arXiv - PHYS - High Energy Astrophysical Phenomena最新文献

{"title":"On the Broadening of the Characteristic Frequency Range towards Higher Photon Energies in the X-ray Variability of the Black Hole Transient MAXI J1820+070","authors":"Chenxu GaoShanghai Astronomical Observatory, Wenfei YuShanghai Astronomical Observatory, Zhen YanShanghai Astronomical Observatory","doi":"arxiv-2409.06414","DOIUrl":"https://doi.org/arxiv-2409.06414","url":null,"abstract":"Energy-dependence of X-ray Fourier power spectral states and the\u0000characteristic frequencies of the Band-Limited Noise (BLN) components have been\u0000seen in the hard state and intermediate states of black hole X-ray binaries.\u0000Here we report our analysis of the emph{Insight}-HXMT observations of the\u0000black hole transient MAXI J1820$+$070 during its 2018 outburst when the source\u0000was brightest in hard X-rays. We found opposite trends of the low-frequency\u0000($<$ 0.1 Hz) and the high-frequency ($>$ 10 Hz) BLN components, i.e.,\u0000decreasing vs. increasing in frequency with increasing photon energy up to\u0000beyond 200 keV, respectively. This establishes an apparent two-way broadening\u0000of the power plateau formed by multiple BLNs in the power spectra towards\u0000higher photon energies. The trend of increasing characteristic frequency of the\u0000highest BLN component with increasing photon energy has been interpreted as due\u0000to that the corresponding seed photons which are up-scatted to relatively\u0000higher energies originate in a region relatively more central in the corona\u0000previously. Following the same framework, the decreasing trend of the\u0000characteristic frequency of the low-frequency BLN component with increasing\u0000photon energy can be interpreted as due to that the corresponding seed photons\u0000which are up-scattered to higher photon energies originate from further out in\u0000the disk flow but on the opposite side of the central corona as to the\u0000observer. The opposite trends then implies that the the plateau in the power\u0000spectra formed by the multiple BLNs represents the radial extension of the\u0000accretion disk that contributes seed photons which produce the observed BLNs;\u0000the higher the photon energy is, the wider the power plateau and the smaller\u0000the fractional variability are, probably approaching to a Power-Law Noise (PLN)\u0000seen in the soft state.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206845","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Discovery of young, oxygen-rich supernova remnants in PHANGS-MUSE galaxies","authors":"Timo KravtsovUniversity of Turku, Joseph P. AndersonEuropean Southern Observatory, Hanindyo KuncarayaktiUniversity of Turku, Keiichi MaedaKyoto University, Seppo MattilaUniversity of Turku","doi":"arxiv-2409.06504","DOIUrl":"https://doi.org/arxiv-2409.06504","url":null,"abstract":"Context. Supernova remnants (SNRs) are the late stages of supernovae before\u0000their merging into the surrounding medium. Oxygen-rich supernova remnants\u0000represent a rare subtype with strong visible light oxygen emission. Aims. We\u0000present a new method to detect SNRs exploiting the capabilities of modern\u0000visible-light integral-field units based on the shapes of the SNR emission\u0000lines. Methods. We search for unresolved shocked regions with broadened\u0000emission lines using the medium-resolution integral-field spectrograph MUSE on\u0000the Very Large Telescope. The spectral resolving power allows shocked emission\u0000sources to be differentiated from photoionised sources based on the linewidths.\u0000Results. We find 307 supernova remnants, including seven O-rich SNRs. For all\u0000O-rich SNRs, we observe the [O III]{lambda}{lambda}4959,5007 emission\u0000doublet. In addition, we observe emissions from [O\u0000I]{lambda}{lambda}6300,6364, [O II]{lambda}{lambda}7320,7330, H{alpha}+[N\u0000II]{lambda}6583 and [S II]{lambda}{lambda}6717,6731 to varying degrees. The\u0000linewidths for the O-rich SNRs are generally broader than the rest of the SNRs\u0000in the sample of this article. The oxygen emission complexes are reminiscient\u0000of SNR 4449-1 and some long-lasting SNe. For the O-rich SNRs, we also search\u0000for counterparts in archival data of other telescopes; we detect X-ray and\u0000mid-IR counterparts for a number of remnants. Conclusions. We have shown\u0000efficacy of the method to detect SNRs presented in this article. In addition,\u0000the method is also effective in detecting the rare O-rich SNRs, doubling the\u0000sample size in the literature. The origin of O-rich SNRs and their link to\u0000specific SN types or environments is still unclear, but further work into this\u0000new sample will unquestionably help us shed light on these rare remnants.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"185 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142226316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Electromagnetic signatures of black hole clusters in the center of super-Eddington galaxies","authors":"Leandro Abaroa, Gustavo E. Romero","doi":"arxiv-2409.06787","DOIUrl":"https://doi.org/arxiv-2409.06787","url":null,"abstract":"Supermassive black holes (SMBHs) at the centers of active galaxies are fed by\u0000accretion disks that radiate from the infrared or optical to the X-ray bands.\u0000Several types of objects can orbit SMBHs, including massive stars, neutron\u0000stars, clouds from the broad- and narrow-line regions, and X-ray binaries.\u0000Isolated black holes with a stellar origin (BHs of $sim10,M_{odot}$) should\u0000also be present in large numbers within the central parsec of the galaxies.\u0000These BHs are expected to form a cluster around the SMBH as a result of the\u0000enhanced star formation rate in the inner galactic region and the BH migration\u0000caused by gravitational dynamical friction. However, except for occasional\u0000microlensing effects on background stars or gravitational waves from binary BH\u0000mergers, the presence of a BH population is hard to verify. In this paper, we\u0000explore the possibility of detecting electromagnetic signatures of a central\u0000cluster of BHs when the accretion rate onto the central SMBH is greater than\u0000the Eddington rate. In these supercritical systems, the accretion disk launches\u0000powerful winds that interact with the objects orbiting the SMBH. Isolated BHs\u0000can capture matter from this dense wind, leading to the formation of small\u0000accretion disks around them. If jets are produced in these \"single\"\u0000microquasars, they could be sites of particle acceleration to relativistic\u0000energies. These particles in turn are expected to cool by various radiative\u0000processes. Therefore, the wind of the SMBH might illuminate the BHs through the\u0000production of both thermal and nonthermal radiation. We conclude that, under\u0000these circumstances, a cluster of isolated BHs could be detected at X-rays\u0000(with Chandra and XMM-Newton) and radio wavelengths (e.g., with the Very Large\u0000Array and the Square Kilometer Array) in the center of nearby super-Eddington\u0000galaxies.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"32 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206841","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Are the shape and flux of X-ray reflection spectra in hard state consistent with an accretion disk reaching close to the black hole?","authors":"Sudeb Ranjan Datta, Michal Dovčiak, Michal Bursa, Wenda Zhang, Jiří Horák, Vladimír Karas","doi":"arxiv-2409.06621","DOIUrl":"https://doi.org/arxiv-2409.06621","url":null,"abstract":"The observed spectra from black hole (BH) X-ray binaries (XRBs) typically\u0000consist of two primary components: multitemperature blackbody (BB) originating\u0000from the accretion disk in soft X-ray, and a power-law like component in hard\u0000X-ray due to Comptonization of soft photons by the hot corona. Illumination of\u0000the disk by the corona gives rise to another key component known as reflection.\u0000A fraction of the incident hard X-ray radiation is naturally absorbed and\u0000re-emitted as a BB at lower energies, referred to as reprocessed BB. For\u0000densities relevant to XRBs and typical ionization values, the reprocessed BB\u0000may become significant in the soft X-ray region and should be noticeable in the\u0000observed spectra as a consequence of reflection. The absence of any BB\u0000component in the low/hard state of BH XRB may not be consistent with reflection\u0000of high irradiating flux observed as power-law from appropriately dense disk of\u0000XRB. We focus on the low/hard state of the BH XRB MAXI J1820+070. We\u0000simultaneously fit the shape and flux of the reflection spectra, allowing us to\u0000estimate the correct density and ionization of the slab and, correspondingly,\u0000the reprocessed BB. Our fitting suggests that the disk in principle may extend\u0000close to the BH and still the reprocessed BB due to disk illumination remains\u0000small enough to be consistent with the data as opposed to earlier study. The\u0000inner reflection component is highly ionized and its fit is primarily driven by\u0000its contribution to the continuum. The reprocessed BB cannot resolve whether\u0000the disk is extended close to the BH or not in the hard state. For this\u0000specific observation, the flux in inner reflection component turns out to be\u0000quite low with respect to outer reflection or power-law. Outflowing slab corona\u0000covering the inner region of the disk could be the possible geometry of the\u0000source with the underlying disk reaching close to the BH. (shortened)","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206844","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Extragalactic Magnetar Giant Flare GRB 231115A: Insights from Fermi/GBM Observations","authors":"Aaron C. Trigg, Rachel Stewart, Alex van Kooten, Eric Burns, Oliver J. Roberts, Dmitry D. Frederiks, George Younes, Dmitry S. Svinkin, Matthew G. Baring, Zorawar Wadiasingh, Peter Veres, Michael S. Briggs, Lorenzo Scotton, Adam Goldstein, Malte Busmann, Brendan O Connor, Lei Hu, Daniel Gruen, Arno Riffeser, Raphael Zoeller, Antonella Palmese, Daniela Huppenkothen, Chryssa Kouveliotou","doi":"arxiv-2409.06056","DOIUrl":"https://doi.org/arxiv-2409.06056","url":null,"abstract":"We present the detection and analysis of GRB 231115A, a candidate\u0000extragalactic magnetar giant flare (MGF) observed by Fermi/GBM and localized by\u0000INTEGRAL to the starburst galaxy M82. This burst exhibits distinctive temporal\u0000and spectral characteristics that align with known MGFs, including a short\u0000duration and a high peak energy. Gamma-ray analyses reveal significant insights\u0000into this burst, supporting conclusions already established in the literature:\u0000our time-resolved spectral studies provide further evidence that GRB 231115A is\u0000indeed a MGF. Significance calculations also suggest a robust association with\u0000M82, further supported by a high Bayes factor that minimizes the probability of\u0000chance alignment with a neutron star merger. Despite extensive follow-up\u0000efforts, no contemporaneous gravitational wave or radio emissions were\u0000detected. The lack of radio emission sets stringent upper limits on possible\u0000radio luminosity. Constraints from our analysis show no fast radio bursts\u0000(FRBs) associated with two MGFs. X-ray observations conducted post-burst by\u0000Swift/XRT and XMM/Newton provided additional data, though no persistent\u0000counterparts were identified. Our study underscores the importance of\u0000coordinated multi-wavelength follow-up and highlights the potential of MGFs to\u0000enhance our understanding of short GRBs and magnetar activities in the cosmos.\u0000Current MGF identification and follow-up implementation are insufficient for\u0000detecting expected counterparts; however, improvements in these areas may allow\u0000for the recovery of follow-up signals with existing instruments. Future\u0000advancements in observational technologies and methodologies will be crucial in\u0000furthering these studies.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"71 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206846","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The relation between Simulated Multiwavelength Blazar Variability and Stochastic Fluctuations","authors":"Hannes Thiersen, Michael Zacharias, Markus Böttcher","doi":"arxiv-2409.05626","DOIUrl":"https://doi.org/arxiv-2409.05626","url":null,"abstract":"Blazars exhibit multiwavelength variability, a phenomenon whose underlying\u0000mechanisms remain elusive. This study investigates the origin of such\u0000variability through leptonic blazar emission simulations, focusing on\u0000stochastic fluctuations in environmental parameters. By analyzing the spectral\u0000indices of the power spectral densities of the variability, we assess their\u0000relationship with the underlying fluctuations. Our findings reveal that the\u0000variability spectral indices remain almost independent of the variations\u0000responsible for their emergence. This suggests a complex interplay of factors\u0000contributing to the observed multiwavelength variability in blazars.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Unveiling the short and faint X-ray transient nature of IGR J17419-2802","authors":"V. Sguera, L. Sidoli","doi":"arxiv-2409.05567","DOIUrl":"https://doi.org/arxiv-2409.05567","url":null,"abstract":"We report new X-ray results from the INTErnational Gamma-Ray Astrophysics\u0000Laboratory (INTEGRAL), Swift, Chandra, and XMM-Newton observations of the\u0000hitherto poorly studied unidentified X-ray transient IGR J17419-2802. We\u0000studied in detail the temporal, spectral, and energetic properties of three\u0000hard X-ray outbursts detected above 20 keV by INTEGRAL. They are all\u0000characterized by an average X-ray luminosity of 3$times$10$^{35}$~erg~s$^{-1}$\u0000and a constrained duration of a few days. This marks a peculiarly short and\u0000faint X-ray transient nature for IGR J17419-2802. From archival unpublished\u0000soft X-ray observations, we found that the source spends most of the time\u0000undetected at very low X-ray fluxes (down to $<4.7times10^{-14}$ erg cm\u0000$^{-2}$ s$^{-1}$) for a dynamic range >2,000 when in outburst. We provided an\u0000accurate arcsecond-sized source error circle. Inside it, we pinpointed the best\u0000candidate near-infrared counterpart whose photometric properties are compatible\u0000with a late-type spectral nature. Based on our new findings, we suggest that\u0000IGR J17419-2802 is a new member of the very faint X-ray transients (VFXTs)\u0000class. Detailed investigations of VFXT outbursts above 20 keV are particularly\u0000rare. In this respect, our reported INTEGRAL outbursts are among the best\u0000studied to date; in particular, their constrained duration of a few days is\u0000among the shortest ever measured for a VFXT.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142226291","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"3D hybrid fluid-particle jet simulations and the importance of synchrotron radiative losses","authors":"Joana A kramer, Nicholas R. MacDonals, Georgios F. Paraschos, L. Ricci","doi":"arxiv-2409.05256","DOIUrl":"https://doi.org/arxiv-2409.05256","url":null,"abstract":"Context. Relativistic jets in active galactic nuclei are known for their\u0000exceptional energy output, and imaging the synthetic synchrotron emission of\u0000numerical jet simulations is essential for a comparison with observed jet\u0000polarization emission. Aims. Through the use of 3D hybrid fluid-particle jet\u0000simulations (with the PLUTO code), we overcome some of the commonly made\u0000assumptions in relativistic magnetohydrodynamic (RMHD) simulations by using\u0000non-thermal particle attributes to account for the resulting synchrotron\u0000radiation. Polarized radiative transfer and ray-tracing (via the RADMC-3D code)\u0000highlight the differences in total intensity maps when (i) the jet is simulated\u0000purely with the RMHD approach, (ii) a jet tracer is considered in the RMHD\u0000approach, and (iii) a hybrid fluid-particle approach is used. The resulting\u0000emission maps were compared to the example of the radio galaxy Centaurus A.\u0000Methods. We applied the Lagrangian particle module implemented in the latest\u0000version of the PLUTO code. This new module contains a state-of-the-art\u0000algorithm for modeling diffusive shock acceleration and for accounting for\u0000radiative losses in RMHD jet simulations. The module implements the physical\u0000postulates missing in RMHD jet simulations by accounting for a cooled ambient\u0000medium and strengthening the central jet emission. Results. We find a\u0000distinction between the innermost structure of the jet and the back-flowing\u0000material by mimicking the radio emission of the Seyfert II radio galaxy\u0000Centaurus A when considering an edge-brightened jet with an underlying purely\u0000toroidal magnetic field. We demonstrate the necessity of synchrotron cooling as\u0000well as the improvements gained when directly accounting for non-thermal\u0000synchrotron radiation via non-thermal particles.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206561","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Searching for redshifted 2.2 MeV neutron-capture lines from accreting neutron stars: Theoretical X-ray luminosity requirements and INTEGRAL/SPI observations","authors":"L. Ducci, A. Santangelo, S. Tsygankov, A. Mushtukov, C. Ferrigno","doi":"arxiv-2409.05535","DOIUrl":"https://doi.org/arxiv-2409.05535","url":null,"abstract":"Accreting neutron stars (NSs) are expected to emit a redshifted 2.2 MeV line\u0000due to the capture of neutrons produced through the spallation processes of\u0000$^4$He and heavier ions in their atmospheres. Detecting this emission would\u0000offer an independent method for constraining the equation of state of NSs and\u0000provide valuable insights into nuclear reactions occurring in extreme\u0000gravitational and magnetic environments. Typically, a higher mass accretion\u0000rate is expected to result in a higher 2.2 MeV line intensity. However, when\u0000the mass accretion rate approaches the critical threshold, the accretion flow\u0000is decelerated by the radiative force, leading to a less efficient production\u0000of free neutrons and a corresponding drop in the flux of the spectral line.\u0000This makes the brightest X-ray pulsars unsuitable candidates for gamma-ray line\u0000detection. In this work, we present a theoretical framework for predicting the\u0000optimal X-ray luminosity required to detect a redshifted 2.2 MeV line in a\u0000strongly magnetized NS. As the INTEGRAL mission nears its conclusion, we have\u0000undertaken a thorough investigation of the SPI data of this line in a\u0000representative sample of accreting NSs. No redshifted 2.2 MeV line was\u0000detected. For each spectrum, we have determined the 3-sigma upper limits of the\u0000line intensity, assuming different values of the line width. Our findings\u0000suggest that advancing our understanding of the emission mechanism of the 2.2\u0000MeV line, as well as the accretion flow responsible for it, will require a\u0000substantial increase in sensitivity from future MeV missions. For example, for\u0000a bright X-ray binary such as Sco X-1, we would need at least a 3-sigma line\u0000point source sensitivity of ~1E-6 ph/cm^2/s, that is, about two orders of\u0000magnitude better than that currently achieved. [Abridged]","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"58 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"NuSTAR Observation of the TeV-Detected Radio Galaxy 3C 264: Core Emission and the Hot Accretion Flow Contribution","authors":"Ka-Wah Wong, Colin M. Steiner, Allison M. Blum, Dacheng Lin, Rodrigo Nemmen, Jimmy A. Irwin, Daniel R. Wik","doi":"arxiv-2409.05943","DOIUrl":"https://doi.org/arxiv-2409.05943","url":null,"abstract":"3C 264 is one of the few FRI radio galaxies with detected TeV emission. It is\u0000a low-luminosity AGN (LLAGN) and is generally associated with a radiatively\u0000inefficient accretion flow (RIAF). Earlier multiwavelength studies suggest that\u0000the X-ray emission originates from a jet. However, the possibility that the\u0000RIAF can significantly contribute to the X-rays cannot be ruled out. In\u0000particular, hard X-ray emission $gtrsim$10 keV has never been detected, making\u0000it challenging to distinguish between X-ray models. Here we report a NuSTAR\u0000detection up to 25 keV from 3C 264. We also present subpixel deconvolved\u0000Chandra images to resolve jet emission down to ~0.2 arcsec from the center of\u0000the unresolved X-ray core. Together with a simultaneous Swift observation, we\u0000have constrained the dominant hard X-ray emission to be from its unresolved\u0000X-ray core, presumably in its quiescent state. We found evidence of a cutoff in\u0000the energy around 20 keV, indicating that at least some of the X-rays from the\u0000core can be attributed to the RIAF. The Comptonization model suggests an\u0000electron temperature of about 15 keV and an optical depth ranging between 4 and\u00007, following the universality of coronal properties of black hole accretion.\u0000The cutoff energy or electron temperature of 3C 264 is the lowest among those\u0000of other LLAGNs. The detected hard X-ray emission is at least an order of\u0000magnitude higher than that predicted by synchrotron self-Compton models\u0000introduced to explain $gamma$-ray and TeV emission, suggesting that the\u0000synchrotron electrons might be accelerated to higher energies than previously\u0000thought.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"9 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142206851","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}