Search

The Axelrod approximation is widely used in astrophysical modelling codes to evaluate electron-impact excitation effective collision strengths for forbidden transitions. Approximate methods such as this are a necessity for many heavy elements with open shells where collisional data is either non existent or sparse as the use of more robust methods prove prohibitively expensive. Atomic data for such forbidden transitions are essential for producing full collisional radiative models that do not assume Local-Thermodynamic-Equilibrium (LTE). In this short work we repeat the optimization of the simple Axelrod formula for a large number of $R$-matrix data sets, ranging from Fe and Ni to the first r-process peak elements of Sr, Y and Zr, to higher Z systems Te, W, Pt and Au. We show that the approximate treatment of forbidden transitions can be a significant source of inaccuracy in such collisional radiative models. We find a large variance of the optimized coefficients for differing systems and charge states, although some general trends can be seen based on the orbital structure of the ground-state-configurations. These trends could potentially inform better estimates for future calculations for elements where $R$-matrix data is not available., Comment: Submitted to JQSRT

PSR J0514$-$4002A is a binary millisecond pulsar located in the globular cluster NGC 1851. The pulsar has a spin period of 4.99 ms, an orbital period of 18.8 days, and is in a very eccentric ($e = 0.89$) orbit around a massive companion. In this work, we present the updated timing analysis of this system, obtained with an additional 1 yr of monthly observations using the Giant Metrewave Radio Telescope and 2.5 yrs of observations using the MeerKAT telescope. This has allowed for a precise measurement of the proper motion of the system, implying a transverse velocity of $30\,\pm\,7\,\mathrm{km}\,\mathrm{s}^{-1}$ relative to the cluster. This is smaller than the cluster's escape velocity and consistent with the pulsar's association to NGC 1851. We have confirmed a large second spin frequency derivative and large associated jerk, which has increased the spin frequency derivative by a factor of 27 since the mid-2000s. The third spin frequency derivative showed that the strength of this jerk has increased by $\sim 65\%$ in the same time period. We take the effect of the changing acceleration into account and this allows for much improved estimates of the orbital period derivative. The large and fast-increasing jerk implies the presence of a third body in the vicinity of the pulsar (no counterpart is detectable within distance limit in HST images). Based on our measured parameters, we constrain the mass, distance and orbital parameters for this third body. The induced tidal contributions to the post-Keplerian parameters are small, and the precise measurement of these parameters allowed us to obtain precise mass measurements for the system: $M_\mathrm{tot} = 2.4734(3)$ M$_{\odot}$, $M_\mathrm{p} = 1.39(3)$ M$_{\odot}$, $M_\mathrm{c} = 1.08(3)$ M$_{\odot}$. This indicates that the pulsar's companion is a massive white dwarf and resolves the earlier ambiguity regarding its nature., Comment: 20 pages, 10 figures, 4 tables. Accepted for publication in Astronomy & Astrophysics

We report results from an $AstroSat$ Target-of-Opportunity (ToO) observation of 4U 1626$-$67, performed on 2023 May 18, soon after the discovery of torque reversal to spin-down in the source. The X-ray emission exhibited significant dependence on both energy and torque state. This work highlights the comparison of timing features of 4U 1626$-$67 with a previous $AstroSat$ observation from 2018, when the neutron star was in the spin-up state. The power density spectrum (PDS) of the 2023 observation comprised a sharp peak corresponding to $\nu_{\rm NS}\sim$130 mHz X-ray pulsations along with a prominent quasi-periodic oscillation (QPO) feature at $\nu_{\rm QPO}\sim$46 mHz with $\sim$20\% rms amplitude, which was positively correlated with energy. We also report the detection of sidebands to QPO occurring at a beat frequency ($\nu_{\rm NS}-\nu_{\rm QPO}$) of $\sim$83 mHz with $\sim$8\% rms amplitude, having $>3\sigma$ detection significance. Additionally, we utilized $Nuclear ~Spectroscopic ~Telescope ~ARray$ ($NuSTAR$) observations from the same torque state (2023 May-July) to analogize the presence and energy dependence of sidebands. The source retains timing properties in this spin-down torque state, similar to those seen in the previous spin-down phase. In sharp contrast, PDS from the 2018 observation was dominated by red noise, an absence of QPOs and a broadening in the wings of the pulse frequency peak, indicating a coupling between periodic and low-frequency aperiodic variability. Furthermore, we detected the known cyclotron resonance scattering feature (CRSF) at 37 keV in the Large Area X-ray Proportional Counter (LAXPC) spectrum. We explore various mechanisms that could possibly explain the presence of QPOs exclusively during the spin-down state., Comment: In press MNRAS

The new black hole transient Swift J1727.8--1613 exhibited a series of X-ray flares during its 2023 outburst extensively observed with Insight-HXMT. We analyze the spectra of the flaring period using a series of models consisting of a multi-color disk and several different non-thermal components, and several consistent conclusions are obtained among these models. First, Swift J1727.8--1613 was in the transition process from the hard intermediate state (HIMS) to the very high state (VHS) during the first flaring period (MJD 60197--60204), and afterwards it exhibited typical VHS parameter characteristics, such as high temperature of the disk inner radius and a steep power-law spectrum with a photon index of 2.6. Second, the flares in the VHS are characterized by a rapid increase in the flux of accretion disk, accompanied by a simultaneous rapid expansion of the inner radius, which could be apparent if the accretion disk hardening factor varies significantly. The strong power-law component during the VHS is likely produced by synchrotron self-Compton process in the relativistic jets, in agreement with the observed weak reflection component and lack of correlation with the disk component., Comment: The manuscript has been accepted for publication in The Astrophysical Journal

Dust grains embedded in gas flow give rise to a class of hydrodynamic instabilities that can occur whenever there exists a relative velocity between gas and dust. These instabilities have predominantly been studied for single grain sizes, for which a strong interaction can be found between drifting dust and a travelling gas wave, leading to fast-growing perturbations (growth rates $\propto \sqrt{\mu}$) even at small dust-to-gas ratios $\mu$. They are called resonant drag instabilities. We focus on the acoustic resonant drag instability, which is potentially important in AGB star outflows, around supernova remnants and star clusters in starburst galaxies. We study the acoustic resonant drag instability, taking into account a continuous spectrum of grain sizes, to determine whether it survives in the polydisperse regime and how the resulting growth rates compare to the monodisperse case. We solve the linear equations for a polydisperse fluid for the acoustic drag instability, focusing on small dust-to-gas ratios. Size distributions of realistic width turn the fast-growing perturbations $\propto \sqrt{\mu}$ of the monodisperse limit into slower growing perturbations $\propto \mu$ due to the fact that the backreaction on the gas involves an integration over the resonance. Furthermore, the large wave numbers that grow fastest in the monodisperse regime are stabilized by a size distribution, severely limiting the growth rates in the polydisperse regime. The acoustic resonant drag instability turns from a singularly perturbed problem in $\mu$ in the monodisperse limit into a regular perturbation for a sufficiently wide size distribution. It can still grow exponentially in the polydisperse regime, but at a slower pace compared to the single size case., Comment: 11 pages, 7 figures, accepted for publication in A&A

Radio galaxies can be classified into two types, FR I and FR II, depending on their morphology. So far, the reasons for the different behaviour of FR I and FR II in observations have not been clarified. While the Unified Model suggests that the viewing angle and the obscuring effect of the dust ring are the main reasons for the difference in the classification of FR I and FR II radio galaxies, it has been found that the accretion rate and the accretion pattern of the central engine may play a more crucial role. In order to investigate the physical properties of these sources, the cloudy program was used to simulate the 3C 348 radio source outlook ionisation model, and it was found that its optical emission in the nuclear region is significantly lower than the theoretical prediction, which suggests the existence of an obscuration effect, which was later further proved by the spectral decomposition method. And using the thermometric photometry-jet relationship, it is found that the accretion rate in its nuclear region is much lower than the accretion rate inverted from the total jet power, indicating that its accretion mode is in the critical stage of the transition from the standard thin disc to the ADAF. Combined with its Bondi accretion rate, the fitted energy spectrum of the nuclear region shows that the evolution of its jet power is controlled by the change of the central accretion engine.

The conversion of CMB photons to axions (or axion-like particles (ALPs)) can lead to a unique spectral distortion in the temperature and polarization sky which can be explored in upcoming CMB experiments. In this work we have developed a numerical simulation-based technique of photons to ALPs conversion in the galaxy clusters and show for the first time that this physical process can lead to large non-Gaussian signal in the temperature and polarization field, which is impacted by the presence of inhomogeneities and turbulence in the electron density and magnetic field. Our simulation-based technique can simulate the theoretical signal for different scenarios of cluster electron density and magnetic field turbulence and provides testable predictions to discover ALPs from galaxy clusters using spatially non-Gaussian and anisotropic spectral distortion of the microwave sky. We show that the presence of turbulence in the magnetic field and electron density can impact the Gaussian part of the signal captured in terms of the angular power spectra of the signal by more than an order of magnitude. Also, the presence of turbulence in different clusters will lead the temperature and polarization fluctuations around the cluster region to have varying non-Gaussian distribution, with peaks and tails different from the Gaussian statistics of the CMB anisotropy. This new numerical technique has made it possible to calculate also the non-Gaussian signals and can be used in future CMB analysis in synergy with X-ray and radio observations to unveil ALPs coupling with photons in the currently unexplored ranges, for the masses between about $10^{-14}$ eV--$10^{-11}$ eV., Comment: 42 pages, 37 figures, Submitted to JCAP

Long-term observations of the Galactic center by Fermi and HESS have revealed a novel phenomenon: the high-energy gamma-ray spectrum from the Galactic center exhibits a double power-law structure. In this study, we propose a new explanation for this phenomenon. We suggest that the low-energy (GeV) power-law spectrum originates from interactions between trapped background ``sea" cosmic ray particles and the dense gaseous environment near the Galactic center. In contrast, the bubble-like structure in the high-energy (TeV) spectrum is produced by protons accelerated during active phases of the Galactic center, through the same physical process. Based on this framework, we first calculate the gamma-ray emission generated by cosmic ray protons accelerated in the Galactic center. Then, using a spatially-dependent cosmic ray propagation model, we compute the energy spectrum of background ``sea" cosmic ray protons and their associated diffuse gamma-ray emission in the Galactic center region. The results closely reproduce the observations from Fermi-LAT and HESS, suggesting that their long-term data support this picture: high-energy cosmic rays in the local region originate from nearby cosmic ray sources, while low-energy cosmic rays are a unified contribution from distant cosmic ray sources. We predict that some extended Galactic sources, which remain undetectable in the GeV energy range, may become observable in the TeV range. We hope that future observations will detect more such sources, allowing us to further test and validate our model.

We present 12 observations of the accreting millisecond X-ray pulsar Aql X-1, taken from August 2022 to October 2023 using the Five-hundred-meter Aperture Spherical Radio Telescope at 1250 MHz. These observations covered both the quiescence and X-ray outburst states, as determined by analyzing the X-ray data from the Neutron Star Interior Composition Explorer and the Monitor of All-sky X-ray Image. Periodicity and single-pulse searches were conducted for each observation, but no pulsed signals were detected. The obtained upper limit flux densities are in the range of 2.86-5.73 uJy, which provide the lowest limits to date. We discuss several mechanisms that may prevent detection, suggesting that Aql X-1 may be in the radio-ejection state during quiescence, where the radio pulsed emissions are absorbed by the matter surrounding the system.

The X-ray quasi-periodic oscillation (QPO) is a remarkable form of variability in systems of compact object accretion. RE J1034+396, harboring the most significant X-ray QPO in active galactic nuclei (AGNs), is the most noteworthy source for in-depth analysis of AGN X-ray QPO properties. A long-term evolution of its QPO has been observed over the course of the observations. However, the short-term variability of its QPO properties remains unexplored within each observation that has long good time intervals (GTIs). We collect 12 XMM-Newton observations of RE J1034+396 with GTIs longer than 60 ks from publicly available data and conduct a detailed wavelet analysis focusing on the short-time modulation of the QPO. The QPO signals are found to undergo amplitude modulation in both the soft and hard bands, with a typical timescale of 17 ks. The soft flux is significantly higher when the hard QPO is present. They are highly correlated, with an average cross-correlation function (CCF) peak coefficient of 0.61 and a lag of approximately 3 ks. This novel finding provides fresh insights into the potential connection between the components of the corona emitting soft and hard X-ray photons. The CCF lag between the soft flux and the hard QPO evolves across the observations, potentially sharing the same origin as the previously observed interconnected evolution between QPO frequency and time lag., Comment: 14 pages, 8 figures, accepted for publication in ApJ

We carry out a search for spatial coincidence between high energy neutrinos detected by the IceCube neutrino detector (using the publicly available 10-year muon track data) and 33 magnetars, including two extragalactic ones. We use the unbinned maximum likelihood method for our analysis. We do not find any such spatial association between any of the galactic magnetars and IceCube-detected neutrinos. Therefore, we conclude that none of the known galactic or extragalactic magnetars contribute to the diffuse neutrino flux observed in IceCube., Comment: 5 pages. arXiv admin note: text overlap with arXiv:2410.16394

We report the multi-band photometric observations of the Type IIb supernova (SN) 2024iss with ultra-violet (UV), optical, and near-infrared (NIR) wavelengths starting one day after the explosion. The UV and optical light curves show the first peak two days after the explosion date. Following a first peak, a secondary maximum is observed in the optical and NIR bands, similar to SNe IIb with double-peaked light curves. The quasi-bolometric light curve shows the fast decay until a week after the explosion. From the analysis of the bolometric light curve, the ejecta mass and kinetic energy are estimated to be $M_{ej}=2.8\pm0.6~M_{\odot}$ and $E_{kin}=9.4\pm4.1\times10^{50}$ erg. The mass of the radioactive $^{56}$Ni is estimated to be $M(^{56}Ni)=0.2~M_{\odot}$. Fitting a black-body function to the spectral energy distribution reveals that the photospheric temperature exhibits a rapid exponential decline during the first week after the explosion. An analytic model describing the cooling emission after shock breakout provides a reasonable explanation for the observed temperature evolution. From these ejecta parameters, we calculated the progenitor radius to be $R_{pro}=50-340$~$R_{\odot}$. We conclude that these explosion properties are consistent with a core-collapse explosion from a yellow supergiant (YSG) progenitor., Comment: 6 pages, 5 figures, accepted for publication on Publications of the Astronomical Society of Japan on 2025-Mar-06

We explore the potential of lunar-based gravitational-wave detectors to broaden the multi-messenger astrophysics landscape by detecting mergers of massive ($\gtrsim 1~M_{\odot}$) double white dwarf (WD) binaries. These systems are potential progenitors of Type Ia supernovae and could serve as independent probes of cosmic expansion. We examine two proposed lunar gravitational-wave detector concepts operating in the sub-hertz band (0.1-1 Hz): the Gravitational-Wave Lunar Observatory for Cosmology (a proxy for suspended test mass detectors) and the Lunar Gravitational-Wave Antenna (a proxy for seismic array detectors). Using both contact and Roche lobe overflow merger scenarios, we estimate that these detectors could reach distances of up to ~1 Gpc for the most massive mergers. We show that lunar detectors could observe up to dozens of massive WD mergers annually, including those originating from globular clusters. Lunar detectors would constrain the masses of these WDs with an unprecedented accuracy of one part in a million. Furthermore, these detectors would provide early warnings of weeks before merger, including sky-localization of square arcminute resolution, enabling a new era of coordinated multi-messenger follow-up of electromagnetic transients-whether they evolve into Type Ia supernovae or accretion-induced collapse events., Comment: 13 pages, 4 figures, 2 tables, submitted to ApJL

Merging our supernova code F{\sc{ornax}} with the Box3D fast-flavor neutrino oscillation formalism, we explore the effects of fast-flavor conversion (FFC) in state-of-the-art 1D and 2D core-collapse supernova simulations. We find that after a few tens of milliseconds after bounce the FFC emerges just interior to and exterior to the stalled shock wave. It does not obtain in the PNS core nor near the average neutrinosphere radii. Interior to the shock, this results in a temporary change in the net neutrino heating rate of $\sim$10\%, due mostly to a hardening of the $\nu_e$ and $\bar{\nu}_e$ neutrino spectra, despite the decrease in their corresponding neutrino number fluxes. In 1D, the hydrodynamic effects are not large, with increases in the stalled shock radius by of order ten to twenty kilometers that abate within a few hundred milliseconds. In 2D, the hydrodynamic effect of the FFC is a bit more noticeable, resulting in slightly earlier explosions for models for lower-mass progenitors, but also potentially inhibiting explosions for some higher-mass progenitors. Fast-flavor conversion continues to operate at larger radii at later times. The net result is a shift upward in the $\nu_{\mu}$ energy and number luminosities and a shift downward in the same quantities for both the $\nu_e$ and $\bar{\nu}_e$ neutrinos. There seems to be a trend at very large radii and later times towards partial species and spectral equipartition. If this is true, it could be an interesting feature of supernova neutrino detection at later times in underground and under-ice facilities., Comment: 16 pages, 8 figures. Submitted to ApJL

Fast radio bursts (FRBs) are millisecond-duration radio bursts with unidentified extra-galactic origin. Some FRBs exhibit mild magneto-ionic environmental variations, possibly attributed to plasma turbulence or geometric configuration variation in a binary system. Here we report an abrupt magneto-ionic environment variation of FRB 20220529, a repeating FRB from a disk galaxy at redshift 0.1839. Initially, its Faraday rotation measure (RM) was $21 \pm 96~{\rm rad~m^{-2}}$ over 17 months. In December 2023, it jumped to $1976.9~{\rm rad~m^{-2}}$, exceeding twenty times of the standard deviation of the previous RM variation, and returned to the typical values within two weeks. Such a drastic RM variation suggests a dense magnetized clump moving across the line of sight, possibly due to coronal mass ejection associated with a stellar flare. It indicates that the FRB likely has a companion star that produced the stellar flare., Comment: 43 pages, 9 figures, under review in Science, the authors' original version

We investigate the indirect detection search of the two-body decay of dark matter particles into final states containing a photon, a process predicted in various promising dark matter models such as axion-like particles and sterile neutrinos. Recent and near-future photon detectors with a resolution $ R \equiv \lambda/\Delta\lambda = O(1000) $ are primarily optimized for the velocity dispersion of dark matter in the Milky Way. When performing indirect detection of dark matter in objects other than the Milky Way, one should take into account the contribution from Milky Way dark matter. As a result, the dark matter signal observed by a detector is predicted to exhibit a two-peak structure in many targets, owing to the Doppler shift, differences in radial velocities and the good energy resolution. An analysis incorporating this two-peak effect was performed using the latest XRISM observation data of the Centaurus galaxy cluster~\cite{XRISM:2025axf}. Although, due to the relatively short observation time, our derived limit is weaker than some existing limits, among dark matter searches in galaxy clusters our limit is one of the most stringent (at least in certain mass ranges). We also perform the usual single-peak analysis, for considering the various scenarios, that prefer narrow-line photon from the faraway galaxy cluster. Future data releases from XRISM as well as other observatories will further strengthen our conclusions., Comment: Comments welcome

Based on the iron and hydrogen similar elliptical morphologies of the type Ia supernova (SN Ia) remnant (SNR) 0509-67.5, I suggest that the ambient gas shaped the SN ejecta, that it is a remnant of an old planetary nebula, and that the explosion was more or less spherical. Adding that there is no observed stellar survivor in this SNR, I conclude that the SN Ia scenarios that best account for the explosion of this SN inside a planetary nebula (SNIP), are the lonely white dwarf scenarios, i.e., the core-degenerate (CD) and the double degenerate (DD) with merger to explosion delay (MED) time, i.e., the DD-MED scenario. Other scenarios encounter challenges, but I cannot completely rule them out. If true, the suggestion of SNR~0509-67.5 being a SNIP implies that the fraction of SNIPs might be higher than the previously estimated 50 percent of all normal SNe Ia. In the frame of the CD and the DD-MED scenarios, I attribute the observed double-shell structure in calcium to Rayleigh-Taylor instability during the explosion process: the caps of the Rayleigh-Taylor instability mushrooms form the outer shell. Instabilities during the explosion process might form clumps of some elements moving much faster than their mean velocity, possibly explaining fast-moving intermediate-mass elements., Comment: Will be submitted in two days to allow for comments (including missing references)

We present simple analytic corrections to the standard blackbody fitting used for early kilonova emission. We consider a spherical, relativistically expanding shell that radiates thermally at a single temperature in its own rest frame. Due to relativistic effects, including Doppler boosting, time delay, and temperature evolution -- the observed temperature is smeared across different polar angles by approximately $\sim10\%$. While the observed spectrum remains roughly consistent with a single-temperature blackbody, neglecting relativistic effects leads to significant systematic inaccuracies: the inferred photospheric velocity and temperature are overestimated by up to $\sim50\%$ for mildly relativistic velocities. By applying our analytic corrections, these deviations are reduced to within $10\%$, even in cases where the photosphere is receding and cooling is considered. Applying our corrections to observed kilonovae (AT2017gfo and the thermal component of GRB211211A) reveals that standard blackbody fitting overestimated the inferred velocities and temperatures by $10\%-40\%$., Comment: 7 pages, 6 figures, submitted to ApJ

Blazars are interesting source candidates for astrophysical neutrino emission. Multi-messenger lepto-hadronic models based on proton-photon (p-gamma) interactions result in predictions for the neutrino spectra which are typically strongly peaked at high energies. In contrast, statistical analyses looking to associate blazars and neutrinos often assume a power-law spectral shape, putting the emphasis at lower energies. We aim to examine the impact of such spectral modelling assumptions on the associations of neutrinos with blazars. We use hierarchical_nu, a Bayesian framework for point source searches, and incorporate the theoretical predictions for neutrino spectra through a dedicated spectral model and priors on the relevant parameters. Our spectral model is based on the predictions presented in Rodrigues et al. (2024) for a selection of intermediate and high synchrotron peaked blazars that have been connected with IceCube neutrino alert events. We apply our model to the 10 years of publicly available IceCube data, focusing on the Northern hemisphere. Out of 29 source candidates, we find five sources, including TXS 0506+056, that have an association probability greater than 0.5 to at least one event. The p-gamma spectra typically lead to a lower overall number of associated events compared to the power-law case, but retain or even enhance strong associations to high-energy events. Our results demonstrate that including more information from theoretical predictions can allow for more interpretable source-neutrino connections., Comment: Submitted to ApJ

Ultralight Dark Matter (ULDM) offers an alternative to cold dark matter, characterized by wavelike behavior on galactic scales. This contribution summarizes our work~\cite{Blas:2024duy} on how solitonic cores induced by ULDM affect gravitational waves (GWs), enabling their detection through next-generation observatories like LISA, Einstein Telescope and Cosmic Explorer. We show that continuous GWs from spinning neutron stars near the Galactic Center (GC) can probe solitons for \(m \lesssim 10^{-22}\, \mathrm{eV}\) and surpass current constraints on the ULDM couplings to the Standard Model for masses \(m \lesssim 10^{-20}\, \mathrm{eV}\). Additionally, GW modulation could reveal solitons in extragalactic systems, particularly in more massive halos, highlighting the broad potential of GW-based methods for uncovering ULDM properties., Comment: Conference Proceeding for the 2nd General Meeting della COST Action COSMIC WISPers (CA21106)

Low-luminosity Active Galactic Nuclei (AGN) are believed to be surrounded by a collisionless, highly magnetized accretion flow. As a result, Particle-in-Cell simulations are the best tools to study the immediate vicinity of the event horizons of these supermassive black holes. We present a GPU-based general relativistic particle-in-cell (GRPIC) code framework called Aperture. Aperture is developed in C++, with compute kernels written in CUDA and HIP to take advantage of the massive acceleration modern GPUs enable. The code is organized in a fully modular way, allowing easy extensions to new physics problems. In this paper, we describe in detail the particle pusher, field solver, and charge-conserving current deposition algorithms employed in Aperture, and present test cases to validate their correctness. Then, we apply the code to study spark gaps and plasma injection in black hole magnetospheres. We find that the apparent location and time-evolution of the gap depend on the observer. Our results reconcile the previous conflicting findings from 1D and 2D simulations in the literature., Comment: 27 pages, 13 figures, comments welcome!

The recent observation of the ultra-high-energy neutrino event KM3-230213A by the KM3NeT experiment offers a compelling avenue to explore physics beyond the Standard Model. In this work, we explore a simplest possibility that this event originates from the decay of a super-heavy dark matter (SHDM). We consider a minimal extension of the type-I seesaw by including a singlet scalar and a singlet fermion DM, both being odd under a $Z_2$ symmetry. At high scale, the $Z_2$ symmetry is spontaneously broken by the vev of the $Z_2$ odd scalar, leading to i) mixing between DM and heavy right-handed neutrinos and ii) formation of domain walls (DW). In the former case, the decay of the DM to $\nu,h$ can give rise to the PeV neutrino event KM3-230213A. While, in the latter case, the disappearance of the DW can give rise to stochastic gravitational waves. We derive constraints on the DM lifetime as a function of DM mass ensuring consistency with IceCube, Auger upper limits and the observed KM3-230213A event. We found that KM3-230213A gives stringent constraint on DM mass ranging from $1.7\times10^8$ GeV to $5.5\times10^9$ GeV with lifetime $6.3\times10^{29}$ s to $3.6\times10^{29}$ s., Comment: 5 pages, 4 captioned figures, 1 table. Comments are welcome!

The detection of gravitational waves from binary black holes (BBHs) started the hunt for their pre-merger electromagnetic emission. In that respect, numerical simulations have been looking for the "smoking gun" signal that could help identify pre-merger systems. Here we study if any of the expected features of circumbinary discs, such as the periodic modulation from the orbiting "lump", could be used to identify pre-merger BBHs or if they could be easily confused with other systems. Indeed, while the timing feature associated with the "lump" seems to be present for a large part of the parameter space defined by the binary separation and mass ratio in circular binaries, it was recently proposed to form thanks to an instability occurring naturally at the edge of accretion discs around single black holes (SBH). In order to check if features of a circumbinary disc could be reproduced by a SBH system, we search for at least one SBH fit able to replicate the given synthetic observations of a circumbinary disc. We found that many of the features from a circumbinary disc can be reproduced by a SBH system with different masses, distances or inner disc positions. Interestingly, while we can always find a SBH model providing a good enough fit to the data, the presence of two variabilities, associated with the lump and the binary, or binary-lump beat, period, is a necessary condition for a wide range of BBH system parameters and should be used as a test to disqualify some BBH candidates., Comment: 9 pages, 7 figures. Accepted for publication in MNRAS

Magnetars are the most magnetic objects in the Universe, serving as unique laboratories to test physics under extreme magnetic conditions that cannot be replicated on Earth. They were discovered in the late 1970s through their powerful X-ray flares, and were subsequently identified as neutron stars characterized by steady and transient emission across the radio, infrared, optical, X-ray, and gamma-ray bands. In this chapter, we summarize the current state of our experimental and theoretical knowledge on magnetars, as well as briefly discussing their relationship with supernovae, gamma-ray bursts, fast radio bursts, and the transient multi-band sky at large., Comment: 16 pages, 8 figures. This is a pre-print of a chapter for the Encyclopedia of Astrophysics (edited by I. Mandel, section editor J. Andrews) to be published by Elsevier as a Reference Module

This paper introduces Firmamento, a new online platform designed for astronomical research, particularly for studying blazars and other multi-messenger emitters. Firmamento provides access to a wealth of astronomical data, including imaging, spectral, and timing information, along with tools for data analysis and machine learning. A key feature is the Error Region Counterpart Identifier (ERCI), which helps locate potential counterparts to gamma-ray and other high-energy sources pinpointing objects exhibiting blazar-like characteristics. Firmamento grants access to spectral data across the entire electromagnetic spectrum, offering well-populated SED generation and VHE detectability estimation. The platform also supports user-provided data, allowing researchers to incorporate their own source lists., Comment: 8 pages, 7 figure, proceedings of the 8th Heidelberg gamma-raysymposium, Milan. Submitted to MemSAIt

Numerical simulations of multidimensional astrophysical fluids present considerable challenges. However, the development of exascale computing has significantly enhanced computational capabilities, motivating the development of new codes that can take full advantage of these resources. In this article, we introduce HERACLES++, a new hydrodynamics code with high portability, optimized for exascale machines with different architectures and running efficiently both on CPUs and GPUs. The code is Eulerian and employs a Godunov finite-volume method to solve the hydrodynamics equations, which ensures accuracy in capturing shocks and discontinuities. It includes different Riemann solvers, equations of state, and gravity solvers. It works in Cartesian and spherical coordinates, either in 1-D, 2-D, or 3-D, and uses passive scalars to handle gases with several species. The code accepts a user-supplied heating or cooling term to treat a variety of astrophysical contexts. In addition to the usual series of benchmarking tests, we use HERACLES++ to simulate the propagation of a supernova shock in a red-supergiant star envelope, from minutes after core collapse until shock emergence. In 1-D, the results from HERACLES++ are in agreement with those of V1D for the same configuration. In 3-D, the Rayleigh-Taylor instability develops and modifies the 1-D picture by introducing density and composition fluctuations as well as turbulence. The focus on a wedge, rather than the full solid angle, and the ability of running HERACLES++ with a large number of GPUs allow for long-term simulations of 3-D supernova ejecta with a sub-degree resolution. Future development is to extend HERACLES++ to a radiation-hydrodynamics code.

We investigate the axially symmetric accretion of low angular momentum hydrodynamic matter onto a rotating black hole. The gravitational field under consideration is assumed to be described by a pseudo-Newtonian Kerr potential. The accreting matter consists of different species defined by a relativistic equation of state with a variable adiabatic index.We construct and solve the hydrodynamical conservation equations governing such a flow, and find out the corresponding stationary integral solutions. We find that depending on the values of initial boundary conditions, accretion flow may exhibit multi-transonic behaviour, and a standing shock may form. We investigate, in minute detail, how the spin angular momentum of the black hole, as well as the composition of the accreting matter influence the dynamics of accretion flow and the astrophysics of shock formation in the aforementioned accreting black hole systems., Comment: 15 pages, 11 figures, uses maras class

We present multiband observations and analysis of EP240801a, a low-energy, extremely soft gamma-ray burst (GRB) discovered on August 1, 2024 by the Einstein Probe (EP) satellite, with a weak contemporaneous signal also detected by Fermi/GBM. Optical spectroscopy of the afterglow, obtained by GTC and Keck, identified the redshift of $z = 1.6734$. EP240801a exhibits a burst duration of 148 s in X-rays and 22.3 s in gamma-rays, with X-rays leading by 80.61 s. Spectral lag analysis indicates the gamma-ray signal arrived 8.3 s earlier than the X-rays. Joint spectral fitting of EP/WXT and Fermi/GBM data yields an isotropic energy $E_{\gamma,\rm{iso}} = (5.57^{+0.54}_{-0.50})\times 10^{51}\,\rm{erg}$, a peak energy $E_{\rm{peak}} = 14.90^{+7.08}_{-4.71}\,\rm{keV}$, a fluence ratio $\rm S(25-50\,\rm{keV})/S(50-100\,\rm{keV}) = 1.67^{+0.74}_{-0.46}$, classifying EP240801a as an X-ray flash (XRF). The host-galaxy continuum spectrum, inferred using Prospector, was used to correct its contribution for the observed outburst optical data. Unusual early $R$-band behavior and EP/FXT observations suggest multiple components in the afterglow. Three models are considered: two-component jet model, forward-reverse shock model and forward-shock model with energy injection. Both three provide reasonable explanations. The two-component jet model and the energy injection model imply a relatively small initial energy and velocity of the jet in the line of sight, while the forward-reverse shock model remains typical. Under the two-component jet model, EP240801a may resemble GRB 221009A (BOAT) if the bright narrow beam is viewed on-axis. Therefore, EP240801a can be interpreted as an off-beam (narrow) jet or an intrinsically weak GRB jet. Our findings provide crucial clues for uncovering the origin of XRFs., Comment: 22 pages, 11 figures, submitted to ApJ

In this work, we investigate the tidal deformability of regular black holes (RBHs). Employing different phenomenological models, we analyze their response to both test fields and gravitational perturbations, interpreting the latter within the framework of Einstein's field equations in the presence of an appropriate exotic matter distribution. Numerical and analytical methods reveal that RBHs exhibit non-trivial tidal responses, influenced by their regularization parameters and exotic matter distributions. The results obtained for test fields and gravitational perturbations are in qualitative agreement. This hints at the possibility that similar conclusions could hold if these spacetimes were interpreted as solutions of a modified gravitational action. Our findings suggest that RBHs possess distinct, though subtle, tidal signatures, which may serve as observational probes of their internal structure in gravitational wave detections.

The velocity-dependent Newtonian analogous potentials (NAPs) corresponding to general relativistic (GR) spacetimes accurately capture most of the relativistic features, including all classical tests of GR, effectively representing spacetime geometries in Newtonian terms. The NAP formulated by Tejeda \& Rosswog (TR13) for Schwarzschild spacetime has been applied to the standard thin accretion disk around a black hole (BH) as well as in the context of streamlines of noninteracting particles accreting onto a Schwarzschild BH, showing good agreement with the exact relativistic solutions. As a further application, here we explore the extent to which TR13 NAP could describe a transonic hydrodynamical spherical accretion flow in Schwarzschild spacetime within the framework of standard Newtonian hydrodynamics. Instead of obtaining a typical single "saddle-type" sonic transition, a "saddle-spiral pair" is produced, with the inner sonic point being an (unphysical) "spiral type" and the outer being a usual "saddle type." The Bondi accretion rate at outer sonic radii, however, remains consistent with that of the GR case. The primary reason for the deviation of our findings from the classical Bondi solution is likely due to the inconsistency between the Euler-type equation in the presence of velocity-dependent TR13 NAP within the standard Newtonian hydrodynamics framework, and the corresponding GR Euler equation, regardless of the fluid's energy. Our study suggests that a (modified) hydrodynamical formalism is needed to effectively implement such potentials in transonic accretion studies that align with the spirit of TR13-like NAP, while remaining consistent with the GR hydrodynamics. This could then essentially circumvent GR hydrodynamics or GR magnetohydrodynamics equations., Comment: 15 pages, 5 figures, Single column

The detection of gamma-ray signals from primordial black holes (PBHs) could provide compelling evidence for their role as a dark matter candidate, particularly through the observation of their Hawking radiation. Future gamma-ray observatories, such as e-ASTROGAM, and the next-generation telescopes, are poised to explore this possibility by measuring both Standard Model (SM) and beyond-the-SM particle emissions. A particularly promising avenue involves production of dark photons by PBHs, which is a hypothetical particle that decays into photons. In this work, we investigate the trident decay of dark photons focusing on their primary emission from PBHs. We assume that the dark photons produced via Hawking radiation decay into photons well before reaching Earth, thereby enhancing the detectable gamma-ray flux. The energy spectrum of the photons decaying from the dark photons is distinct from that of direct Hawking-radiated photons due to higher degree of freedom, leading to observable modifications in the gamma-ray signal. Using the asteroid-mass PBHs as a case study, we demonstrate that future gamma-ray missions could detect dark-photon signatures and distinguish them from conventional Hawking radiation. This approach enables the exploration of previously inaccessible parameter spaces in dark photon mass $m_{A^{\prime}}$ and their coupling to photons, offering a novel pathway to uncover the properties of dark sectors and the nature of PBHs., Comment: 20 pages, 3 figures

The next generation of gravitational-wave observatories will achieve unprecedented strain sensitivities with an expanded observing band. They will detect ${\cal O}(10^5)$ binary neutron star (BNS) mergers every year, the loudest of which will be in the band for $\approx 90$ minutes with signal-to-noise ratios $\approx 1500$. Current techniques will not be able to determine the astrophysical parameters of the loudest of next-gen BNS signals. We show that subtleties arising from the rotation of the Earth and the free-spectral range of gravitational-wave interferometers dramatically increases the complexity of next-gen BNS signals compared to the one-minute signals seen by LIGO--Virgo. Various compression methods currently relied upon to speed up the most expensive BNS calculations -- reduced-order quadrature, multi-banding, and relative binning -- will no longer be effective. We carry out reduced-order inference on a simulated next-gen BNS signal taking into account the Earth's rotation and the observatories' free-spectral range. We show that standard data compression techniques become impractical, and the full problem becomes computationally infeasible, when we include data below $\approx 16$Hz -- a part of the observing band that is critical for precise sky localisation. We discuss potential paths towards solving this complex problem.

Swift J1727.8--1613 is a black hole X-ray binary that differs from other black hole X-ray binaries in that it has an extra hard component in addition to a reflection component. We perform spectral analysis with simultaneous Insight-HXMT, NICER and NuSTAR observations when the source was in the hard and hard intermediate states. For the presentation of the extra components, we investigate the correlation between the relxill parameters. We find that the correlation between the spectral index and the reflection fraction is consistent with MAXI J1820+070 when the jet dominates the reflection. This provides the second sample to have such a correlation during an outburst. Interestingly, when the reflection component is attributed to the corona, the spectral fit results in a small reflection fraction and the correlation between the spectral index and reflection fraction is in agreement with the overall trend built-in You et al. 2023 with a large sample of outbursts from other X-ray binaries. Hence Swift J1727.8--1613 turns out to be the first sample to bridge the MAXI J1820+070 to the majority of X-ray binaries according to the dual correlations observed between the spectral index and the reflection fraction. We speculate that a configuration of a jet plus a hot inner flow may account for this peculiar outburst behavior of Swift J1727.8--1613., Comment: 12 pages, 4 figures, 4 tables. Published in JHEAp

In this work, we numerically explore the dynamics of a point mass (e.g., a stellar-mass black hole) moving within a thin accretion disk of a massive object (i.e., a supermassive black hole) with three dimensional hydrodynamical simulations using \texttt{Athena++}. We are particularly interested in the regime that the Hill radius of the point mass is greater than the disk thickness, but the point mass is not sufficiently massive to open a ``gap" in a high viscosity disk. This parameter regime may be seen for stellar-mass objects moving within thin accretion disks of massive black holes, but less studied for the planet migration scenario in protoplanetary disks. We find that the disk migration may be significantly slower than the type I migration, depending on the surface density gradient of the disk. Furthermore, the circumsingle disk around the point mass plays an important role in damping the orbital eccentricity. If the gravitational interaction between the point mass and circumsingle disk material is turned off, the orbital eccentricity may be pumped to $\mathcal{O}(10^{-2})$ level. Because space-borne gravitational wave detectors such as LISA (Laser Interferometer Space Antenna) is able to measure the eccentricity of extreme mass-ratio inspirals to the level of $\mathcal{O}(10^{-5})$, this finding highlights the importance of understanding stellar-mass black hole feedback mechanisms which will modify the structures of the circumsingle disk, as they will impact LISA observables such as the eccentricity., Comment: 17 pages, 15 figures, accepted for publication in PRD

Relativistic jets from accreting black holes (BHs) radiate non-thermal emission which is highly variable in different time scales. Magnetic fields anchored to a rotating BH or accretion disc accelerate and collimate jets of the BH systems. Previous studies on black holes of different mass scales, including supermassive and stellar-mass black holes, only report flux quasi-periodic oscillations in radio, optical, X-ray and gamma-ray bands. No quasi-periodic variations in polarization have yet been detected in any black hole systems. Here, we report the first detection of GHz radio polarization oscillations in GRS 1915+105, which harbors a spinning stellar-mass BH with a relativistic jet. Our observations show that during the increasing phase of radio emission, linear polarization and flux exhibit similar oscillation periods of $\sim 17$ and $33$ seconds, and their variation patterns anti-correlate with each other. These rare, short-period oscillations in both polarization and flux would be important to understand instabilities and special dynamics in magnetized jets., Comment: 26 pages, 6 figures, the author version of the paper to be published in Nature Communications

This study investigates polarimetric characteristics of the blazar 3C~454.3 at 22-129~GHz using decadal~(2011-2022) data sets. In addition, we also delve into the origin of the polarization flare observed in 2019. The data sets were obtained from the single-dish mode observations of the Korean VLBI Network~(KVN) and the 43-GHz Very Long Baseline Array~(VLBA). We compared the consistency of the measurements between milli-arcsecond and arcsecond scales. The Faraday rotation measure values were obtained via two approaches, model fitting to a linear function in all frequency ranges, and calculation from adjacent frequency pairs. We found that the linear polarization angle is preferred to be $\sim100^{\circ}$ when the source is highly polarized. At 43~GHz, we found that the polarized emission at scales of mas and arcsecond is consistent when we compare its flux density and polarization angle. The ratio of quasi-simultaneously measured polarized flux density is $1.02\pm0.07$, and the polarization angles display similar rotation. These suggest that the extended jet beyond the scale of VLBA 43~GHz has a negligible convolution effect on the polarization angle from the KVN. We found an interesting, notable flaring event in the KVN single-dish data from the polarized emission in 2019 in the frequency range of 22-129~GHz. During the flare, the observed polarization angles~($\chi_{\rm obs}$) rotate from $\sim150^{\circ}$ to $\sim100^{\circ}$ at all frequencies with a chromatic polarization degree~($m_{\rm p}$). Based on the observed $m_{\rm p}$ and $\chi_{\rm obs}$, and also the Faraday rotation measure, we suggest that the polarization flare in 2019 is attributed to the shock-shock interaction in the stationary jet region. The change in the viewing angle of the jet alone is insufficient to describe the increase in brightness temperature, indicating the presence of source intrinsic processes., Comment: Accepted for publication in A&A

Supergiant Fast X-ray Transients (SFXT) are a sub-class of High Mass X-ray Binaries (HMXB) in which a compact object accretes part of the clumpy wind of the blue supergiant companion, triggering a series of brief, X-ray flares lasting a few kiloseconds. Currently, only about fifteen SFXTs are known. The EXTraS catalog provides the timing signatures of every source observed by the EPIC instrument on-board XMM-Newton. Among the most peculiar sources, in terms of variability, we selected 4XMM J181330.1-17511 (J1813). We analyzed all publicly available X-ray data pointed at the J1813 position to determine the source's duty cycle and to provide a comprehensive description of its timing and spectral behavior during its active phase. Additionally, we searched for the optical and infrared counterpart of the X-ray source in public databases and fitted its Spectral Energy Distribution (SED). The optical-to-MIR SED of J1813 is consistent with a highly-absorbed (A$_V\sim38$) B0 star at $\sim$10 kpc. During its X-ray active phase, the source is characterized by continuous $\sim$thousands seconds-long flares with peak luminosities (2-12 keV) ranging from $10^{34}$ to $4 \times 10^{35}$ erg s$^{-1}$. Its X-ray spectrum is consistent with a high-absorbed power-law model with N$_H \sim 1.8 \times 10^{23}$ cm$^{-2}$ and $\Gamma \sim 1.66$. No spectral variability was observed as a function of time or flux. J1813 is in a quiescent state $\sim$60\% of the time, with an upper-limit luminosity of $8 \times 10^{32}$ erg s$^{-1}$ (at 10 kpc), implying an observed long-term X-ray flux variability $>$500. The optical counterpart alone indicates J1813 is a HMXB. Its transient nature, duty cycle, the amplitude of observed X-ray variability, the shape and luminosity of the X-ray flares -- and the lack of known X-ray outbursts ($>10^{36}$ erg s$^{-1}$) -- strongly support the identification of J1813 as an SFXT., Comment: 9 pages, 7 figures, 3 tables, Accepted for publication in A&A

Modern Imaging Atmospheric Cherenkov Telescopes (IACTs) generate a huge amount of data that must be classified automatically, ideally in real time. Currently, machine learning-based solutions are increasingly being used to solve classification problems. However, these classifiers require proper training data sets to work correctly. The problem with training neural networks on real IACT data is that these data need to be pre-labeled, whereas such labeling is difficult and its results are estimates. In addition, the distribution of incoming events is highly imbalanced. Firstly, there is an imbalance in the types of events, since the number of detected gamma quanta is significantly less than the number of protons. Secondly, the energy distribution of particles of the same type is also imbalanced, since high-energy particles are extremely rare. This imbalance results in poorly trained classifiers that, once trained, do not handle rare events correctly. Using only conventional Monte Carlo event simulation methods to solve this problem is possible, but extremely resource-intensive and time-consuming. To address this issue, we propose to perform data augmentation with artificially generated events of the desired type and energy using conditional generative adversarial networks (cGANs), distinguishing classes by energy values. In the paper, we describe a simple algorithm for generating balanced data sets using cGANs. Thus, the proposed neural network model produces both imbalanced data sets for physical analysis as well as balanced data sets suitable for training other neural networks., Comment: 19 pages, 10 figures, Proceedings of The 8th International Conference on Deep Learning in Computational Physics, June 19-21, 2024, Moscow, Russia

In view of the great uncertainty of the equation of state (EOS) of high-density nuclear matter, establishing EOS-independent universal relations between global properties of neutron stars provides a practical way to constrain the unobservable or difficult-to-observe properties through astronomical observations. It is common to construct universal relations between EOS-dependent properties (e.g., moment of inertia, tidal deformation, etc.) or combined properties (e.g., compactness). Improving the precision of the universal relations may provide stricter constraint on the properties of neutron star. We find that in 3-dimensional space with mass and radius as the base coordinates, the points corresponding to a certain property of neutron star described by different EOSs are almost located in the same surface. Thus the universal relation between the property and the stellar mass-radius can be expressed through describing the surface. It is shown that the resulting universal relations have higher precisions. As an example, we construct high-precision universal relations for the moment of inertia, the $f$-mode frequency, and the dimensionless tidal deformation respect to the mass-radius. As the observational data of neutron star mass and radius from NICER grows in data and accuracy, these universal relations allow for more precise constraints on the unobservable or difficult-to-observe properties., Comment

We present photometric and spectroscopic data of the type IIb supernova (SN) 2024abfo in NGC 1493 (at 11 Mpc). The ATLAS survey discovered the object just a few hours after the explosion, and observed a fast rise on the first day. Signs of the sharp shock break-out peak and the subsequent cooling phase are observed in the ultraviolet and the bluest optical bands in the first couple of days, while no peak is visible in the reddest filters. Subsequently, in analogy with normal SNe IIb, the light curve of SN 2024abfo rises again in all bands to the broad peak, with the maximum light reached around one month after the explosion. Its absolute magnitude at peak is $M_r=-16.5\pm0.1$ mag, making it a faint SN IIb. The early spectra are dominated by Balmer lines with broad P-Cygni profiles indicating ejecta velocity of 22,500 \kms. One month after the explosion, the spectra display a transition towards being He-dominated, though the H lines do not completely disappear, supporting the classification of SN 2024abfo as a relatively H-rich SN IIb. We identify the progenitor of SN 2024abfo in archival images of the Hubble Space Telescope, the Dark Energy Survey, and the XMM-Newton space telescope, in multiple optical filters. From its spectral energy distribution, the progenitor is consistent with being a white supergiant, Deneb-like star, with a photospheric temperature of 8110 K, a radius of 176 \Rsun, a luminosity of $\log(L/L_{\odot})=5.08$, having an initial mass of 15-16 \Msun. This detection supports an emerging trend of SN IIb progenitors being more luminous and hotter than SN II ones, and being primaries of massive binaries. Within the SN IIb class, fainter events such as SN 2024abfo tend to have cooler and more expanded progenitors than luminous SNe IIb., Comment: 9 pages, 9 figures, 4 tables, submitted to A&A

The impact of neutrino flavor conversion on the supernova mechanism is yet to be fully understood. We present multi-energy and multi-angle solutions of the neutrino quantum kinetic equations in three flavors, taking into account neutrino advection and non-forward collisions with the background medium. Flavor evolution is explored within a spherically symmetric shell surrounding the region of neutrino decoupling in the interior of a core-collapse supernova, relying on the outputs of a spherically symmetric core-collapse supernova model with a mass of $18.6 M_\odot$. We select two representative post-bounce times: $t_{\rm pb} = 0.25$ s (no angular crossings are present and flavor conversion is triggered by slow collective effects) and $t_{\rm pb} = 1$ s (angular crossings trigger fast flavor instabilities). We find that flavor equipartition is achieved in the antineutrino sector between $\bar\nu_e$ and $\bar\nu_x = (\bar\nu_\mu + \bar\nu_\tau)/2$ for both post-bounce times. In the neutrino sector, flavor equipartition between $\nu_e$ and $\nu_x$ seems more likely at later post-bounce times, where the neutrino emission properties among different flavors tend to approach each other, but it is not a generic feature. The exponential growth of the $\nu_\mu$--$\nu_\tau$ asymmetry due to three-flavor effects is responsible for differences between the quasi-steady configurations obtained in the three-flavor solution and in the two-flavor approximation. This has consequences on the neutrino heating rate, which is generally larger when all three flavors are taken into account and can increase up to $30\%$ with respect to the case where flavor conversion is neglected., Comment: 22 pages, 8 Figures

We study particle acceleration in strongly turbulent pair plasmas using novel 3D Particle-in-Cell simulations, featuring particle injection from an external heat bath and diffusive escape. We demonstrate the formation of steady-state, nonthermal particle distributions with maximum energies reaching the Hillas limit. The steady state is characterized by the equilibration of plasma kinetic and magnetic pressures, which imposes upper limits on the acceleration rate. With growing cold plasma magnetization $\sigma_0$, nonthermal power-law spectra become harder, and the fraction of energy channeled into escaping cosmic rays increases. At $\sigma_0 \gtrsim 1$, the escaping cosmic rays amount to more than 50% of the dissipated energy. Our method allows for kinetic studies of particle acceleration under steady-state conditions, with applications to a variety of astrophysical systems.

We constrain the neutrino-dark matter cross-section using the $13 \pm 5$ neutrino event excess observed by IceCube in 2014-2015 from the direction of the blazar TXS 0506+056. Our analysis takes advantage of the dark matter overdensity spike surrounding the supermassive black hole at the center of the blazar. In our results, we take into account uncertainties related to the different types of neutrino emission models and the features of the dark matter spike, considering cross-sections that scale with energy as $\sigma \propto (E_{\nu} /E_0)^n$, for values of $n = 1, 0, -1, -2$. In our best-case scenario, we obtain limits competitive with those derived from other active galaxies, tidal disruption events (TDEs), and the IC-170922A event., Comment: 20 pages, 7 figures, 2 tables

Binary population synthesis simulations allow detailed modelling of gravitational-wave sources from a variety of formation channels. These population models can be compared to the observed catalogue of merging binaries to infer the uncertain astrophysical input parameters describing binary formation and evolution, as well as relative rates between various formation pathways. However, it is computationally infeasible to run population synthesis simulations for all variations of uncertain input physics. We demonstrate the use of normalising flows to emulate population synthesis results and interpolate between astrophysical input parameters. Using current gravitational-wave observations of binary black holes, we use our trained normalising flows to infer branching ratios between multiple formation channels, and simultaneously infer common-envelope efficiency and natal spins across a continuous parameter range. Given our set of formation channel models, we infer the natal spin to be $0.04^{+0.04}_{-0.01}$, and the common-envelope efficiency to be $>3.7$ at 90% credibility, with the majority of underlying mergers coming from the common-envelope channel. Our framework allows us to measure population synthesis inputs where we do not have simulations, and better constrain the astrophysics underlying current gravitational-wave populations., Comment: 20 pages, 6 figures, 2 tables, 1 appendix. Submitted to Astrophysical Journal. Data release at https://doi.org/10.5281/zenodo.14967688

The detection of over a hundred gravitational wave signals from double compacts objects have confirmed the existence of such binaries with tight orbits. Two main formation channels are generally considered to explain the formation of these merging binary black holes (BBHs): the isolated evolution of stellar binaries, and the dynamical assembly in dense environments, namely star clusters. Although their relative contributions remain unclear, several analyses indicate that the detected BBH mergers probably originate from a mixture of these two distinct scenarios. We study the formation of massive star clusters across time and at a cosmological scale to estimate the contribution of these dense stellar structures to the overall population of BBH mergers. To this end, we propose three different models of massive star cluster formation based on results obtained with zoom-in simulations of individual galaxies. We apply these models to a large sample of realistic galaxies identified in the $(22.1\ \mathrm{Mpc})^3$ cosmological volume simulation \firebox. Each galaxy in this simulation has a unique star formation rate, with its own history of halo mergers and metallicity evolution. Combined with predictions obtained with the Cluster Monte Carlo code for stellar dynamics, we are able to estimate populations of dynamically formed BBHs in a collection of realistic galaxies. Across our three models, we infer a local merger rate of BBHs formed in massive star clusters consistently in the range $1-10\ \mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$. Compared with the local BBH merger rate inferred by the LIGO-Virgo-KAGRA Collaboration (in the range $17.9-44\ \mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$ at $z=0.2$), this could potentially represent up to half of all BBH mergers in the nearby Universe. This shows the importance of this formation channel in the astrophysical production of merging BBHs., Comment: 19 pages, 10 figures

In classic time-dependent 1D accretion disk models, the inner radiation pressure dominated regime is viscously unstable. However, late-time observations of accretion disks formed in tidal disruption events (TDEs) do not exhibit evidence of such instabilities. The common theoretical response is to modify the viscosity parametrization, but typically used viscosity parametrization are generally ad hoc. In this study, we take a different approach, and investigate a time-dependent 1D $\alpha$-disk model in which the pressure is dominated by magnetic fields rather than photons. We compare the time evolution of thermally stable, strongly magnetized TDE disks to the simpler linear viscosity model. We find that the light curves of magnetized disks evolve as $L_{\rm UV}\propto t^{-5/6}$ for decades to centuries, and that this same evolution can be reproduced by the linear viscosity model for specific parameter choices. Additionally, we show that TDEs remain UV-bright for many years, suggesting we could possibly find fossil TDEs decades after their bursts. We estimate that ULTRASAT could detect hundreds of such events, providing an opportunity to study late-stage TDE physics and supermassive black hole (SMBH) properties. Finally, we explore the connection between TDE disks and quasi-periodic eruptions (QPEs) suggested by recent observations. One theoretical explanation involves TDE disks expanding to interact with extreme mass ratio inspirals (EMRIs), which produce X-ray flares as the EMRI passes through the disk. Our estimates indicate that magnetized TDE disks should exhibit QPEs earlier than those observed in AT2019qiz, suggesting that the QPEs may have begun before their first detection., Comment: Reader comments very welcome

This work introduces a novel deep learning-based approach for gravitational wave anomaly detection, aiming to overcome the limitations of traditional matched filtering techniques in identifying unknown waveform gravitational wave signals. We introduce a modified convolutional neural network architecture inspired by ResNet that leverages residual blocks to extract high-dimensional features, effectively capturing subtle differences between background noise and gravitational wave signals. This network architecture learns a high-dimensional projection while preserving discrepancies with the original input, facilitating precise identification of gravitational wave signals. In our experiments, we implement an innovative data augmentation strategy that generates new data by computing the arithmetic mean of multiple signal samples while retaining the key features of the original signals. In the NSF HDR A3D3: Detecting Anomalous Gravitational Wave Signals competition, it is honorable for us (group name: easonyan123) to get to the first place at the end with our model achieving a true negative rate (TNR) of 0.9708 during development/validation phase and 0.9832 on an unseen challenge dataset during final/testing phase, the highest among all competitors. These results demonstrate that our method not only achieves excellent generalization performance but also maintains robust adaptability in addressing the complex uncertainties inherent in gravitational wave anomaly detection., Comment: 6 pages, 3 figures, A concise introduction to the winning solution for NSF HDR A3D3 GW challenge. Our training code is publicly available at https://github.com/yan123yan/HDR-anomaly-challenge-submission

We present the first photometric population study of double-peaked Type IIb supernovae (SNe IIb). SNe IIb are produced from the core-collapse of massive stars whose outermost Hydrogen layer has been partially stripped prior to explosion. These double-peaked light curves, consisting of a shock-cooling emission peak (SCE) followed by the main nickel-powered peak, contain more crucial information about the progenitor system than the typical single-peaked light curves. We compiled and analyzed a sample of 14 spectroscopically confirmed SNe IIb -- including previously unpublished and re-classified -- with publicly available photometric observations, discovered between 2018--2022, from the ZTF and ATLAS surveys. We developed and fit a piecewise linear model, referred to as the ``lightning bolt model,'' to describe the early-time behavior of these objects to measure population statistics. Notably, we find the SCE peak lasts, on average, fewer than five days above half-maximum light with a mean rise time of $2.07\pm1.0$ and $1.1\pm0.8$ mags/day in the g- and r-band respectively. These SCE rise rates are over 10x faster than -- and last only a third the duration of -- the rise to the nickel-powered peak. These rise times are comparable to those of fast blue optical transient (FBOT) events and we discuss the implications in the text. Finally, we present a proof-of-concept alert filter, using the ANTARES broker, to demonstrate how to translate these population statistics into simple and effective filters to find potential double-peaked SNe IIb in large-scale survey alert streams, like the imminent Vera C. Rubin Observatory Legacy Survey of Space and Time (Rubin LSST)., Comment: Key figures are Fig 3 and Fig 5. 23 pages, 6 figures, submitted to ApJ

In hydrogen-rich (H-rich) Supernova (SN) events, the collision between the H-rich ejecta and the Circum-Stellar Medium (CSM) can accelerate particles and produce high-energy neutrinos (HE-$\nu$, TeV-PeV) through proton-proton inelastic scattering. Despite understanding the production mechanism of these neutrinos, the lack of direct observations raises questions about particle acceleration efficiency and the involved astrophysical conditions. This study focuses on neutrino emission from H-rich SNe with low-mass CSM, such as SN 2023ixf. We developed a semi-analytical model to characterize the progenitor and CSM at the explosion time, allowing us to infer the expected neutrino flux at Earth during the SN's interaction phase. Our model shows that neutrino emission depends not only on shock velocity and CSM mass but also on the spatial matter distribution of the CSM. By analysing the bolometric light curve of SN 2023ixf beyond 100 days post-explosion, we find that its ejecta, consisting of $9\,\text{M}_{\rm \odot}$ (including $0.07\,\text{M}_{\rm \odot}$ of radioactive $^{56}$Ni) and having a kinetic energy of $1.8\,\text{foe}$, collides with a low-mass CSM of $0.06\,\text{M}_{\rm \odot}$ distributed according to a power-law density profile with an exponent of $s=2.9$. Through these parameters, we estimate that up to $4\pm1\times 10^{-2}$ muon (anti-)neutrino events could be detected by IceCube within 50 days post-explosion. Although the predicted flux ($\lesssim 3\times 10^{-9}\,\text{GeV} \, \text{cm}^{-2} \, \text{s}^{-1}$) is below current IceCube sensitivity, future telescopes like IceCube-Gen2 and KM3NeT could detect HE-$\nu$ from similar SN events., Comment: 19 pages, 11 figures, under revision in Monthly Notices of the Royal Astronomical Society - Main Journal (First submission 23-Aug-2024; Revised version submitted 23-Feb-2025; currently awaiting reviewer report)

The scale invariance of accretion processes (SIAP) is crucial for understanding the physical processes of black hole accretion systems at different scales. When applying this rule to high-frequency quasi-periodic oscillations (HFQPOs), there is an observation-theory confrontation in active galactic nuclei (AGNs). By compiling an updated X-ray HFQPO catalog, we found that the ultraluminous X-ray sources support the HFQPO models, similar to black hole X-ray binaries. More importantly, we identified two supermassive black hole (SMBH) sources (Sgr A and NGC 1365) with possible advection-dominated accretion flow (ADAF) configurations that support existing HFQPO models, even though many AGNs still do not. Furthermore, we report a new HFQPO candidate in NGC 5506. This source exhibits an accretion state similar to that of Sgr A* and NGC 1365, and it also supports the HFQPO models. Our results are consistent with previous numerical simulations and suggest that the accretion state of HFQPOs in SMBHs may differ from that of stellar-mass black holes (SBHs). To reconcile the sources that do not support the models, either a global general-relativistic HFQPO model based on magnetohydrodynamics needs to be considered, or the HFQPOs in these sources may originate from entirely different physical processes. This discovery significantly extends the SIAP rule to a broader scale, confirming that the paradigm of accretion scale invariance remains consistent from SBHs to SMBHs., Comment: 10 pages, 6 figures,1 table, accepted for publication in MNRAS