Pub Date : 2025-10-21DOI: 10.1016/j.jheap.2025.100499
Shang Li
A systematic search for γ-ray emission from luminous infrared galaxies is conducted using 16 years of Fermi-LAT data in the energy range from 300 MeV to 500 GeV. Five galaxies are first identified with a test statistic (TS) greater than 16.0. A significant γ-ray signal, spatially coincident with IRAS 17578-0400, has been detected with a significance of ∼ 6.3σ. The γ-ray flux exhibits significant variability over the observation period. Moreover, the γ-ray luminosity exceeds the value predicted by the correlation between γ-ray luminosity and total infrared luminosity. The γ-ray emission may originate from an active galactic nucleus in IRAS 17578-0400. Gamma-ray emissions have been detected from two galaxies (NGC 2369 and IC 4280) with a significance greater than 5σ. However, since there are other potential γ-ray emitters spatially coincident with the two sources, the possibility that these signals are caused by other sources cannot be ruled out. Two other galaxies, IRAS 21101+5810 and MCG+08-11-002, show evidence of γ-ray emission, making them promising targets for future studies.
{"title":"Search for GeV emission from luminous infrared galaxies with 16 years of Fermi-LAT data","authors":"Shang Li","doi":"10.1016/j.jheap.2025.100499","DOIUrl":"10.1016/j.jheap.2025.100499","url":null,"abstract":"<div><div>A systematic search for <em>γ</em>-ray emission from luminous infrared galaxies is conducted using 16 years of <em>Fermi</em>-LAT data in the energy range from 300 MeV to 500 GeV. Five galaxies are first identified with a test statistic (TS) greater than 16.0. A significant <em>γ</em>-ray signal, spatially coincident with IRAS 17578-0400, has been detected with a significance of ∼ 6.3<em>σ</em>. The <em>γ</em>-ray flux exhibits significant variability over the observation period. Moreover, the <em>γ</em>-ray luminosity exceeds the value predicted by the correlation between <em>γ</em>-ray luminosity and total infrared luminosity. The <em>γ</em>-ray emission may originate from an active galactic nucleus in IRAS 17578-0400. Gamma-ray emissions have been detected from two galaxies (NGC 2369 and IC 4280) with a significance greater than 5<em>σ</em>. However, since there are other potential <em>γ</em>-ray emitters spatially coincident with the two sources, the possibility that these signals are caused by other sources cannot be ruled out. Two other galaxies, IRAS 21101+5810 and MCG+08-11-002, show evidence of <em>γ</em>-ray emission, making them promising targets for future studies.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100499"},"PeriodicalIF":10.5,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145364108","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}
Pub Date : 2025-10-21DOI: 10.1016/j.jheap.2025.100498
Muhammad Yarahmadi, Amin Salehi
<div><div>We present a comprehensive analysis of the Barrow–Tsallis Holographic Dark Energy (BTHDE) model within a spatially flat FLRW cosmology, focusing on a comparative assessment between traditional Markov Chain Monte Carlo (MCMC) methods and a Bayesian Physics-Informed Neural Network (PINN). By embedding the modified Friedmann dynamics directly into the learning architecture, the Bayesian PINN framework enforces physical consistency while enabling efficient posterior sampling. We employ a broad suite of cosmological observations, including Planck 2018 CMB temperature and polarization data, CMB lensing, Baryon Acoustic Oscillations (BAO), Cosmic Chronometers (CC), and the Pantheon+ Type Ia supernovae compilation, to jointly constrain the Hubble constant <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span>, the Tsallis nonextensive parameter <em>q</em>, Barrow exponent Δ, Granda–Oliveros cutoff parameters <em>α</em> and <em>β</em>, and the total neutrino mass <span><math><mi>Σ</mi><msub><mrow><mi>m</mi></mrow><mrow><mi>ν</mi></mrow></msub></math></span>. In the late-time (CC + Pantheon+) analyses, we adopt flat, physically motivated priors on the baryon and cold dark matter densities (<span><math><msub><mrow><mi>Ω</mi></mrow><mrow><mi>b</mi></mrow></msub><msup><mrow><mi>h</mi></mrow><mrow><mn>2</mn></mrow></msup></math></span> and <span><math><msub><mrow><mi>Ω</mi></mrow><mrow><mi>c</mi></mrow></msub><msup><mrow><mi>h</mi></mrow><mrow><mn>2</mn></mrow></msup></math></span>) solely for the internal calibration of the sound horizon <span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>d</mi></mrow></msub></math></span>, without employing any Planck-based or early-universe likelihoods. The Bayesian PINN consistently yields sharper posterior distributions than MCMC, particularly for <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> and <span><math><mi>Σ</mi><msub><mrow><mi>m</mi></mrow><mrow><mi>ν</mi></mrow></msub></math></span>, while ensuring solution smoothness and dynamical compatibility. Both methods place the inferred <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> values between the Planck and SH<sub>0</sub>ES estimates, lowering the Hubble tension to the 1.3<em>σ</em>–2.1<em>σ</em> range. In the MCMC framework, combined CMB and low-redshift datasets constrain <span><math><mi>Σ</mi><msub><mrow><mi>m</mi></mrow><mrow><mi>ν</mi></mrow></msub><mo><</mo><mn>0.114</mn><mspace></mspace><mtext>eV</mtext></math></span> and <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>=</mo><mn>70.6</mn><mo>±</mo><mn>1.35</mn><mspace></mspace><mtext>km/s/Mpc</mtext></math></span>. Our results demonstrate the viability of the BTHDE model as a compelling alternative to ΛCDM and highlight the complementary strengths of Bayesian PINNs and MCMC in probing extended dark energy scenarios governed by generalized entropy frameworks.</div><
{"title":"A comparative Bayesian PINN–MCMC analysis of Barrow–Tsallis holographic dark energy with neutrinos: Toward resolving the Hubble tension","authors":"Muhammad Yarahmadi, Amin Salehi","doi":"10.1016/j.jheap.2025.100498","DOIUrl":"10.1016/j.jheap.2025.100498","url":null,"abstract":"<div><div>We present a comprehensive analysis of the Barrow–Tsallis Holographic Dark Energy (BTHDE) model within a spatially flat FLRW cosmology, focusing on a comparative assessment between traditional Markov Chain Monte Carlo (MCMC) methods and a Bayesian Physics-Informed Neural Network (PINN). By embedding the modified Friedmann dynamics directly into the learning architecture, the Bayesian PINN framework enforces physical consistency while enabling efficient posterior sampling. We employ a broad suite of cosmological observations, including Planck 2018 CMB temperature and polarization data, CMB lensing, Baryon Acoustic Oscillations (BAO), Cosmic Chronometers (CC), and the Pantheon+ Type Ia supernovae compilation, to jointly constrain the Hubble constant <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span>, the Tsallis nonextensive parameter <em>q</em>, Barrow exponent Δ, Granda–Oliveros cutoff parameters <em>α</em> and <em>β</em>, and the total neutrino mass <span><math><mi>Σ</mi><msub><mrow><mi>m</mi></mrow><mrow><mi>ν</mi></mrow></msub></math></span>. In the late-time (CC + Pantheon+) analyses, we adopt flat, physically motivated priors on the baryon and cold dark matter densities (<span><math><msub><mrow><mi>Ω</mi></mrow><mrow><mi>b</mi></mrow></msub><msup><mrow><mi>h</mi></mrow><mrow><mn>2</mn></mrow></msup></math></span> and <span><math><msub><mrow><mi>Ω</mi></mrow><mrow><mi>c</mi></mrow></msub><msup><mrow><mi>h</mi></mrow><mrow><mn>2</mn></mrow></msup></math></span>) solely for the internal calibration of the sound horizon <span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>d</mi></mrow></msub></math></span>, without employing any Planck-based or early-universe likelihoods. The Bayesian PINN consistently yields sharper posterior distributions than MCMC, particularly for <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> and <span><math><mi>Σ</mi><msub><mrow><mi>m</mi></mrow><mrow><mi>ν</mi></mrow></msub></math></span>, while ensuring solution smoothness and dynamical compatibility. Both methods place the inferred <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> values between the Planck and SH<sub>0</sub>ES estimates, lowering the Hubble tension to the 1.3<em>σ</em>–2.1<em>σ</em> range. In the MCMC framework, combined CMB and low-redshift datasets constrain <span><math><mi>Σ</mi><msub><mrow><mi>m</mi></mrow><mrow><mi>ν</mi></mrow></msub><mo><</mo><mn>0.114</mn><mspace></mspace><mtext>eV</mtext></math></span> and <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>=</mo><mn>70.6</mn><mo>±</mo><mn>1.35</mn><mspace></mspace><mtext>km/s/Mpc</mtext></math></span>. Our results demonstrate the viability of the BTHDE model as a compelling alternative to ΛCDM and highlight the complementary strengths of Bayesian PINNs and MCMC in probing extended dark energy scenarios governed by generalized entropy frameworks.</div><","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100498"},"PeriodicalIF":10.5,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145364147","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}
Pub Date : 2025-10-18DOI: 10.1016/j.jheap.2025.100497
Ambrose C. EZE , Romanus N.C. EZE
MAXI J1535-571 outburst evolution is driven by physical mechanisms that mediate the accretion flow dynamical behavior/characteristics. In this study, MAXI J1535-571 data were analyzed. Spectral fitting and modelling were performed using phenomenological and physical models. MAXI J1535-571 X-ray spectra with an acceptable statistical fit were obtained. Accretion flow characteristics and their correlations were determined. The components of the accretion flow/rates show variations/fluctuations at different epochs. This indicates the dynamical behavior. The accretion flow geometry is “sombrero” or patchy-flaring turbulence flow. The decrease in accretion rate ratio (ARR) and shock location (Xs) shows that the outburst evolution progresses on timescales. A compression ratio (R) of 3.7 – 4.0 shows that the oscillating shock in the accretion flow is strong. The resonance condition of (0.62 – 0.79) ± 0.04 indicates that the timescales of components of the accretion flow roughly matched. A Quasi-Periodic Oscillation frequency (vQPO) of 0.560 Hz – 2.239 Hz is consistent with the type-C signature. Moreover, the components of the accretion flow/rate variations/fluctuations caused a uniform distribution of energy spectral indices and variations/fluctuations in the power-law photon index. The variations/fluctuations in mass accretion rate create the same physical features observed in other accretion flow parameters. Hence, mass accretion rate variations/fluctuations cause the decrease in the ARR, shock location, and perhaps, delay in the transition period and spectral evolution of MAXI J1535-571 as the outburst progresses.
{"title":"On the role of mass accretion rates during the outburst evolution of MAXI J1535-571","authors":"Ambrose C. EZE , Romanus N.C. EZE","doi":"10.1016/j.jheap.2025.100497","DOIUrl":"10.1016/j.jheap.2025.100497","url":null,"abstract":"<div><div>MAXI J1535-571 outburst evolution is driven by physical mechanisms that mediate the accretion flow dynamical behavior/characteristics. In this study, MAXI J1535-571 data were analyzed. Spectral <strong>fitting and modelling</strong> were performed using phenomenological and physical models. MAXI J1535-571 X-ray spectra with an acceptable statistical fit were obtained. Accretion flow characteristics and their correlations were determined. The components of the accretion flow/rates show variations/fluctuations at different epochs. This indicates the dynamical behavior. The accretion flow geometry is “sombrero” or patchy-flaring turbulence flow. The decrease in accretion rate ratio (ARR) and shock location (Xs) shows that the outburst evolution progresses on timescales. A compression ratio (R) of 3.7 – 4.0 shows that the oscillating shock in the accretion flow is strong. The resonance condition of (0.62 – 0.79) ± 0.04 indicates that the timescales of components of the accretion flow roughly matched. A Quasi-Periodic Oscillation frequency (vQPO) of 0.560 Hz – 2.239 Hz is consistent with the type-C signature. Moreover, the components of the accretion flow/rate variations/fluctuations caused a uniform distribution of energy spectral indices and variations/fluctuations in the power-law photon index. The variations/fluctuations in mass accretion rate create the same physical features observed in other accretion flow parameters. Hence, mass accretion rate variations/fluctuations cause the decrease in the ARR, shock location, and perhaps, delay in the transition period and spectral evolution of MAXI J1535-571 as the outburst progresses.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100497"},"PeriodicalIF":10.5,"publicationDate":"2025-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145417672","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}
Pub Date : 2025-10-16DOI: 10.1016/j.jheap.2025.100496
Zanyar Ebrahimi , Kayoomars Karami
This paper examines the growth of dark matter and dark energy perturbations within a non-canonical scalar field model characterized by an exponential potential. Through dynamical system analysis, we identify critical points and track the background evolution of a spatially flat FLRW universe dominated by dark energy and pressureless dark matter. We systematically derive key cosmological quantities, including the Hubble parameter, deceleration parameter, density parameters, and the scalar field's equation of state, and explore their dependence on model parameters. Within the linear perturbation framework, employing the pseudo-Newtonian formalism, we compute the growth factor of matter density perturbations. To investigate the non-linear regime of structure formation, we employ the spherical collapse model and derive its key parameters. Building on these findings, we compute the function and the relative number density of halo objects exceeding a given mass threshold. Our results indicate that non-canonical scalar field models can effectively account for both background cosmic evolution and the growth of structure, offering potential insights into observational constraints and large-scale dynamics.
{"title":"Structure formation in a non-canonical scalar field model of clustering dark energy","authors":"Zanyar Ebrahimi , Kayoomars Karami","doi":"10.1016/j.jheap.2025.100496","DOIUrl":"10.1016/j.jheap.2025.100496","url":null,"abstract":"<div><div>This paper examines the growth of dark matter and dark energy perturbations within a non-canonical scalar field model characterized by an exponential potential. Through dynamical system analysis, we identify critical points and track the background evolution of a spatially flat FLRW universe dominated by dark energy and pressureless dark matter. We systematically derive key cosmological quantities, including the Hubble parameter, deceleration parameter, density parameters, and the scalar field's equation of state, and explore their dependence on model parameters. Within the linear perturbation framework, employing the pseudo-Newtonian formalism, we compute the growth factor of matter density perturbations. To investigate the non-linear regime of structure formation, we employ the spherical collapse model and derive its key parameters. Building on these findings, we compute the function <span><math><mi>f</mi><mo>(</mo><mi>z</mi><mo>)</mo><msub><mrow><mi>σ</mi></mrow><mrow><mn>8</mn></mrow></msub><mo>(</mo><mi>z</mi><mo>)</mo></math></span> and the relative number density of halo objects exceeding a given mass threshold. Our results indicate that non-canonical scalar field models can effectively account for both background cosmic evolution and the growth of structure, offering potential insights into observational constraints and large-scale dynamics.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100496"},"PeriodicalIF":10.5,"publicationDate":"2025-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145364076","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}
Pub Date : 2025-10-15DOI: 10.1016/j.jheap.2025.100495
Amit Samaddar, S. Surendra Singh
We examine a modified teleparallel gravity model defined by by introducing an exponential diagnostic of the form . This novel form captures smooth redshift evolution and allows for a flexible, model-independent probe of dark energy dynamics. We derive a Hubble function from this expression and use MCMC analysis with 31 CC, 26 BAO and 1701 Pantheon+ data points to constrain the model parameters. The best-fit results yield km/s/Mpc, and which is consistent with local values. Statistical model selection using AIC and BIC shows that while our model fits the data comparably to ΛCDM, AIC indicates only moderate disfavor, whereas BIC—due to its stronger penalty for additional parameters—provides strong to very strong evidence in favor of the simpler ΛCDM model. Our model predicts a transition redshift , present , and . It satisfies NEC and DEC, closely tracks ΛCDM in the statefinder plane and estimates a cosmic age of Gyr which confirms its strength in explaining late-time acceleration. Our findings demonstrate that the exponential parameterization provides a robust and insightful approach to trace dark energy evolution within modified gravity frameworks.
{"title":"Cosmological insights from an exponential Om(z) function in f(T,TG) gravity framework","authors":"Amit Samaddar, S. Surendra Singh","doi":"10.1016/j.jheap.2025.100495","DOIUrl":"10.1016/j.jheap.2025.100495","url":null,"abstract":"<div><div>We examine a modified teleparallel gravity model defined by <span><math><mi>f</mi><mo>(</mo><mi>T</mi><mo>,</mo><msub><mrow><mi>T</mi></mrow><mrow><mi>G</mi></mrow></msub><mo>)</mo><mo>=</mo><mi>T</mi><mo>+</mo><mi>γ</mi><msqrt><mrow><msub><mrow><mi>T</mi></mrow><mrow><mi>G</mi></mrow></msub></mrow></msqrt><mo>+</mo><mi>δ</mi><msqrt><mrow><mi>T</mi></mrow></msqrt></math></span> by introducing an exponential <span><math><mi>O</mi><mi>m</mi><mo>(</mo><mi>z</mi><mo>)</mo></math></span> diagnostic of the form <span><math><mi>O</mi><mi>m</mi><mo>(</mo><mi>z</mi><mo>)</mo><mo>=</mo><mi>α</mi><msup><mrow><mi>e</mi></mrow><mrow><mfrac><mrow><mi>z</mi></mrow><mrow><mn>1</mn><mo>+</mo><mi>z</mi></mrow></mfrac></mrow></msup><mo>+</mo><mi>β</mi></math></span>. This novel form captures smooth redshift evolution and allows for a flexible, model-independent probe of dark energy dynamics. We derive a Hubble function from this expression and use MCMC analysis with 31 CC, 26 BAO and 1701 Pantheon+ data points to constrain the model parameters. The best-fit results yield <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>∈</mo><mo>[</mo><mn>68.46</mn><mo>,</mo><mn>77.38</mn><mo>]</mo></math></span> km/s/Mpc, <span><math><mi>α</mi><mo>∈</mo><mo>[</mo><mo>−</mo><mn>0.232</mn><mo>,</mo><mo>−</mo><mn>0.068</mn><mo>]</mo></math></span> and <span><math><mi>β</mi><mo>∈</mo><mo>[</mo><mn>0.218</mn><mo>,</mo><mn>0.560</mn><mo>]</mo></math></span> which is consistent with local <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> values. Statistical model selection using AIC and BIC shows that while our model fits the data comparably to ΛCDM, AIC indicates only moderate disfavor, whereas BIC—due to its stronger penalty for additional parameters—provides strong to very strong evidence in favor of the simpler ΛCDM model. Our model predicts a transition redshift <span><math><msub><mrow><mi>z</mi></mrow><mrow><mi>t</mi><mi>r</mi></mrow></msub><mo>≈</mo><mo>(</mo><mn>0.48</mn><mo>−</mo><mn>0.54</mn><mo>)</mo></math></span>, present <span><math><msub><mrow><mi>q</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>≈</mo><mo>−</mo><mn>0.34</mn></math></span>, and <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>≈</mo><mo>−</mo><mn>0.33</mn></math></span>. It satisfies NEC and DEC, closely tracks ΛCDM in the statefinder plane and estimates a cosmic age of <span><math><mo>(</mo><mn>13.28</mn><mo>−</mo><mn>13.87</mn><mo>)</mo></math></span> Gyr which confirms its strength in explaining late-time acceleration. Our findings demonstrate that the exponential <span><math><mi>O</mi><mi>m</mi><mo>(</mo><mi>z</mi><mo>)</mo></math></span> parameterization provides a robust and insightful approach to trace dark energy evolution within modified gravity frameworks.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100495"},"PeriodicalIF":10.5,"publicationDate":"2025-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145321809","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}
Pub Date : 2025-10-15DOI: 10.1016/j.jheap.2025.100494
L. Giridharan, Neal Titus Thomas, S.B. Gudennavar, S.G. Bubbly
This study presents the spectro-temporal analysis of the neutron star low mass X-ray binary 4U 1820−30, using data from three observations conducted by AstroSat's Soft X-ray Telescope and Large Array X-ray Proportional Counter. Spectral analysis revealed that the source spectra could be modelled using an absorbed blackbody and a multi-temperature disk model along with a Comptonization model with Γ=1.24 − 1.89 and the inner accretion disk located at an distance of ∼17 km from the neutron star. This showed the source to be in the hard spectral state. Temporal analysis revealed the presence of kHz quasi-periodic oscillations (QPOs) with frequencies in the 640 − 1090 Hz range with root mean squared (RMS) amplitudes between 6 − 10 per cent and quality factors between 8 − 42. The RMS amplitude−energy and time lag−energy spectra of the upper and lower kHz QPOs hint them to be caused by modulations of photons having a common radiative mechanism. Moreover, the maximum RMS amplitude and time lag exhibited an anti-correlation with mass accretion rate. Using an analytical relation based on the relativistic precession model, the mass of the neutron star in the system was estimated to be 1.8 M⊙. The emission radius of one of the detected kHz QPOs was estimated to be ∼ 17 km.
{"title":"AstroSat's view of kHz quasi-periodic oscillations from 4U 1820−30","authors":"L. Giridharan, Neal Titus Thomas, S.B. Gudennavar, S.G. Bubbly","doi":"10.1016/j.jheap.2025.100494","DOIUrl":"10.1016/j.jheap.2025.100494","url":null,"abstract":"<div><div>This study presents the spectro-temporal analysis of the neutron star low mass X-ray binary 4U 1820−30, using data from three observations conducted by <em>AstroSat</em>'s Soft X-ray Telescope and Large Array X-ray Proportional Counter. Spectral analysis revealed that the source spectra could be modelled using an absorbed blackbody and a multi-temperature disk model along with a Comptonization model with Γ=1.24 − 1.89 and the inner accretion disk located at an distance of ∼17 km from the neutron star. This showed the source to be in the hard spectral state. Temporal analysis revealed the presence of kHz quasi-periodic oscillations (QPOs) with frequencies in the 640 − 1090 Hz range with root mean squared (RMS) amplitudes between 6 − 10 per cent and quality factors between 8 − 42. The RMS amplitude−energy and time lag−energy spectra of the upper and lower kHz QPOs hint them to be caused by modulations of photons having a common radiative mechanism. Moreover, the maximum RMS amplitude and time lag exhibited an anti-correlation with mass accretion rate. Using an analytical relation based on the relativistic precession model, the mass of the neutron star in the system was estimated to be 1.8 M<sub>⊙</sub>. The emission radius of one of the detected kHz QPOs was estimated to be ∼ 17 km.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100494"},"PeriodicalIF":10.5,"publicationDate":"2025-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145364109","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}
Pub Date : 2025-10-14DOI: 10.1016/j.jheap.2025.100488
Qiqi Jiang , Guang-Xing Li , Chandra B. Singh
The Rayleigh–Taylor instability (RTI) arises at the interface between two fluids of different densities, notably when a heavier fluid lies above a lighter one in an effective gravitational field. In astrophysical systems with high velocities, relativistic corrections are necessary. We investigate the linear theory of the relativistic Rayleigh-Taylor instability (R-RTI) in a magnetized medium, where fluids can move with relativistic velocities. We chose an “intermediate frame” in which the fluids on each side of the interface move in opposite directions with identical Lorentz factors and derive the new dispersion relation of the R-RTI. This symmetry facilitates analytical derivations and the study of relativistic effects on the dynamics of instabilities. We find that the instability is activated when the Atwood number = , where and are densities measured in the rest of the fluids. The relativistic effect is mostly contained in the Lorentz transformation of the effective acceleration , which, combined with time dilation, leads to a much slower growth of instability (), and a slightly elongated length of the unstable patch, due to weaker g in the intermediate frame. Taking time dilation into account, when viewed in the rest frame of the medium, we expect the instability to grow at a much reduced rate. The analytical results should guide further explorations of instability in systems such as microquasars (μQSOs), Active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and radio pulsars (PSRs), where the apparent stability of the jet can be attributed to either the intrinsic stability (e.g. the Atwood number)
{"title":"Dispersion relation for the linear theory of relativistic Rayleigh–Taylor instability in a magnetized medium revisited","authors":"Qiqi Jiang , Guang-Xing Li , Chandra B. Singh","doi":"10.1016/j.jheap.2025.100488","DOIUrl":"10.1016/j.jheap.2025.100488","url":null,"abstract":"<div><div>The Rayleigh–Taylor instability (RTI) arises at the interface between two fluids of different densities, notably when a heavier fluid lies above a lighter one in an effective gravitational field. In astrophysical systems with high velocities, relativistic corrections are necessary. We investigate the linear theory of the relativistic Rayleigh-Taylor instability (R-RTI) in a magnetized medium, where fluids can move with relativistic velocities. We chose an “intermediate frame” in which the fluids on each side of the interface move in opposite directions with identical Lorentz factors <span><math><msub><mrow><mi>γ</mi></mrow><mrow><mo>⁎</mo></mrow></msub></math></span> and derive the new dispersion relation of the R-RTI. This symmetry facilitates analytical derivations and the study of relativistic effects on the dynamics of instabilities. We find that the instability is activated when the Atwood number <span><math><mi>A</mi></math></span> = <span><math><mo>(</mo><msub><mrow><mi>ρ</mi></mrow><mrow><mn>1</mn></mrow></msub><msub><mrow><mi>h</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>−</mo><msub><mrow><mi>ρ</mi></mrow><mrow><mn>2</mn></mrow></msub><msub><mrow><mi>h</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo><mo>/</mo><mo>(</mo><msub><mrow><mi>ρ</mi></mrow><mrow><mn>1</mn></mrow></msub><msub><mrow><mi>h</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>+</mo><msub><mrow><mi>ρ</mi></mrow><mrow><mn>2</mn></mrow></msub><msub><mrow><mi>h</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo><mo>></mo><mn>0</mn></math></span>, where <span><math><msub><mrow><mi>ρ</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>ρ</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> are densities measured in the rest of the fluids. The relativistic effect is mostly contained in the Lorentz transformation of the effective acceleration <span><math><msup><mrow><mi>g</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>=</mo><mi>g</mi><msubsup><mrow><mi>γ</mi></mrow><mrow><mo>⁎</mo></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msubsup></math></span>, which, combined with time dilation, leads to a much slower growth of instability (<span><math><msup><mrow><mi>ω</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>=</mo><msubsup><mrow><mi>γ</mi></mrow><mrow><mo>⁎</mo></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msubsup><msub><mrow><mi>ω</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span>), and a slightly elongated length of the unstable patch, due to weaker <em>g</em> in the intermediate frame. Taking time dilation into account, when viewed in the rest frame of the medium, we expect the instability to grow at a much reduced rate. The analytical results should guide further explorations of instability in systems such as microquasars (<em>μ</em>QSOs), Active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and radio pulsars (PSRs), where the apparent stability of the jet can be attributed to either the intrinsic stability (e.g. the Atwood number)","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100488"},"PeriodicalIF":10.5,"publicationDate":"2025-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145364148","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}
Pub Date : 2025-10-09DOI: 10.1016/j.jheap.2025.100492
M.S. Pshirkov , A.S. Kovankin
We present a search for spatio-temporal clusters in 16 years of Fermi-LAT very-high-energy (VHE; GeV) data using the DBSCAN algorithm, focusing on high Galactic latitude () clusters with ≥5 events and transient doublets (two events within ≤3 days). Of 107 detected clusters, two correspond to previously unidentified VHE sources: weak BL Lacertae objects 4FGL J0039.1-2219 and 4FGL J0212.2-0219, promising targets for next-generation VHE observatories.
Due to the low VHE photon background, even doublets with a duration of several days exhibited high statistical significance. While most of the 114 detected doublets originated from bright TeV emitters (e.g., Mrk 421, Mrk 501), we identified six VHE flares lacking TeVCat associations. Five of these flares correlate with sources from the Third Catalog of Fermi-LAT High-Energy Sources (3FHL), while one 'orphan' flare lacks a high-energy (HE; GeV) source counterpart. Some of these flares reached extreme luminosities of .
No consistent temporal correlation emerged between HE and VHE activity: HE flares preceded, coincided with, or followed VHE emission across sources, with some showing no HE counterpart. Remarkably, 3FHL J0308.4+0408 (NGC 1218) is a Seyfert Type I galaxy, while no object of this class was known as a VHE emitter before. The ‘orphan’ flare without any known HE source in the vicinity may originate from NGC 5549, a low-luminosity LINER galaxy. Both sources expand the limited sample of non-blazar AGN detected at VHE energies. The fact that some weak sources with non-aligned jets and, sometimes, even without any traces of HE activity, could demonstrate very short and powerful VHE flares cannot be easily accounted in many current AGN models and calls for their further development.
{"title":"Detection of new very-high-energy sources outside the galactic plane in the Fermi-LAT data","authors":"M.S. Pshirkov , A.S. Kovankin","doi":"10.1016/j.jheap.2025.100492","DOIUrl":"10.1016/j.jheap.2025.100492","url":null,"abstract":"<div><div>We present a search for spatio-temporal clusters in 16 years of Fermi-LAT very-high-energy (VHE; <span><math><mi>E</mi><mo>></mo><mn>100</mn></math></span> GeV) data using the DBSCAN algorithm, focusing on high Galactic latitude (<span><math><mo>|</mo><mi>b</mi><mo>|</mo><mo>></mo><msup><mrow><mn>10</mn></mrow><mrow><mo>∘</mo></mrow></msup></math></span>) clusters with ≥5 events and transient doublets (two events within ≤3 days). Of 107 detected clusters, two correspond to previously unidentified VHE sources: weak BL Lacertae objects 4FGL J0039.1-2219 and 4FGL J0212.2-0219, promising targets for next-generation VHE observatories.</div><div>Due to the low VHE photon background, even doublets with a duration of several days exhibited high statistical significance. While most of the 114 detected doublets originated from bright TeV emitters (e.g., Mrk 421, Mrk 501), we identified six VHE flares lacking TeVCat associations. Five of these flares correlate with sources from the Third Catalog of Fermi-LAT High-Energy Sources (3FHL), while one 'orphan' flare lacks a high-energy (HE; <span><math><mi>E</mi><mo>></mo><mn>10</mn></math></span> GeV) source counterpart. Some of these flares reached extreme luminosities of <span><math><mi>O</mi><mo>(</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>47</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><mo>)</mo></math></span>.</div><div>No consistent temporal correlation emerged between HE and VHE activity: HE flares preceded, coincided with, or followed VHE emission across sources, with some showing no HE counterpart. Remarkably, 3FHL J0308.4+0408 (NGC 1218) is a Seyfert Type I galaxy, while no object of this class was known as a VHE emitter before. The ‘orphan’ flare without any known HE source in the vicinity may originate from NGC 5549, a low-luminosity LINER galaxy. Both sources expand the limited sample of non-blazar AGN detected at VHE energies. The fact that some weak sources with non-aligned jets and, sometimes, even without any traces of HE activity, could demonstrate very short and powerful VHE flares cannot be easily accounted in many current AGN models and calls for their further development.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100492"},"PeriodicalIF":10.5,"publicationDate":"2025-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145269258","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}
We study quark star configurations in regularized four-dimensional Einstein-Gauss-Bonnet (4DEGB) gravity using a QCD-motivated equation of state with parameters , , and . The modified Tolman-Oppenheimer-Volkoff equations, incorporating 4DEGB corrections, are solved to examine mass-radius relations, tidal deformability, and stability across a range of α, , and . Positive α or larger yields more massive, compact stars than in general relativity, with some configurations below the GR Buchdahl limit, potentially eliminating the mass gap with black holes. The dimensionless tidal deformability Λ decreases markedly with α and , while has only a minor effect. Models consistent with NICER, GW170817, and HESS J1731−347 constraints remain dynamically stable and causal. Our results demonstrate that the interplay between higher-curvature gravity and QCD microphysics can produce observationally viable deviations from general relativity, offering promising targets for future multimessenger constraints on dense matter and alternative gravity theories.
{"title":"Effects of QCD-based equation of state on the structure and tidal deformability of compact stars in regularized 4D Einstein-Gauss-Bonnet gravity","authors":"Takol Tangphati , Ayan Banerjee , Anirudh Pradhan , Javlon Rayimbaev","doi":"10.1016/j.jheap.2025.100493","DOIUrl":"10.1016/j.jheap.2025.100493","url":null,"abstract":"<div><div>We study quark star configurations in regularized four-dimensional Einstein-Gauss-Bonnet (4DEGB) gravity using a QCD-motivated equation of state with parameters <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>eff</mi></mrow></msub></math></span>, <span><math><msub><mrow><mi>a</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>, and <span><math><msub><mrow><mi>a</mi></mrow><mrow><mn>4</mn></mrow></msub></math></span>. The modified Tolman-Oppenheimer-Volkoff equations, incorporating 4DEGB corrections, are solved to examine mass-radius relations, tidal deformability, and stability across a range of <em>α</em>, <span><math><msub><mrow><mi>a</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>, and <span><math><msub><mrow><mi>a</mi></mrow><mrow><mn>4</mn></mrow></msub></math></span>. Positive <em>α</em> or larger <span><math><msub><mrow><mi>a</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> yields more massive, compact stars than in general relativity, with some configurations below the GR Buchdahl limit, potentially eliminating the mass gap with black holes. The dimensionless tidal deformability Λ decreases markedly with <em>α</em> and <span><math><msub><mrow><mi>a</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>, while <span><math><msub><mrow><mi>a</mi></mrow><mrow><mn>4</mn></mrow></msub></math></span> has only a minor effect. Models consistent with NICER, GW170817, and HESS J1731−347 constraints remain dynamically stable and causal. Our results demonstrate that the interplay between higher-curvature gravity and QCD microphysics can produce observationally viable deviations from general relativity, offering promising targets for future multimessenger constraints on dense matter and alternative gravity theories.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100493"},"PeriodicalIF":10.5,"publicationDate":"2025-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145269260","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}
Pub Date : 2025-10-03DOI: 10.1016/j.jheap.2025.100491
L.M. Becerra , F. Cipolletta , A. Drago , M. Guerrini , A. Lavagno , G. Pagliara , J.A. Rueda
Strange quark stars (SQSs), namely compact stars entirely composed of deconfined quark matter, are characterized by similar masses and compactness to neutron stars (NSs) and have been theoretically proposed to exist in the Universe since the 1970s. However, multiwavelength observations of compact stars in the last 50 years have not yet led to an unambiguous SQS identification. This article explores whether SQSs could form in the supernova (SN) explosion of an evolved star (e.g., carbon-oxygen, or Wolf-Rayet) occurring in a binary with the companion being a neutron star (NS). The collapse of the iron core of the evolved star generates a newborn NS and the SN explosion. Part of the ejected matter accretes onto the NS companion as well as onto the newborn NS via matter fallback. The accretion occurs at hypercritical (highly super-Eddington) rates, transferring mass and angular momentum to the stars. We present numerical simulations of this scenario and demonstrate that the density increase in the NS interiors during the accretion process may induce quark matter deconfinement, suggesting the possibility of SQS formation. We discuss the astrophysical conditions under which such a transition may occur and possible consequences.
{"title":"On the formation of strange quark stars from supernova in compact binaries","authors":"L.M. Becerra , F. Cipolletta , A. Drago , M. Guerrini , A. Lavagno , G. Pagliara , J.A. Rueda","doi":"10.1016/j.jheap.2025.100491","DOIUrl":"10.1016/j.jheap.2025.100491","url":null,"abstract":"<div><div>Strange quark stars (SQSs), namely compact stars entirely composed of deconfined quark matter, are characterized by similar masses and compactness to neutron stars (NSs) and have been theoretically proposed to exist in the Universe since the 1970s. However, multiwavelength observations of compact stars in the last 50 years have not yet led to an unambiguous SQS identification. This article explores whether SQSs could form in the supernova (SN) explosion of an evolved star (e.g., carbon-oxygen, or Wolf-Rayet) occurring in a binary with the companion being a neutron star (NS). The collapse of the iron core of the evolved star generates a newborn NS and the SN explosion. Part of the ejected matter accretes onto the NS companion as well as onto the newborn NS via matter fallback. The accretion occurs at hypercritical (highly super-Eddington) rates, transferring mass and angular momentum to the stars. We present numerical simulations of this scenario and demonstrate that the density increase in the NS interiors during the accretion process may induce quark matter deconfinement, suggesting the possibility of SQS formation. We discuss the astrophysical conditions under which such a transition may occur and possible consequences.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100491"},"PeriodicalIF":10.5,"publicationDate":"2025-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145269728","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}
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