Journal of High Energy Astrophysics最新文献

{"title":"Detection of new very-high-energy sources outside the galactic plane in the Fermi-LAT data","authors":"M.S. Pshirkov ,&nbsp;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>&gt;</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>&gt;</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>&gt;</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}

{"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 ,&nbsp;Ayan Banerjee ,&nbsp;Anirudh Pradhan ,&nbsp;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}

{"title":"On the formation of strange quark stars from supernova in compact binaries","authors":"L.M. Becerra ,&nbsp;F. Cipolletta ,&nbsp;A. Drago ,&nbsp;M. Guerrini ,&nbsp;A. Lavagno ,&nbsp;G. Pagliara ,&nbsp;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}

{"title":"VegasAfterglow: A high-performance framework for gamma-ray burst afterglows","authors":"Yihan Wang ,&nbsp;Connery Chen ,&nbsp;Bing Zhang","doi":"10.1016/j.jheap.2025.100490","DOIUrl":"10.1016/j.jheap.2025.100490","url":null,"abstract":"<div><div>Gamma-ray bursts (GRBs) are the most luminous astrophysical transients, known to be associated with core collapse of massive stars or mergers of two compact objects such as two neutron stars. They are followed by multi-wavelength afterglow emission originating from the deceleration of the relativistic jets by the ambient medium. The study of afterglow emission offers crucial insights into the physics of relativistic shocks, the properties of the circumburst environment, the physical and geometrical structure of relativistic jets, as well as the viewing geometry of the observer. We present <span>VegasAfterglow</span>, a newly developed, high-performance C++ framework designed for modeling GRB afterglows with flexibility and computational efficiency as key features of design. The framework self-consistently solves forward and reverse shock dynamics and calculates synchrotron (including self-absorption or all spectral regimes) and inverse Compton radiation (including Klein–Nishina corrections); it can handle arbitrary user-defined ambient density profiles, central engine activity histories, viewing angles, and the jet structures of energy, Lorentz factor, and magnetization profiles. It supports both relativistic and non-relativistic regimes and includes lateral jet spreading effects. In this paper, we describe the numerical implementation of the framework and assess its computational performance. Our results demonstrate that <span>VegasAfterglow</span> is well-suited for interpreting current and future multi-wavelength observations in the era of multi-messenger astronomy.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100490"},"PeriodicalIF":10.5,"publicationDate":"2025-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145269259","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":"First-principles formulation of high-energy radiation from magnetar giant flares","authors":"Umer Rehman ,&nbsp;Joseph Zhao Zhang ,&nbsp;Bin-Bin Zhang","doi":"10.1016/j.jheap.2025.100489","DOIUrl":"10.1016/j.jheap.2025.100489","url":null,"abstract":"<div><div>We develop a first-principles atmosphere model for neutron stars with ultra-strong magnetic fields (<span><math><mi>B</mi><mo>∼</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>14</mn></mrow></msup><mo>,</mo><mi>G</mi></math></span>). In this framework, a magnetar giant flare (MGF) arises when a large energy release into confined field lines launches an expanding fireball (FB); thermal photons from the FB are Comptonized by relativistic <span><math><msup><mrow><mi>e</mi></mrow><mrow><mo>±</mo></mrow></msup></math></span> pairs, producing a modified blackbody spectrum with a Rayleigh–Jeans low-energy slope and a high-energy tail. We derive polarization-dependent opacities for a magnetized <span><math><msup><mrow><mi>e</mi></mrow><mrow><mo>±</mo></mrow></msup></math></span> pair plasma (including plasma and vacuum polarization effects) and formulate the coupled radiative-transfer equations for the ordinary and extraordinary modes. The calculations show that, in deep magnetospheric layers with <span><math><mi>n</mi><mo>∼</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>24</mn></mrow></msup></math></span>–<span><math><msup><mrow><mn>10</mn></mrow><mrow><mn>28</mn></mrow></msup><mo>,</mo><mrow><mi>c</mi><msup><mrow><mi>m</mi></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></mrow></math></span> and path length <span><math><mi>l</mi><mo>∼</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>3</mn></mrow></msup></math></span>–<span><math><msup><mrow><mn>10</mn></mrow><mrow><mn>6</mn></mrow></msup><mo>,</mo><mrow><mi>cm</mi></mrow></math></span>, plasma effects substantially reshape the opacities and generate a broad spectral feature (<span><math><mi>Δ</mi><mi>ω</mi><mo>/</mo><mi>ω</mi></math></span>) around the electron cyclotron frequency <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mi>B</mi></mrow></msub></math></span> via resonant polarization/mode conversion. Identifying this feature in data would enable a direct estimate of the surface magnetic field. Despite current observational limitations, the model reproduces key spectral properties of GRB200415A and GRB231115A, providing insight into their radiation mechanisms and the emission physics of MGFs.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100489"},"PeriodicalIF":10.5,"publicationDate":"2025-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145222606","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":"Modified cosmology through generalized mass-to-horizon entropy: Implications for structure growth and primordial gravitational waves","authors":"Giuseppe Gaetano Luciano","doi":"10.1016/j.jheap.2025.100487","DOIUrl":"10.1016/j.jheap.2025.100487","url":null,"abstract":"<div><div>In the framework of entropic cosmology, entropic forces arising at the cosmological horizon have been proposed as an alternative mechanism to explain the Universe's current accelerated phase. However, recent studies have shown that, under the Clausius relation and assuming a linear mass-to-horizon (MHR) relation, all entropic force models reduce to the original Bekenstein-Hawking formulation, regardless of the specific form of the horizon entropy. As a result, they inherit the same observational limitations in accounting for cosmic dynamics. To address this issue, a generalized MHR has been introduced, providing the foundation for a modified cosmological scenario rooted in the gravity-thermodynamics conjecture. In this work, we explore the implications of this generalized framework for early-Universe dynamics. Specifically, we analyze the growth of matter perturbations within the spherical Top-Hat formalism in the linear regime, showing that the density contrast profile is significantly influenced by the modified background dynamics predicted by the model. Moreover, considering the sensitivity of upcoming gravitational wave detectors in the sub-<span><math><msup><mrow><mn>10</mn></mrow><mrow><mn>3</mn></mrow></msup><mspace></mspace><mrow><mi>Hz</mi></mrow></math></span> range, we examine the impact on the relic abundance of Primordial Gravitational Waves (PGWs), identifying parameter regions where deviations from standard cosmology may arise through an enhanced PGW spectrum.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100487"},"PeriodicalIF":10.5,"publicationDate":"2025-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145222605","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":"Durgapal-Fuloria Bose-Einstein condensate stars within f(R,T) gravity theory","authors":"Meghanil Sinha,&nbsp;S. Surendra Singh","doi":"10.1016/j.jheap.2025.100486","DOIUrl":"10.1016/j.jheap.2025.100486","url":null,"abstract":"<div><div>This manuscript studies the Bose-Einstein condensate (BEC) stars in the light of <span><math><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><mi>T</mi><mo>)</mo></math></span> gravity here with Durgapal-Fuloria (DP) metric ansatz. The function under this study features as <span><math><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><mi>T</mi><mo>)</mo><mo>=</mo><mi>R</mi><mo>+</mo><mn>2</mn><mi>η</mi><mi>T</mi></math></span>, where <em>η</em> represents the coupling constant. With the help of it, we have formulated a stellar model describing the isotropic matter here within. Our analysis covers energy conditions, equation of state (EoS) parameter and gradients of the energy-momentum tensor components for a valid BEC stellar framework within <span><math><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><mi>T</mi><mo>)</mo></math></span> gravitational theory with satisfactory results. The model's stability has been validated via multiple stability criteria viz., the velocity of sound, study of adiabatic index and surface redshift where all are found to be lying within the acceptable range for our stellar model. Thus in all the cases we have found our model to be stable and realistic. From the graphical representations the impact of the coupling constant and the parameter of the DP metric potential are clearly visible. Thus we can state that with all the above-mentioned features we have introduced new stellar solutions for BEC stars with enhanced precise results in this modified gravity.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100486"},"PeriodicalIF":10.5,"publicationDate":"2025-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145159860","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":"Identification of vortical coherent modes during relativistic jet propagation from active galactic nuclei using data-driven techniques","authors":"Ribhu Pal,&nbsp;Arnab Roy","doi":"10.1016/j.jheap.2025.100485","DOIUrl":"10.1016/j.jheap.2025.100485","url":null,"abstract":"<div><div>In this article, two-dimensional numerical simulations of magnetized relativistic jets propagating through a uniform interstellar medium (ISM) were conducted by solving the relativistic magnetohydrodynamic (RMHD) equations using a high-order finite volume method in PLUTO solver <span><span>Mignone et al. (2007)</span></span>. Vortical coherent structures generated by jet–ISM interactions were identified through the application of both standard Dynamic Mode Decomposition (DMD) and Hankel DMD. While dominant coherent modes were extracted using linear DMD, transient and nonlinear structures were more effectively captured by Hankel DMD due to its time-delay embedding formulation. A parametric study was performed to investigate the mechanisms governing energy dissipation, with variations introduced in jet Lorentz factor, magnetization strength, and the comparison between relativistic hydrodynamic (RHD) and magnetized (RMHD) configurations. Across all cases, eigenvalues were consistently located within the unit circle, signifying temporal decay of vortical modes due to strong dissipation imposed by the jet head shock. It was shown that dissipation was sustained with increasing Lorentz factor, that magnetization exerted control over the stability and coherence of vortical structures, and that RMHD jets followed distinct dissipation pathways relative to RHD jets. Overall, nonlinear coherent dynamics were more effectively revealed through Hankel DMD, and dissipation trends were elucidated via systematic parametric variation.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100485"},"PeriodicalIF":10.5,"publicationDate":"2025-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145222604","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":"How many VHE gamma-ray binaries with young pulsars can be observed?","authors":"A.M. Bykov ,&nbsp;A.G. Kuranov ,&nbsp;A.E. Petrov ,&nbsp;K.A. Postnov","doi":"10.1016/j.jheap.2025.100484","DOIUrl":"10.1016/j.jheap.2025.100484","url":null,"abstract":"<div><div>A population of Galactic gamma-ray binaries is currently emerging due to ever increasing sensitivity of gamma-ray observatories. The detection of very high energy (VHE) photons with energies well above 10 TeV from a dozen of sources and the estimated power of those sources make them potentially interesting cosmic ray accelerators. Multi-wavelength observations of gamma-ray binaries revealed that most of them include a young massive star in pair with a relativistic companion, either a black hole or energetic pulsar. Fast stellar winds interacting with powerful relativistic outflows from pulsars or the black hole jets in microquasars are favorable sites for very high energy particle acceleration. To estimate the expected number of gamma-ray binaries, we present here results of population synthesis calculations predicting the number of Galactic binaries in which a young massive OB- or Be-star is accompanied by a pulsar capable of producing a powerful relativistic outflow. The distributions over the binary eccentricities, orbital periods, Be-disk inclinations, and the pulsar braking energy losses are taken into account. Conditions for a binary to accelerate very high energy particles, radiate and absorb the non-thermal photons that may reach the observer are discussed. We model the anisotropic structure of the zone of interaction of the relativistic pulsar wind with the strongly magnetized massive star's wind. The stellar winds with strong (in a Gauss range) magnetic fields at ∼ AU distances colliding with powerful pulsar outflows are capable of accelerating particles up to PeV energies at some orbital configurations and phases. The strong magnetic field in the interaction region produces a highly anisotropic structure of the particle accelerator and the emitter in the pulsar outflow. The anisotropic radiation pattern may affect the gamma-ray photon absorption and the number of the observed gamma-ray loud systems.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100484"},"PeriodicalIF":10.5,"publicationDate":"2025-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145222608","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":"Clues on the X-ray emission mechanism of blazars PKS 2155−304 and 3C 454.3 through polarization studies","authors":"Athira M. Bharathan ,&nbsp;C.S. Stalin ,&nbsp;Sunder Sahayanathan ,&nbsp;Blesson Mathew","doi":"10.1016/j.jheap.2025.100472","DOIUrl":"10.1016/j.jheap.2025.100472","url":null,"abstract":"<div><div>X-ray polarization measurable with the imaging X-ray Polarimetry Explorer (<em>IXPE</em>) could constrain the long debated leptonic versus hadronic origin for the high energy component in the broad band spectral energy distribution (SED) of blazars. We report here the results from <em>IXPE</em> and SED modeling of PKS 2155−304 and 3C 454.3, a high and low synchrotron peaked blazar. For PKS 2155−304, from model-independent analysis, we found polarization angle <span><math><msub><mrow><mi>Ψ</mi></mrow><mrow><mi>X</mi></mrow></msub></math></span> = (130 ± 2.5) deg and polarization degree <span><math><msub><mrow><mi>Π</mi></mrow><mrow><mi>X</mi></mrow></msub></math></span> = (20.9 ± 1.8)% in the 2−8 keV band in agreement with spectro-polarimetric analysis. We found <span><math><msub><mrow><mi>Π</mi></mrow><mrow><mi>X</mi></mrow></msub></math></span> to vary with time and indications of it to vary between energies, suggesting that the emission regions are stratified. For 3C 454.3, we did not detect X-ray polarization in the June 2023 observation, analyzed here for the first time. The detection of X-ray polarization in PKS 2155−304 and its non-detection in 3C 454.3 is in accordance with the X-ray emission from synchrotron and inverse Compton process, respectively, operating in these sources. Further, our division of the dataset into finer time bins allows a more granular view of polarization variability. Additionally, we modeled the broadband SEDs of both the sources using data acquired quasi-simultaneously with <em>IXPE</em>, in the optical, UV and X-rays from <em>Swift</em>, <em>AstroSat</em> and <em>γ</em>-rays from <em>Fermi</em>. In PKS 2155−304, the observed X-ray is found to lie in the high energy tail of the synchrotron component of the SED, while in 3C 454.3 the observed X-ray lies in the rising part of the inverse Compton component of the SED. Our SED modeling along with X-ray polarization observations favor a leptonic scenario for the observed X-ray emission in PKS 2155−304. The SED modeling for these specific <em>IXPE</em> epochs has not been presented before, allowing us to place additional constraints on the physical conditions in the jet. These results strengthen the case for a structured jet model where X-ray emission originates from a compact acceleration zone near the shock front, while lower-energy optical emission is produced in a broader, more turbulent region.</div></div>","PeriodicalId":54265,"journal":{"name":"Journal of High Energy Astrophysics","volume":"50 ","pages":"Article 100472"},"PeriodicalIF":10.5,"publicationDate":"2025-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145222607","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}