High Energy Astrophysical Phenomena
The high entropy of the UHECR arrival direction distribution favors a light composition
Nimrod Strasman and Eli Waxman
We analyze the constraints on the composition of ultra-high-energy
cosmic rays (UHECRs), and on the density and distribution of their sources, that may be inferred from their arrival-direction distribution, using a novel semi-analytical description of the propagation energy loss of atomic
nuclei ($A>4$) with energy $>2\times10^{19}~\text{eV}$, that allows generating UHECR arrival maps faster than by using detailed propagation simulations and yields insights to the impact of propagation energy loss. We show that the anisotropy of the UHECR arrival direction distribution due to the large-scale structure (LSS) of matter distribution is larger for heavy
nuclei composition compared to
protons, despite their larger deflections by
magnetic fields, due to their shorter propagation distance and weaker dependence of rigidity on observed energy. Identifying the LSS anisotropy signal is hampered for heavy
nuclei due to their large deflections by the uncertain Galactic
magnetic field (GMF). We introduce a new measure of anisotropy, an "
entropy" of the arrival-direction distribution, that is largely independent of the GMF configuration and has strong discriminating power between heavy- and light-composition models. Analyzing the public $>3.2\times10^{19}$~eV Auger data, we show that the correlation with the LSS on large angular scales is weak and requires a low source density, $s_0\le10^{-4}{\rm Mpc}^{-3}$, to allow masking the LSS signature by "
cosmic-variance" ($s_0=10^{-2}{\rm Mpc}^{-3}$ is ruled out at $>99\%$ confidence level (CL)). The high
entropy of the distribution is consistent with
proton models and inconsistent with heavy
nuclei models at $>96\%$ CL for $s_0\ge10^{-5}{\rm Mpc}^{-3}$. Reducing the absolute energy calibration uncertainty may allow detection of the LSS correlation for
proton models (increased exposure alone will not suffice due to the dominance of
cosmic variance).
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High Energy Astrophysical Phenomena · Cross-listed from nucl-ex
Revised $^{45}$V($p,\gamma$)$^{46}$Cr reaction rate and its impact on the production of $^{44}$Ti in core-collapse supernovae
R.S. Sidhu, Y. Luo, C. Sarma et al. (+2 more)
The thermonuclear $^{45}$V($p,\gamma$)$^{46}$Cr reaction is the primary leakage pathway from the $^{44}$Ti–$^{45}$V quasi-
equilibrium cluster during $\alpha$-rich freeze-out in core-collapse
supernovae (CCSN), governing the final abundance of the $\gamma$-ray-emitting isotope $^{44}$Ti. A recent high-resolution $\gamma$-ray study [C. Cousins et al., Phys. Rev. Lett. 136, 252701 (2026)] identified ten previously unknown low-
spin proton-unbound states in $^{46}$Cr, enabling the first experimentally constrained $^{45}$V($p,\gamma$)$^{46}$Cr reaction rate using the AME2020 mass excess, $\text{ME}(^{46}\text{Cr}) = -29472(11)$~keV. Here, we adopt the four-fold more precise CSRe mass excess $\text{ME}(^{46}\text{Cr}) = -29477.2(2.6)$~keV [M.~Wang et al., Phys. Rev. C 106, L051301 (2022)] to recalculate the reaction rate. Including
proton capture on the ground and first two excited states of $^{45}$V alongside new shell-model
proton spectroscopic factors, we reduce mass-related rate uncertainties to a subdominant level. The revised rate is up to 69% higher than that of Cousins et al. at $\alpha$-rich freeze-out temperatures ($T \simeq 1.5$–$2$~GK). CCSN nucleosynthesis calculations show this revised rate increases the ejected $^{44}$Ti yield by $\sim$26% in a $20\,M_\odot$ model compared to The et al. [ApJ 504, 500 (1998)], while causing negligible changes for the SN~1987A trajectory. We demonstrate that $^{44}$Ti production sensitivity is dictated by the ejecta electron fraction ($Y_e$): the reaction significantly affects
proton-rich ejecta ($Y_e \approx 0.50$) but has little impact on
neutron-rich ejecta ($Y_e \approx 0.496$), where lower free-
proton abundances suppress reaction flow. This reconciles conflicting results from past sensitivity studies.
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All authors R.S. Sidhu, Y. Luo, C. Sarma, M. Wiescher, X. Xu
High Energy Astrophysical Phenomena
The initial evolution of SN 2011dh: The importance of inhomogeneities
Claes-Ingvar Bjornsson
SN 2011dh is rather unique in that it offered detailed observations of the initial phase in the
radio as well as optical regimes. This makes possible a comparison between models used to deduce properties of the outer envelope of the
supernova ejecta. It is shown that a consistent description suggests the forward shock to have started in the piston phase with constant velocity, and only later, around 50 days, transitioned to the standard model, which is independent of initial conditions. In addition, observations imply that the
radio source is inhomogeneous with a covering factor of, approximately, 50%. It is emphasised that the deduced properties of the synchrotron source are very sensitive to the presence of inhomogeneities; for example, a covering factor of 50% increases the ratio of the energy densities of relativistic electrons and
magnetic field by several orders of magnitude as compared to a homogeneous source. The shallow density gradient in the envelope causes substantial deceleration of the forward shock. This is used to argue that the
magnetic field strength scales inversely with radius rather than inversely with time; this is similar to SN 1993J.
Attention is also drawn to the similarities between the flat spectra of compact, extragalatic
radio sources and the
evolution of
radio supernovae; e.g., the scaling of the
magnetic field and the constant brightness temperature.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
An axion constraint from the diffuse supernova neutrino background indicated by Super-Kamiokande
Kanji Mori, Tomoya Takiwaki, Kazunori Kohri et al. (+1 more)
Recently, the Super-Kamiokande Collaboration reported an indication of the diffuse
supernova neutrino background (DSNB) with a statistical significance of $2.6\sigma$. Motivated by this possible discovery, we investigate the impact of
axion cooling on the DSNB flux on the basis of long-term
neutrino-radiation hydrodynamic simulations. We compare the observed flux and our models and obtain a $1\sigma$ upper limit $|g_{ap}|<1.3\times10^{-9}$ on the
axion-
proton coupling constant, which is comparable to the conventional limit based on the SN 1987A
neutrino burst. In contrast to the SN 1987A bound, the DSNB constraint does not rely on the properties of a single observed
supernova, because the DSNB represents the cumulative
neutrino emission from a
cosmic population of core-collapse events. More generally, this approach can be applied to other feebly interacting particles that modify protoneutron-
star cooling.
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All authors Kanji Mori, Tomoya Takiwaki, Kazunori Kohri, Masamitsu Mori
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.CO
A stochastic forward model for the intergalactic dispersion-measure distribution of Fast Radio Bursts
Jéferson A. S. Fortunato, Valerio Marra, Wiliam S. Hipólito-Ricaldi et al. (+1 more)
Fast
Radio Bursts probe ionised baryons through their observed dispersion measures. We present \turbofrb, a semi-analytic
stochastic forward model for the intergalactic dispersion-measure distribution, $P({\rm DM}_{\rm IGM}\mid z)$, that resolves the diffuse IGM,
halo, and filament contributions as explicit physical channels, with the
halo and filament encounter rates coupled by a latent line-of-sight environmental variable. Only four effective parameters are calibrated against hydrodynamical ray-traced IllustrisTNG
benchmark. The model matches the
benchmark mean DM to the percent level and yields a per-
redshift Jensen-Shannon divergence of at most $5\times10^{-3}$ across $z = 0.5$-$2.5$. The per-sightline channel decomposition makes explicit what closed-form parametric descriptions cannot show: the diffuse IGM sets the body of the distribution, while
halos and filaments populate the high-DM tail. Applied to representative localised FRBs, the forward likelihood quantifies host-excess events independently of their astrophysical signatures and recovers the injected $H_0$ within $1\sigma$ in a closed-loop consistency test. The \turbofrb package is available at \href{https://github.com/jefersonfortunato/turbofrb}{github.com/jefersonfortunato/turbofrb}.
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All authors Jéferson A. S. Fortunato, Valerio Marra, Wiliam S. Hipólito-Ricaldi, Amanda Weltman
High Energy Astrophysical Phenomena
Revisiting neutrino event epochs for the blazar PKS 0735+178 with TESS
Shubham Kishore, Alok C. Gupta and Debanjan Bose
We present here the results of the optical light curve variability analysis of the blazars PKS 0735+178, in weeks-scale
flare state, observed in three sectors with the Transiting
Exoplanet Survey Satellite (TESS). The TESS observations in this study coincide with a well-known
neutrino emission phase detected with four different
neutrino observatories at multiple epochs in a narrow time window. We segmented the rising and decaying parts of the
flare and individually analyzed their flux distribution, excess variance, variability timescale, and the power spectral density (PSD). The source displayed an elevated excess variance of ~25%, with a multi-modal flux distribution (coherent in the rising and distorted in the decaying phase). The variability timescale analysis highlights a much faster decay than the rising scale, and the PSDs depict a nominal change in the power spectral slope. We discuss a likely connection in the optical variations and the
neutrino events, and briefly explain a possible physical scenario for the observed optical flux behavior in view of previously discovered
radio-band results.
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High Energy Astrophysical Phenomena
SST-1M: Recent results and prospects for observation of the Galactic Center region
Jakub Juryšek and for the SST-1M Collaboration
The Galactic Center is a crowded region containing powerful particle accelerators and objects producing non-thermal radiation, including the diffuse very-high-energy (VHE) gamma-ray component known as the `Ridge', whose hard spectrum suggests particle acceleration up to PeV energies. The relevant processes can be tested, and the source parameters can be constrained via Cherenkov
telescope observations. Two Single-Mirror Small-Size Cherenkov
Telescopes (SST-1M) are currently operated in stereoscopic mode at the Ondřejov Observatory. Their future relocation is being considered, including a site with excellent visibility of the Galactic Center. We present recent observations demonstrating SST-1M capabilities for detecting extended emission and discuss prospects for probing the Galactic Center region, including searches for a spectral cut-off above 10 TeV. We show that the large field-of-view and good VHE sensitivity make SST-1M an ideal instrument for the search for PeVatrons.
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High Energy Astrophysical Phenomena
NMMA-Astro-COLIBRI: An Automated Light-Curve Supernovae Classification Service in the Multi-Survey Era
R. Weizmann Kiendrebeogo, Bernardo Cornejo Avila, Sofia Bisero et al. (+6 more)
The surge in publicly available photometric alerts from wide-field surveys requires automated tools for real-time transient classification. We present NMMA–Astro-COLIBRI, an on-demand
Bayesian classification service that couples the Nuclear-physics and Multi-Messenger Astrophysics (NMMA) inference framework to the Astro-COLIBRI real-time multi-messenger platform. After the detection of an optical transient, if photometry is available, it is quality-filtered. The filtered photometry is fitted by nested sampling against a user-selected model from a library of eleven
supernova templates; results are delivered to every user within minutes. Applying two or more models on the same optical transient, the service reports the corresponding log Bayes factors as a quantitative ranking of competing subtypes. We demonstrate the workflow on SN 2021ugl (ZTF21abotose), a Type IIb
supernova initially mistaken for a kilonova candidate by automated real-time pipelines, comparing competing
supernova and kilonova models. In an early-time configuration using only the first ~ 6 days of photometry in two bands (ZTF g and r), so ten days before spectroscopic confirmation, the empirical Type IIb template recovers the correct classification, favored over both the kilonova template and the kilonova-mimicking shock-cooling model. In the full 47-day, three-band baseline, it again achieves the highest evidence over every competing
supernova and kilonova template. These results highlight the importance of a comprehensive
supernova template library for kilonova discrimination in the multi-survey era.
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All authors R. Weizmann Kiendrebeogo, Bernardo Cornejo Avila, Sofia Bisero, Maxime Cellier, Antoine Ciric, Ilja Jaroschewski, Henrik Rose, Alexandre Saint-Paul, Fabian Schüssler
High Energy Astrophysical Phenomena
From Variability to SED Modeling: A Multiwavelength Study of the Neutrino Blazar TXS 0506+056
Shiyu Du, Hanxiao Xia, Jianghua Wu et al. (+1 more)
The blazar TXS 0506+056 is the first source that was reported to be associated with high-energy extragalactic
neutrino events and is one of the major targets for multi-messenger studies. We carried out multi-wavelength optical monitoring of this object on 24 nights in the period from 2018 to 2023. The overall light curves exhibit a dimming trend superposed by some small-amplitude fluctuations, and intraday variability was detected on four nights. Bluer-when-brighter behaviors were observed on both intraday and long timescales and were more pronounced on long timescales, while a weak redder-when-brighter trend was detected on one night. No significant time lags were found between variations at different optical wavelengths. We also retrieved the multi-broadband data from some monitoring programs. The data reveal complex, asynchronous flaring in different wavebands. A cross-correlation analysis shows that the high-energy emission (optical to gamma-ray) is co-spatial and leads the
radio emission by a substantial time of about 800 to 900 days, suggesting that the
radio emission originates from a downstream region of the jet. We performed time-dependent lepto-hadronic modeling of the spectral energy distributions for three representative epochs, the 2017
neutrino-associated
flare, a post-
flare phase, and a deep quiescent state, revealing an
evolution in the radiative properties of the emission regions. The modeling results provide a phenomenological framework for interpreting the long-term multiwavelength behavior of TXS 0506+056 in a multi-messenger context.
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All authors Shiyu Du, Hanxiao Xia, Jianghua Wu, Yue Fang
High Energy Astrophysical Phenomena
Modelling mountains on accreting magnetized neutron stars
T. Brusco, B. Haskell, M. Razzano et al. (+2 more)
Continuous gravitational waves from accreting
neutron stars in Low Mass X-ray Binaries are one of the main targets for current and next generation ground based detectors. In order to select the most promising astrophysical sources, however, reliable predictions for the signals are required, and it is therefore necessary to develop models that consistently account for the combined effects of
magnetic stresses,
accretion-induced heating, and the elastic response of the crust.}{We present a model for computing the quadrupolar deformation, incorporating for the first time the coupled effects of a poloidal
magnetic field, deep crustal heating, and crustal elasticity. Perturbations to the
star's structure driven by the Lorentz force density and by thermally-induced density variations are computed by solving a system of linearised deformation equations in the crust, for which we consider the full elastic response, while the ocean and core treated as barotropic fluids. We identify a threshold
accretion rate whose value depends on crustal microphysics and the superfluid gaps in the core, above which
magnetic stresses and asymmetric
accretion drive deformations of opposite sign, while below this threshold their roles are reversed. The predicted eccentricities reach magnitudes up to $\varepsilon\sim 10^{-11}$, corresponding to characteristic gravitational-wave strains accessible to next-generation detectors such as the Einstein
Telescope or
Cosmic Explorer, but generally below the sensitivity of current LIGO, Virgo and KAGRA interferometers. These results are consistent with the non-detection of continuous gravitational waves from accreting
neutron stars in Low Mass X-ray Binaries in recent observational campaigns, but highlight the need of reliable models to understand the impact of gravitational wave emission in these systems and select relevant targets for future searches.
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All authors T. Brusco, B. Haskell, M. Razzano, M. Bejger, J.L. Zdunik
High Energy Astrophysical Phenomena
Impact of Upstream Clumpiness on Supernova Remnant Forward Shock Evolution in Molecular Cloud Environments
Kenta Tatsumi and Tsuyoshi Inoue
Supernova remnants (SNRs) are widely considered to be the primary accelerators of Galactic
cosmic rays. In recent years, detailed observations have significantly progressed for young SNRs interacting with molecular clouds, a
prime example being RX J1713.7-3946. When molecular clouds are clumpy, their impact can affect not only radiation properties but also shock wave propagation. Therefore, a quantitative understanding linking observational quantities with the ambient medium structure is highly required. In this study, we perform three-dimensional hydrodynamic simulations to model a molecular cloud with an inhomogeneous density structure driven by supersonic
turbulence and subsequent SNR formation. To investigate various pre-
supernova environments, we systematically vary the medium clumpiness by replacing gas below a threshold number density with a low-density hot gas, quantifying the relationship between the forward shock velocity and the volume filling factor of the high-density clumps. As a result, we find that at an elapsed time of 1000 yr-a typical age for a young SNR-the forward shock can evolve consistently with the fast shock velocity measured in RX J1713.7-3946, provided that the clump volume filling factor is approximately 10% or less. Considering that hadronic gamma-ray emission originates exclusively from the clumpy, high-density gas, our findings suggest that the total energy of
cosmic-ray
protons in RX J1713.7-3946 is higher than previously estimated, amounting to at least a few percent of the typical
supernova explosion energy.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
Ejecta clumps revealed by study of reverse-shocked ejecta through MUSE integral field spectroscopy of SNR 0509-67.5
Priyam Das, Ivo Seitenzahl, J. Martin Laming et al. (+3 more)
We report the discovery of a spatially resolved clumpy ejecta structure in the reverse-shocked ejecta of SNR 0509-67.5, revealed through multiple faint and broad forbidden coronal emission lines in deep MUSE observations. We also identify two new broad coronal emission lines not reported before in this remnant, [Fe xi] 7894 A and [Fe x] 6374.5 A , which extend the set of previously reported [Fe xv] 7059.59 A, [Fe xiv] 5302.86 A , [Fe ix] 8236.55 A , [Ca xv] 5695 A, and [S xii] 7611.0 A. Near-continuous ionisation states of Fe allow us to follow the ionisation progression behind the reverse shock. We use a 1D analytical model to evolve Fe charge states following reverse shock interaction to compare with observations, indicating the need for preshock clumping or over-density in order to reproduce the observed surface brightness of the [Fe xiv] line. Additionally, we report the spatially resolved distribution of ejecta clumps and show that reverse-shock interaction drives their compression and fragmentation. We also find a clear trend of decreasing velocity width with increasing Fe ionisation state, from the broadest [Fe ix] emission to the narrowest [Fe xv], with intermediate-ionisation species ([Fe x], [Fe xi], [Fe xiv]) showing intermediate widths. Finally, we compare our observations to a dynamically driven double-degenerate double detonation (D6) 3D remnant model at similar Fe and S ionisation states and conclude that the observed clumps are predominantly due to Rayleigh-Taylor instabilities.
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All authors Priyam Das, Ivo Seitenzahl, J. Martin Laming, Gilles Ferrand, Simon J. Murphy, Ashley Ruiter
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Generative artificial intelligence for reconstructing neutron-star matter
Julia Yu. Panteleeva, Herzallah Alharazin and Evgeny Epelbaum
Neutron-
star cores hold the only known matter in the universe that is simultaneously cold and strongly interacting, compressed beyond nuclear density into a state of unknown composition. The equation of state links stellar masses, radii and tidal deformabilities to this regime, but recovering this key quantity from sparse observations is an ill-posed inverse problem. Existing analyses bury a prior in a fixed functional form, unevenly weighting admissible solutions and biasing the result. We reconstruct the equation of state with a denoising
diffusion model that keeps prior, physics and data separate: it learns an inspectable, physically motivated prior anchored to first-principles nuclear theory, while perturbative-QCD and astrophysical constraints are imposed exactly. Future measurements therefore will update the posterior by reweighting alone, without retraining or resampling. The inferred radius of 12.6 km and tidal deformability of 469 at 1.4 solar masses reproduce Gaussian-process and heavy-ion-informed inferences despite a far broader prior. We find near-conformal but still stiff matter in the heaviest
stars, consistent with a gradual
hadron-
quark crossover and disfavouring a strong first-order phase transition. More broadly, coupling a learned prior to exactly enforced physics establishes a template for ill-posed inverse problems where theory and data constrain different regions.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
Ashwathi Nair and Simon Stevenson
The high total mass of GW190425 challenges our understanding of double
neutron star (DNS) formation, as no such heavy ($\ge 3$\, M$_\odot$) DNS system has been observed in the Milky Way disk. Numerous formation scenarios have been proposed to explain its formation. We test these within a self-consistent binary
evolution framework calibrated to the Galactic DNS population. In Paper~I of this series, we studied the
evolution of a $1.4$\,M$_\odot$
neutron star (NS) in a binary with a $2.5$–$10$\,M$_\odot$ helium
star at solar
metallicity ($Z = Z_\odot$), assuming Eddington-limited
accretion onto the NS using MESA. In this paper, we consider the
evolution of NS-He
star binaries with a broad range of NS masses from $1.1$–$1.9$\,M$_\odot$ at $Z=Z_\odot$, 0.1\,$Z_\odot$ and 0.01\,$Z_\odot$. We find that the formation of heavy DNSs is rare, accounting for only $\sim 0.5$ per cent of DNSs. The majority of these are formed through the `standard formation' channel, widely believed to form GW170817 and observed Galactic DNSs. We find no contribution through the `fast-merger' channel at solar
metallicity, but systems at low
metallicity predominantly form through unstable mass transfer. Furthermore, we find no significant dependence of the heavy DNS formation fraction on
metallicity over the range considered here. We conclude that heavy DNSs do not form a separate subpopulation and merely represent the high-mass tail of the standard DNS population.
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High Energy Astrophysical Phenomena
Density-induced dark-baryon conversion in $\Delta-$admixed hypernuclear neutron stars
Niyar Prabhat Kalita, Vivek Baruah Thapa, Bhanu Prakash Pant et al. (+2 more)
We investigate density-induced conversion of
neutrons into a neutral dark baryon $\chi$ in cold, charge-neutral, $\beta$-equilibrated
neutron-
star matter containing hyperons and all $\Delta(1232)$ quartet. The hadronic sector is modeled within a density-dependent covariant density-functional framework using the DDME2 parametrization. A scalar
Higgs portal is included as a possible interaction channel between the visible and dark sectors, although its mean-field contribution is negligible for the couplings adopted here. Unlike fixed dark-matter admixture models or scenarios in which nucleon-to-DM conversion is driven by
Higgs exchange, the $\chi$ abundance is determined self-consistently from chemical
equilibrium and baryon-number conservation. We find that hyperons and $\Delta$ resonances alter the
neutron chemical potential, delay the onset of $\chi$, and suppress its abundance relative to nucleonic matter. This competition induces characteristic changes in the equation of state, particle fractions, sound speed, and adiabatic index. For $m_\chi=1250$, $1300$, and $1400$ MeV, the maximum masses of the complete $N+Y+\Delta+\chi$ configurations are $1.806$, $1.899$, and $2.024,M_\odot$, respectively, indicating that the massive-
pulsar constraint disfavors the lighter dark-baryon
benchmarks. The radial profiles further show that for $m_\chi=1400$ MeV, $\chi$ is confined to the inner core of the most massive
stars, while canonical configurations remain essentially unaffected. Thus, the stellar modifications arise primarily from conversion-induced rearrangement of the
equilibrium composition rather than from
Higgs-mediated interactions. These results highlight the importance of treating conventional non-nucleonic degrees of freedom and density-generated dark baryons on an equal footing when assessing the astrophysical viability of dark-sector extensions of dense matter.
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All authors Niyar Prabhat Kalita, Vivek Baruah Thapa, Bhanu Prakash Pant, Anil Kumar, Partha Konar
High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph
The FLARE Facility
Hantao Ji, Jongsoo Yoo, Peiyun Shi et al. (+53 more)
The Facility for Laboratory Reconnection Experiments (
FLARE) has been constructed to study
magnetic reconnection in multiple X-line regimes relevant to space, astrophysical, and fusion
plasmas. Building upon the successful design of the
Magnetic Reconnection Experiment (MRX),
FLARE features a larger physical volume, stronger
magnetic fields, and an independent ohmic heating drive to significantly extend the accessible parameter space, targeting Lundquist numbers up to S ~ 10^5 and normalized system sizes up to \lambda ~ 10^3. This paper details the facility's core engineering components, including the primary
vacuum vessel, internal flux cores, highly segmented external coil systems, modular capacitor banks, and the safety interlock and control architecture. An initial diagnostic suite is presented, comprising high-resolution 2D
magnetic probe arrays, triple Langmuir probes, a fully fiber-coupled interferometer, ion Doppler spectroscopy, and fast camera imaging. Initial operations demonstrate the device's experimental flexibility and reliability, successfully executing symmetric push-pull reconnection, spheromak merging, and asymmetric downstream configurations. Currently operating within "Stage 2.5" with S ~ 2,500 and \lambda ~ 60 for anti-parallel reconnection,
FLARE provides immediate access to the multiple X-line regimes. Planned hardware upgrades, advanced diagnostic additions, and integration with fully kinetic simulations will further expand its capabilities as it transitions into a collaborative user facility for the broader
plasma science community.
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All authors Hantao Ji, Jongsoo Yoo, Peiyun Shi, Euichan Jung, Kush Maheshwari, Adam Robbins, Sunghyun Son, Adam Stanier, Yang Ren, Sayak Bose, Dylan Corl, Keith Corrigan, Robert Cutler, William Daughton, Robert Ellis, Geoffrey Gettelfinger, Ronald Hatcher, Philip Heitzenroeder, Frank Hoffmann, Jonathan Jara-Almonte, Michael Kalish, Thomas Kozub, Enrique Merino, Weiguo Que, Benjamin Smith, John Wallace, Xin Zhao, Sofia Avrutsky, Neal Crocker, Seth Dorfman, Yuka Doke, Corina Dunn, William Fox, Boting Li, Xiaocan Li, Clayton Myers, Shohgo Okazaki, Joshua Pawlak, Tongnyeol Rhee, Byonghoon Seo, Taiju Suzuki, Yang Zhang, Stuart Bale, Amitava Bhattacharjee, Troy Carter, Chuanfei Dong, James Drake, Jan Egedal, Erik Gilson, Michiaki Inomoto, Jonathan Menard, Yasushi Ono, Stewart Prager, John Sarff, Hiroshi Tanabe, Masaaki Yamada
High Energy Astrophysical Phenomena
Sudden emergence of a low-frequency hard X-ray lag in the Seyfert 1 galaxy Mrk 1044
Jia-Lai Kang and Jun-Xian Wang
Hard X-ray lags, where low frequency variations in the hard X-ray band lag behind those in the soft band, have been detected in many active galactic
nuclei (AGNs) and are generally attributed to the inward propagation of
accretion-flow fluctuations through an extended corona. In a long XMM-Newton observation of the Seyfert 1
galaxy Mrk 1044, we found a remarkable transition in the lag behavior within a single exposure, while the X-ray flux and spectral shape remained largely unchanged. During the first 60 ks, no significant hard X-ray lag was detected, whereas in the subsequent 60 ks, a pronounced lag emerged. The lag was so prominent that a large-amplitude flux variation event during the lag-detected interval, characterized by a gradual dimming followed by recovery, produced a remarkable clockwise loop in the flux-softness diagram. The sudden appearance of the hard X-ray lag suggests that the X-ray corona underwent a rapid transition from a compact to an extended configuration. This scenario is further supported by two independent observational signatures: (1) the variability became noticeably smoother, with a redder power spectral density (PSD), during the lag-detected interval, and (2) the broad Fe K$\alpha$ line profile became narrower and the reflection continuum weaker. These findings highlight the diagnostic power of tracking rapid changes in hard X-ray lags for probing the physical structure and
evolution of AGN coronae, and demonstrate that identifying prominent loops in the flux-softness diagram provides an effective way to locate intervals with significant hard X-ray lags.
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High Energy Astrophysical Phenomena
AT 2020afjz (TSS2020a): The First Fast Extragalactic Transient Discovered by TESS
Ryan Ridden-Harper, Hugh Roxburgh, Clarinda Montilla et al. (+13 more)
We report the discovery of AT 2020afjz (TSS2020a): the first hour-scale extragalactic transient discovered in optical wavelengths whose complete
evolution – from explosion onset to decay – is temporally resolved, and the first such transient discovered by TESS. AT 2020afjz was identified as a $>10\sigma$ detection in the pilot HiLaTS program run within the TESSELLATE Sky Survey, which blindly searches for transient phenomena in TESS data with the TESSELLATE pipeline. Through cross-matching with legacy imaging, we associate it with DES J042144.37$-$383311.3, a member of an interacting
galaxy pair at $z_{\rm phot}=0.67^{+0.07}_{-0.10}$. While AT 2020afjz is similar in duration and brightness to GRB afterglows, it exhibits a slow rise time of $\sim1$ hr and lasts for only 2.4 hr above the half-max brightness; modeling the TESS light curve with VegasAfterglow finds that it is best described as either an on-axis "dirty-fireball" or off-axis orphan afterglow. Each of these rare classifications hinge upon a non-detection at gamma-ray energies, but as Fermi-GBM was Earth-occulted at the time of explosion, AT 2020afjz's gamma-quiet nature cannot be definitively confirmed. Regardless, AT 2020afjz demonstrates TESS's power to discover fast extragalactic transients, and heralds a new population awaiting discovery with TESSELLATE.
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All authors Ryan Ridden-Harper, Hugh Roxburgh, Clarinda Montilla, Lancia Hubley, James Freeburn, Brayden Leicester, Andrew Moore, Zachary G. Lane, Jaime Luisi, Koji Shukawa, Armin Rest, Jeff Cooke, Michele T. Bannister, Lilly Fox, Tait Keller, Qinan Wang
High Energy Astrophysical Phenomena
Shin'ichirou Yoshida
A warm
neutron star is expected to have a fluid "ocean" of heavy elements at its outermost part of the outer crust. As is on the terrestrial ocean, the
neutron star ocean also has surface
gravity waves. Around a
magnetic pole of a
star, the ocean may have a dip due to the strong
magnetic pressure coming into play in the hydrostatic balance of the ocean. The dip enables the surface
gravity wave to be trapped around the
magnetic pole to form eigenmodes. The frequency of the mode is much lower than the dynamical frequency at the stellar surface, owing to the weak Coriolis force and the gradient in the ocean's depth that makes the eigenmodes present. We solve the equation of surface
gravity waves in the local $\beta$-plane approximation and obtain the spectrum of discrete eigenmodes. We see that there are no axisymmetric modes and that the mode frequency decreases and asymptotes to zero as the number of nodes of the corresponding eigenfunction increases. This is reminiscent of the g-modes in the context of asteroseismology. Observations of X-ray binaries containing
neutron stars reveal that some of the systems exhibit low-frequency quasi-periodic oscillations (QPOs) whose frequency is $1-10^3$mHz. We investigate whether the eigenmodes considered here may explain the low-frequency QPO spectrum. It is suggested that some of the QPOs in the system whose
neutron star spins at the period less than $10$s may be consistent with the model. As far as the
spin period is larger than $10$s, the eigenmode frequencies are too low to explain the observed QPOs.
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