Instrumentation and Methods for Astrophysics
GALFITools: A Python library to enhance GALFIT usage in galaxy image modeling
Christopher Añorve
Understanding how
galaxies form and evolve requires measuring their light distributions in images taken by
telescopes. This process often involves fitting mathematical models to
galaxy images to extract properties such as size, brightness, components, and shape. GALFIT is a widely used tool for this purpose, but it requires careful preparation of input files and interpretation of results, which can be a barrier to efficient use. GALFITools is a Python library that streamlines this workflow by automating many of the tasks surrounding the use of GALFIT. These include generating image masks, estimating sky background, modeling the
telescope's point spread function (PSF), and extracting physical parameters from GALFIT outputs. The software is designed for researchers and students who work with
galaxy image modeling and aims to make the process more reproducible, accessible, and scalable.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Future Rip Scenarios in Fractional Holographic Dark Energy
Ayush Bidlan, Paulo Moniz and Oem Trivedi
In this paper, we investigate the occurrence of late-time cosmological singularities, namely, the rip scenarios within the framework of interacting Fractional
Holographic Dark Energy (FHDE). We start our investigation with the Granda-Oliveros (GO) cutoff, i.e., $L=(\gamma H^{2}+\delta\dot{H})^{-\frac{1}{2}}$, and highlight the range of allowed $\alpha$ (Lévy's index) values for which big, little and pseudo rip can occur. In particular, we highlight the occurrence of a big rip for fractional values of the Lévy's index in the allowed range $1<\alpha\leq2$. Moreover, we conclude that the occurrence of a pseudo-rip requires Lévy's index to be $\alpha>2$. Therefore, we reject the possibility of pseudo-rip within the GO cutoff. Furthermore, we demonstrate that the occurrence of the little rip in FHDE equipped with a GO cutoff is rather contrived and requires a specific functional form of the IR cutoff $L\sim(\gamma H^{2}+g(H))^{-\frac{1}{2}}$, which belongs to a larger class of Nojiri-Odintsov (NO) cutoffs. To extend our perspective beyond the GO cutoff, we investigate the interacting FHDE framework equipped with the Hubble cutoff, i.e., $L=H^{-1}$, in developing an ansatz-based approach to the little and pseudo-rip singularities as they fail to appear in the GO cutoff. Within this approach, we invoke the expression of the Hubble parameter, $H(t)$, which corresponds to the little and pseudo-rip, into the cosmological parameters such as the Equation of State (EoS) and Squared Sound Speed (SSS) as a function of
cosmic time $t$. We produce numerical plots of these parameters in both linear and non-linear $Q$ regimes, which supplement our theoretical findings. In summary, our results highlight the occurrence of little and pseudo-rip singularities within a Hubble cutoff for a non-linear $Q$ term within the FHDE framework.
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High Energy Astrophysical Phenomena
Can tidal disruption event models reliably measure black hole masses?
C. R. Angus, A. J. Smith, D. Magill et al. (+15 more)
Tidal disruption event (TDE) light curves are increasingly used to infer the masses of quiescent supermassive black holes ($M_{\rm{BH}}$), offering a powerful probe of low-mass black hole demographics independent of host-
galaxy scaling relations. However, the reliability of most semi-analytic TDE models assume full
stellar disruption, despite theoretical expectations that partial disruptions dominate the TDE population. In this work we test the robustness of current TDE models using three repeating partial TDEs (rpTDEs), in which the multiple
flares produced by the same surviving
stellar core must yield consistent black hole masses. We present spectroscopic observations establishing AT 2023adr as a rpTDE, making it the third such spectroscopically confirmed event. We independently model the
flares of the three rpTDEs; 2020vdq, 2022dbl, and 2023adr, applying fallback-
accretion fits, stream-stream collision scaling relations, luminosity-based empirical relations, and cooling-envelope fits. After accounting for statistical and model-specific systematics, we find that all TDE models generally return self-consistent $M_{\rm{BH}}$ values between
flares, and are broadly consistent with host-
galaxy $M_{\rm{BH}}$ proxies, recovering $M_{\rm{BH}}$ to within 0.3-0.5 dex. However, the convergence of fallback models towards unphysical
stellar masses and impact parameters reveals limitations in the existing fallback model grids. We also show that light curve coverage, particularly in the near-UV, is critical for constraining model parameters. This has direct implications for interpreting the thousands of TDE light curves expected from upcoming surveys such as the Rubin Observatory's Legacy Survey of Space and Time, where from simulations, we find that $M_{\rm{BH}}$ may be underestimated on average by 0.5 dex without additional follow-up.
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All authors C. R. Angus, A. J. Smith, D. Magill, P. Ramsden, N. Sarin, M. Nicholl, B. Mockler, E. Hammerstein, R. Stein, Y. Yao, T. de Boer, K. C. Chambers, M. E. Huber, C.-C. Lin, T. B. Lowe, E. A. Magnier, S. J. Smartt, R. J. Wainscoat
High Energy Astrophysical Phenomena
Formation of Recycled Pulsars in Common Envelope Binaries
Yu-Dong Nie, Yong Shao, Jian-Guo He et al. (+4 more)
We present a systematic study of the
evolution of low- and intermediate-mass X-ray binaries (L/IMXBs) consisting of a $1.4\,M_{\odot}$
neutron star (NS) and a donor
star of mass $1-8\,M_{\odot}$. Using grids of detailed MESA simulations, we show that for donor masses of $2-8\,M_{\odot}$, mass transfer may be dynamically unstable, leading to a common envelope (CE) phase. By adopting CE ejection efficiencies in the range $\alpha_{\rm CE} = 0.3-3.0$, we find that post-CE binaries frequently experience a CE decoupling phase (CEDP), which plays a critical role in determining their final orbital and compositional properties. Systems with initial donor masses $\gtrsim 3.5\,M_{\odot}$ predominantly evolve into NS binaries with carbon-oxygen or oxygen-neon white
dwarfs (WDs) with masses between $0.5\,M_{\odot}$ and $1.4\,M_{\odot}$. Comparison with the observed population of binary
pulsars with a WD companion shows better agreement with higher CE ejection efficiencies ($\alpha_{\rm CE} = 3.0$). Furthermore, we demonstrate that NSs can accrete a sufficient amount of matter ($\gtrsim 0.01\,M_{\odot}$) during the CEDP and subsequent Case BA/BB/BC mass transfer phases to be effectively recycled into millisecond
pulsars. We identify two distinct evolutionary channels capable of reproducing the observed characteristics of the millisecond
pulsar PSR J1928+1815 with a helium-
star companion. Our results highlight the importance of the CEDP in the formation of recycled
pulsars and provide constraints on the CE ejection efficiency during binary
evolution.
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All authors Yu-Dong Nie, Yong Shao, Jian-Guo He, Ze-Lin Wei, Shi-Jie Gao, Xiao-Jie Xu, Xiang-Dong Li
Instrumentation and Methods for Astrophysics
The Impact of Robotic Telescopes on Time-Domain Astronomy
Yakubu Mu'allim, J. O.Vwavware and A. Ohwofosirai
The field of time-domain astronomy has experienced unprecedented growth due to the increasing deployment of robotic
telescopes capable of autonomous, round-the-clock sky monitoring. These instruments have revolutionized the detection and characterization of transient phenomena such as
supernovae, gamma-ray bursts, variable
stars, and gravitational wave counterparts. This paper explores the transformative role of robotic
telescopes such as ZTF, ATLAS, and LCOGT in enabling rapid-response observations and building large time-series
datasets. We review the design principles and scheduling
algorithms behind robotic observatories and assess their scientific contributions across different wavelength regimes. Particular
attention is given to the synergy between robotic systems and machine learning pipelines that enable real-time classification of transient events. We also discuss challenges such as data deluge, follow-up prioritization, and observational biases, as well as future directions in global
telescope networks
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Astrophysics of Galaxies
Nitrogen enhancement of GN-z11 by metal pollution from supermassive stars
Sho Ebihara, Michiko S. Fujii, Takayuki R. Saitoh et al. (+4 more)
Spectroscopic observations by the James Webb Space
Telescope (JWST) have revealed young, compact, high-
redshift ($z$)
galaxies with high nitrogen-to-oxygen (N/O) ratios. GN-z11 at z=10.6 is one of these
galaxies. One possible scenario for such a high N/O ratio is pollution from supermassive
stars (SMSs), from which
stellar winds are expected to be nitrogen-rich. The abundance pattern is determined by both
galaxy evolution and SMS pollution, but so far, simple one-zone models have been used. Using a
galaxy formation simulation, we tested the SMS scenario. We used a cosmological zoom-in simulation that includes chemical
evolution driven by rotating massive
stars (Wolf-Rayet
stars),
supernovae, and asymptotic
giant branch
stars. As a post-process, we assumed the formation of an SMS with a mass between $10^3$ and $10^5$ $M_\odot$ and investigated the contribution of its ejecta to the abundance pattern. The N/O ratio was enhanced by the SMS ejecta, and the abundance pattern of GN-z11, including carbon-to-oxygen and oxygen-to-hydrogen ratios, was reproduced by our SMS pollution model if the pollution mass fraction ranges within 10-30 per cent. Such a pollution fraction can be realized when the gas ionized by the SMS is polluted, and the gas density is $10^4$-$10^5$ cm$^{-3}$ assuming a Strömgren sphere. We also compared the abundance pattern with those of other N/O-enhanced high-$z$
galaxies. Some of these
galaxies can also be explained by SMS pollution.
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All authors Sho Ebihara, Michiko S. Fujii, Takayuki R. Saitoh, Yutaka Hirai, Hideyuki Umeda, Yuki Isobe, Chris Nagele
Cosmology and Nongalactic Astrophysics
Dark QCD Origin of the NANOGrav Signal and Self-Interacting Dark Matter
Zihan Wang
The NANOGrav 15-year
stochastic gravitational wave background (SGWB) amplitude $A_{\rm yr} \approx 2.4 \times 10^{-15}$ lies at the upper edge of population synthesis predictions for supermassive black hole binaries (SMBHBs), motivating exploration of additional cosmological sources. We present a phenomenological framework based on an $\text{SU}(3)_D$ gauge theory that can simultaneously accommodate the gravitational wave signal and resolve small-scale structure anomalies via Self-Interacting Dark Matter (SIDM). The dark matter candidate is a heavy dark
baryon $\chi = QQQ$ with mass $m_\chi \approx 40$~GeV, which self-interacts through a light pseudo-dilaton $d$ $m_d \approx 20$–$50$~MeV as a pseudo-Goldstone
boson of approximate scale invariance arising in near-conformal gauge theories with $N_f \sim 6$–$8$ light
flavors. A first-order phase transition at the MeV scale, enabled by walking dynamics near the conformal window, produces gravitational waves in the PTA band. For representative parameters $T_n \approx 5$–$6$~MeV, $\alpha \sim 500$–$1000$, $\beta/H_* \sim 30$–$50$, the model provides a fit to NANOGrav data comparable to SMBHB while naturally connecting the gravitational wave amplitude to the dark matter relic density through
entropy dilution $D \approx \alpha^{3/4}$. We present explicit calculations of the bounce action, bubble wall velocity, and $\Delta N_{\rm eff}$, demonstrating that the
benchmark parameters are theoretically consistent and cosmologically safe ($\Delta N_{\rm eff} \lesssim 0.1$ for $m_\pi > 2m_d$). The distinctive spectral shape ($f^3 \to f^{-4}$) provides a robust prediction testable with future PTAs.
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Solar and Stellar Astrophysics
Polarization of decayless kink oscillations in a 3D MHD coronal loop model
Sudip Mandal, Cosima Breu and Hardi Peter
Decayless kink oscillations are frequently observed in
solar coronal loops and are considered potential contributors to coronal heating. Despite the ubiquity of this wave phenomenon, its driving mechanism remains unclear. Studies to derive the polarization state of these oscillations, which would be a key to identifying the drivers, have been limited due to observational constraints. We analyze a 3D MHD simulation of coronal loops using the MURaM code. Synthetic extreme ultraviolet (EUV) emission maps, combined with velocity diagnostics, are used to identify and characterize transverse wave motions in the simulated loop structures. This is the first demonstration of decayless kink waves emerging self-consistently in a 3D MHD loop-in-a-box model. The simulation produces persistent, low-amplitude, decayless kink oscillations that closely match observed properties. These oscillations arise spontaneously, without any imposed periodic driver, and exhibit clear linear polarization with oscillation planes not aligned to the principal axes. The observed coherency of linear polarization with oscillation cycles favors a self-sustained or quasi-steady type wave driver over a
stochastic or broadband source.
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Solar and Stellar Astrophysics
KL Dra as a Benchmark Laboratory for Accretion-Disk Physics: Constraints from TESS and Ground-Based Surveys
Luis E. Salazar Manzano, Liliana E. Rivera Sandoval, Jean-Marie Hameury et al. (+4 more)
We present the longest-term optical analysis of the AM CVn system KL Dra using $\sim11$ years of monitoring from TESS and wide-field ground-based surveys. The continuous TESS coverage allows us to characterise its frequent outbursts with unprecedented detail, providing the first comprehensive study of an AM CVn during outbursts and enabling detailed modelling of these systems. The superoutbursts in KL Dra generally include a precursor, and are followed by a series of rebrightenings after which a sequence of 3-4 large amplitude normal outbursts is observed. We fit parametric profiles to each superoutburst component (precursor, rise to plateau, plateau, decay), to rebrightenings, and to normal outbursts, which let us quantify every high state feature and investigate correlations with the system's long term supercyle
evolution. Our continuous coverage reveals an average value for the supercycles, superoutbursts and normal outbursts of $60.4 \pm 0.1$ d, $5.67\pm0.03$ d and $1.17 \pm0.01$ d, respectively. The supercycle duration may be correlated with the rebrightenings duration and superoutburst amplitude, and anticorrelated with the plateau length. Within a supercycle, normal outbursts grow in amplitude and duration, and the first normal outburst is usually highly asymmetric, while subsequent normal outbursts are more symmetric. We detected superhumps in TESS superoutbursts but not in the rebrightenings or normal outbursts. We interpret the results within the disk instability model, considering additional effects, such as changes in the donor mass transfer rate.
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All authors Luis E. Salazar Manzano, Liliana E. Rivera Sandoval, Jean-Marie Hameury, Craig O. Heinke, Iwona Kotko, Thomas J. Maccarone, Manuel Pichardo Marcano
Astrophysics of Galaxies
Investigating HII Regions in the Disk of NGC 7331 with the Circumgalactic H$\alpha$ Spectrograph
Nazende Ipek Kerkeser, Nicole Melso, David Schiminovich et al. (+3 more)
We investigate the ionized gas kinematics of HII regions in the disk of NGC 7331 using integral field unit data collected with the Circumgalactic H$\alpha$ Spectrograph (CH$\alpha$S). NGC 7331 is a well-studied nearby
galaxy with HII regions resolved by seeing-limited observations, making it ideally suited for this work. The
galaxy disk features vigorous
star formation, especially in the central ring of starburst activity. We present a catalog of 136 HII regions detected in the SIRTF Nearby
Galaxies Survey (SINGS) H$\alpha$ image. Using this refined catalog, we perform aperture photometry on the SINGS narrowband H$\alpha$ images of NGC 7331, extracting the H$\alpha$ luminosity L(H$\alpha$) of these regions. We present corresponding measurements of the average line-of-sight ionized gas velocity dispersion $\sigma$ in these HII regions with CH$\alpha$S. High-resolution velocity and dispersion maps of the
galactic disk are produced from the CH$\alpha$S spectral imaging, selecting spaxels with high signal to noise in order to measure velocity dispersions as low as 12 km s$^{-1}$. Our measurements of the L(H$\alpha$), $\rm \Sigma_{SFR}$ and $\sigma$ in NGC 7331 are consistent with spatially resolved observations of HII regions in large surveys of nearby
galaxies. We explore the L(H$\alpha$)$- \sigma$ relationship, identifying turbulent HII regions with nonthermal dispersions likely driven by
stellar feedback. The dispersion is correlated with the
star formation rate surface density, and using the relation $\rm \sigma \propto \epsilon \Sigma_{SFR}^{\alpha}$, HII regions in NGC 7331 are best fit by $\epsilon = 80$ , $\alpha =0.285$.
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All authors Nazende Ipek Kerkeser, Nicole Melso, David Schiminovich, Erika Hamden, Meghna Sitaram, Ignacio Cevallos-Aleman
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Metastable cosmic strings are broken at the start
Lorenzo Tranchedone, Ethan Carragher, Edward Hardy et al. (+1 more)
We show that metastable
cosmic strings break at early times, either via finite-temperature effects or by attaching to pre-existing monopoles during network percolation. The resulting segments can be initially super-horizon in size and thus persist for a significant amount of time. If the strings do not re-percolate, the network's eventual destruction is typically due to this early-time breaking rather than late-time
quantum tunnelling. Survival of strings to epochs probed by NANOGrav requires $m_M^2/\mu\gtrsim 10^3$, where $m_M$ and $\mu$ are the monopole mass and the string tension respectively, over an order of magnitude larger than previous estimates. We also revisit
quantum-tunnelling induced breaking. Results from numerical simulations suggest that this occurs mainly at rare high-tension points on the strings, yielding a rate much larger than is usually assumed. We briefly discuss the related scenario of flux tubes in a dark QCD-like hidden sector with dark-
quark masses above the confinement scale.
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All authors Lorenzo Tranchedone, Ethan Carragher, Edward Hardy, Natálie Koscelanská van IJcken
Astrophysics of Galaxies
Gasflows in Barred Galaxies with Big Orbital Loops-A Comparative Study of Two Hydrocodes
Stavros Pastras, Panos A. Patsis and E. Athanassoula
We study the flow of gas in a barred-
galaxy model, in which a considerable part of the underlying stable periodic orbits have loops where, close to the ends of the bar, several orbital families coexist and chaos dominates. Such conditions are typically encountered in a zone between the 4:1 resonance and corotation. The purpose of our study is to understand the gaseous flow in the aforementioned environment and trace the morphology of the shocks that form. We use two conceptually different hydrodynamic schemes for our calculations, namely, the mesh-free Lagrangian SPH method and the adaptive mesh refinement code RAMSES. This allows us to compare responses by means of the two
algorithms. We find that the big loops of the orbits, mainly belonging to the x1 stable periodic orbits, do not help the shock loci to approach corotation. They deviate away from the regions occupied by the loops, bypass them and form extensions at an angle with the straight-line shocks. Roughly at the distance from the center at which we start to observe the big loops, we find characteristic "tails" of dense gas streaming towards the straight-line shocks. The two codes give complementary information for understanding the hydrodynamics of the models.
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High Energy Astrophysical Phenomena
Simulating the Formation of the Young "Fermi Bubbles" in the Circinus Galaxy
Shaokun Xie, Fulai Guo, Ruiyu Zhang et al. (+3 more)
The
Fermi and eROSITA bubbles in the Milky Way represent an archetypal case of
galactic nucleus feedback, yet their origin remains highly debated. Here we use hydrodynamic simulations to investigate the formation of the "
Fermi bubbles" in the nearby Circinus
galaxy, a pair of kpc-scaled elliptical bubbles seen in both
radio and X-ray observations. We find that a pair of active
galactic nucleus (AGN) jets drive forward shocks in the circumgalactic medium, and after evolving for ~0.95 Myr, the shock-delineated bubble pair roughly matches the observed Circinus bubbles in size and morphology. Our mock X-ray image and spectrum reproduce the observed edge-brightened X-ray surface brightness distribution and spectrum quite well, and suggest that non-thermal emissions from the jet ejecta also contribute substantially to
radio and X-ray emissions from the inner "hotspot" region. We further show that AGN winds tend to produce more spherical bubbles with a wider base near the
galactic plane, inconsistent with observations. The hotspot emissions and the misalignment between the
galaxy rotational axis and the bubble's axis argue against a starburst wind origin. Our study thus corroborates the AGN jet-shock model for the origin of both the Circinus bubbles and the
Fermi bubbles, and suggests that AGN jet feedback may be a common origin of extended gaseous bubbles in regular disk
galaxies, potentially playing an important role in their
evolution.
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All authors Shaokun Xie, Fulai Guo, Ruiyu Zhang, B. Mingo, Fangzheng Shi, Jiang-Tao Li
Earth and Planetary Astrophysics
Self-consistent Dynamical and Chaotic Tides in the REBOUNDx framework
Donald J. Liveoak, Sarah C. Millholland, Michelle Vick et al. (+1 more)
At high eccentricities,
tidal forcing excites vibrational modes within orbiting bodies known as dynamical tides. In this paper, we implement the coupled
evolution of these modes with the body's orbit in the REBOUNDx framework, an extension to the popular $N$-body integrator REBOUND. We provide a variety of test cases relevant to
exoplanet dynamics and demonstrate overall agreement with prior studies of dynamical tides in the secular regime. Our implementation is readily applied to various high-eccentricity scenarios and allows for fast and accurate $N$-body investigations of astrophysical systems for which dynamical tides are relevant.
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All authors Donald J. Liveoak, Sarah C. Millholland, Michelle Vick, Daniel Tamayo
Astrophysics of Galaxies
The early Universe with JWST and ALMA
Rodrigo Herrera-Camus, Natascha Förster Schreiber, Livia Vallini et al. (+2 more)
The Atacama Large Millimeter/submillimeter Array and the James Webb Space
Telescope are transforming our understanding of
galaxy formation and
evolution in the early Universe. By combining their capabilities, these observatories provide unprecedented insights into the gas,
dust, and
stars of high-
redshift galaxies at spatially resolved scales, unveiling the complexities of their interstellar medium, kinematics, morphology, active
galactic nuclei, and
star formation activity. This review summarizes recent breakthroughs in the study of
galaxies during the first billion years of
cosmic history, highlighting key discoveries, open questions, and current limitations. We discuss how observations, theoretical models, and simulations are shaping our understanding of early
galaxy evolution and identify promising directions for future research. While significant progress can be achieved through optimized use of existing facilities and collaborative efforts, further advances will require enhanced angular resolution and sensitivity, motivating upgrades to current instruments and the development of next-generation observatories.
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All authors Rodrigo Herrera-Camus, Natascha Förster Schreiber, Livia Vallini, Rychard Bouwens, John D. Silverman
Cosmology and Nongalactic Astrophysics
Neutrino decays as a natural explanation of the neutrino mass tension
Guillermo Franco Abellán
A new tension is emerging between the tight cosmological upper bounds on the total
neutrino mass ($\sum m_\nu \lesssim 0.06 \, \rm{eV}$) and the lower limits from oscillation experiments, with potentially far-reaching implications for cosmology and particle physics.
Neutrinos decaying into massless BSM particles with lifetimes $\tau_\nu \sim 0.01-1\, \rm{Gyr}$ represent a theoretically well-motivated mechanism to reconcile such measurements. Using DESI DR2 and CMB
datasets, we show that such decays relax the bound on the total
neutrino mass up to $\sum m_\nu < 0.23 \, \rm{eV}$ (95%), restoring full agreement with oscillation data. We also present the first late-time cosmological analysis of
neutrino decays into lighter
neutrinos in a manner consistent with the measured mass splittings. In contrast to the decays into massless BSM particles, we find that this scenario only marginally alleviates - or even tightens - the cosmological
neutrino mass bounds, depending on the mass ordering.
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High Energy Astrophysical Phenomena
Disk-to-Corona State Transition and Extreme X-ray Variability in the Tidal Disruption Event AT2019teq
Vera Berger, Erin Kara, Joheen Chakraborty et al. (+2 more)
We present a five-year X-ray spectral and timing analysis of the optically selected
Tidal Disruption Event (TDE) AT2019teq, which displays extreme variability, including order-of-magnitude changes in flux on minute-to-day timescales, and a rare late-time emergence of hard X-ray emission leading to the longest-lived corona in a known TDE. In one epoch, we detect sub-mHz quasi-periodic oscillations with significance tested via MCMC-based red-noise simulations (p $\leq 0.03$). AT2019teq exhibits a clear spectral
evolution from a soft (blackbody-dominated) state to a hard (power-law-dominated) state, with a late-time
radio brightening that may be associated with the state transition. We identify similarities between AT2019teq's
evolution and X-ray binary soft-to-hard state transitions, albeit at higher luminosity and much faster timescales. We use the presence of both a disk-dominated and a corona-dominated state to apply multiple mass
estimators from X-ray spectral and variability properties. These techniques are mutually consistent within $2\sigma$ and systematically yield a lower black hole mass ($\log(M_{BH}/M_{\odot}) = 5.67 \pm 0.09$) than inferred from host
galaxy scaling ($\log(M_{BH}/M_{\odot})=6.14 \pm 0.19$).
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All authors Vera Berger, Erin Kara, Joheen Chakraborty, Megan Masterson, Kevin Burdge
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Spectator Composes a Gravitational Canon: Spectator-field-triggered Phase Transition During Inflation and its Anisotropic Gravitational Wave Signals
Yunjia Bao and Keisuke Harigaya
We propose a general framework in which a phase transition is triggered during
cosmic inflation by the slow-roll dynamics of a spectator field. The topological defects formed at the transition are inflated outside the horizon, reenter it after inflation, and can subsequently generate characteristic gravitational-wave (GW) signals.
Quantum fluctuations of the spectator field modulate the timing of the transition, imprinting large-scale anisotropies in the resulting GW background. As an explicit realization, the spectator field may be identified with the
Higgs field in a supersymmetric Standard Model. More generally, our framework applies to a wide class of spectator-modulated phenomena, providing a generic mechanism for producing anisotropic GW signals.
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Astrophysics of Galaxies
Morphologies arising from the gas flow in the innermost kiloparsec of barred galaxy models
Stavros Pastras, Panos A. Patsis and E. Athanassoula
Context. We study a series of response models to investigate the formation of specific morphological features in the central 1 kpc region of the gas component in barred spiral
galaxies. Aims. We aim to understand how structures, such as
nuclear rings and spirals, form by varying the parameters of a general gravitational potential and gas properties. Our goal is to determine how much the shape of these structures is driven by the orbital dynamics of the models compared to the influence of the hydrodynamics of the gas. In particular, we examine the effects of the bar strength, bar shape, pattern speed, and central density, as well as their mutual interdependence. Methods. We modeled the gas flow using hydrodynamical simulations run with the Eulerian RAMSES code. The underlying gravitational potential was a two-dimensional Ferrers bar and the gas was considered to be isothermal. Alongside analyzing the gas response to the imposed gravitational potentials, we carried out orbital studies for all models. This involved assessing the shapes and stability of periodic orbits and analyzing the distribution of regular versus chaotic regions within the systems. Results. The parameters of the gravitational potential alone are insufficient to accurately predict the gas dynamics in a system. The morphology of the gaseous response varies substantially with changes in sound speed, emphasizing the fundamental role of hydrodynamic processes in determining the structure of the gas within the central region. We identify the factors that affect the morphology of
nuclear rings and trailing and leading
nuclear spirals. The best
alignment between our models and structures observed in local barred
galaxies is achieved by assuming a sound speed of $c_s=20\,\rm{km\,s^{-1}}$.
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High Energy Astrophysical Phenomena
A New Bayesian Framework with Mass-Radius-Space Priors to Constrain the Neutron Star Equation of State
Boyang Sun, Tianqi Zhao and James M. Lattimer
We propose a new
Bayesian framework to infer the
neutron star equation of state (EOS) from mass and radius observations and
neutron matter theory by defining priors that directly parameterize mass-radius space instead of pressure-energy density space. We use direct and accurate inversion approximations to map mass-radius relations to the underlying EOS. We systematically compare its EOS inferences with those inferred from traditional EOS parameterizations, taking care to quantify the systematic prior uncertainties of both. Our results show that prior uncertainties should be included in all
Bayesian approaches. The alternative framework provides broader and more uniform coverage of the physically allowed mass-radius space, especially small radius configurations, with enhanced computational efficiency. Substantially reduced dependence on prior choices seems to result from having both prior and posterior distributions in the same observational mass-radius space. Results indicate that direct parameterization in observed space offers a robust and efficient alternative to traditional methods.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
A Relativistic MOND
Tejinder P. Singh
We present a minimal relativistic completion of MOND in which (i) General Relativity is recovered exactly in the high-acceleration regime, while (ii) the Bekenstein–Milgrom (AQUAL) equation emerges in the low-acceleration regime, without introducing additional propagating fields beyond those already present in a right-handed gauge sector. The construction is motivated by an $E_6\times E_6$ framework in which $SU(3)_R\rightarrow SU(2)_R\times U(1)_{Y'}\rightarrow U(1)_{\rm dem}$, leaving a healthy repulsive $U(1)_{\rm dem}$ interaction whose charge is the square-root mass label.
Gravity itself arises from the $SU(2)_R$ connection via a Plebanski/MacDowell–Mansouri mechanism, yielding an emergent tetrad and the Einstein–
Hilbert action. MOND is implemented by an infrared (IR) metric deformation $\Delta S_{\rm IR}[g]$ that is UV-vanishing (so GR is recovered) while its deep-MOND/static limit is fixed by a
symmetry principle: in three spatial dimensions, the deep-MOND action is conformally invariant with a 10-parameter group isomorphic to $SO(4,1)$ (the de Sitter group). The single MOND acceleration scale is set by a de Sitter radius selected dynamically in the IR, $a_0=c^2/(\xi\,\ell_{\rm dS})$ with $\xi={ O}(1)$ fixed by matching to the static limit. MOND resides in perturbations and quasistatic systems; the homogeneous FRW background is controlled by the IR
vacuum kinematics rather than an ad hoc cosmological constant.
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Instrumentation and Methods for Astrophysics
Search for Precessing Binary Black Holes in Advanced LIGO's Third Observing Run using Harmonic Decomposition
Rahul Dhurkunde and Ian Harry
Binary black holes (BBHs) exhibiting
spin-induced orbital precession offer unique insight into compact-binary formation channels, cosmology, and tests of general relativity. We conduct a dedicated search for precessing BBHs with unequal masses in Advanced LIGO's third observing run (O3) using the harmonic decomposition method of precessing waveforms. We introduce a novel scheme to reduce the number of filters in a harmonic search. With our new approach, our template bank requires $5\times$ fewer filters compared to another proposed precessing search in the same region. We do not find any new significant events. Our new search method achieves up to $\sim 28\%$ improvement in sensitivity and up to $5\times$ lower computational costs compared to existing precessing search pipelines. Our method enables scalable, sensitive searches for precessing BBHs in future gravitational-wave observing runs.
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