High Energy Astrophysical Phenomena · Cross-listed from astro-ph.EP
Energy deposition in planetary and exoplanetary atmospheres induced by cosmic rays
Jesse Polman and Ingo Leya
Cosmic rays can significantly alter the abundances of certain species in the upper layers of planetary atmospheres, especially in terms of their biosignatures. To fully understand the extent of this effect, it is essential to accurately model the interactions of
cosmic rays with planetary
magnetic fields. We used the CosmicTransmutation code to study the effect of a planetary
magnetic field on the flux of galactic
cosmic rays and stellar energetic particles. We found that both particle sources are significantly affected by
magnetic fields, even though the effects are different due to the varying energy ranges that characterize each source. The stellar energetic particle energy flux is significantly higher for an Earth-like
planet with no
magnetic field, but with a
magnetic field of 30\,$\mu$T or higher, the energy flux of the two sources becomes comparable. We find that the atmospheric pressures the
cosmic rays reach are significantly lower than those found in previous studies using simpler models and that the effect of the atmospheric composition on this outcome is small. We found similar results using the model for the
exoplanet K2-18b, even though the radius is significantly larger than Earth's. Because the two
cosmic ray sources cover different energy ranges and are affected by the
magnetic field in different ways as a result, both sources should be considered. Future studies should focus on combining an accurate modelling procedure of the interaction between
cosmic rays and planetary
magnetic fields with atmospheric chemistry models. This will require general circulation models to capture the latitudinal and longitudinal dependencies in full.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Implications of Inelastic Dark Matter for Primordial Dark-Star Evolution: Kinematic Thresholds and Nonthermal Capture
Qinxun Li and Shengyi Liu
The recent 248-keV nuclear recoil candidate reported by LUX-ZEPLIN has renewed interest in endothermic inelastic dark matter, motivating us to examine its capture in primordial dark
stars. Relative to the conventional elastic-capture picture in dark
star evolution, endothermic capture adds two qualitative features. First, it opens only after the growing
star crosses a compactness threshold, expressed as a kinematic radius $R_{\rm kin}\propto\mu_{\chi}M_\star/\delta$ set by the stellar mass, the dark-matter–
nucleus reduced mass and the mass splitting. The accreting growth carries the
star through the threshold, and the capture rate turns on quadratically above it. Second, although newly captured particles generically begin on nonthermal bound orbits, endothermic kinematics can keep this normally transient population spatially extended, turning it into a persistent reservoir rather than an intermediate step toward a thermal core. Following complete chains of state-changing collisions, we find that the reservoir compacts sharply and then stalls, because a ground state particle below a compactness-dependent orbital energy has no allowed up-scatter anywhere in the
star. A percent-level radius contraction reopens the relaxation. These kinematic results do not depend on whether the excited state decays promptly or is long-lived. As a result, inelastic capture does not replenish a thermal annihilation core. The captured population forms an evolving orbital distribution that sets up the co-evolutionary dynamics between the
star and the dark matter in the core and the reservoir, which we develop in a companion paper.
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High Energy Astrophysical Phenomena · Cross-listed from physics.hist-ph
The Crab Nebula progenitor: recovering the 1054 AD supernova event as galactic Gamma-ray burst
Costantino Sigismondi and Remo Ruffini
In 1054 AD a daytime
star appeared in the constellation of Taurus, for three weeks, and it was reported in various sources from Europe to China/Japan: it was one of the few documented galactic
supernovae of the last two millenia. This paradigm has been established about sixty years ago, as the comprehension of the physics of
supernovae progressed with enough observational data. The Gamma-ray bursts were discovered in the same period, but only in the past few years have their observations become daily and their distances have been fully understood as cosmological. After the explosion, the exponential decay of the luminosity in gamma-rays and X-rays has been followed with
telescopes onboard dedicated satellites. Also the exponential decay of the afterglow's optical and
radio frequencies have been observed with the largest optical and
radio telescopes. Within the binary-driven hypernova framework, successful in explaining all the observed phases of the Gamma-ray bursts, the universal exponential decay can be extended to 1000 years after the burst, to account for the present values of Gamma and X-rays as well as optical and
radio frequencies of the Crab Nebula. Both the daytime visibility of the burst, and the simultaneous radiation plagues appeared in Constantinople and Cairo is a strong evidence of the presence of Gamma-rays in the lower atmosphere, coming from the same source originating the Crab nebula. The association to the daytime visibility of that
star and the following plague meets exactly the etymology of the word dis-aster, bad
star.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM
Wide Field Localization Using Fixed Modulation Collimators
Steven E. Boggs
Rapid, precise localization of gamma-ray bursts (GRBs) requires continuous wide-field imaging at hard X-ray and soft gamma-ray energies. We develop a fixed (non-rotating) modulation-collimator architecture to address this challenge. A bigrid collimator, a pair of aligned, periodic slit grids in front of a simple, non-imaging
photon-counting detector, transmits an off-axis source through a triangular fringe pattern whose local angular position, the source phase, is recovered from simultaneous count rates in several grid pairs at fixed relative phase offsets, rather than by mechanically rotating a single grid pair as in the classical rotating modulation collimator. Four-phase demodulation of these count rates robustly cancels detector background and grid leakage without requiring rotation. Because the fringe pattern repeats across the sky, a phase measurement corresponds to many candidate source positions; we resolve this ambiguity over an arbitrarily wide field of view using a cascade of progressively coarser-pitched grid stages, generalizing the two-grid vernier-scale technique originally used to localize Sco X-1. This vernier cascade technique reduces the required
photon counts and grid-calibration accuracy required to achieve fine angular resolution over a broad field of view. Generalized to two dimensions with orthogonal cascades, the resulting architecture achieves wide-field localization with no moving parts, no time modulation, and only simple
photon-counting detectors, a promising candidate for simple, inexpensive, continuous-monitoring instruments supporting time-domain and multi-messenger astrophysics.
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High Energy Astrophysical Phenomena
Associating binary black holes with galactic centres using lensed gravitational waves
Laura Uronen, Tian Li, Qiuhan He et al. (+4 more)
Binary black holes (BBHs) have been theorised to form through various different channels, but current LIGO-Virgo-KAGRA (LVK) sky locations make the direct study of formation channels a challenge. Association of strongly lensed BBHs to their hosts has been shown to be possible with current detector networks at upgraded sensitivity and survey
telescopes like Euclid, with localisations that can reach sub-galactic scales in the source plane. With Hubble Space
Telescope-like high-resolution imaging, we report that strong-
lensing localisation of BBHs allows us to confidently associate the BBH with specific structures within their host
galaxies, specifically, galactic centres (GCs). We demonstrate that a BBH localised to the GC of the
galaxy can reject light-tracing BBH populations ($p < 5\%$) in a single observation, and in most cases demonstrate high confidence rejection ($p < 1\%$), providing a conservative basis to exclude light-tracing spatial distributions associated with field-like or non-central formation channels. Such association therefore directly supports formation channels confined to GCs, such as active galactic
nuclei and nuclear stellar clusters.
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All authors Laura Uronen, Tian Li, Qiuhan He, Justin Janquart, Thomas Collett, Léon V.E. Koopmans, Otto Hannuksela
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Testing Source Dependence in Gravitational-Wave Tests of General Relativity with Mutual Information
Yi-Fan Wang
Phenomenological deviation parameters used in gravitational-wave tests of general relativity need not represent universal fundamental properties of the sources. Instead, a deviation parameter can be a derived quantity that depends on source properties. Apparent violations of general relativity arising from waveform systematics or data-quality issues can also depend on source properties. In addition to diagnosing individual events, it is helpful to identify systematic trends at the population level. We introduce a nonparametric framework that uses mutual information to test whether the deviations depend on source properties. We validate the framework using simulations with massive graviton waveforms. Assuming we do not have prior knowledge of the underlying theory, massive graviton effects can be captured by a parameterized post-Einstein coefficient that is expected to depend on the luminosity distance and source mass. The results show that the mass and distance dependencies become clear for graviton masses of $\geq 1\times10^{-22}\,\mathrm{eV}$ at detector sensitivities representative of the current fourth observing run, while the controlled general relativity simulations yield null results. We then analyze public real-data products for tests of general relativity from GWTC-4.0 and 4-OGC, including phenomenological parameterized tests, modified dispersion tests, and parity violation tests. The phenomenological deviation parameters have tentative correlations with effective
spin, and correlations of modified-dispersion or parity-violation parameters with source mass are visible. These results demonstrate that catalog-level dependence can identify patterns and thus be used to diagnose the origin of deviations in testing general relativity. The framework therefore complements single-event analyses and parameterized hierarchical population tests.
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High Energy Astrophysical Phenomena
Anisotropic wind in tidal disruption events
Paola Martire, Elena Maria Rossi, Nicholas Chamberlain Stone et al. (+2 more)
Over the coming years, the number of tidal disruption events (TDEs) is expected to substantially increase with observations from the Vera Rubin Observatory (g and r band) and ULTRASAT (near UV) wide-field surveys. These future samples have great promise to characterize the bottom end of the massive black hole mass function, but existing detections of intermediate mass black hole TDEs are primarily in X-rays, leaving their optical/UV emission largely unexplored. We present a time- and angle-dependent analysis of the outflow produced by dissipation near pericentre in a three-dimensional end-to-end radiation-hydrodynamics simulation of a TDE by a $10^4 M_\odot$ black hole with realistic parameters, run with the code RICH. We find that outflow anisotropy produces viewing-angle-dependent observables. Towards the poles and the pericentre region, mass-loss rates are low and bolometric luminosities reach $\sim2$–$3$ times the Eddington luminosity. Towards the stream, the properties show a stronger dependence on latitude: the mass-loss rate increases and the bolometric luminosity decreases as the line of sight approaches the orbital plane. These denser regions favour H$\alpha$ and H$\beta$ emission. Despite these variations, all viewing directions show a common spectral
evolution, with an initial soft X-ray
flare followed (around $1.25t_{\rm fb}\approx3$~days) by the reprocessing of shock-powered emission into the UV and optical bands. Although the optical/UV luminosities we predict for this TDE are likely too dim for past surveys (e.g. ASAS-SN, ZTF), they are within the detection capabilities of LSST and ULTRASAT to horizons of $\sim 790$ and $\sim 340$ Mpc, respectively, for the brightest viewing directions.
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All authors Paola Martire, Elena Maria Rossi, Nicholas Chamberlain Stone, Elad Steinberg, Itamar Giron
High Energy Astrophysical Phenomena
The first MeerKAT S-band globular cluster pulsar survey
Rouhin Nag, Marta Burgay, Alessandro Ridolfi et al. (+19 more)
Globular clusters are efficient factories of recycled
pulsars, but searches toward high-dispersion-measure (DM) clusters can be strongly limited near 1 GHz by dispersive smearing and interstellar scattering. We present the first MeerKAT S-band (nu ~ 2.4 GHz)
pulsar survey of 14 globular clusters. High time- and frequency-resolution observations were searched using segmented acceleration and jerk techniques, followed by candidate folding and targeted folding with available timing ephemerides. We re-detected 39 known
pulsars and discovered four new millisecond
pulsars in Glimpse-C01: J1848-0129C, D, E, and F. Multi-epoch follow-up enabled preliminary Keplerian orbital fits for J1848-0129C and J1848-0129D. J1848-0129C is an eclipsing MSP in a ~5 d orbit, placing it among long-period eclipsing systems known as huntsman binaries, while J1848-0129D is in a ~3.4 d nearly circular orbit with a massive white-dwarf companion of about 1 solar mass. Two Glimpse-C01
pulsars show large DM offsets from the cluster average. Comparison with other Galactic globular clusters indicates that intracluster DM spreads tend to increase with foreground DM, implying that narrow DM search windows may be sub-optimal for high-DM clusters. From detections and non-detections, we infer a practical single-epoch MeerKAT S-band tied-array detectability scale of about 10-20 microJy. These results demonstrate the value of high-frequency searches for
pulsars in strongly dispersed and scattered cluster environments.
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All authors Rouhin Nag, Marta Burgay, Alessandro Ridolfi, Federico Abbate, Andrea Possenti, Paulo C. C. Freire, Scott M. Ransom, Miquel Colom i Bernadich, Michael Kramer, Benjamin W. Stappers, Ewan D. Barr, Rene P. Breton, Vivek Venkatraman Krishnan, Prajwal V. Padmanabh, Weiwei Chen, David J. Champion, Maciej Serylak, Alessandro Corongiu, Mario Cadelano, Vishnu Balakrishnan, Arunima Dutta, Dhanraj Risbud
High Energy Astrophysical Phenomena
Extended gamma-ray emission in the vicinity of the Westerlund 1 massive star cluster and Kes 41 supernova remnant seen by the Fermi Large Area Telescope
L. Tibaldo, R. Bernet, L. Härer et al. (+5 more)
There is growing evidence for
cosmic-ray acceleration in massive stellar clusters. Furthermore, extended gamma-ray emission suggests that particle transport in the vicinity of their sources is influenced by physical processes markedly different from large-scale
diffusion in the Milky Way. We characterize extended gamma-ray emission in the direction of the Westerlund 1 stellar cluster and Kes 41
supernova remnant using > 16 years of data from the Fermi Large Area
Telescope (LAT) at energies > 0.8 GeV. We test whether clusters of gamma-ray sources not associated to multiwavelength counterparts are better described by extended emission components. We report the detection of three new extended emission components with soft spectra towards regions of high gas column density in the Galactic plane. One extended component associated with the natal cloud of Kes 41 is statistically preferred over the point source previously reported towards the
supernova remnant shell. The other two extended components overlap with neutral gas within ~100 pc from the edge of the Westerlund 1 superbubble. The extended emission may be explained either by mismodeled gas in the interstellar background model or by the local injection of particles. Under the latter hypothesis, explaining the component associated with Kes 41 requires converting $\lesssim 5\%$ of the
supernova remnant energy into accelerated particles, while accounting for the two components near Westerlund 1 requires converting $10^{-4}$ of the cluster wind mechanical power into gamma rays. Nevertheless, our results strengthen the evidence for gamma-ray emission structures arising at intermediate spatial scales between isolated objects and the large-scale diffuse emission from the interstellar medium. This could explain a part of the soft unassociated Galactic sources detected by the Fermi LAT. (Abridged)
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All authors L. Tibaldo, R. Bernet, L. Härer, M. Lemoine-Goumard, L. Mohrmann, G. Peron, B. Reville, T. Vieu
High Energy Astrophysical Phenomena
Hadronic origin of gamma rays and neutrinos from blazars: Multi-messenger implications and observational constraints
Rodrigo Sasse and Rita de Cássia dos Anjos
We investigate whether cosmogenic gamma rays and
neutrinos from ultra-high-energy
cosmic rays (UHECRs) produced in hadronically active blazars can significantly contribute to the observed spectral energy distribution (SED), and examine the potential of the Cherenkov
Telescope Array Observatory (CTAO) to detect and discriminate this component. For four nearest
neutrino bright blazars modeled by Rodrigues (2024), specifically AP Librae, TXS 1700+685, PKS 2326$-$502, and PKS 2345$-$16, we constrain the UHECR luminosity by requiring that the total emission does not overshoot available multi-wavelength data, assuming acceleration in the optically thin large scale jet, propagate UHECRs through realistic Galactic and extragalactic
magnetic fields, and forecast CTAO performance. We find that cosmogenic gamma rays contribute up to about 7.5% of the total gamma-ray emission at the highest energies ($10^{20}$ eV), and thus remain subdominant in the SED. In contrast, the associated
neutrino emission, at approximately $10^{44}$ to $10^{46}$ erg s$^{-1}$, offers a robust propagation signature of hadronic acceleration. Our simulations of 50 hour CTAO exposures show that the observatory can accurately reconstruct the intrinsic gamma ray spectrum, enabling strong constraints on the hadronic origin and propagation of UHECRs. These results demonstrate the power of combining CTAO gamma-ray measurements with
neutrino observations to probe blazar hadronic processes.
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High Energy Astrophysical Phenomena
Search for refractive substructure in active galactic nuclei using ground-based VLBI observations
Tatiana A. Koryukova, Alexander V. Plavin, Alexander B. Pushkarev et al. (+1 more)
We present the results of the first systematic search for refractive scattering substructure in active galactic
nuclei (AGN) using ground-based very long baseline interferometry (VLBI) data. We selected 1074 AGNs showing a steep frequency dependence of their angular sizes and compared the observed long-baseline visibility amplitudes with the predictions of the refractive substructure model for scatter-broadened images. Nine sources showed consistency with the expected level of refractive noise, including the
quasar TXS 2005+403 (J2007+4029), which confirms previously reported results for this source. Remarkably, the majority of these AGNs are located in the Cygnus region – one of the key “hotspots” of strong Galactic scattering. For five selected AGNs, we identified at least two epochs with sufficiently high data quality showing long-baseline detections, suggesting the presence of scattering substructure. We showed that refractive scattering substructure in AGN is a rare effect, requiring high sensitivity, sufficient source brightness, and lines of sight with particularly strong
turbulence in the interstellar medium. Nevertheless, AGNs can serve as powerful probes of the turbulent interstellar medium. We discuss strategies for improving the sensitivity of VLBI observations and identify the most promising sources for reliable detection and investigation of refractive substructure in future observations.
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All authors Tatiana A. Koryukova, Alexander V. Plavin, Alexander B. Pushkarev, Yuri Y. Kovalev
High Energy Astrophysical Phenomena
Orthogonal polarization modes of nonbirefringent origin in a geometric radio pulsar signal model
J. Dyks, L. Saha and A. Frankowski
Motion of
plasma in
pulsar magnetospheres essentially follows bent
magnetic field lines which may result in radiation beams sweeping past the observer's sightline. We show that under certain conditions such a passing beamlet can produce two orthogonal polarization modes (OPMs) solely from averaging of radiative contributions, without involving birefringence. This requires that radiation from different stages of the passage is contributed incoherently, hence that the timescale for the coherence is much shorter than the typical sampling time. The model produces two OPMs of comparable amount, with a wide range of (single-pulse) polarized fractions, which is consistent with general observed
pulsar properties. Under the specific conditions required (essentially incoherent summation of signal at appropriate time scale) the averaging effects alone can thus lead to the appearance of two orthogonal polarization tracks with OPM jumps.
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High Energy Astrophysical Phenomena
Evidence of a Low-Energy Cutoff in the Injected Spectrum of a Pulsar Wind Nebula
Zhihong Shi, C.-Y. Ng, Niccol`o Bucciantini et al. (+5 more)
Bow-shock
pulsar wind nebulae (PWNe) are synchrotron sources formed when the outflow of supersonic
pulsars is confined by the surrounding interstellar medium. These sources are dominated by freshly injected particles, thus providing a unique laboratory for studying particle acceleration in relativistic outflows. The Mouse is a prototypical bow-shock PWN and is bright in the
radio and X-ray bands, enabling detailed multi-wavelength spectral modeling. With data from 17
telescopes, the Mouse is detected from 118 MHz to 353 GHz, covering over 3 decades in frequency, and in X-rays from 0.5 to 30 keV. A clear spectral break is identified at 3.7 GHz. The
radio spectrum exhibits a rising trend at low frequency, peaks at the break, and then declines. We find a change in spectral index $\Delta\alpha=0.65\pm0.05$ across the break. We attribute this to an intrinsic cutoff or steepening in the injected particle distribution. This could indicate the characteristic energy of leptons leaving the
pulsar magnetosphere, or energy dissipation after the particles cross the termination shock.
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All authors Zhihong Shi, C.-Y. Ng, Niccol`o Bucciantini, B. M. Gaensler, Zhen Yan, David J. Wilner, Douglas C.-J. Bock, Hua-bai Li
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Prospects of electromagnetic follow-up of neutron star-black hole mergers in the LIGO-India era
Yogita Kumari, Kanchan Soni and Sanjit Mitra
Neutron star-black hole (NSBH) mergers are promising multimessenger sources, but only a subset is expected to produce detectable electromagnetic (EM) counterparts, depending on the binary mass ratio, black hole (BH)
spin, and
neutron star (NS) equation of state (EoS). We investigate the prospects for detecting kilonova counterparts to NSBH mergers in the LIGO-India era using the Vera C. Rubin Observatory (Rubin). We simulate GW230529-motivated NSBH populations with two effective tidal deformability ranges, estimate gravitational-wave detections for the LHV (LIGO-Livingston, LIGO-Hanford, Virgo) and LHVA (LHV with LIGO-India at Aundha) detector networks, and model the detectability of the associated kilonova emission with Rubin. We find that adding LIGO-India approximately doubles the number of EM follow-ups, primarily by increasing the duty cycle and reducing the median sky-localization area, and notably increases the number of such detections at large distances. For fixed-exposure strategies, the EM detection rate saturates at exposure times of a few hundred seconds, reflecting the trade-off between depth and sky coverage. We therefore introduce an event-specific exposure-time optimization strategy based on the expected counterpart brightness and sky-localization area. With this strategy, the expected NSBH GW+EM detection rate per year is 4.19(-3.58,+9.66) for the optimistic and 0.79(-0.68,+1.83) for the conservative population with the LHVA network, compared to 1.46(-1.25,+3.37) and 0.27(-0.23,+0.62), respectively, for LHV. The required Rubin follow-up time remains within the expected Target-of-Opportunity allocation. These results show that in the next decade, a few such NSBH follow-ups may take place, with a fraction of them in the
redshift range of about 0.1-0.2, which will not only be useful for measuring the Hubble constant but can also help us in probing the Hubble parameter.
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High Energy Astrophysical Phenomena
Time-Correlated Profile Variability in the MeerKAT Pulsar Timing Array
Bhavnesh Bhat, Michael J. Keith, E. Carli et al. (+2 more)
Long-term pulse-profile variability has emerged as a potentially important source of uncertainty for high-precision
pulsar timing, as changes in the integrated pulse shape can bias pulse times of arrival and affect the sensitivity of
pulsar timing arrays to nanohertz gravitational waves. We present a systematic search for long-term pulse-profile variability in the six-year MeerKAT
Pulsar Timing Array data, analysing observations of 84 millisecond
pulsars using a two-dimensional Gaussian-process framework to identify coherent temporal and phase-dependent profile
evolution. We detect pulse-profile variability in 18
pulsars. Using the frequency dependence of the observed profile
evolution together with scattering simulations, we classify six
pulsars as exhibiting chromatic variability consistent with interstellar scattering, while the remaining twelve display predominantly frequency-independent behaviour suggestive of intrinsic changes in the
pulsar emission process. Correcting for the S/N-dependent detection bias, we infer that intrinsic profile variability is substantially more common than implied by the detected sample, with at least 40 per cent of millisecond
pulsars exhibiting intrinsic profile variability at the 95 per cent credible level. Motivated by the association between pulse-profile variability and
spin-down-rate ($\dot{\nu}$) switching in canonical
pulsars, we search for corresponding $\dot{\nu}$ variations but find no statistically significant detections. Simulations indicate that the expected variations remain below the sensitivity of current
datasets, although unresolved changes may contribute to weak achromatic timing noise. These results suggest that long-term pulse-profile variability may be common among millisecond
pulsars and should be explicitly modelled in future high-precision
pulsar-timing experiments.
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All authors Bhavnesh Bhat, Michael J. Keith, E. Carli, R. M. Shannon, Benjamin W. Stappers
High Energy Astrophysical Phenomena
1LHAASO J1852+0050u: GeV-100TeV Gamma-ray emission Powered by Star-forming Region?
The LHAASO Collaboration
Star-forming regions (SFRs), including HII regions, have recently attracted significant
attention as potential sites of particle acceleration capable of producing PeV
cosmic rays, i.e. as potential Galactic PeVatrons. Yet, SFRs known as candidate PeVatrons are still very rare. Here we report a highly likely physical association between the UHE gamma-ray source 1LHAASO J1852+0050u and coincident
star-forming regions. Using $\sim$4 years of LHAASO data, the extended source 1LHAASO J1852+0050u (called J1852 in this study) was reanalyzed with a significance of $\sim$13$\sigma$ and 39%-containment radius of 0.35$\deg$. This extended source projectively covers dozens of HII regions and an energetic
pulsar PSR J1853+0056. We reanalyzed $\sim$16 years of Fermi-LAT data and found a GeV source (named SrcAG) coincident with the LHAASO source J1852. The CO-line observation shows a molecular clump which coincides with the gamma-ray sources and is related with the ultra-compact HII region G34.26+0.15 at the distance of $\sim$3.3 kpc. Fitting to the spectral energy distribution indicates that PSR J1853+0056 cannot afford the observed gamma-ray flux either for J1852 or SrcAG. Although the contribution from hidden
pulsars to the gamma-ray emission could not be excluded, it is most likely that the GeV-100TeV gamma-ray emission is dominantly powered by SFR through p-p hadronic interaction between the
protons accelerated in the SFR and MCs: the GeV emission is ascribed to the
protons accelerated by protostars' activities, while the TeV emission ascribed to the
protons accelerated by massive
stars in the SFR.
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High Energy Astrophysical Phenomena
Aarmed with Data: Bumps, Outflows, and Disk-like Emission in TDE 2025aarm
Aysha Aamer, Kate D. Alexander, Charlotte R. Angus et al. (+43 more)
The origin of the optical emission in tidal disruption events (TDEs) remains one of the major outstanding questions in the field, in part due to the limited number of nearby events with high-cadence monitoring to track their evolving photometric and spectroscopic properties. We present multi-wavelength observations of the nearby ($z=0.01368$) TDE\,2025aarm, including near-daily spectroscopic coverage prior to the optical peak. Its proximity makes it one of the brightest TDEs discovered, reaching a peak magnitude of $m_r\sim15.5$ ($M_r\sim-18$). The light curve deviates from a smooth
evolution, exhibiting multiple rebrightening episodes visible in both the individual filter light curves and the bolometric luminosity. Blackbody modelling reveals that these rebrightenings are associated with an increase in temperature of $> 5,000-10,000$\,K, while the inferred photospheric radius remains approximately constant. Simultaneously, the H$\alpha$ line not only increases in blueshift but also broadens, suggesting a link between the continuum rebrightenings to changes in the kinematics of the line-forming gas. We identify a persistent absorption component at $\sim-3900$\,km\,s$^{-1}$ in multiple Balmer lines, providing further evidence for outflowing material. The H$\alpha$ profile also exhibits excess flux compared to a Gaussian on both sides of the line, inconsistent with simple scattering-dominated outflow models. Disk-profile modelling provides evidence for the emergence of a disk-like component least $\sim20$ days after peak, with substantial changes in the disk properties between $\sim50$ and 60 days. These observations highlight the complexity of TDE emission processes and demonstrate how dense multi-wavelength monitoring can disentangle the roles of
accretion, reprocessing, and outflows in shaping TDE emission.
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All authors Aysha Aamer, Kate D. Alexander, Charlotte R. Angus, Panos Charalampopoulos, Megan Newsome, Iair Arcavi, Giorgos Leloudas, Matt Nicholl, Jennifer Andrews, Katie Auchettl, Thomas de Boer, K. Azalee Bostroem, Y.-Z. Cai, Kenneth C. Chambers, Collin T. Christy, Sara Faris, Noah Franz, Sebastian Gomez, Maider González-Bañuelos, Mariusz Gromadzki, Paul J. Groot, Claudia Gutiérrez, Brian Hsu, Mark Huber, Thomas L. Killestein, Chien-Cheng Lin, Thomas B. Lowe, Peter Lundqvist, Dylan Magill, Seppo Mattila, Francesca Onori, Gregory S. H. Paek, Jeniveve Pearson, Miika Pursiainen, Niko Pyykkinen, Conor Ransome, Sara Romagnoli, Jennifer Shi, Manisha Shrestha, Nathan Smith, Maximilian Stritzinger, Bhagya Subrayan, Richard Wainscoat, Ziyang Y. Wang, Simon de Wet, Hannah Wichern
High Energy Astrophysical Phenomena
The Evolution of Thermal and Non-thermal Emission Components in GRB 250920C
Jia-Ming Chen, Ke-Rui Zhu, Shan Chang et al. (+5 more)
We present a temporal and time-resolved spectral analysis of GRB 250920C using Fermi/GBM and Swift/BAT data. The
prompt emission consists of two distinct episodes, EI and EII, separated by a significant quiescent interval. We perform
Bayesian spectral fitting with empirical, thermal, composite, and physical synchrotron models. In EI, the spectra show clear evidence for an additional thermal component. The BB+PL model is preferred in most bright time bins, and joint Fermi/GBM+Swift/BAT fits further support the presence of this component. The blackbody temperature generally decreases with time, the blackbody flux follows the pulse profile, and the thermal flux fraction remains high. Fireball-parameter estimates give a photospheric Lorentz factor of a few hundred and an initial radius of $r_{0}\sim10^{9}$–$10^{10}$ cm, with $1+\sigma_{0}$ of order unity and $\eta\gg1$, supporting a thermally dominated baryonic outflow. In contrast, EII is dominated by non-thermal emission. Its low-energy
photon indices do not significantly exceed the synchrotron line of death, and the spectra are well described by fast-cooling synchrotron radiation in a decaying
magnetic field. The magnetization constraint gives $\sigma_{\min}\sim1.1$–$4.3$. Since these values exceed unity, they suggest that EII may be Poynting-flux dominated. These results therefore suggest a possible transition in GRB 250920C from a fireball-dominated EI phase to a Poynting-flux-dominated EII phase.
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All authors Jia-Ming Chen, Ke-Rui Zhu, Shan Chang, Dan Zhu, Yu-Lu Gong, Zhao-Yang Peng, Yong-Gang Zheng, Li Zhang
High Energy Astrophysical Phenomena
Searching for Type Ia Supernovae in the Dark Energy Spectroscopic Instrument
Xiaoyu Zhuang, Song Ran, Dezheng Meng et al. (+9 more)
With the development of large-scale photometric surveys, an increasing number of
supernova candidates are being discovered, leading to a rapidly growing demand for
supernova spectra. In addition to equipping photometric surveys with follow-up spectroscopic facilities, archival spectra from large multi-object spectroscopic surveys can be mined to provide spectroscopic classifications for candidates and to find
supernovae missed by previous surveys. In this work, we combine Principal Component Analysis (PCA), the Local Outlier Factor (LOF)
algorithm, and the
supernova classification tool SNID to search for Type Ia
supernovae among 1,757,303
galaxy spectra from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1). We finally obtain 247 Type Ia
supernovae and 17
supernovae of other types. Among these, 202
supernovae lack classification records in the Transient Name Server (TNS) and represent newly identified SNe. These results demonstrate the potential of multi-object spectroscopic surveys to supplement
supernova samples, particularly for transients missed by traditional photometric surveys.
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All authors Xiaoyu Zhuang, Song Ran, Dezheng Meng, Weiyu Ding, Ranfang Zheng, Yao Yao, Zheyu Lin, Bingxue Fu, Fujia Li, Zelin Xu, Jie Song, Xu Kong
High Energy Astrophysical Phenomena
Pulse Signal Simulation of Pulsars
Jalormi Brahmachari and Mayuresh Surnis
The present thesis is a work in progress on improving the simulation of integrated pulse profiles of
pulsars.
Pulsars, highly magnetized rotating
neutron stars, serve as precise
cosmic clocks useful for studying
gravity and the interstellar medium. Although periodic pulses from many
pulsars are observed and modeled at differ- ent
radio frequencies, a robust realistic simulation of their profiles utilizing their parameters remain underdeveloped. The present study focuses on developing a physically consistent model to reproduce observed pulse shapes across multiple frequencies. This study will be useful in coherently understanding the various as- pects of the
pulsar emission mechanism. These integrated pulse profiles are the time-averaged properties of
pulsar emission and are obtained after averaging indi- vidual pulses over a few thousand rotations. Observed to be highly stable, these are indicative of the global properties of the
pulsar magnetosphere. By refining simulation techniques and incorporating the propagation effects of the interstellar medium, this work will prove to be helpful in generating synthetic, yet realistic models. The results are expected to contribute to the interpretation of observa- tional data and to the development of improved timing and emission models for
pulsars
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA
Time-Domain Dust Astrophysics. II. TransRAT: Time-Dependent Grain Alignment and Disruption by Cosmic Transients and Their Observational Signatures
Thiem Hoang
We introduce TransRAT, a self-consistent time-domain framework that follows the coupled dynamical response of dust to transient irradiation and predicts its observable signatures. We apply TransRAT to a Type~IIP
supernova illuminating a one-zone molecular cloud. Radiative heating raises the grain temperature, modifying the
magnetic susceptibility and Larmor precession, while the enhanced radiation field accelerates radiative precession and can switch the
alignment axis from the
magnetic field (B-RAT) to the radiation direction (k-RAT). Simultaneously, strong RATs align grains faster than gas randomization, extending fast
alignment to smaller grain sizes, and disrupt large grains through RAT disruption (RAT-D), irreversibly modifying the grain size distribution. As the transient fades, the
alignment axis returns to ${\bf B}$ at a rate controlled by the
magnetic susceptibility, whereas the enhanced aligned-grain population and RAT-D-modified grain size distribution can persist long after the radiation has faded- referred to as physical
memory effects. The time-dependent
evolution of grain
alignment and disruption produces distinctive observational signatures: a
flare in extinction and thermal dust polarization followed by a RAT-D-induced dip; a blueward shift of the polarization peak $\lambda_{\max}$; a polarization-angle rotation equal to the projected ${\bf B}$–${\bf k}$ separation ($45^{\circ}$ for our adopted geometry) when RAT-D removes large high-$J$ aligned grains and leaves low-$J$ grains aligned with kRAT followed by angle reverberation as
alignment returns to ${\bf B}$; and a non-monotonic
evolution of $R_V$. The persistent observational manifestations of the transient irradiation, including enhanced polarization, blueshifted $\lambda_{\max}$, modified $R_V$, and polarization-angle
evolution, constitute fossil imprints of past
cosmic transients.
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