and utilise these for a cluster age estimate. Model comparisons allow constraints on the stellar physics, and here we investigate the efficiency of convective-core overshoot and effects of rotation during the main-sequence, which has a significant influence on the age for these relatively massive giants. We identify six giant members of NGC 6866 and derive asteroseismic measurements for five of them. This constrains the convective-core overshoot and enables a more precise and accurate age estimate than previously possible. Asteroseismology establishes the helium-core burning evolutionary phase for the giants, which have a mean mass of 2.8 $M_{\odot}$. Their radii are significantly smaller than predicted by current 1D stellar models unless the amount of convective-core overshoot on the main sequence is reduced to $\alpha_{ov} \leq 0.1 H_p$ in the step-overshoot description. Our measurements also suggest that rotation has affected the evolution of the stars in NGC 6866 in a way that is consistent with 3D simulations but not with current 1D stellar models. The cluster age is estimated to be 0.43 $\pm$ 0.05 Gyr, significantly younger and more precise than most previous estimates. We derive a precise cluster age while constraining convective-core overshooting and effects of rotation in the models. We uncover potential biases for automated age estimates of helium-core burning stars.

The Cherenkov Telescope Array is the next generation of observatory using imaging air Cherenkov technique for very-high-energy gamma-ray astronomy. Its first prototype telescope is operational on-site at La Palma and its data acquisitions allowed to detect known sources, study new ones, and to confirm the performance expectations. The application of deep learning for the reconstruction of the incident particle physical properties (energy, direction of arrival and type) have shown promising results when conducted on simulations. Nevertheless, its application to real observational data is challenging because deep-learning-based models can suffer from domain shifts. In the present article, we address this issue by implementing domain adaptation methods into state-of-art deep learning models for Imaging Atmospheric Cherenkov Telescopes event reconstruction to reduce the domain discrepancies, and we shed light on the gain in performance that they bring along.

Searching for the sources of high-energy cosmic particles requires sophisticated analysis techniques, frequently involving hypothesis tests with unbinned log-likelihood (LLH) functions. SkyLLH is an open-source, Python-based software tool to build these LLH functions and perform likelihood-ratio tests. We present a new easy-to-use and modular extension of SkyLLH that allows the user to perform neutrino point source searches in the entire sky using ten years of IceCube public data. To guide the user, SkyLLH provides tutorials showing how to analyze the experimental data and calculate useful statistical quantities. Here we describe the details of the analysis workflow and illustrate some of the possible methods to work with the IceCube public dataset. Additionally, we show that SkyLLH can reproduce the results from a previous IceCube publication that used the public data release. We obtain a similar local significance for the neutrino emission from a list of candidate sources within a maximum shift of 0.5$\sigma$. Finally, the measured neutrino flux from the most significant source candidate, NGC 1068, shows substantial agreement with the previously published result.

The IceCube Neutrino Observatory is a one-cubic-kilometer-sized neutrino telescope deployed deep in the Antarctic ice at the South Pole. One of IceCube's major goals is finding the origins of astrophysical high-energy neutrinos. In 2022, IceCube identified the strongest point-like neutrino source so far, the active galaxy NGC 1068. Analyzing 9 years of muon-neutrino data from the Northern Sky recorded between 2011 and 2020, the emission from NGC 1068 is significant at 4.2$\,\sigma$. We present a planned extension to this search with additional years of data. One of these years includes data from 2010 when IceCube was only partially constructed. We discuss the improvement in sensitivity and discovery potential for neutrino point sources across the Northern sky. We show that by building on the established analysis techniques, previous observations could be improved, not only for NGC 1068 but for all possible sources in the Northern sky.

We aim to combine asteroseismology, spectroscopy, and evolutionary models to establish a comprehensive picture of the evolution of Galactic blue supergiant stars (BSG). To start such an investigation, we selected three BSG candidates for our analysis: HD 42087 (PU Gem), HD 52089 ($\epsilon$ CMa) and HD 58350 ($\eta$ CMa). These stars show pulsations and were suspected to be in an evolutionary stage either preceding or succeding the red supergiant (RSG) stage. For our analysis, we utilized the 2-min cadence TESS data to study the photometric variability and obtained new spectroscopic observations at the CASLEO observatory. We calculated CMFGEN non-LTE radiative transfer models and derived stellar and wind parameters using the iterative spectral analysis pipeline XTGRID. The spectral modeling was limited to changing only the effective temperature, surface gravity, CNO abundances, and mass-loss rates. Finally, we compared the derived metal abundances with predictions from Geneva stellar evolution models. The frequency spectra of all three stars show either stochastic oscillations, nonradial strange modes, or a rotational splitting. We conclude that the rather short sectoral observing windows of TESS prevent establishing a reliable mode identification of low frequencies connected to mass-loss variabilities. The spectral analysis confirmed gradual changes in the mass-loss rates and the derived CNO abundances comply with the values reported in the literature. We were able to achieve a quantitative match with stellar evolution models for the stellar masses and luminosities. However, the spectroscopic surface abundances turned out to be inconsistent with theoretical predictions. The stars show N enrichment, typical for CNO cycle processed material, but the abundance ratios do not reflect the associated levels of C and O depletion.

The discovery of high-energy astrophysical neutrinos in the TeV-PeV range by IceCube marked the start of neutrino astronomy, and the search for their sources continues. Two promising source candidates have been identified by IceCube: NGC 1068 in the 1 TeV-10 TeV range and TXS 0506+056 in the 0.1-1 PeV range. Both sources have gamma-ray counterparts, but additional time information of both neutrinos and gamma rays were essential for the identification of TXS 0506+056. The Planetary Neutrino Monitoring (PLEnuM) concept is an approach for combining the exposures of all current and future neutrino observatories - such as KM3NeT, Baikal-GVD, P-ONE in the Northern Hemisphere, and IceCube-Gen2 in the Southern Hemisphere. Using this PLEnuM approach, we estimate how the detection capability for transient sources candidates like blazars and GRBs improves once the future neutrino observatories come online. In addition, we present how the combined, instantaneous field of view of PLEnuM improves the real-time detection rate of rare, very-high-energy neutrinos across the entire sky.

Inertial wave modes in the Sun are of interest owing to their potential to reveal new insight into the solar interior. These predominantly retrograde-propagating modes in the solar subsurface appear to deviate from the thin-shell Rossby-Haurwitz model at high azimuthal orders. We present new measurements of sectoral equatorial inertial modes at $m>15$ where the modes appear to become progressively less retrograde compared to the canonical Rossby-Haurwitz dispersion relation in a co-rotating frame. We use a spectral eigenvalue solver to compute the spectrum of solar inertial modes in the presence of differential rotation. Focussing specifically on equatorial Rossby modes, we find that the numerically obtained mode frequencies lie along distinct ridges, one of which lies strikingly close to the observed mode frequencies in the Sun. We also find that the $n=0$ ridge is deflected strongly in the retrograde direction. This suggests that the solar measurements may not correspond to the fundamental $n=0$ Rossby-Haurwitz solutions as was initially suspected, but to a those for a higher $n$. The numerically obtained eigenfunctions also appear to sit deep within the convection zone -- unlike those for the $n=0$ modes -- which differs substantially from solar measurements and complicates inference.

We present very-long-baseline interferometry (VLBI) observations of a continuum radio source potentially associated with the fast radio burst source FRB 20190520B. Using the European VLBI network (EVN), we find the source to be compact on VLBI scales with an angular size of $<2.3$ mas ($3\sigma$). This corresponds to a transverse physical size of $<9$ pc (at the $z=0.241$ redshift of the host galaxy), confirming it to be an FRB persistent radio source (PRS) like that associated with the first-known repeater FRB 20121102A. The PRS has a flux density of $201 \pm 34 \rm{\mu Jy}$ at 1.7 GHz and a spectral radio luminosity of $L_{1.7 \rm GHz} = (3.0 \pm 0.5) \times 10^{29}\,\mathrm{erg s^{-1} Hz^{-1}}$ (also similar to the FRB 20121102A PRS). Comparing to previous lower-resolution observations, we find that no flux is resolved out on milliarcsecond scales. We have refined the PRS position, improving its precision by an order of magnitude compared to previous results. We also report the detection of a FRB 20190520B burst at 1.4 GHz and find the burst position to be consistent with the PRS position, at $\lesssim20$ mas. This strongly supports their direct physical association and the hypothesis that a single central engine powers both the bursts and the PRS. We discuss the model of a magnetar in a wind nebula and present an allowed parameter space for its age and the radius of the putative nebula powering the observed PRS emission. Alternatively, we find that an accretion-powered 'hypernebula' model also fits our observational constraints.

Explosive phenomena are known to trigger a wealth of shocks in warm plasma environments, including the solar chromosphere and molecular clouds where the medium consists of both ionised and neutral species. Partial ionisation is critical in determining the behaviour of shocks, since the ions and neutrals locally decouple, allowing for substructure to exist within the shock. Accurately modelling partially ionised shocks requires careful treatment of the ionised and neutral species, and their interactions. Here we study a partially-ionised switch-off slow-mode shock using a multi-level hydrogen model with both collisional and radiative ionisation and recombination rates that are implemented into the two-fluid (P\underline{I}P) code, and study physical parameters that are typical of the solar chromosphere. The multi-level hydrogen model differs significantly from MHD solutions due to the macroscopic thermal energy loss during collisional ionisation. In particular, the plasma temperature both post-shock and within the finite-width is significantly cooler that the post-shock MHD temperature. Furthermore, in the mid to lower chromosphere, shocks feature far greater compression then their single-fluid MHD analogues. The decreased temperature and increased compression reveal the importance of non-equilibrium ionised in the thermal evolution of shocks in partially ionised media. Since partially ionised shocks are not accurately described by the Rankine-Hugoniot shock jump conditions, it may be incorrect to use these to infer properties of lower atmospheric shocks.

Fulfilling the rich promise of rapid advances in time-domain astronomy is only possible through confronting our observations with physical models and extracting the parameters that best describe what we see. Here, we introduce {\sc Redback}; a Bayesian inference software package for electromagnetic transients. {\sc Redback} provides an object-orientated {\sc python} interface to over 12 different samplers and over 100 different models for kilonovae, supernovae, gamma-ray burst afterglows, tidal disruption events, engine-driven transients, X-ray afterglows of gamma-ray bursts driven by millisecond magnetars among other explosive transients. The models range in complexity from simple analytical and semi-analytical models to surrogates built upon numerical simulations accelerated via machine learning. {\sc Redback} also provides a simple interface for downloading and processing data from Swift, Fink, Lasair, the open-access catalogues, and BATSE and fit this or private data. {\sc Redback} can also be used as an engine to simulate transients for telescopes such as the Zwicky Transient Facility and Vera Rubin with realistic cadences, limiting magnitudes, and sky-coverage or a hypothetical user-constructed survey with arbitrary settings. We also provide a more general simulation interface suitable for target of opportunity observations with different telescopes. We demonstrate through a series of examples how {\sc Redback} can be used as a tool to simulate a large population of transients for realistic surveys, fit models to real, simulated, or private data, multi-messenger inference and serve as an end-to-end software toolkit for parameter estimation and interpreting the nature of electromagnetic transients.

In this letter, we report the discovery of the highest redshift, heavily obscured, radio-loud QSO candidate selected using JWST NIRCam/MIRI, mid-IR, sub-mm, and radio imaging in the COSMOS-Web field. Using multi-frequency radio observations and mid-IR photometry, we identify a powerful, radio-loud (RL), growing supermassive black hole (SMBH) with significant spectral steepening of the radio SED ($f_{1.32 \mathrm{GHz}} \sim 2$ mJy, $q_{24\mu m} = -1.1$, $\alpha_{1.32-3\mathrm{GHz}}=-1.2$, $\Delta \alpha = -0.4$). In conjunction with ALMA, deep ground-based observations, ancillary space-based data, and the unprecedented resolution and sensitivity of JWST, we find no evidence of QSO contribution to the UV/optical/NIR data and thus infer heavy amounts of obscuration (N$_{\mathrm{H}} > 10^{23}$ cm$^{-2}$). Using the wealth of deep UV to sub-mm photometric data, we report a singular solution photo-z of $z_\mathrm{phot}$ = 7.65$^{+0.4}_{-0.3}$ and estimate an extremely massive host-galaxy ($\log M_{\star} = 11.92 \pm 0.06\,\mathrm{M}_{\odot}$). This source represents the furthest known obscured RL QSO candidate, and its level of obscuration aligns with the most representative but observationally scarce population of QSOs at these epochs.

Pre-stellar cores represent a critical evolutionary phase in low-mass star formation. We aim to unveil the detailed thermal structure and density distribution of three early-stage cores, starless core L1517B, and prestellar core L694-2 and L429, with the high angular resolution observations of the NH$_{3}$ (1,1) and (2,2) inversion transitions obtained with VLA and GBT. In addition, we explore where/if NH$_{3}$ depletes in the central regions. Applying the mid-infrared extinction method to the $\textit{Spitzer}$ 8$~\mu$m map we obtain a high angular resolution hydrogen column density map, and derive the gas density profile to assess the variation of NH$_{3}$ abundance as a function of gas volume density. The measured temperature profiles of L429 and L1517B show a minor decrease towards the core center, dropping from $\sim$9\~K to below 8\~K, and $\sim$11 K to 10 K, while L694-2 has a rather uniform temperature distribution around $\sim$9 K. Among the three cores, L429 has the highest central gas density, close to sonic velocity line-width, and largest localised velocity gradient, all indicative of an advanced evolutionary stage. We resolve that the abundance of NH$_{3}$ becomes two times lower in the central region of L429, occurring around a gas density of 4.4$\times$10$^{4}$$~cm^{-3}$. Compared to Ophiuchus/H-MM1 which shows an even stronger drop of the NH$_{3}$ abundance at 2$\times$10$^{5}$$~cm^{-3}$, the abundance variations of the three cores plus Ophiuchus/H-MM1 suggest a progressive NH$_{3}$ depletion with increasing central density of the core.

In this paper, we study the properties of accretion flow including its spectral features in Johannsen and Psaltis (JP) non-Kerr spacetime. In doing so, we numerically solve the governing equations that describe the flow motion around the compact objects in a general relativistic framework, where spin ($a_{k}$) and deformation parameters ($\varepsilon$) demonstrate the nature of the central source, namely black hole (BH) or naked singularity (NS). With this, we obtain all possible classes of global accretion solutions ($i. e.$, O, A, W and I-type) by varying the energy ($E$) and angular momentum ($\lambda$) of the relativistic accretion flow, and examine the role of thermal bremsstrahlung emission in studying the spectral energy distributions (SEDs) of the accretion disc. We divide the parameter space in $\lambda-E$ plane in terms of the different classes of accretion solutions for BH and NS models. We further calculate the disc luminosity ($L$) corresponding to these accretion solutions, and observe that I-type solutions yield higher $L$ and SEDs than the remaining types of solutions for both BH and NS models. For BH model, SEDs for W and I-type solutions differ significantly from the results for O and A-type solutions for low $E$ values. On the contrary, for NS model, SEDs for different accretion solutions are identical in the whole parameter space of $\lambda$ and $E$. We also examine the effect of $\varepsilon$ on the SEDs and observe that a non-Kerr BH yields higher SEDs than the usual Kerr BH. Finally, for accretion solutions of identical $E$ and $\lambda$, we compare the SEDs obtained from BH and NS models, and find that naked singularity objects produce more luminous power spectra than the black holes.

Photoevaporation from high energy stellar radiation has been thought to drive the dispersal of protoplanetary discs. Different theoretical models have been proposed, but their predictions diverge in terms of the rate and modality at which discs lose their mass, with significant implications for the formation and evolution of planets. In this paper we use disc population synthesis models to interpret recent observations of the lowest accreting protoplanetary discs, comparing predictions from EUV-driven, FUV-driven and X-ray driven photoevaporation models. We show that the recent observational data of stars with low accretion rates (low accretors) point to X-ray photoevaporation as the preferred mechanism driving the final stages of protoplanetary disc dispersal. We also show that the distribution of accretion rates predicted by the X-ray photoevaporation model is consistent with observations, while other dispersal models tested here are clearly ruled out.

Previous observations of dark vortices in Neptune's atmosphere, such as Voyager-2's Great Dark Spot, have been made in only a few, broad-wavelength channels, which has hampered efforts to pinpoint their pressure level and what makes them dark. Here, we present Very Large Telescope (Chile) MUSE spectrometer observations of Hubble Space Telescope's NDS-2018 dark spot, made in 2019. These medium-resolution 475 - 933 nm reflection spectra allow us to show that dark spots are caused by a darkening at short wavelengths (< 700 nm) of a deep ~5-bar aerosol layer, which we suggest is the H$_2$S condensation layer. A deep bright spot, named DBS-2019, is also visible on the edge of NDS-2018, whose spectral signature is consistent with a brightening of the same 5-bar layer at longer wavelengths (> 700 nm). This bright feature is much deeper than previously studied dark spot companion clouds and may be connected with the circulation that generates and sustains such spots.

Pulse profile modelling is a relativistic ray-tracing technique that can be used to infer masses, radii and geometric parameters of neutron stars. In a previous study, we looked at the performance of this technique when applied to thermonuclear burst oscillations from accreting neutron stars. That study showed that ignoring the variability associated with burst oscillation sources resulted in significant biases in the inferred mass and radius, particularly for the high count rates that are nominally required to obtain meaningful constraints. In this follow-on study, we show that the bias can be mitigated by slicing the bursts into shorter segments where variability can be neglected, and jointly fitting the segments. Using this approach, the systematic uncertainties on the mass and radius are brought within the range of the statistical uncertainty. With about 10$^6$ source counts, this yields uncertainties of approximately 10% for both the mass and radius. However, this modelling strategy requires substantial computational resources. We also confirm that the posterior distributions of the mass and radius obtained from multiple bursts of the same source can be merged to produce outcomes comparable to that of a single burst with an equivalent total number of counts.

Recent discoveries of gas giant exoplanets around M-dwarfs (GEMS) from transiting and radial velocity (RV) surveys are difficult to explain with core-accretion models. We present here a homogeneous suite of 162 models of gravitationally unstable gaseous disks. These models represent an existence proof for gas giants more massive than 0.1 Jupiter masses to form by the gas disk gravitational instability (GDGI) mechanism around M-dwarfs for comparison with observed exoplanet demographics and protoplanetary disk mass estimates for M-dwarf stars. We use the Enzo 2.6 adaptive mesh refinement (AMR) 3D hydrodynamics code to follow the formation and initial orbital evolution of gas giant protoplanets in gravitationally unstable gaseous disks in orbit around M-dwarfs with stellar masses ranging from 0.1 $M_\odot$ to 0.5 $M_\odot$. The gas disk masses are varied over a range from disks that are too low in mass to form gas giants rapidly to those where numerous gas giants are formed, therefore revealing the critical disk mass necessary for gas giants to form by the GDGI mechanism around M-dwarfs. The disk masses vary from 0.01 $M_\odot$ to 0.05 $M_\odot$ while the disk to star mass ratios explored range from 0.04 to 0.3. The models have varied initial outer disk temperatures (10 K to 60 K) and varied levels of AMR grid spatial resolution, producing a sample of expected gas giant protoplanets for each star mass. Broadly speaking, disk masses of at least 0.02 $M_\odot$ are needed for the GDGI mechanism to form gas giant protoplanets around M-dwarfs.

We present dense-gas--tracing molecular observations of six resolved Giant Molecular Clouds (GMCs) in the Andromeda Galaxy (M31). Using the NOEMA interferometer, we observed the transitions of HCN(1-0), HCO$^+$(1-0), and HNC(1-0), as well as $^{13}$CO(1-0) and 100 GHz continuum emission. This complements our earlier work with the Submillimeter Array (SMA), including resolved dust continuum detections of these clouds at 230 GHz. In this work, we first compare different continuum measurements to conclude that the average free-free contamination of the observed flux is 71% at 3 mm but only 13% at 1 mm, confirming that emission at 3 mm is less reliable than that at 1 mm for calculating dust masses of star-forming clouds. While the $^{13}$CO emission is more extended than both HCN and HCO$^+$ emission, which in turn is more extended than HNC emission, we find that both HCN and HCO$^+$ are spatially coincident with, and similarly extended as, the 230 GHz dust emission. This suggests that both the 230 GHz dust continuum and most importantly the HCN emission traces the dense gas component of these GMCs. From comparison of the molecular emission with dust masses derived from the 230 GHz continuum emission, we obtain the first direct measurements of the dust-mass-to-light ratios ($\alpha^\prime_{HCN}$ and $\alpha^\prime_{HCO^+}$) in GMCs of an external galaxy. For HCN, the result is broadly similar to a measurement in the local Perseus cloud suggesting that these are indeed dense gas conversion factors. A larger cloud sample will be required to assess whether HCN is tracing comparable cloud-scale density regimes across the environments of M31.

We observed the low-mass X-ray binary Sco X-1 for 12 nights simultaneously using the Rossi X-Ray Timing Explorer and the Otto Struve Telescope at McDonald Observatory at 1 second time resolution. This is among the most comprehensive simultaneous X-Ray/optical data sets of Sco X-1. Evidence of reprocessing was observed in the form of nine positive, near-zero lag peaks in the cross correlation function, eight of which were relatively small and took the shape of piecewise exponential functions. These peaks were initially identified by eye, after which a computational identification scheme was developed to confirm their significance. Based on their short lags (less than 4 seconds), as well as their occurrence on the flaring branch and soft apex, the small cross correlation features are likely to be caused by reprocessing off the outer disc, although the companion could still make a contribution to their tails. The Z track was parameterized using a rank number scheme so that the system's location on the track could be numerically defined. Plotting the results against the optical reveals an increasing step function when moving from the horizontal to the normal to the flaring branch, with differential optical levels at ~0.47, ~0.57, and ~1.1 respectively. An additional correlation between Z track location and the optical was found on the upper flaring branch. An optical intensity histogram reveals a transition region between the normal and flaring branches with only intermediate fluxes.

Radial substructures have now been observed in a wide range of protoplanetary discs (PPDs), from young to old systems, however their formation is still an area of vigorous debate. Recent magnetohydrodynamic (MHD) simulations have shown that rings and gaps can form naturally in PPDs when non-ideal MHD effects are included. However these simulations employ ad-hoc approximations to the magnitudes of the magnetic diffusivities in order to facilitate ring growth. We replace the parametrisation of these terms with a simple chemical network and grain distribution model to calculate the non-ideal effects in a more self-consistent way. We use a range of grain distributions to simulate grain formation for different disc conditions. Including ambipolar diffusion, we find that large grain populations (> 1{\mu}m), and those including a population of very small polyaromatic hydrocarbons (PAHs) facilitate the growth of periodic, stable rings, while intermediate sized grains suppress ring formation. Including Ohmic diffusion removes the positive influence of PAHs, with only large grain populations still producing periodic ring and gap structures. These results relate closely to the degree of coupling between the magnetic field and the neutral disc material, quantified by the non-dimensional Elsasser number {\Lambda} (the ratio of magnetic forces to Coriolis force). For both the ambipolar-only and ambipolar-ohmic cases, if the total Elsasser number is initially of order unity along the disc mid-plane, ring and gap structures may develop.

The field of Heliophysics has a branding problem. We need an answer to the question: ``What is Heliophysics\?'', the answer to which should clearly and succinctly defines our science in a compelling way that simultaneously introduces a sense of wonder and exploration into our science and our missions. Unfortunately, recent over-reliance on space weather to define our field, as opposed to simply using it as a practical and relatable example of applied Heliophysics science, narrows the scope of what solar and space physics is and diminishes its fundamental importance. Moving forward, our community needs to be bold and unabashed in our definition of Heliophysics and its big questions. We should emphasize the general and fundamental importance and excitement of our science with a new mindset that generalizes and expands the definition of Heliophysics to include new ``frontiers'' of increasing interest to the community. Heliophysics should be unbound from its current confinement to the Sun-Earth connection and expanded to studies of the fundamental nature of space plasma physics across the solar system and greater cosmos. Finally, we need to come together as a community to advance our science by envisioning, prioritizing, and supporting -- with a unified voice -- a set of bold new missions that target compelling science questions - even if they do not explore the traditional Sun- and Earth-centric aspects of Heliophysics science. Such new, large missions to expand the frontiers and scope of Heliophysics science large missions can be the key to galvanizing the public and policymakers to support the overall Heliophysics program.

In this article, using gravitational decoupling by means of minimal geometric deformation approach, we obtain a new spherically symmetric and static black hole solution. To progress, we close the system by assuming that the average pressure of the $\theta$-sector is vanishing. Also, we tackle the problem regarding how, for a given minimally deformed black hole solution, one can connect it to a wormhole space-time.

The next generation of ground-based gravitational-wave detectors, Einstein Telescope (ET) and Cosmic Explorer (CE), present a unique opportunity to put constraints on dense matter, among many other groundbreaking scientific goals. In a recent study the science case of ET was further strengthened, studying in particular the performances of different detector designs. In this paper we present a more detailed study of the nuclear physics section of that work. In particular, focusing on two different detector configurations (the single-site triangular-shaped design and a design consisting of two widely separated "L-shaped" interferometers), we study the detection prospects of binary neutron star (BNS) mergers, and how they can reshape our understanding of the underlying equation of state (EoS) of dense matter. We employ several state-of-the-art EoS models and state-of-the-art synthetic BNS merger catalogs, and we make use of the Fisher information formalism (FIM) to quantify statistical errors on the astrophysical parameters describing individual BNS events. To check the reliability of the FIM method, we further perform a full parameter estimation for a few simulated events. Based on the uncertainties on the tidal deformabilities associated to these events, we outline a mechanism to extract the underlying injected EoS using a recently developed meta-modelling approach within a Bayesian framework. Our results suggest that with $\gtrsim 500$ events with signal-to-noise ratio greater than $12$, we will be able to pin down very precisely the underlying EoS governing the neutron star matter.

We investigate the properties of the gravitational waves (GWs) generated during a strongly first order electroweak phase transition (EWPT) in models with the classical scale invariance (CSI). Here, we distinguish two parameter space regions that correspond to the cases of (1) light dilaton and (2) purely radiative Higgs mass (PRHM). In the CSI models, the dilaton mass, or the Higgs mass in the PRHM case, in addition to some triple scalar couplings are fully triggered by the radiative corrections (RCs). In order to probe the RCs effects on the EWPT strength and on the GW spectrum, we extend the standard model by a real singlet to assist the electroweak symmetry breaking and an additional scalar field $Q$ with multiplicity $N_Q$ and mass $m_Q$. After imposing all theoretical and experimental constraints, we show that a strongly first order EWPT with detectable GW spectra can be realized for the two cases of light dilaton and PRHM. We also show the corresponding values of the relative enhancement of the cross section for the di-Higgs production process, which is related to the triple Higgs boson coupling. We obtain the region in which the GW spectrum can be observed by different future experiments such as LISA and DECIGO. We also show that the scenarios (1) and (2) can be discriminated by future GW observations and measurements of the di-Higgs productions at future colliders.

We study the phenomenology of leptophilic $Z'$ gauge bosons at the future high-energy $e^+e^-$ or $\mu^+\mu^-$ colliders, as well as at the gravitational wave observatories. The leptophilic $Z'$ model, although well-motivated, remains largely unconstrained from current low-energy and collider searches for $Z'$ masses above ${\cal O}(100~{\rm GeV})$, thus providing a unique opportunity for future lepton colliders. Taking leptophilic $U(1)_{L_\alpha-L_\beta}~(\alpha,\beta=e,\mu,\tau)$ models as concrete examples, we show that future $e^+e^-$ and $\mu^+\mu^-$ colliders with multi-TeV center-of-mass energies provide unprecedented sensitivity to heavy $Z'$ bosons. Moreover, if these $U(1)$ models are classically scale-invariant, the phase transition at the $U(1)$ symmetry-breaking scale tends to be strongly first-order with ultra-supercooling, and leads to observable stochastic gravitational wave signatures. We find that the future sensitivity of gravitational wave observatories, such as advanced LIGO-VIRGO and Cosmic Explorer, can be complementary to the collider experiments, probing higher $Z'$ masses up to ${\cal O}(10^4~{\rm TeV})$.

We study the gravitational wave (GW) spectrum produced by acoustic waves in the early universe, such as would be produced by a first order phase transition, focusing on the low-frequency side of the peak. We confirm with numerical simulations the Sound Shell model prediction of a steep rise with wave number $k$ of $k^9$ to a peak whose magnitude grows at a rate $(H/k_\text{p})H$, where $H$ is the Hubble rate and $k_\text{p}$ the peak wave number, set by the peak wave number of the fluid velocity power spectrum. We also show that hitherto neglected terms give a shallower part with amplitude $(H/k_\text{p})^2$ in the range $H \lesssim k \lesssim k_\text{p}$, which in the limit of small $H/k$ rises as $k$. This linear rise has been seen in other modelling and also in direct numerical simulations. The relative amplitude between the linearly rising part and the peak therefore depends on the peak wave number of the velocity spectrum and the lifetime of the source, which in an expanding background is bounded above by the Hubble time $H^{-1}$. For slow phase transitions, which have the lowest peak wave number and the loudest signals, the acoustic GW peak appears as a localized enhancement of the spectrum, with a rise to the peak less steep than $k^9$. The shape of the peak, absent in vortical turbulence, may help to lift degeneracies in phase transition parameter estimation at future GW observatories.

We compute the gravitational wave (GW) spectrum sourced by the sound waves produced during a first-order phase transition during radiation domination. The correlator of the velocity field is evaluated according to the sound shell model. In our derivation, we include the effects of the expansion of the Universe, showing their importance, in particular for sourcing processes with time duration comparable to the Hubble time. From the exact solution of the GW sourcing integral, we find a causal growth at small frequencies, $\Omega_{\rm GW} \sim k^3$, possibly followed by a linear regime $\Omega_{\rm GW} \sim k$ at intermediate $k$, depending on the phase transition parameters. Around the peak, we find a steep growth that approaches the $k^9$ scaling found in the sound shell model. This growth causes a bump around the GW spectrum peak, which may represent a distinctive feature of GWs produced from acoustic motion, since nothing similar has been observed for vortical turbulence. Nevertheless, we find that the $k^9$ scaling is much less extended than expected in the literature, and it does not necessarily appear. The dependence on the duration of the source, $\tau_{\rm fin} - \tau_*$, is quadratic at small frequencies $k$, and proportional to $\ln^2 (\tau_{\rm fin} {\cal H}_*)$ for an expanding Universe. At frequencies around the peak, the growth is suppressed by a factor $\Upsilon = 1 - 1/(\tau_{\rm fin} {\cal H}_*)$, which becomes linear for short duration. We discuss the linear or quadratic dependence on the source duration for stationary processes, which affects the amplitude of the GW spectrum, both in the causality tail and at the peak, showing that the assumption of stationarity is a very relevant one, as far as the GW spectral shape is concerned. Finally, we present a general semi-analytical template of the resulting GW spectrum, which depends on the parameters of the phase transition.