High Energy Astrophysical Phenomena
Time-dependent multi-energy neutrino emission from symbiotic recurrent novae: the role of accretion disks
Rui Xu, Yudong Cui, Yihan Shi et al. (+1 more)
Symbiotic recurrent novae provide a unique laboratory for studying thermonuclear explosions, shock
evolution, and nonthermal particle acceleration in dense circumstellar environments. In this work, we develop a time-dependent, multi-energy framework to describe
neutrino emission from such systems, consistently incorporating both MeV
neutrinos produced during thermonuclear runaway and GeV
neutrinos generated through hadronic interactions in nova-driven shocks. Using RS Oph as a
benchmark source, we model the
evolution of the shock interacting with both the red giant wind and a dense
accretion disk surrounding the white dwarf. We show that the resulting
neutrino signal exhibits a characteristic two-component temporal structure: an early, rapidly rising MeV component tracing nuclear burning, followed by a delayed GeV component governed by shock propagation and particle acceleration. The presence of an
accretion disk can significantly enhance the early-time GeV
neutrino emission by providing a dense target for
proton-
proton interactions. This leads to a pronounced
neutrino flux within the first few hours after eruption, a feature absent in wind-dominated scenarios. We further evaluate the detectability of these signals and find that while the MeV component remains below current detection thresholds, the GeV
neutrino emission from nearby systems may become accessible to next-generation detectors. Our results highlight the critical role of the circumstellar structure in shaping nova
neutrino emission and demonstrate that symbiotic recurrent novae are promising targets for future multi-messenger observations.
Read the full abstract ▾
All authors Rui Xu, Yudong Cui, Yihan Shi, Lili Yang
High Energy Astrophysical Phenomena
The second Arcminute Microkelvin Imager - Large Array Gamma-ray burst radio afterglow catalog
L. Rhodes, D. Ibrahim, N. Sqalli et al. (+13 more)
Radio observations of gamma-ray burst afterglows provide insight in to the different emitting regions within the jet, its hydrodynamics and burst environment. In this paper, we present the second iteration of the Arcminute Microkelvin Imager - Large Array (AMI-LA) Gamma-ray burst (GRB)
radio afterglow catalog. The catalog consists of 1035 observations of 210 bursts. Our observations range from 0.04 to 900days post-burst. We detect
radio emission associated with 19 events with flux densities spanning 0.1-40mJy, and present a detailed analysis of six events whose light curves have not been published elsewhere. In our individual afterglow analyses, we find that our
radio counterparts show evidence of reverse shock emission 60% of the time. Two of the detected afterglows show evidence of scintillation which we use to place source size limits at tens of days. Of the whole catalog, 50 events have
redshift measurements which we use to find the
radio afterglow luminosity distribution for our sample. Our luminosity distribution spans five orders of magnitude, a larger range than seen in optical and X-ray bands, indicative of the strong dependence of the
radio counterparts on the GRB's physical parameters.
Read the full abstract ▾
All authors L. Rhodes, D. Ibrahim, N. Sqalli, G.E. Anderson, R. Fender, A.J. van der Horst, J.S. Bright, A.K. Hughes, D.R.A. Williams-Baldwin, D.A. Green, D. Haggard, A. Horesh, Y. Perrott, P. Scott, T. Staley, D. Titterington
High Energy Astrophysical Phenomena
High-Energy Neutrinos from Supernova Shock Breakouts in Circumstellar Media: Light Curves, Spectra, and Contribution to the Extragalactic Neutrino Background
Tal Wasserman, Eli Waxman and Kohta Murase
Enhanced mass loss from core-collapse
supernova (SN) progenitors shortly before explosion appears to be common, creating a compact, optically thick circumstellar medium (CSM) at $\sim10^{14}-10^{15}$ cm. We derive an analytic description of the light curves and spectra of high-energy
neutrinos emitted by nonrelativistic SN shock breakouts through such CSM, as a function of shock velocity and CSM parameters, accounting for the
evolution of the hydrodynamic structure and the electromagnetic (EM) spectrum as the shock transitions from being radiation-mediated to collisionless. This
evolution determines the time-dependent
neutrino production efficiency, the maximum
proton/
neutrino energy, and the pair-production optical depth. A significant fraction of the
neutrino energy is typically emitted within a few days of explosion, during breakout and before the EM light curve peak, with $1-100$ TeV
neutrinos carrying $\approx10\%$ of the energy of shock-accelerated
protons. The escape of high-energy
photons ($>1$~GeV) is suppressed by pair-production for compact CSM configurations. If enhanced mass losses are common, and assuming that shock-accelerated
protons carry $\approx10\%$ of the collisionless shock energy, CSM SN breakouts may significantly contribute to the observed high-energy
neutrino background, without overproducing a corresponding high-energy gamma-ray background. SNe producing $>1$
neutrino events in a $1\left(10\right){\rm km^2}$ detector are expected at a rate of $\sim0.05\left(1\right){\rm yr^{-1}}$.
Read the full abstract ▾
High Energy Astrophysical Phenomena
No Evidence for Nearby Circumstellar Material in the Type Ia Supernova 2025rbs
Aravind P. Ravi, Griffin Hosseinzadeh, Stefano Valenti et al. (+28 more)
We present a high-resolution spectral time series of the Type Ia
supernova (SN) 2025rbs discovered in the nearby
galaxy NGC 7331. The Automated
Planet Finder (APF) at Lick Observatory and the MAROON-X/IGRINS-2 at Gemini North were used to obtain echelle spectra between -5 and 15 days with respect to the epoch of maximum light. Several unsaturated NaID absorption components along the line of sight are identified, but there is no evidence of time variance in any of them. We measure the equivalent width of the observed diffuse interstellar band around 5780 A and constrain the extinction along the line of sight to SN 2025rbs as $A_V = 0.64\,\pm\,0.32$ mag, corresponding to a moderate reddening of $E(B-V) = 0.21\,\pm\,0.10$ mag (assuming $R_\mathrm{V}$ = 3.1). The observed Ca II H & K interstellar absorption roughly traces NaID in velocity space, suggesting a common origin. Quantitative comparisons between the column densities of Na and Ca gas in these host clouds ($N_{NaID}$ / $N_{Ca II}$ of order unity) argue against their origin in the Galactic
halo gas and instead support absorption due to the interstellar gas of NGC 7331. Time invariance of all the observed absorption features suggests a lack of nearby circumstellar material ($\lesssim$ 10$^{16}$ cm) around the progenitor system of SN 2025rbs. This supports a progenitor scenario for SN 2025rbs with minimal ambient circumstellar gas, consistent with a double-degenerate CO white dwarf binary system.
Read the full abstract ▾
All authors Aravind P. Ravi, Griffin Hosseinzadeh, Stefano Valenti, Saurabh W. Jha, Jennifer Andrews, David J. Sand, Benjamin J. Fulton, William D. Vacca, Melissa L. Graham, Alexei V. Filippenko, Noah Franz, Jeniveve Pearson, Moira Andrews, K. Azalee Bostroem, Collin Christy, Yize Dong, Sebastian Gomez, Daichi Hiramatsu, Emily Hoang, D. Andrew Howell, Brian Hsu, Daryl Janzen, Lindsey A. Kwok, Michael J. Lundquist, Darshana Mehta, Nicolas Meza-Retamal, Curtis McCully, Manisha Shrestha, Bhagya Subrayan, Lauren Weiss, Weikang Zheng
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
Radio Properties of RS Canum Venaticorum Variables in VLASS and RACS
Suhasini S. Rao, Gregory R. Sivakoff, Craig O. Heinke et al. (+6 more)
We performed a systematic search for
radio emission from RS Canum Venaticorum (RS CVn) binaries, selected from the International Variable
Star Index (VSX) catalog, in the Very Large Array Sky Survey (VLASS; three epochs) and Rapid ASKAP Continuum Survey (RACS; two epochs) data. We detected 108 candidate
radio-emitting RS CVn in at least one epoch. Several of these systems rank among the most
radio-luminous RS CVn binaries reported to date. The
radio and X-ray luminosities, obtained from cross-matching with the eROSITA and ROSAT X-ray catalogs, are consistent with the Guedel-Benz relation for magnetically active
stars, but are also comparable to
radio-luminous quiescent black hole X-ray binaries, indicating a potential for misidentification between these two classes. Analysis of optical,
radio, and stellar properties indicates that optically bright RS CVn (i.e., those with at least one giant component) are
radio-quieter and have periods that are consistent with lower coronal activity. However, two of these optically bright RS CVn systems show persistent and unusually high
radio specific luminosities (>2e17 erg/s/Hz) across all observed epochs, showing that stellar activity can produce relatively persistent
radio signals as bright as quiescent black hole binaries.
Read the full abstract ▾
All authors Suhasini S. Rao, Gregory R. Sivakoff, Craig O. Heinke, Swetha Arumugam, Dougal Dobie, Laura Driessen, David L. Kaplan, Emil Lenc, Joshua Pritchard
High Energy Astrophysical Phenomena
A binary black hole merger rate comparison within the same metallicity-star formation rate framework
Lumen Boco, Michela Mapelli, Michele Bosi et al. (+2 more)
Recent studies have suggested that binary population synthesis models, when coupled with observationally based,
metallicity-dependent SFRD, overpredict the observed local BBH merger rate density. The significance of this tension might vary depending on the specific code and parameters adopted. Thus, a more extensive exploration of the parameter space is required. Here, we perform such an extended analysis. We first carry out a comprehensive analysis by using a large set of BBH merger efficiencies across a wide range of physical assumptions, parameters, and initial conditions. We combine these efficiencies with an observationally motivated SFRD and explore 18
metallicity variations to encompass observational uncertainties. We find that the tension between predicted and observed BBH merger rate density persists: in 17 out of 18
metallicity variations none of the models considered predicts a local BBH merger rate within or below the observed 90% credible interval. Even in the most favorable
metallicity variation, only <10% of the models are consistent with the observational constraints. Then, we perform a full calculation, including a self-consistent delay time distribution, for the models yielding the lowest BBH merger rate densities. This analysis confirms that even the most conservative models overpredict the observed local BBH merger rate for almost all the
metallicity variations. We show that the inclusion of the low-
metallicity tail contributed by low-mass
galaxies and starbursts, together with a treatment of iron rather than oxygen abundance, systematically shift the predicted rates toward higher values. Consequently, even literature models that predict moderate BBH merger rates can instead produce substantially higher rates when coupled to an observationally motivated SFRD.
Read the full abstract ▾
All authors Lumen Boco, Michela Mapelli, Michele Bosi, Cecilia Sgalletta, Amedeo Romagnolo
High Energy Astrophysical Phenomena
Observational Constraints on Horizonless Compact Objects from Thermal Emission in AGNs
Ekin Oran, Avery Broderick and Kiana Salehi
The Swift Burst Alert
Telescope Active Galactic
Nuclei Spectroscopic Survey (BASS DR2) provides one of the largest and most complete samples of bright, local (z < 0.1) active galactic
nuclei (AGNs) with high-quality spectroscopic measurements. These sources are typically interpreted within the framework of Kerr black holes; however, a wide range of horizonless compact-object scenarios-including naked singularities, black hole mimickers, and other exotic compact objects-have been proposed as alternatives. Largely independent of the physics of the particular horizonless model invoked, an
accretion powered, thermally radiating photosphere is expected to develop on astronomically short timescales. In this paper, we investigate whether the presence of such a photosphere is consistent with the observed properties of an appropriate subsample of BASS AGNs. We find that in no instances is such a spectral feature present, and can exclude its existence in significant fraction of objects. For the remaining sources, modest improvements in observational sensitivity and spectral coverage could enable robust exclusion. Our results extend previous horizon-scale tests performed for M87* and Sgr A* to a large AGN population, providing strong, population-level evidence against horizonless alternatives. We conclude by outlining future observational strategies that can further tighten these constraints and significantly increase the number of objects for which horizons are required.
Read the full abstract ▾
High Energy Astrophysical Phenomena · Cross-listed from hep-th
Quasinormal modes as exterior probes of black hole interiors in our Universe
Sašo Grozdanov, Vita Movrin and Samuel Valach
We consider a scenario in which a black hole is enclosed in a reflecting timelike cavity and linearly perturbed. For the resulting quasinormal spectra of gravitational, electromagnetic, and other perturbations, in conjunction with our arXiv:2606.11297, we establish a thermal product formula and derive a universal asymptotic expression for high quasinormal overtones. Both results hold in asymptotically flat, de Sitter, and Anti-de Sitter spacetimes (known previously). This spectral signature directly encodes information about the black hole interior and its singularity, and is, at least in principle, accessible to an observer outside the event horizon. We then propose a concrete observational setup in which accreting
plasma plays the role of a partially transmissive mirror. For small, hypothetical, primordial black holes, we argue that one may thereby be able to extract concrete information about the black hole interior from electromagnetic waves in the radiowave spectrum.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Explosions from Rotating Very Massive Star Collapses to Black Holes: Effects of Nuclear Burning
Sho Fujibayashi, Alan Tsz-Lok Lam, Yuichiro Sekiguchi et al. (+1 more)
We investigate the collapse of rotating very massive and supermassive stellar cores using numerical relativity simulations including an alpha-chain nuclear reaction network and
neutrino cooling. Our main survey focuses on newly constructed models with initial core masses of $2 \times {10}^{3}-5\times 10^4M_\odot$. The collapse is triggered either by pair instability in lower-mass cores or by general-relativistic instability in higher-mass cores. We find that higher-mass cores undergo a nearly homologous collapse, whereas lower-mass cores show a more runaway-like collapse because
neutrino cooling becomes more efficient at their higher densities and temperatures. Consequently, the black hole formed in lower-mass models initially contains a smaller fraction of the core mass, and disk formation occurs while a larger amount of matter remains outside the black hole. The lower compactness of pair-unstable cores also allows larger dimensionless angular momentum, favoring the formation of rapidly rotating black holes and massive disks. The disk bounce drives mass ejection with ejecta masses of order $10-10^3M_\odot$ and kinetic energies of order $10^{53}-10^{55}\,\mathrm{erg}$. Significant $^{56}$Ni production in the disk-bounce ejecta occurs only in the lowest-mass models. For selected models, we further follow the viscous
evolution of the disk and find that viscosity enhances the ejecta mass and kinetic energy. In models with $\lesssim10^4M_\odot$, the viscosity-driven ejecta can originate from disk matter that has reached nuclear statistical
equilibrium and can therefore become rich in $^{56}$Ni. These results suggest that rotating very massive
star collapses can produce massive, energetic ejecta and, for sufficiently low core masses, substantial iron-group elements.
Read the full abstract ▾
All authors Sho Fujibayashi, Alan Tsz-Lok Lam, Yuichiro Sekiguchi, Masaru Shibata
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA
Orbital Migration of Interacting Stellar Mass Black Holes in Disks around Supermassive Black Holes. III. Mass Distribution of Hierarchical Mergers
Katherine L. Gonglewski, Amy Secunda, Mordecai-Mark Mac Low et al. (+3 more)
Active galactic
nucleus (AGN) disks are a promising location for the formation of binary black holes (BBHs) that will merge on relatively short timescales and be detected by LIGO-Virgo-KAGRA (LVK). To compare the mass function (MF) of black holes (BHs) undergoing hierarchical mergers in AGN disks to the inferred MFs from LVK observations, we perform 360 simulations with an N-body code augmented to include an analytic model for migration torques and other gas forces. We focus on the region surrounding migration traps in AGN disks where migration torques cancel out and BHs converge. We find that regardless of changes in the initial MF and BBH merger criteria, frequent mergers deplete the number of BHs with masses $\lesssim 10$~$M_\odot$ and fill the upper mass gap with a roughly uniform distribution from 40–100~$M_\odot$, with a slight overabundance around ${\approx}70~M_\odot$ from resonant orbiters. We also find an average merger rate of $\sim 6$~Gpc$^{-3}$~yr$^{-1}$ for migration-trap-aided BBH mergers in our AGN disk model. $\sim 40\%$ of these mergers have uneven mass ratios and 16% have a primary mass $\in[50-100]~M_\odot$. Therefore, AGN disks could easily be the source of BBH mergers observed by LVK that are difficult to produce through traditional stellar
evolution channels. Our simulations also form a separate higher-mass intermediate mass black hole (IMBH) population $>200~M_\odot$ after $\sim 2$~Myr. Future gravitational wave detectors can use observations of this IMBH population to constrain models of AGN
accretion disks.
Read the full abstract ▾
All authors Katherine L. Gonglewski, Amy Secunda, Mordecai-Mark Mac Low, K. E. Saavik Ford, Barry McKernan, Fabian R. N. Schneider
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM
Laser Metrology for Precision Alignment of Transmission Gratings in the REDSoX Soft X-ray Polarimeter
Swati Ravi, Alan Garner, Jill Juneau et al. (+4 more)
The Rocket Experiment Demonstration of a Soft X-ray Polarimeter (REDSoX) is a NASA sounding-rocket mission designed to perform the first astrophysical spectropolarimetry in the 0.2-0.4 keV energy band. The instrument uses critical-angle transmission (CAT) gratings to disperse incident X-rays onto laterally graded multilayer (LGML) mirrors, requiring 48 individual gratings to be co-aligned to within 6 arcminutes in yaw, pitch, and roll. To support the systematic assembly of the grating array, we adapted a scanning
laser-reflection metrology technique in which normal-reflected, angled-reflected, and diffracted ultraviolet
laser beams are measured using three position-sensitive detectors (PSDs). Changes in the measured beam positions are used to reconstruct the local yaw, pitch, and roll of each grating and provide real-time feedback during mechanical adjustment. We demonstrate the system using a prototype miniature grating structure containing two gratings. Following co-
alignment, the assembly underwent a flight-level random-vibration test followed by a qualification-level sine sweep. Measurements obtained before and after testing showed that the relative grating orientations were retained to within 1 arcminute, less than 17% of the REDSoX co-
alignment tolerance. This work establishes a reproducible and scalable approach to the assembly and verification of large transmission-grating arrays for REDSoX and future X-ray spectroscopic instruments.
Read the full abstract ▾
All authors Swati Ravi, Alan Garner, Jill Juneau, F. Elio Angile, Ralf K. Heilmann, Herman L. Marshall, Sarah N.T. Heine
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
The Production of Electron-Capture Elements in Thermonuclear Supernovae: Theory vs. Observations
S. Shiber, P. Hoeflich, T. Mera et al. (+9 more)
Type Ia
supernovae (SNe Ia) explosively destroy carbon-oxygen white dwarfs (WDs) in multiple stellar systems. They produce approximately 50% of the iron-group elements in the Universe, synthesize electron-capture (EC) elements, drive nuclear physics experiments, and underpin high-precision cosmology. To first order, the outcome is governed by nuclear physics, a property often described as stellar amnesia. Recently, this stellar amnesia has begun to be broken by the nearly universal detection of EC elements with JWST. These elements trace high-density burning, largely ruling out the currently popular helium-triggered, sub-Mch detonation models as the dominant channel. Instead, the ubiquitous presence of EC is shifting back the focus to dynamical and secular mergers, and near-Mch explosions similar to the deflagration model W7, but in which the nuclear flame undergoes a deflagration-to-detonation transition. The early deflagration phase is especially important because spherical simulations identify the central WD density, and thus the WD mass, as a key parameter governing the explosion. Here, we present detailed magneto-hydrodynamical simulations. We find that small-scale, pre-existing
turbulence expected from the pre-explosion smoldering phase is essential for overcoming the fundamental challenges imposed by the intrinsic 3D physics. This
turbulence systematically reduces the production of EC elements by about a factor of two, implying the need for WD central densities closer to those associated with
accretion-induced collapse to a
neutron star. We also demonstrate the effect of
magnetic fields near the saturation field strength and highlight the need for higher-precision EC rates at low Ye.
Read the full abstract ▾
All authors S. Shiber, P. Hoeflich, T. Mera, E. Fereidouni, Z. Levy, D. Maci, C. Ashall, K. Medler, J. M. DerKacy, E. Baron, M. Shahbandeh, C. M. Pfeffer
High Energy Astrophysical Phenomena
Radio Monitoring of Classical Novae using the ASKAP Variable and Slow Transients Survey
Aishani Majumder, David L. Kaplan, Laura N. Driessen et al. (+3 more)
We present a search for
radio emission from classical novae at 887.5 MHz using data from the Australian SKA Pathfinder Variable And Slow Transient (VAST) survey. We cross-matched 43 optically discovered classical novae that erupted between 2021 September and 2025 November within the 1200-square-degree Galactic survey footprint, and found three which show significant
radio emission: V6598 Sgr, V1716 Sco, and V1723 Sco. To analyse their
radio light curves, we use both thermal free-free and non-thermal synchrotron emission models. We fit the data using the Markov chain Monte Carlo (MCMC) method to constrain parameters, including the ejected mass and ejecta velocities for the thermal models, and mass-loss rate, explosion energy, wind velocity, and filling factor for the non-thermal model. All three novae show evidence of non-thermal synchrotron emission as the dominant emission mechanism at this frequency. We use a broken power law to describe the radial density structure of a non-uniform circumbinary material, which provides a better fit than a standard wind density profile. This strong early-time synchrotron emission is strong evidence of shock-driven particle acceleration, which may be related to detections of gamma-rays from all three novae as well. In contrast to earlier studies that used multi-frequency data to distinguish between emission models, our analysis is based on single-frequency
radio light curves, which can still provide useful constraints on the dominant emission mechanism when interpreted with physically motivated models
Read the full abstract ▾
All authors Aishani Majumder, David L. Kaplan, Laura N. Driessen, Ashna Gulati, Tara Murphy, Dougal Dobie
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
JWST Detects a Dusty AGB-like Source Before the Type Ia-CSM Supernova 2026sqf
Tamás Szalai, Dan Milisavljevic, Noah Zimmer et al. (+22 more)
Supernova (SN) 2026sqf recently appeared in the nearby face-on spiral
galaxy NGC 3310 and has shown signs of strong interaction with a circumstellar medium (CSM). Such intense interaction, rare among nearby SNe, offers a valuable opportunity to reveal details on the origin and nature of its progenitor system. We analyzed the early-phase spectra and light curves (LCs) of SN 2026sqf. The general shapes of the observed spectra, the strengths of the emission lines, and the LC
evolution all suggest that SN 2026sqf belongs to the rare SN Ia-CSM subclass. If confirmed, this would be the closest known member of this class, at D~19 Mpc. We also report the first candidate progenitor system for a thermonuclear
supernova identified in JWST pre-explosion imaging, and the first evidence for a (probable) carbon-rich AGB donor to the exploding white dwarf (WD). Our results are consistent with the expectation that SNe Ia-CSM emerge from a system consisting of a WD and an AGB
star undergoing a common-envelope phase. The CSM mass and dust content are consistent with expectations for an AGB environment, but the narrow-line width exceeds superwind expansion velocities, favoring an episodic ejection. Binary interaction shortly before the explosion is a natural explanation, though the channel and timescale remain uncertain. Late-time follow-up, especially with JWST, will test the identification and the conclusions of our early-phase analysis.
Read the full abstract ▾
All authors Tamás Szalai, Dan Milisavljevic, Noah Zimmer, Braden Garretson, Thomas Moore, Schuyler D. Van Dyk, Anan Lu, Selcuk Topal, Ori D. Fox, Tuomas Kangas, Seppo Mattila, Andrea Reguitti, Uliana Pylypenko, Chuck Cynamon, Ting-Wan Chen, Amar Aryan, Dylan Caudill, Danielle Dickinson, Martin Bureau, Woorak Choi, Timothy A. Davis, Daryl Haggard, Thomas M. Reynolds, Maximilian Stritzinger, Patrick Wiggins
High Energy Astrophysical Phenomena
X-ray Flaring and Variability in NGC 1275, the Heart of the Perseus Cluster
Sarah Ketchum, Jon M. Miller, S. W. Allen et al. (+6 more)
NGC 1275 is the central
galaxy in the Perseus Cluster. The active galactic
nucleus (AGN) within NGC 1275 is notable for its strong and variable
radio activity, tied to the production of
radio jets that inflate large bubbles in the hot intracluster medium (ICM). High spatial resolution X-ray imaging can separate the AGN from the bright ICM, but monitoring the mass
accretion rate onto the black hole and establishing disk-jet connections in NGC 1275 requires a high cadence. Here, we report on X-ray monitoring of NGC 1275 using data taken over 20 years with the Neil Gehrels Swift Observatory. Modeling the temporally constant ICM in each observation allows X-ray emission from
accretion onto the black hole to be traced reliably, with typical flux errors of $\sim 3\%$. X-ray flaring by a factor of $\sim2$ over mere days is detected starting on MJD 59956 (2023 Feb. 21). The
flares imply an emission region consistent with $r \leq 870~(10^{8}~M_{\odot}/M_{BH})~ GM/c^{2}$. The profile of the flaring is inconsistent with simple predictions for tidal disruption events. A
flare appears roughly 300 days later in
radio monitoring data at 43 GHz. Overall, our results indicate that coordinated, moderate-resolution X-ray imaging and
radio monitoring could potentially trace disk-jet connections in the AGN that most vividly impact large-scale structure, and be extended to other sources that impact their hosts.
Read the full abstract ▾
All authors Sarah Ketchum, Jon M. Miller, S. W. Allen, Doyee Byun, Tianyin Hu, Missagh Mehdipour, Veronica Tananko, Xin Xiang, Irina Zhuravleva
High Energy Astrophysical Phenomena
The low luminosity end of Galactic HMXBs with eROSITA: Establishing a luminosity floor for accreting BeXRBs
Aafia Zainab, Philipp Thalhammer, Nico Zalot et al. (+18 more)
We present a first look at the Galactic population of heretofore known HMXBs as observed by SRG/eROSITA during its first four surveys. eROSITA's sensitivity of $\sim10^{-13}\,\mathrm{erg}\,\mathrm{s}^{-1}\,\mathrm{cm}^{-2}$, translating to $10^{32}$-$10^{34},\mathrm{erg}\,\mathrm{s}^{-1}$ in luminosity for most known HMXBs in the Milky Way, has thus far never been reached by any wide-area survey instrument. We present the extended log N-log L distribution of known HMXBs reaching down to $10^{32}\,\mathrm{erg}\,\mathrm{s}^{-1}$ using eROSITA, and show the large scatter that can be induced by source intrinsic variability. We present sub-type resolved luminosity distributions, showing that the Supergiant X-ray binaries (SgXBs) and Be X-ray binaries (BeXRBs) occupy different parts of the overall distribution, and reanalyse RXTE/ASM data and MAXI for comparison to eROSITA. The luminosity regime uncovered by eROSITA allows a systematic study of the "transient" BeXRBs, which are typically below the detection threshold of monitors outside of outburst, and whose low luminosity behavior has been a longstanding question. Signatures of stable
accretion at low luminosities have been observed with pointed instruments for a fraction of the overall sample, so far. With the eROSITA results, we posit that
accretion outside of outburst is likely the norm, since a vast majority (> 80%) of BeXRBs are detected at luminosities at least an order of magnitude higher than expected for the most X-ray luminous Be
stars. We discuss the observed luminosity in the context of cold disk
accretion and the "propeller" mechanism. We highlight a small subpopulation of "isolated" Be-
stars that reach luminosities comparable to the least luminous BeXRBs, hinting at the presence of compact object companions.
Read the full abstract ▾
All authors Aafia Zainab, Philipp Thalhammer, Nico Zalot, Artur Avakyan, Jakob Stierhof, Ekaterina Sokolova-Lapa, Victor Doroshenko, Victoria Grinberg, Peter Kretschmar, Galina Lipunova, Nazma Islam, Matthias R. Schreiber, Christian Kirsch, Steven Hämmerich, Philipp Weber, Ralf Ballhausen, Alicia Rouco Escorial, Joel Coley, Richard Rothschild, Katja Pottschmidt, Joern Wilms
High Energy Astrophysical Phenomena
Complex Energy-Dependent Behaviour of Quasi-Periodic Oscillation Observed in GRS 1915+105
Vaibhav Sharma, Ranjeev Misra, V. Jithesh et al. (+5 more)
We present complex energy-resolved properties of quasi-periodic oscillations (QPOs) in the black hole X-ray binary GRS 1915+105 using an observation from the LAXPC instrument onboard AstroSat. Power density spectra (PDSs) are constructed in multiple energy bands and modeled with multi-Lorentzian components to investigate the energy dependence of QPO properties. The QPO frequency shows a modest increase with energy. Dynamic PDS analysis does not reveal clear evidence for time-dependent
evolution of the QPO frequency, suggesting that the observed frequency shift is not primarily driven by temporal variability. We perform simultaneous fitting of energy-resolved PDSs and find that a model in which the QPO feature is described by two Lorentzian components provides a better fit. The two components exhibit different
evolution in fractional root mean square amplitude as a function of energy. We further examine the phase-lag properties by simultaneously modeling the PDS and the real and imaginary parts of the cross-spectrum and find distinct phase-lag behavior for the two components. Overall, these results indicate that the apparent energy-dependent
evolution of the QPO feature may be a result of the presence of more than one variability component.
Read the full abstract ▾
All authors Vaibhav Sharma, Ranjeev Misra, V. Jithesh, Shivani Chaudhary, Khushi Jirawala, J S Yadav, Pankaj Jain, N J Juris
High Energy Astrophysical Phenomena
AT 2024qfm: a luminous fast blue optical transient at a redshift of z = 0.2267 identified by Lasair-ZTF
M. Fulton, S. J. Smartt, S. Srivastav et al. (+20 more)
Luminous fast blue optical transients (LFBOTs) emit from x-ray to
radio wavelengths, epitomised by the discovery of AT 2018cow in a host
galaxy at 65 Mpc. In the following eight years eleven more have been found, at
redshifts $0.075 \lesssim z \lesssim0.34$, plus one identified retrospectively from 2016. Here we present the discovery of AT 2024qfm, classified as an LFBOT in a host
galaxy at $z = 0.2267 \pm 0.0002$. Its ultraviolet-to-optical luminosity and rapid 13 day fade closely match AT 2018cow. We describe how the transient was identified in the Zwicky Transient Facility alert stream using a custom filter in the Lasair broker that flags flux gradients over time. Another LFBOT candidate was identified with the same methodology (AT 2024kth). The physical origin of LFBOTs remains debated with no firm consensus, and further progress requires more discoveries, host-
galaxy characterisation, and multi-wavelength analysis to constrain theory. We discuss this discovery in the context of Rubin Observatory's Legacy Survey of Space and Time (LSST), whose sensitivity will increase the effective LFBOT survey volume tenfold relative to ZTF, out to $z \lesssim 0.6$, and show that our FastFinder filter could recover such events. We highlight the challenge of detecting their fast
evolution with sufficiently low latency to trigger multi-wavelength follow-up that can constrain theoretical models.
Read the full abstract ▾
All authors M. Fulton, S. J. Smartt, S. Srivastav, J. H. Gillanders, J. W. Tweddle, M. E. Huber, M. Nicholl, C. R. Angus, K. W. Smith, K. C. Chambers, A. Lawrence, R. Williams, D. R. Young, K. Auchettl, T. de Boer, T.-W. Chen, C.-H. Lai, C. C. Lin, G. S. H. Paek, M. Pursiainen, S. I. Raimundo, R. Wainscoat, S. Yang
High Energy Astrophysical Phenomena
Cross-spectral Analysis of the Type-C Quasi-periodic Oscillation Shoulder Component in GX 339-4
Haifan Zhu, Mariano Méndez, Pengcheng Yang et al. (+8 more)
We revisit Rossi X-ray Timing Explorer (RXTE) observations of GX~339$-$4 during the rising phase of its 2006/2007 outburst and apply a joint power-density-spectrum (PDS)–cross-spectrum (CS) decomposition to the type-C quasi-periodic oscillation (QPO) region. Within this framework, the QPO region is described by a narrow QPO fundamental and a neighboring high-frequency shoulder, whose amplitudes and phase lags can be measured separately. The shoulder is first detected at MJD~54142.04, mainly through the imaginary part of the CS and a narrow local structure in the phase-lag spectrum, before becoming a resolved high-frequency shoulder in the PDS. It follows the QPO frequency
evolution on the high-frequency side, with $R_{\nu}=\nu_{\rm sh}/\nu_{\rm QPO}\simeq1.04$–$1.18$. The QPO lag remains small, typically below $\sim0.17$~rad, whereas the shoulder carries a larger hard lag of $\sim0.5$–$0.8$~rad. Energy-resolved fits show the same separation: the QPO lag is close to zero or only weakly positive across most of the energy band, while the shoulder lag is systematically larger and generally increases with
photon energy. The two components have broadly similar rms–energy shapes, although their relative strengths evolve during the observed sequence. Although the shoulder remains broad, with $Q\sim2$–$4$, its lag and rms–energy behavior resemble those of the type-B QPO detected shortly after our observations. This similarity raises the interesting possibility that the shoulder is related to an earlier, broader stage of the variability later seen as the type-B QPO.
Read the full abstract ▾
All authors Haifan Zhu, Mariano Méndez, Pengcheng Yang, Pei Jin, Candela Bellavita, Federico García, Wei Wang, Diego Altamirano, Liang Zhang, Chenxu Gao, Xiao Chen
High Energy Astrophysical Phenomena
An Evolving Leptonic Jet Model for Delayed Radio Flares in Neutrino Blazars
Alina Kochocki, Xavier Rodrigues and Nathan Whitehorn
The jets of blazar active galactic
nuclei (AGN) are promising sites of
hadron acceleration and subsequent
neutrino production, owing to their extreme intrinsic power and high radiation density. Potential associations of IceCube
neutrinos with blazars displaying delayed
radio flares, such as TXS~0506+056 and PKS~1424+240, may support this scenario. However, the mechanisms and location of particle acceleration in the jet remain unclear. The 2017 IceCube event associated with TXS 0506+056 was concurrent with the initial peak of a
flare in gamma rays, followed by a longer
flare at
radio frequencies peaking three years later. State-of-the-art single-zone radiative source models focus on the compact high-energy-emitting region, and thus fail to describe this subsequent
radio enhancement. In this work, we model the time-domain multi-frequency
evolution of TXS 0506+056 by considering electron emission along the physically extended jet. We couple a numerical particle interaction framework with a dynamic description of the temporal and spatial jet
evolution down to the parsec scale. We fit the model to multi-wavelength data, including multi-frequency
radio light curves. The results suggest that the parsec-scale jet meets a population of older, cooled electrons near the edge of the observable
radio core, establishing a causal relation between the initial high-energy emission and trailing
radio activity. This spatially and temporally resolved modeling approach can offer new insights into the physical conditions along the jet of flaring
neutrino candidate blazars.
Read the full abstract ▾