High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Survey of Novel Deep Learning Architectures for Denoising Gravitational-wave Signals
Rohan Raha and Prayush Kumar
Gravitational-wave denoising must handle the full diversity of spinning, precessing binaries, since the recovered waveform underpins parameter estimation, tests of general relativity, and population studies. Matched filtering achieves this at a cost that becomes prohibitive as next-generation detectors push event rates higher; deep learning offers real-time reconstruction, but current methods are developed on narrow parameter spaces, precluding principled comparison and reliable deployment. We present the first controlled comparison of five neural-network architectures for gravitational-wave denoising, trained identically across the full astrophysically-motivated spinning binary-black-hole parameter space. A unifying principle emerges: matching network structure to the spectral anatomy of a coalescence – inspiral, merger, ringdown – outperforms brute-force model scaling. Our Multi-Scale Frequency-Aware architecture embodies this via dedicated parallel branches per frequency regime, achieving the best fidelity while using fewer parameters than larger models. It generalizes from simulated training to real LIGO-Virgo-KAGRA data without retraining, recovering merger morphology across confirmed events spanning three observing runs and both detectors, despite training on a single detector's simulated noise. We construct population-level uncertainty bands from denoising residuals, validate their calibration, and stress-test the framework on extended mass ratios and a
spin population resembling hierarchical-merger remnants. Applied to real noise with no known signal, the network suppresses its output almost everywhere, with rare exceptions traced to noise transients rather than a general weakness – indicating the statistic discriminates signal from noise and motivating a future detection study. Released weights give a deployable, reproducible
benchmark for future extensions.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
The Association of Solar Radio Bursts with Eruptive and Confined Flares
Stephen M. White, Maria D. Kazachenko and Edward W. Cliver
We classify the metric
radio emission associated with eruptive (CME-associated) and confined
flares using the sample of events between 2010 and 2016 identified by Kazachenko (2023). We find striking differences in the occurrence of
radio bursts between the two classes of
flare: for soft X-ray
flare sizes above M1.4, confined
flares largely lack Type II (1% association rate) and Type IV (6%) emission. Approximately 15% of the sample of $\geq$M1.4 confined
flares are associated with impulsive-phase Type III bursts. On the other hand, eruptive
flares are associated with Type II, Type III (both impulsive and late phase), and Type IV bursts 45-60% of the time. The different types of
radio burst are associated with different drivers (IIIs with electron beams, IIs with shocks, IVs with post-
flare loops), so it is striking that the connection of all three burst types to eruptive
flares is so pronounced. These results can be interpreted in terms of the reconnection
topology of the principle candidate
flare types, viz., reconnection between closed field lines for confined
flares and X-point reconnection in a CSHKP model for eruptive
flares, with interchange reconnection for jet-type
flares and Type III bursts.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
SN 2024afyu interpreted as a Pair Instability Supernova
P. J. Pessi, S. Barmentloo, Ł. Wyrzykowski et al. (+63 more)
Pair-instability
supernovae (PISNe) are the predicted explosions of very massive
stars triggered by electron-positron pair production. Numerous transients have been proposed as PISN candidates, yet none has provided unambiguous confirmation of this explosion mechanism. The predicted strengths of nebular emission lines offer a powerful means of testing the PISN scenario. We investigate the nature of SN 2024afyu, a nearby (z = 0.0085), long-lived (trise = 85 +- 11.7 days) SN with peculiar spectral
evolution, with the aim of identifying its powering mechanism. We analyse multi-band photometry and optical and near-infrared spectroscopy from shortly after explosion to the nebular phase (around 500 days past peak). Besides early appearance of [Ca II] features, we identify a number of sulfur and silicon emission lines, for which we estimate electron temperatures and elemental masses. SN 2024afyu has an inferred 56Ni mass of around 0.4 to 1.0 solar masses and an inferred sulfur mass of the order of 3 solar masses, substantially larger than expected for conventional core-collapse explosions. SN 2024afyu is photometrically similar (although fainter, M_Peak(r) = -18.9 +- 0.04 mag) but spectroscopically distinct to other proposed PISNe. Yet, existing PISN models broadly reproduce several key characteristics, including the overall spectral appearance and broad photometric
evolution. SN 2024afyu is a strong PISN candidate, since alternative scenarios would struggle to explain the combination of broad light curve, large intermediate-mass-element abundance, and general spectroscopic
evolution. The discrepancies between the observations and currently available theoretical models highlight the need for new PISN calculations spanning a wider range of progenitor masses,
metallicities, mixing prescriptions, and circumstellar environments.
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All authors P. J. Pessi, S. Barmentloo, Ł. Wyrzykowski, S. Schulze, J. Sollerman, A. Gangopadhyay, P. J. Mikołajczyk, S. Rose, K. Kotysz, C. Fremling, A. Jerkstrand, R. Lunnan, L. Yan, C. Fransson, J. L. Wise, M. Dubey, K. Misra, A. P. Cotter, D. Athanasopoulos, A. Bochenek, M. Bronikowski, U. Burgaz, W. Burzynski, J. M. Carrasco, E. Concepcion, C. Galdies, A. F. Gillan, A. Gkini, E. Gkiokas, E. Głowacki, F-J. Hambsch, J. Japelj, N. Karaman, P. King, S. Kurowski, C. Liu, M. Maskoliunas, Z. McGrath, M. Mihelčič, M. Nikolajuk, W. Ogloza, E. Pakštienė, U. Pylypenko, A. Pucek, N. Rehemtulla, R. M. Rich, A. O. Simon, A. Singh, C. Skoglund, E. Stonkute, Y. Stsefanenka, P. Szober, K. Tsalapatas, B. F. A. van Baal, C. Ventura, K. Vrontaki, A. Wozniak, J. Zdanavicius, S. Zola, E. C. Bellm, J. Castaneda Jaimes, M. J. Graham, G. Helou, F. J. Masci, J. N. Purdum, R. Riddle
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Nonradial oscillations of realistic anisotropic neutron stars: Polar modes
L. M. Becerra, José F. Rodríguez-Ruiz, E.A. Becerra-Vergara et al. (+1 more)
In this work, we study the polar perturbations of static, spherically symmetric
neutron stars with anisotropic pressure in full general relativity, including linear-order perturbations of both the metric and the fluid. We calculate the $f$-mode frequencies and the corresponding damping times using a consistent treatment of the perturbation of the radial vector $k^\alpha$. In particular, its Lagrangian perturbation $\Delta k^\alpha$ is determined by the metric perturbations and the fluid Lagrangian displacement and is constrained to the $(\tilde{u},\tilde{k})$ plane, where $\tilde{u}^\alpha$ is the normalized fluid four-velocity. This constraint introduces an additional dynamical degree of freedom into the perturbation equations. Considering three equations of state and the Horvat and Bowers-Liang prescriptions for pressure anisotropy, we find that the $f$-mode frequency increases with stellar mass, ranging from $1$ to $3$~kHz, while the damping time decreases, ranging from $0.5$ to $1.25$~s. Increasing anisotropy, in the sense of tangential pressure exceeding radial pressure, generally lowers the oscillation frequency, while its effect on the damping time depends on the anisotropy prescription: the damping time decreases with increasing anisotropy for the Horvat model but increases with increasing anisotropy for the Bowers-Liang model. We further find quasi-universal relations between the real and imaginary parts of the $f$-mode frequency, $M\omega_R$ and $M\omega_I$, and the stellar compactness $\mathcal{C}=M/R$, which are largely insensitive to the equation of state.
Polynomial fits to these relations achieve an accuracy better than $10\%$, providing a simple phenomenological framework for constraining
neutron-
star pressure anisotropy through future asteroseismology observations.
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All authors L. M. Becerra, José F. Rodríguez-Ruiz, E.A. Becerra-Vergara, F. D. Lora-Clavijo
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA
A pilot submillimeter search for IceCube neutrino counterparts: JCMT follow-up and dusty-galaxy catalog associations
Yuji Urata and Kuiyun Huang
The submillimeter band offers a complementary route to identifying electromagnetic counterparts of high-energy
neutrinos, tracing relativistic transients and persistent dust-obscured
galaxies. We present a pilot search combining JCMT/SCUBA-2 follow-up of IceCube events with catalog searches for bright high-
redshift dusty systems. Among nine rapidly observed IceCube fields, sources of particular interest were found in three: JCMT0402-0424 ("Shadow Blaster") in IC 210922A, a transient-like source following IC 220115A, and two known blazars in IC 240105A. ALMA resolved the Shadow Blaster into a strongly lensed dusty
star-forming
galaxy at z=2.988 with a compact gas-rich starburst core. Motivated by this result, we cross-matched IceCube localizations with the Herschel Bright Sources (HerBS) and Planck High-
Redshift Source Candidate (PHZ) catalogs. Among 51 historical IceCube events with A_bbox,90 <= pi deg^2, four fields contain at least one HerBS source, compared with 0.723 expected from right-ascension scrambling (fixed-cut p=4.18e-3). Scanning the localization-area threshold gives p_global,A=0.0135. Applying the same IceCube selection to PHZ gives four associated fields versus 3.544 expected (p=0.478). Because the focused HerBS selection followed a broader exploratory analysis with trials-corrected p_global=0.130, the focused result is suggestive rather than definitive. The four well-localized HerBS fields contain six high-
redshift DSFGs with apparent L_IR~10^13 L_sun. ALMA imaging and published spectroscopy reveal compact or multiple-component morphologies, extreme molecular-gas kinematics, and possible obscured nuclear activity. These results support a hierarchical strategy: identify luminous submillimeter candidates through wide-field imaging and catalogs, then characterize them at high angular resolution to test for compact gas-rich calorimetric conditions and obscured AGN activity.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
An EOS-Driven Extension of NSCool for Compact Star Cooling with Hadronic and Quark Degrees of Freedom
Federico Nola and Fernando Arias-Aragón
We present an EOS-driven extension of the NSCool thermal
evolution code that enables complete tabulated equations of state to be treated within a single composition-based input structure. The generalized NEW interface includes additional baryonic fractions, a bosonic composition variable, the hadronic volume fraction, and
quark fractions, allowing nucleonic, hyperonic, resonant-baryonic and hybrid
hadron-
quark configurations to be handled within the same workflow. The
neutrino sector is extended accordingly, including updated nucleonic modified Urca and bremsstrahlung rates, additional baryonic direct Urca channels, hyperonic processes, baryonic pair breaking and formation and
quark direct Urca, modified Urca, bremsstrahlung and PBF contributions. In mixed phases, emissivities and the corresponding core heat capacity contributions are evaluated from phase-local quantities and combined using the hadronic volume fraction. The implementation is validated against the original NSCool calculation for a controlled nucleonic
benchmark and demonstrated with representative hadronic and
quark-containing EOSs. These calculations are intended as software validation tests of the generalized workflow rather than as observational fits or statistical EOS inference.
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High Energy Astrophysical Phenomena
Abundance Stratification in Type Ia Supernovae – VIII. The 03fg-like SN\,2012dn: a double-degenerate merger interpretation
Charles J. Aouad, Paolo A. Mazzali, Stephan Hachinger et al. (+1 more)
A detailed study using abundance
tomography of SN 2012dn, a peculiar Type Ia
supernova, is presented. Despite exhibiting a normal peak luminosity, it retains early-phase super-Chandrasekhar (03fg-like) characteristics: weak Fe III, narrow intermediate-mass element (IME), persistent carbon, and the absence of high-velocity Ca II features. Its nebular spectrum is unusually faint due to grey dimming beginning $\sim$60 days after maximum and shows [O I] emission, rare in SNe Ia. While a Chandrasekhar-mass density profile reproduces the photospheric phase, it fails at late times. The [O I] emission requires additional low-velocity mass, implying a total ejecta mass of $1.66$ $M_\odot$, including $0.33$ $M_\odot$ of oxygen (with $0.1$ $M_\odot$ in the core). The $^{56}$Ni mass is estimated to be $0.45$–$0.49$ $M_\odot$, a range set by uncertainties in the grey-extinction correction applied at the nebular phase, and is insufficient on its own to account for the peak luminosity. Stable iron is confined to intermediate layers and absent from both the core and outer ejecta, the latter indicating sub-solar progenitor
metallicity. Silicon and sulfur span the full ejecta, while carbon extends down to $v \sim 6000$ ${\rm km,s^{-1}}$. These properties favour a double-degenerate CO–CO white dwarf merger scenario. The remaining luminosity deficit may be explained by additional energy input from a weak interaction with a low-mass, carbon-rich circumstellar shell.
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All authors Charles J. Aouad, Paolo A. Mazzali, Stephan Hachinger, Chris Ashall
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA
A New Sample of $\sim$ 100 Intermediate-mass Black Holes Reaching $z \approx 1$
Wen-Juan Liu, Luis C. Ho, Su Yao et al. (+2 more)
We present a systematic search for intermediate-mass black hole (IMBH) active galactic
nuclei (AGNs) at $0.5 < z \lesssim 1$ using DESI DR1 spectroscopy.We identify 98 broad-line IMBH AGNs with black hole masses $M_\mathrm{BH}<10^6$ $M_{\odot}$ through quantitative spectral decomposition and broad-H$\beta$ selection. This sample spans $M_\mathrm{BH}=10^{5.5}-10^{6.0}$ $M_{\odot}$ and Eddington ratios from 1.2 to 9.0 extending systematic IMBH AGN searches to intermediate
redshift. Compared with a consistently selected $z<0.6$ IMBH sample, the $0.5<z<1$ sources reach higher broad-H$\beta$ luminosities and substantially higher Eddington ratios, indicating more extreme
accretion states at earlier
cosmic times. They also show broader [O III] profiles and stronger blueshifted wing components, with these kinematic differences persisting after matching in black hole mass and Eddington ratio. These results reveal two distinct signatures of
evolution among IMBH AGNs at $z<1$: ability of IMBHs to reach increasingly extreme
accretion states toward higher
redshift, and systematic changes in their ionized-gas kinematics. The former demonstrates that rapid, including super-Eddington, growth of IMBHs can persist to relatively late
cosmic times, while the latter may indicate
evolution in the ionized-gas environment and associated outflow activity of actively growing IMBHs. Together, these findings provide new constraints on the evolutionary pathways of IMBHs at $z<1$, and show that seed-mass black holes can continue to undergo rapid growth well after the
cosmic dawn.
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All authors Wen-Juan Liu, Luis C. Ho, Su Yao, Xiao-Bo Dong, Yaqi Zhao
High Energy Astrophysical Phenomena
Two-Phase Structure of Synchrotron-Cooling-Unstable Relativistic Plasma
Agnieszka Wierzchucka, Pablo J. Bilbao, Robert J. Ewart et al. (+2 more)
Using analytic theory, radiative particle-in-
cell (PIC) simulations, and fluid simulations, we show that relativistic, synchrotron-cooling, collisionless, high-$\beta$ pair
plasmas filament into a two-phase medium. This process occurs through the interplay of the synchrotron cooling instability (SCI) with the synchrotron firehose instability (SFHI). One phase has high
plasma~$\beta$ and is infested with small-scale firehose fluctuations, which scatter particles and pin the pressure anisotropy to the firehose-marginal level. The other phase has much lower~$\beta$, causing the suppression of firehose modes and thus allowing large pressure anisotropies. We propose a fluid model for this two-phase
plasma, which we use to study the linear and nonlinear
evolution of the SCI and SFHI, and to predict the emergence time of the two-phase structure.
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All authors Agnieszka Wierzchucka, Pablo J. Bilbao, Robert J. Ewart, Dmitri A. Uzdensky, Alexander A. Schekochihin
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM
Search for Long-Transient Gravitational Waves from Supernova SN2023ixf using GFH-v2 Pipeline
Sandhya Sajith Menon, Lorenzo Pierini, Pia Astone et al. (+24 more)
We present a directed search for long-transient gravitational waves from the possible newborn magnetar remnant of SN2023ixf, a nearby Type II core-collapse
supernova in the M101
galaxy. The analysis uses LIGO Hanford and Livingston data from Engineering Run 15, using coincident data lying within the on-source window associated with the
supernova. We target signals from a rapidly rotating, non-axisymmetric
neutron star whose
spin-down is dominated by gravitational-wave emission, producing a power-law decrease in frequency and a corresponding decrease in strain amplitude. The search is performed with the GFH-v2 pipeline, based on the Generalized Frequency Hough transform. No candidate survives the coincidence and follow-up analysis. We therefore set upper limits on the maximum detectable distance as a function of initial frequency and ellipticity. For the highest ellipticity interval, the 90% upper limits reach distances of about 1-2.5~Mpc across most of the analysed band. Although these limits are below the distance to M101, the search provides the first application of GFH-v2 to a nearby core-collapse
supernova and characterizes its performance on real detector data.
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All authors Sandhya Sajith Menon, Lorenzo Pierini, Pia Astone, Cristiano Palomba, Francesco Safai Tehrani, Lorenzo Silvestri, Ornella Juliana Piccinni, Simone Dall'Osso, Stefano Dal Pra, Sabrina D'Antonio, Sergio Frasca, Dafne Guetta, Paola Leaci, Michal Bejger, Alicia Calafat, Evan Goetz, Rafel Jaume Amengual, Ian Jones, David Keitel, Andrzej Krolak, Iuri La Rosa, Andrew Melatos, Joan-Rene Merou, Lorenzo Mirasola, Claudio Salvadore, Alicia M. Sintes, Karl Wette
High Energy Astrophysical Phenomena
Bridging the Population Synthesis of Supermassive Binary Black Holes and the Gravitational Wave Background
Kanyuni Iemoto, Boris Goncharov, Gabriela Sato-Polito et al. (+1 more)
Pulsar Timing Arrays (PTAs) constrain population properties of supermassive binary black holes (SMBHBs) through the observation of the gravitational wave background (GWB). Unlike other approaches that interpolate population-synthesis libraries or only consider the mean of the strain spectrum, here we capture its full strain probability density directly from semi-analytic population models. We apply our new method to the semi-analytic SMBHB population model, independently reproducing the parameter estimation for this model performed by the NANOGrav Collaboration with their 15-yr data. We also show the extent to which discrete SMBHB contributions to the GWB resolve degeneracies in the population parameter space. Finally, using the source-count intensity as the intermediate product in our calculation, we map PTA observations, as a proof of principle, to the SMBHB model based on the
galaxy merger prescriptions from numerical hydrodynamical simulations "Illustris". We find the effect of delay times $\tau$ between kiloparsec and subparsec SMBHB separations following
galaxy mergers, finding $h_{\rm c}$ spanning $(1$-$6)\times10^{-16}$ and $N_{\rm c}$ spanning $(0.3$-$7.1)\times10^{-3}$ for $\tau$ up to 8 Gyr.
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All authors Kanyuni Iemoto, Boris Goncharov, Gabriela Sato-Polito, Xiaoming Bi
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM
Approximating the statistics of a gravitational wave background
Mikel Falxa
The astrophysical origin of the gravitational wave background (GWB) reported by
pulsar timing array (PTA) collaborations has yet to be confirmed. A GWB signal made of the sum of individual gravitational wave (GW) from the population of supermassive black hole binaries (SMBHB) would show the imprint of a discrete Poissonian statistics in its spectral properties. In this work, we propose a tool based on the saddlepoint approximation method to estimate the distribution of characteristic strain for any given population model. This tool can be used for
Bayesian inference or for a quick visualization of the statistics of the GWB from the output of more realistic semi-analytical models. We introduce the general family of variance mixture Gaussian distributions that models heavy-tailed behavior distributions that is expected for a non-Gaussian GWB signal. We show that setting the correct hierarchical priors to a Gaussian free spectrum PTA likelihood is effectively equivalent to a non-Gaussian likelihood. Using ideal simulations, we compare the performance of the saddlepoint approximation with a log-Normal distribution to infer the parameters of the astrophysical model from the statistics of the GWB and show that correctly modeling higher order moments is essential. Future PTA analyses should include the statistics of the GWB in their pipelines.
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High Energy Astrophysical Phenomena
Raj Kishor Joshi, Brynmor Haskell, William Cook et al. (+1 more)
Magnetic fields are fundamental for
neutron star physics and play a central role in powering the extreme phenomenology of magnetars, including Soft Gamma Repeaters and Anomalous X-ray
Pulsars. However, the structure and stability of their internal
magnetic fields remain largely unconstrained, as they cannot be directly probed by electromagnetic observations. Using 3D general-relativistic magnetohydrodynamics simulations across a range of rotation rates and
magnetic field strengths, we identify two distinct evolutionary regimes leading towards dynamically stable
magnetic configurations. In rapidly rotating
stars, the Alfvén crossing timescale exceeds the rotation period, allowing differential winding to amplify a strong toroidal
magnetic component before the onset of instabilities, leading to long-lived, stable configurations. In contrast, in magnetically dominated
stars, instabilities in the poloidal field drive rapid field decay, leaving only a comparatively weak toroidal component. These results imply that the internal
magnetic structure of
neutron stars depends sensitively on their rotational state: rotation-dominated
stars like
radio pulsars develop strong toroidal fields, while magnetars are characterized by predominantly poloidal configurations. Our findings therefore show that a
neutron star's rotational history shapes its internal
magnetic structure, providing a unifying physical picture that connects the observed diversity of
neutron star classes to their hidden field configurations.
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All authors Raj Kishor Joshi, Brynmor Haskell, William Cook, Sebastiano Bernuzzi
High Energy Astrophysical Phenomena
A cosmic-ray database update: CRDB v4.2
Davud Maurin
The
cosmic-ray database, CRDB, has provided data and meta-data to the community since 2013. We present a new release, CRDB v4.2, which includes data and time series published in the last three years (from AMS-02, CALET, DAMPE, LHAASO, etc.),
datasets missed in previous releases, and all peer-reviewed ultra-high energy
cosmic-ray data (both historical and recent
datasets). These data and meta-data are available from the web interface or from the CRDB pip-installable Python library. This release includes results from more than 60 experiments and publications, corresponding to 4534 new data points and 131624 time-series data points.
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High Energy Astrophysical Phenomena
Mining the time axis with TRON - III. Discovery of a nulling pulsar towards the SMC with MeerKAT
T. Blecher, M. Geyer, O. M. Smirnov et al. (+21 more)
We report on the discovery of a nulling
pulsar, PSR J0052$-$7551, in archival MeerKAT L-band observations of the Small Magellanic Cloud (SMC). The discovery was made using the image-plane transient detection pipeline, TRON, which creates a residual image for each time sample and uses a heuristic
pruning strategy to identify promising candidates in the resulting temporal image cube. The TRON pipeline triggered on the approximately minute timescale variability associated with the nulling behaviour of a canonical
pulsar. Follow-up MeerKAT UHF-band beamformer observations revealed a
pulsar with a
spin period of 0.55 s and a measured period derivative of 6.1(6)$\times$10$^{-17}$s$\cdot$s$^{-1}$. The source is seen in projection toward the periphery of the SMC, and has a dispersion measure value of 29.24(2) pc$\cdot$cm$^{-3}$, which is on the order of the expected Milky Way contribution along the line of sight. We use a Gaussian Mixture Model to fit the nulling behaviour which yielded a nulling fraction of $\sim 32$%. We find that the null lengths are consistent with an exponential distribution indicating a
stochastic process. Additionally, power spectra of the UHF visibility data reveal an unexplained quasi-periodic feature at ~5$-$7 s that cannot be attributed to the source itself, RFI, or standard instrumental effects. Following on from previous image-plane detections of
pulsars by the TRON approach, which relied on either scintillation or eclipsing behaviour, this is the first detection triggered by nulling. This discovery confirms TRON's sensitivity to a wide range of astrophysical phenomena of medium timescale duration.
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All authors T. Blecher, M. Geyer, O. M. Smirnov, A. Coelen, I. Heywood, I. Pelisoli, A. K. Hughes, J. S. Bright, V. Prayag, T. Myburgh, C. Tasse, B. Hugo, J. S. Kenyon, H. L. Bester, S. J. Perkins, J. Dawson, V. G. Samboco, A. J. T. Ramaila, B. Ngcebetsha, I. Sihlangu, C. Choza, V. S. Dhillon, N. Castro Segura, J. McCormac
High Energy Astrophysical Phenomena
Oblique Collision of a Relativistic Cold Shell with an Ideal Reflecting Wall
Jonathan Granot, Prasanta Bera, Michael Rabinovich et al. (+1 more)
Relativistic flows are common in astrophysics and often form shocks when different parts of the flow collide at relativistic relative velocities. Such collisions are often oblique, forming two shocks whose shocked fluids are separated by a contact discontinuity, which is treated here as an ideal reflecting “wall” where the flow on either side is modeled separately. The latter is modeled in the lab frame $S$ as a uniform cold planar shell propagating into
vacuum at velocity $v_1=\beta_1c$ normal to its
vacuum interface, colliding with the wall at an incidence angle $\alpha_1$. The collision point $P$ moves along the wall at a velocity $v_p=v_{1}/\sin\alpha_1$, and a boost along the wall at $v_p$ leads to a steady-state frame $S'$ where this problem is highly simplified. However, a “super-luminal” regime exists where $v_p>c\Leftrightarrow\tan\alpha_1<\Gamma_{1}\beta_{1}=(1-\beta_{1}^2)^{-1/2}\beta_1$ and no steady-state frame $S'$ exists. It corresponds to only very small $\alpha_1$ in the Newtonian regime, but nearly all $\alpha_1$ in the relativistic regime. We solve this problem \textit{fully analytically} using integral conservation laws, in the attachmrnt region where point $P$ is attached to the wall. This region of parameter space is bound at high $\alpha_1$ by the detachment line, which coincides with the sonic line for a cold initial shell. A weak-shock solution exist in all this region, while a strong-shock solution exists only in the sub-luminal attachment region – between the luminal line and the detachment/sonic line where the two solutions coincide and beyond which point $P$ detaches from the wall and shocked fluid spills into the
vacuum.
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All authors Jonathan Granot, Prasanta Bera, Michael Rabinovich, Paz Beniamini
High Energy Astrophysical Phenomena
Timing Gravity with Pulsars in the Strong Field
Riccardo Della Monica and Ivan de Martino
We propose a novel approach for the timing of
pulsars orbiting a supermassive black hole, which implements the fully relativistic calculations of the
photon travel time into a robust timing model. We generate realistic mock catalogues of
pulsar times-of-arrival for several putative
pulsars on tight orbits around the Galactic Center supermassive black hole, Sagittarius A* (Sgr A*). Then, we perform a proof-of-concept sensitivity analysis to forecast the accuracy that future observational facilities, like the Squared Kilometer Array, will achieve in the characterization of the parameters of our timing model. Our analysis shows how the observation of
pulsars at the Galactic Center will open an incredibly promising avenue for the characterization of the physical properties of Sgr A*, which can improve by at least three orders of magnitude the current constraints on the black hole's mass achieved with the S-
stars and event-horizon scale observations.
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High Energy Astrophysical Phenomena
Correlation between X-ray and gamma data of Swift measurements
Istvan I. Racz, Lajos G. Balazs, Istvan Horvath et al. (+1 more)
Several studies over the last two decades have used canonical correlation analysis (CCA) to study the relationships between main {\gamma}-ray (e.g. fluence, peak flux, and duration) and main X-ray (flux, decay and spectral index, and hydrogen column density) data from gamma-ray bursts (GRBs). In this paper, we revisit this approach using a much larger
dataset to identify potential new insights into these relationships. We used CCA to investigate the interrelationship of the aforementioned gamma-ray and X-ray parameters. Using the derived canonical variables, we calculated their correlations (canonical loadings) with the original data. Consistently with previous research, the analysis revealed that gamma-ray fluence and X-ray flux have the strongest correlation, while the X-ray decay index and spectral index have a lower contribution. Interestingly, our analysis of a much larger
dataset reveals that the HI column density makes a significant contribution to the overall correlation. This finding, in the context of the collapsar model for long GRBs, could be interpreted as an indication that the progenitor
star ejected an HI envelope during the GRB.
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All authors Istvan I. Racz, Lajos G. Balazs, Istvan Horvath, Sandor Pinter
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Exact Cancellation of Horizon Modes in Kerr Ringdown
Kei-ichiro Kubota, Yusuke Manita, Hayato Motohashi et al. (+1 more)
Ringdown gravitational waves probe black hole spacetimes via quasinormal modes (QNMs). Recent studies have reported oscillatory features in QNM-filtered waveforms, and have led to conflicting interpretations as to whether they represent a near-horizon "direct wave". Reexamining a particle plunging into a Kerr black hole, we show that the saddle-point approximation underlying the proposed interpretation fails near the horizon. Our exact analysis reveals that every source-induced horizon-mode pole is canceled by an infinite tower of Matsubara zeros, independently of orbital and black-hole parameters. The first four stages of this sequential screening are also confirmed by time-domain numerical integration. Thus, within the near-horizon perturbative framework, source-induced horizon-mode signals do not survive at late times.
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All authors Kei-ichiro Kubota, Yusuke Manita, Hayato Motohashi, Daiki Watarai
High Energy Astrophysical Phenomena
LOFAR follow-up of sources in the First LHAASO Catalogue
Maria Arias, Timothy Shimwell, Martin Hardcastle et al. (+1 more)
The First LHAASO Catalogue lists 90 sources of very-high-energy gamma-ray emission, many without an established counterpart at other frequencies, reopening the question of which Galactic accelerators produce the highest-energy
cosmic rays. We search for low-frequency
radio counterparts to the 55 1LHAASO sources that fall within the Galactic fields of the LOFAR Two-metre Sky Survey Data Release Three (LoTSS-DR3), using 144~MHz continuum maps at $6''$ and $20''$ resolution, complemented with archival data from other
radio surveys where available. We present an overview of the
radio emission towards all 55 sources, and identify the structures potentially associated with the gamma-ray emission. We report 24 new
supernova remnant (SNR) candidates, nine flat-spectrum
radio shells with faint or no infrared counterpart, and six sources with no clear Galactic
radio emission present in the LOFAR maps. A bootstrap analysis shows that 23 of the 50 sources in the Galactic plane footprint (46%, for $|b| \leq 5$) overlap a catalogued SNR, whereas random placement yields only $10.0\pm2.8$ matches even if the underlying Galactic SNR population is ten times larger than currently catalogued; in the outer
Galaxy, where chance
alignment is rarest, 4 of 12 sources coincide with an SNR against a null expectation of $\lesssim2$. We estimate that at least a quarter, and up to half, of the 1LHAASO Galactic-plane sources genuinely reside in SNR environments, consistent with a population dominated by
pulsar wind nebulae, SNR–PWN composites, and
cosmic-ray-illuminated clouds. Individual results include a new SNR candidate inside the TeV shell HESS~J1912+101, a
radio candidate for the SNR hypothesised to explain the GeV emission of 1LHAASO~J1945+2424, and the first proposed counterparts of 1LHAASO~JJ0056+6343u and 1LHAASO~J2200+5643u.
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All authors Maria Arias, Timothy Shimwell, Martin Hardcastle, Roland Timmerman
High Energy Astrophysical Phenomena
NEXUS: Transient Searches and First Results from Year One Observations
Ming-Yang Zhuang, Lei Hu, Justin D. R. Pierel et al. (+10 more)
We describe ongoing efforts of high-
redshift transient searches using multi-epoch NIRCam imaging (F200W+F444W) and NIRSpec MSA/PRISM spectroscopy from the NEXUS JWST multi-cycle Treasury program targeting the north ecliptic pole region. The transient search area covers $\sim 61.5\,{\rm arcmin^2}$ between the reference epoch and each subsequent NEXUS-Deep epoch at a cadence of $\sim2$~months. In the first year of observations from NEXUS, we detect 68 robust transients, with the host photometric
redshift distribution declining rapidly at $z>2$ but extending to $z_{\rm phot}\approx 6$. In addition, we obtained secure spectroscopic
redshifts for 37 transients ($\sim54\%$) from NIRSpec/PRISM and NIRCam/WFSS, with seventeen at $1 < z < 2$, eight at $2 < z < 3$, two at $3 < z < 4$, and one tentative host association at z = 6.151. Overall, the NEXUS program recovers observed
supernova (SN) rates broadly consistent with other SN search programs with JWST. While NEXUS achieves the highest transient detection efficiency, 6.6 SNe per imaging hr ($2.6\times$ COSMOS-SN and $26\times$ JADES-SN), the limited filter coverage (F200W+F444W only) limits robust identification and classification of high-$z$ SNe for deep spectroscopic follow-up. We describe the details of the data reduction and transient detection pipeline, and report the Year-1 transient sample along with their light curves, available MSA spectroscopy, host association, and the raw detection rate. We also describe and release a new PSF photometry package that properly accounts for correlated pixel noise from combining drizzled images.
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All authors Ming-Yang Zhuang, Lei Hu, Justin D. R. Pierel, Zhiwei Pan, Yue Shen, Adam J. Burgasser, Xiaohui Fan, Luis C. Ho, Junyao Li, Alice E. Shapley, Zachary Stone, Feige Wang, Lifan Wang
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
A New Window for Testing the PPN in the Strong-Field Regime: Stellar Rotation of S301
Mohsen Khodadi and Salvatore Capozziello
The recently discovered S301
star, with an orbital period of 8.7 years and eccentricity $e = 0.982$, reaches a pericenter of just $140\,R_{\mathrm{s}}$ — approximately nine times closer than S2's $\sim 1200R_{\mathrm{s}}$ — offering an unprecedented laboratory for testing strong-field
gravity. We demonstrate that S301's stellar
spin precession provides a novel probe of the PPN parameter $\gamma$, scaling as $(2\gamma_{\mathrm{PPN}} + 1)/3$ relative to general relativity (GR). For maximum projected velocity shifts of $46.1~\mathrm{km\,s^{-1}}$, next-generation spectrographs could constrain $\gamma_{\mathrm{PPN}}$ to $\sim 10\%$ precision. When combined with S301's orbital precession — a substantial $\sim 1.95^\circ$ pericenter advance per orbit (GR prediction), approximately an order of magnitude larger than S2's $\sim 0.2^\circ$, constraining $(2\beta_{\mathrm{PPN}} + 2\gamma_{\mathrm{PPN}} - 1)/3$ — the
spin measurement breaks the $\beta$-$\gamma$ degeneracy. A MCMC analysis of projected S2 and S301 observations yields $\sigma_\beta \approx 2.3 \times 10^{-4}$, with the $\gamma$ precision limited by the
spin precession measurement to $\sigma_\gamma \approx 0.1$. While the
spin precession provides an independent consistency check, its true significance lies in probing
gravity at $\phi/c^2 \sim 10^{-4}$ and $v/c \sim 0.08$ — four orders of magnitude stronger than Solar System tests and an order of magnitude stronger than current S-
star constraints. This complementary approach opens a new window for testing the PPN framework in the strong-field regime and demonstrates the power of combining multiple stellar probes at the Galactic Center.
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