Journal of High Energy Astrophysics最新文献

{"title":"Energetics of magnetized accretion-induced outflows around black holes: Description of a unified disk-jet connection","authors":"Shubhrangshu Ghosh , Sudip Bhattacharyya","doi":"10.1016/j.jheap.2025.100469","DOIUrl":"10.1016/j.jheap.2025.100469","url":null,"abstract":"<div><div>We investigate the global energetics of the magnetized accretion-induced outflow in the context of a two-temperature accreting plasma around black holes (BHs), explicitly incorporating the effect of the ‘Ohmic heating’. We obtain substantially high electron temperature, with <span><math><msub><mrow><mi>T</mi></mrow><mrow><mi>e</mi></mrow></msub></math></span> even reaching <span><math><mo>∼</mo><mn>5</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>10</mn></mrow></msup><mi>K</mi></math></span> in the inner regions of the flow. The radiative cooling is primarily determined by the synchrotron loss which mostly dominates the inner accretion region, more so, in the context of flows towards super massive BHs (SMBHs). However, at a relatively high <span><math><mover><mrow><mi>M</mi></mrow><mrow><mo>˙</mo></mrow></mover><mo>∼</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><msub><mrow><mover><mrow><mi>M</mi></mrow><mrow><mo>˙</mo></mrow></mover></mrow><mrow><mi>Edd</mi></mrow></msub></math></span>, bremsstrahlung emission dominates most of the accretion region. For stellar mass BHs, on the other hand, synchrotron dominates the cooling for a considerable portion of the inner and middle accretion region, with emission cooling rates significantly higher. Electron heating is primarily governed by turbulent Ohmic dissipation, with <span><math><msub><mrow><mi>T</mi></mrow><mrow><mi>e</mi></mrow></msub></math></span> primarily determined by the balance between Ohmic heating and synchrotron cooling. We obtain relatively high values of luminosity reaching <span><math><mo>∼</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>42</mn></mrow></msup><mspace></mspace><mrow><mi>erg</mi><mspace></mspace><msup><mrow><mi>s</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math></span> and surpassing <span><math><msup><mrow><mn>10</mn></mrow><mrow><mn>35</mn></mrow></msup><mspace></mspace><mrow><mi>erg</mi><mspace></mspace><msup><mrow><mi>s</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math></span>, from the inner accretion region, corresponding to <span><math><msub><mrow><mi>M</mi></mrow><mrow><mi>BH</mi></mrow></msub><mo>=</mo><mo>(</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>8</mn></mrow></msup><mo>,</mo><mn>10</mn><mo>)</mo><mspace></mspace><msub><mrow><mi>M</mi></mrow><mrow><mo>⊙</mo></mrow></msub></math></span>, respectively, for moderately advective flows. Based on the estimates of the ratio of ‘mass flow rate into the jet’ to ‘mass inflow rate’ <span><math><mo>(</mo><msub><mrow><mover><mrow><mi>M</mi></mrow><mrow><mo>˙</mo></mrow></mover></mrow><mrow><mi>j</mi></mrow></msub><mo>/</mo><mover><mrow><mi>M</mi></mrow><mrow><mo>˙</mo></mrow></mover><mo>)</mo></math></span>, and comparing our theoretical finding with the ratio of radio-to-X-ray luminosities for several BH X-ray binaries (BHXRBs), we tentatively suggest that both steady and transient jets in BHXRBs could primarily be accretion powered, indicating a ","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100469"},"PeriodicalIF":10.5,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145099039","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Morphology of young massive stellar clusters with next-generation IACTs","authors":"A. Bonollo ,&nbsp;P. Esposito ,&nbsp;A. Giuliani ,&nbsp;P. Caraveo ,&nbsp;G. Galanti ,&nbsp;S. Crestan ,&nbsp;M. Rigoselli ,&nbsp;S. Mereghetti","doi":"10.1016/j.jheap.2025.100465","DOIUrl":"10.1016/j.jheap.2025.100465","url":null,"abstract":"<div><div>The term PeVatron designates astrophysical objects capable of accelerating particles to PeV energies (1 PeV = 10¹⁵ eV). Their nature and particle acceleration mechanisms are uncertain, but ultra-high-energy gamma rays (&gt;100 TeV) are produced when particles accelerated by either leptonic and hadronic PeVatrons interact with the surrounding medium or radiation fields. The atmospheric air shower observatory LHAASO detected photons with energies above 100 TeV from 43 sources in the Galactic Plane, proving the existence of PeVatrons within the Milky Way. In particular, one of the detections was a 1.4 PeV photon in spatial correspondence with Cygnus OB2, providing a strong hint that young massive stellar clusters (YMSCs) can act as PeVatrons.</div><div>The next-generation ground-based Cherenkov telescopes will have unprecedented energy and angular resolution. Therefore, they will be able to resolve spatially YMSCs better than LHAASO. We focused on a sample of 5 YMSCs and their environments visible from either hemisphere with the CTAO or ASTRI Mini-Array. We modelled the secondary gamma-ray emission above 1 TeV and simulated observations of all sources. We devised methods for classifying YMSCs that could be detected as unidentified extended TeV sources and estimate the observational time needed to distinguish the morphology of different classes of sources.</div><div>We study the morphology of the sources in our sample in order to identify their main features. We simulated observations of all sources with the instrument response function (IRF) of CTAO or ASTRI Mini-Array. We compare their emission distribution to the one of the TeV halos observed by HAWC. We parametrize their radial profiles in order to develop methodologies to classify them and to distinguish YMSCs from TeV halos based on their morphology. We expect some feature, such as the emission peak, to be key in differentiating between the two classes of objects. We then test them on a sample of sources of the first LHAASO catalogue.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100465"},"PeriodicalIF":10.5,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145110176","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Exploring year-timescale transient and long-term quasi-periodic oscillations in optical and gamma-ray light curves of blazars","authors":"Ajay Sharma ,&nbsp;Sakshi Chaudhary ,&nbsp;Aishwarya Sarath ,&nbsp;Debanjan Bose","doi":"10.1016/j.jheap.2025.100466","DOIUrl":"10.1016/j.jheap.2025.100466","url":null,"abstract":"<div><div>A comprehensive analysis of quasi-periodic oscillations (QPOs) in the multi-wavelength observations of blazars has been carried out. Utilizing 15 years of Fermi-LAT observations of seven blazars in our sample, we identify both long-term and transient QPOs in the gamma-ray light curves, with timescales ranging from a few months to years. These periodicities were detected using the Lomb-Scargle periodogram (LSP) and REDFIT techniques. To robustly evaluate the statistical significance of the quasi-periodic signals observed in the LSPs, 2<span><math><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>5</mn></mrow></msup></math></span> synthetic <em>γ</em>-ray light curves were generated for each source using a stochastic model known as the Damped Random Walk (DRW). These gamma-ray QPOs are further supported by the detection of optical QPOs exhibiting similar timescales. A cross-correlation analysis between <em>γ</em>-rays and optical emissions reveals a significant peak (<span><math><mo>&gt;</mo><mn>3</mn><mi>σ</mi></math></span>) at or close to zero-lag. To investigate the physical origin of the observed gamma-ray QPOs with different timescales, we explore several plausible scenarios, with particular emphasis on a relativistic jet hosted by one of the black holes in a supermassive binary black hole (SMBBH) system, accretion disc model, and helical motion of magnetized plasma blob within the jet. The transient gamma-ray QPOs of month-like timescales are interpreted within the framework of the helical motion of plasma blob in jet, while the long-duration QPOs with multi-year timescales are explained using the SMBBH scenario. The gamma-ray light curves were modeled by employing a Markov Chain Monte Carlo (MCMC) approach, allowing us to constrain key physical parameters such as the jet Lorentz factor (Γ) and the viewing angle between the observer's line of sight (<em>ψ</em>) relative to the spin axis of SMBH.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100466"},"PeriodicalIF":10.5,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145098696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Galaxy evolution in the local Universe: Group richness effects on mergers and non-mergers","authors":"Pius Privatus ,&nbsp;Umananda Dev Goswami","doi":"10.1016/j.jheap.2025.100468","DOIUrl":"10.1016/j.jheap.2025.100468","url":null,"abstract":"<div><div>In this study, we use the luminous volume-limited samples obtained from the twelfth release of Sloan Digital Sky Survey data and mergers from Galaxy Zoo Project to investigate the influence of group richness in shaping galaxy properties' distributions and their relationships in the local Universe by comparison of mergers and non-mergers. The galaxies were restricted into mass-limited subsamples of low-mass, intermediate-mass and high-mass, assigned into groups from poor to rich group systems, where the distributions of star formation rate (SFR), specific SFR (SSFR), spectral index <span><math><msub><mrow><mtext>D</mtext></mrow><mrow><mi>n</mi></mrow></msub></math></span> (4000) and <span><math><mi>u</mi><mo>−</mo><mi>r</mi></math></span> colour properties between mergers and non-mergers for all subsamples and their relations with stellar mass of galaxies are compared. The study revealed a significant difference in the distributions between mergers' and non-mergers' properties for low-mass galaxies, while for high-mass galaxies the difference is very weak. For the low-mass sample, mergers possess higher SFR, SSFR than non-mergers when the group richness is kept constant, while for high-mass poor group galaxies have higher SFR, SSFR than rich group galaxies when merging status is kept constant. Mergers resemble young stellar populations and are bluer than non-mergers for low-mass, while for high-mass, mergers and non-mergers have comparable SFR, SSFR, <span><math><msub><mrow><mtext>D</mtext></mrow><mrow><mi>n</mi></mrow></msub></math></span> (4000), and <span><math><mi>u</mi><mo>−</mo><mi>r</mi></math></span> colour. The study concludes that group richness and stellar mass influence the mergers' and non-mergers' properties' distributions, and their relationships.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100468"},"PeriodicalIF":10.5,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145098695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spectral energy distribution analysis of the supersoft X-ray source CAL 87: Multiwavelength constraints","authors":"Paulo E. Stecchini ,&nbsp;Francisco Jablonski ,&nbsp;Marcos P. Diaz ,&nbsp;Alexandre S. Oliveira ,&nbsp;Flavio D'Amico ,&nbsp;Natália Palivanas","doi":"10.1016/j.jheap.2025.100467","DOIUrl":"10.1016/j.jheap.2025.100467","url":null,"abstract":"<div><div>We analyse the spectral energy distribution (SED) of the eclipsing supersoft X-ray source CAL<!--> <!-->87 covering wavelengths from X-rays to the near-infrared. Our study incorporates 26 data points across ultraviolet to near-infrared, sourced from published literature, unpublished data, and new observations. In addition, archival <em>XMM-Newton</em> spectra were used to represent the X-ray emission. Care was taken to use out-of-eclipse flux measurements when the irradiated side of the companion faces the observer. The SED model includes contributions from a central source, a reprocessed accretion disk, and an irradiated companion star atmosphere, resulting in a good match to the observed fluxes. The revised and new parameters for the disk and the central source align with previous studies and match expectations for such systems. The temperature of the irradiated side of the companion star was estimated based on its <span><math><mi>B</mi><mo>−</mo><mi>V</mi></math></span> colour during the secondary eclipse. This work highlights the importance of broad wavelength coverage for understanding the properties of supersoft X-ray sources.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100467"},"PeriodicalIF":10.5,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145099037","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Short GRB 090510: A magnetized neutron star binary merger leading to a black hole","authors":"J.A. Rueda ,&nbsp;R. Ruffini ,&nbsp;Yu Wang","doi":"10.1016/j.jheap.2025.100464","DOIUrl":"10.1016/j.jheap.2025.100464","url":null,"abstract":"<div><div>We model the short gamma-ray bursts (GRB) 090510 as the product of a magnetized neutron star (NS) binary merger. Accounting for the NS critical mass constraint given by the mass of PSR J0952–0607, we infer that GRB 090510 was a highly-magnetized NS-NS merger that left as remnant a Kerr black hole (BH) of <span><math><mn>2.4</mn><msub><mrow><mi>M</mi></mrow><mrow><mo>⊙</mo></mrow></msub></math></span> with a low-mass accretion disk. The gamma-ray precursor is powered by the magnetic energy released during the merger of the NSs. The prompt emission originates at the transparency of an ultra-relativistic <span><math><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math></span> pair-plasma produced by the overcritical electric field induced by the rotating strong magnetic field around the merged object before it reaches the critical mass, the GeV emission by the extractable energy of the newborn BH, and the X-ray afterglow by accretion onto it. We derive the masses of the merging NSs, their magnetic fields, the BH mass, spin, and irreducible mass, the strength of the magnetic field, the disk mass, and obtain an estimate of the gravitational-wave emission during the merger phase preceding the prompt short GRB emission. The inferred parameters agree with up-to-date numerical relativity simulations, confirming that strong magnetic fields above 10¹⁴ G develop in NS-NS mergers and that mergers leading to a central BH remnant have low-mass disks of <span><math><mo>∼</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><msub><mrow><mi>M</mi></mrow><mrow><mo>⊙</mo></mrow></msub></math></span>. We also advance the possibility that quasi-period oscillations of tens of Hz of frequency due to Lense-Thirring precession of the matter surrounding the merged object before BH formation can explain the successive spikes following the prompt emission peak.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100464"},"PeriodicalIF":10.5,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145099040","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Is the BKL map an intrinsic feature of the Quantum Mixmaster Universe?","authors":"Simone Lo Franco ,&nbsp;Giovanni Montani","doi":"10.1016/j.jheap.2025.100463","DOIUrl":"10.1016/j.jheap.2025.100463","url":null,"abstract":"<div><div>We study the quantum Mixmaster dynamics by constructing the corresponding Wheeler-DeWitt equation as a relativistic quantum theory in a pseudo-Riemannian Mini-superspace. The transition amplitude from a Kasner regime to the next one is built via the standard S-matrix of a relativistic scattering, and mediated by a single wall potential. We provide a coherent and convincing representation of the original Misner's idea that quasi-classical states can survive arbitrarily close to the cosmological singularity. By constructing a complete set of states, we demonstrate that the quasi-classical BKL map is preserved by the resulting transition amplitude to a new state when their mean total momentum is high enough (exactly coinciding with Misner's high occupation numbers). This scheme is naturally iterated to the initial singularity without appreciable shape changes. We also clarify the role played by the state localization, and, in particular, we outline that when the incoming state is spread, the possibility of violating the Kasner map is no longer negligible. Thus, Kasner-like wave packets can approach the initial singularity.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"49 ","pages":"Article 100463"},"PeriodicalIF":10.5,"publicationDate":"2025-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145095335","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Search for spatial coincidences between galaxy mergers and Fermi-LAT 4FGL-DR4 sources","authors":"Siddhant Manna,&nbsp;Shantanu Desai","doi":"10.1016/j.jheap.2025.100460","DOIUrl":"10.1016/j.jheap.2025.100460","url":null,"abstract":"<div><div>We present a systematic search for spatial association between a high confidence sample of 3,166 morphologically selected galaxy mergers drawn from the initial convolutional neural network (CNN) catalog of 328,151 candidate mergers (<span><span>Ackermann et al., 2018</span></span>) and refined through SDSS cross-matching and the Fermi Large Area Telescope Fourth Source Catalog Data Release 4 (4FGL-DR4) catalog of gamma-ray sources detected by the Fermi Large Area Telescope (LAT). Using a conservative 4<em>σ</em> positional uncertainty threshold and a Poisson based statistical framework, we identify 21 statistically significant associations with match probabilities <span><math><mi>p</mi><mo>&lt;</mo><mn>0.05</mn></math></span>. Among these are known classes of gamma-ray emitters such as Flat-Spectrum Radio Quasars (FSRQs), BL Lacertae objects (BLL), and radio galaxies bolstering the hypothesis that merger driven processes can fuel high energy activity. Intriguingly, five of the associated sources remain unclassified in 4FGL-DR4, hinting at a possible link between galaxy mergers and a hitherto unrecognized population of gamma-ray sources. The dominance of AGN like matches supports the scenario in which mergers trigger accretion onto central supermassive black holes, initiating AGN activity observable at gamma-ray energies. Moreover, the recurrent presence of unassociated sources among secure matches underscores the potential of merger catalogs as physically motivated priors in gamma-ray source identification efforts. This work constitutes the first dedicated effort to explore associations between gamma-ray sources and a large, morphologically selected sample of galaxy mergers (<span><span>Ackermann et al., 2018</span></span>) catalog, opening new avenues for understanding the role of galaxy interactions in high-energy astrophysics. We additionally examined the sample of 70 galaxy pairs from the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey and found no statistically significant matches, with <span><math><mi>p</mi><mo>&lt;</mo><mn>0.05</mn></math></span> within the 4<em>σ</em> positional uncertainty threshold.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"49 ","pages":"Article 100460"},"PeriodicalIF":10.5,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145049371","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pulse-phase resolved spectroscopy of SMC X-1 with AstroSat and NuSTAR","authors":"Pravat Dangal ,&nbsp;Ranjeev Misra ,&nbsp;Nand Kumar Chakradhari","doi":"10.1016/j.jheap.2025.100462","DOIUrl":"10.1016/j.jheap.2025.100462","url":null,"abstract":"<div><div>We report the results of pulse phase-averaged and phase-resolved analyses of the X-ray spectra of SMC X-1 within the 1 to 60 keV energy band during high superorbital phases, observed by AstroSat and NuSTAR. The phase-averaged spectra were well described by both the cutoff powerlaw and Comptonized blackbody models, including Fe emission lines and absorption features. The pulsar was found to be accreting in the Super-Eddington regime, with a mass accretion rate of ∼ (8.7 ± 0.26) × 10¹⁸ gm s⁻¹. A prominent cyclotron absorption line at ∼ 46 keV (NuSTAR) is interpreted as the first harmonic, while weaker features at ∼ 23 keV (AstroSat) and 27 keV (NuSTAR) are likely the supressed fundamental cyclotron resonances. The 6.4 keV Fe line as well as cyclotron line exhibited a clear dependence on the double-peaked pulse profile. The negative correlation of Fe line's equivalent width with X-ray intensity suggests an origin in highly ionized accretion disk transitions, where fluorescence efficiency decreases with high ionization. The positive correlation of cyclotron absorption energy and optical depth with intensity likely arises from beam geometry or accretion dynamics. We estimate the magnetic moment of the neutron star to be within (2.44 ± 0.09 to 2.86 ± 0.08) × 10³⁰ G m³, the Alfven radius (R_<em>A</em>) within (1.77 ± 0.07 to 1.79 ± 0.07) × 10⁸ cm and the Co-rotation radius (R<span><math><msub><mrow></mrow><mrow><mi>c</mi><mi>o</mi></mrow></msub></math></span>) ∼ (1.2 ± 0.09) × 10⁸ cm. Since R_<em>A</em> &gt; R<span><math><msub><mrow></mrow><mrow><mi>c</mi><mi>o</mi></mrow></msub></math></span>, a possible Super-Keplerian Inhibition may potentially induce spin-down episodes—a phenomenon not yet observed in SMC X-1.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"49 ","pages":"Article 100462"},"PeriodicalIF":10.5,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145095334","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spectral and type I X-ray burst studies of M15 X-2 using NICER observations","authors":"M. Varun,&nbsp;Neal Titus Thomas,&nbsp;L. Giridharan,&nbsp;S.B. Gudennavar,&nbsp;S.G. Bubbly","doi":"10.1016/j.jheap.2025.100461","DOIUrl":"10.1016/j.jheap.2025.100461","url":null,"abstract":"<div><div>In this work, we present spectral and burst analyses of three thermonuclear type I X-ray bursts (B1, B2, and B3) detected from the ultracompact neutron star low-mass X-ray binary M15 X-2, using data from the <em>Neutron Star Interior Composition Explorer (NICER)</em>. Time-averaged spectral fitting with the model <span><math><mrow><mi>tbabs</mi><mo>×</mo></mrow><mrow><mo>(</mo><mi>thcomp</mi><mo>×</mo><mi>diskbb</mi></mrow><mo>)</mo></math></span> suggests that the source was in a soft or soft-intermediate spectral state, characterized by a photon power law index of <span><math><mi>Γ</mi><mo>∼</mo><mn>2</mn></math></span> and an average mass accretion rate of ∼0.09 <span><math><msub><mrow><mover><mrow><mi>m</mi></mrow><mrow><mo>˙</mo></mrow></mover></mrow><mrow><mi>E</mi><mi>d</mi><mi>d</mi></mrow></msub></math></span>. The type I X-ray bursts exhibited rapid rise times of 1.25−2.75 s, followed by longer decay phases lasting 14.50−23.25 s, with characteristic burst timescales (<em>τ</em>) of ∼11 s, which are consistent with pure helium burning. Notably, burst B3 displayed a double-peaked profile indicative of a photospheric radius expansion event, from which we inferred the neutron star radius to be <span><math><mn>10.8</mn><mtable><mtr><mtd><mo>+</mo><mn>2.4</mn></mtd></mtr><mtr><mtd><mo>−</mo><mn>2.2</mn></mtd></mtr></mtable></math></span> km. Based on the peak flux of the burst, we estimated the source distance to be <span><math><mn>10.54</mn><mtable><mtr><mtd><mo>+</mo><mn>1.43</mn></mtd></mtr><mtr><mtd><mo>−</mo><mn>1.26</mn></mtd></mtr></mtable></math></span> kpc under the assumption of isotropic emission, and <span><math><mn>14.06</mn><mtable><mtr><mtd><mo>+</mo><mn>1.90</mn></mtd></mtr><mtr><mtd><mo>−</mo><mn>1.68</mn></mtd></mtr></mtable></math></span> kpc for anisotropic emission geometry. A strong ∼420 Hz burst oscillation candidate was detected in the cooling tail of burst B1.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"49 ","pages":"Article 100461"},"PeriodicalIF":10.5,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145095333","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}