Pub Date : 2026-04-06DOI: 10.3847/1538-4357/ae4b39
Ross Silver, Núria Torres-Albà, Stefano Marchesi, Vittoria E. Gianolli, Isaiah Cox, Dhrubojyoti Sengupta, Indrani Pal, Marco Ajello, Xiurui Zhao, Kouser Imam and Anuvab Banerjee
This work discusses the broadband X-ray spectral analysis of 11 candidate heavily obscured active galactic nuclei (AGN) selected based on their infrared and X-ray properties by a recently published machine learning algorithm. This paper is part of a larger work to identify and characterize all AGN in the local Universe (z < 0.1) with the largest line-of-sight (los) column densities (NH), the so-called Compton-thick (NH,los ≥ 1024 cm−2) AGN. We modeled the X-ray spectra using two physically motivated models: UXClumpy and RXTorusD. Of the 11 AGN in our sample, we found 3 to be obscured with 22.7 < LogNH,los ≤ 23.0, 5 with 23.0 < LogNH,los ≤ 23.25, and 3 with 23.4 < LogNH,los ≤ 23.9, according to UXClumpy. Meanwhile, according to RXTorusD, we found 3 AGN to be obscured with 22.7 < LogNH,los ≤ 23.0, 4 with 23.0 < LogNH,los ≤ 23.4, and 4 with 23.85 < LogNH,los ≤ 23.96. Additionally, this work served as a comparison between UXClumpy and RXTorusD. We found broad agreement between the two, with 8 of 11 sources agreeing on the value of the photon index Γ, while only 5 of 11 sources agree on the NH,los value within the 90% confidence level.
{"title":"Compton-thick AGN in the NuSTAR Era. XI. Analyzing 11 CT-AGN Candidates Selected with Machine Learning","authors":"Ross Silver, Núria Torres-Albà, Stefano Marchesi, Vittoria E. Gianolli, Isaiah Cox, Dhrubojyoti Sengupta, Indrani Pal, Marco Ajello, Xiurui Zhao, Kouser Imam and Anuvab Banerjee","doi":"10.3847/1538-4357/ae4b39","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4b39","url":null,"abstract":"This work discusses the broadband X-ray spectral analysis of 11 candidate heavily obscured active galactic nuclei (AGN) selected based on their infrared and X-ray properties by a recently published machine learning algorithm. This paper is part of a larger work to identify and characterize all AGN in the local Universe (z < 0.1) with the largest line-of-sight (los) column densities (NH), the so-called Compton-thick (NH,los ≥ 1024 cm−2) AGN. We modeled the X-ray spectra using two physically motivated models: UXClumpy and RXTorusD. Of the 11 AGN in our sample, we found 3 to be obscured with 22.7 < LogNH,los ≤ 23.0, 5 with 23.0 < LogNH,los ≤ 23.25, and 3 with 23.4 < LogNH,los ≤ 23.9, according to UXClumpy. Meanwhile, according to RXTorusD, we found 3 AGN to be obscured with 22.7 < LogNH,los ≤ 23.0, 4 with 23.0 < LogNH,los ≤ 23.4, and 4 with 23.85 < LogNH,los ≤ 23.96. Additionally, this work served as a comparison between UXClumpy and RXTorusD. We found broad agreement between the two, with 8 of 11 sources agreeing on the value of the photon index Γ, while only 5 of 11 sources agree on the NH,los value within the 90% confidence level.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"63 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147625681","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}
Pub Date : 2026-04-06DOI: 10.3847/1538-4357/ae41bf
Padilla Gonzalez E., Joshi B. A., Strolger L. G., Khatri B., Rest F., Rest A., Rose B., Angulo R., Coulter D., Derkacy J. M., Fox O., Griggio M., Larison C., Moore T., Pierel J. D. R., Shahbandeh M., Shukawa K. and Siebert M.
Despite the tremendous impact of Type Ia supernovae (SNe Ia) on the field of cosmology, their underlying physics are still poorly understood. Studies have found an intriguing correlation between standardized SN Ia luminosities and host galaxy masses, commonly referred to as the “mass-step.” SNe Ia in massive galaxies appear systematically brighter than in lower-mass, star-forming hosts after standardization. However, previous analyses utilize host galaxy mass estimates derived largely from optical data alone and assume parametric forms for host star formation histories (SFHs), both of which are known to misestimate galaxy stellar masses. In this work we reexamine the mass-step relation with a sample of SN Ia host galaxies complete in broadband optical (∼3000Å–1 μm) and near-IR (∼1–1.8 μm) and in some cases, with data up to the mid-IR (to ∼4.5 μm), using prospector to derive nonparametric SFHs. We find that while the masses for these sample galaxies have indeed been underestimated, the overall trend in SN Ia luminosity versus host mass remains largely unchanged. However, we also uncover an environmental metallicity-dependent trend, in which low-metallicity galaxies (Z < −1 Z⊙) may drive much of the observed SN Ia luminosity–mass correlation, suggesting that chemical composition of the SN environment may play a central role in shaping the standardized brightness of SNe Ia.
{"title":"Revisiting the Mass Step: Environmental Dependence of Type Ia Supernovae in Low-metallicity Host Galaxies","authors":"Padilla Gonzalez E., Joshi B. A., Strolger L. G., Khatri B., Rest F., Rest A., Rose B., Angulo R., Coulter D., Derkacy J. M., Fox O., Griggio M., Larison C., Moore T., Pierel J. D. R., Shahbandeh M., Shukawa K. and Siebert M.","doi":"10.3847/1538-4357/ae41bf","DOIUrl":"https://doi.org/10.3847/1538-4357/ae41bf","url":null,"abstract":"Despite the tremendous impact of Type Ia supernovae (SNe Ia) on the field of cosmology, their underlying physics are still poorly understood. Studies have found an intriguing correlation between standardized SN Ia luminosities and host galaxy masses, commonly referred to as the “mass-step.” SNe Ia in massive galaxies appear systematically brighter than in lower-mass, star-forming hosts after standardization. However, previous analyses utilize host galaxy mass estimates derived largely from optical data alone and assume parametric forms for host star formation histories (SFHs), both of which are known to misestimate galaxy stellar masses. In this work we reexamine the mass-step relation with a sample of SN Ia host galaxies complete in broadband optical (∼3000Å–1 μm) and near-IR (∼1–1.8 μm) and in some cases, with data up to the mid-IR (to ∼4.5 μm), using prospector to derive nonparametric SFHs. We find that while the masses for these sample galaxies have indeed been underestimated, the overall trend in SN Ia luminosity versus host mass remains largely unchanged. However, we also uncover an environmental metallicity-dependent trend, in which low-metallicity galaxies (Z < −1 Z⊙) may drive much of the observed SN Ia luminosity–mass correlation, suggesting that chemical composition of the SN environment may play a central role in shaping the standardized brightness of SNe Ia.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"19 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147625630","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}
Pub Date : 2026-04-06DOI: 10.3847/1538-4357/ae52f3
Yukiya Saito, Ante Ravlić, Pranav Nalamwar and Rebecca Surman
β-decay is known to play an essential role in the rapid neutron capture process (r-process) during (n, γ) ↔ (γ, n) equilibrium and freeze-out when the neutron-rich nuclei decay back to stability. Recent systematic theoretical studies on β-decay at finite temperature indicated that under hot conditions (T ∼ 10 GK), a significant acceleration of β-decay rates is expected, especially for nuclei near stability. This corresponds to the early stage of the r-process. In this study, we investigate the effect of the β-decays in finite temperature using the rates calculated with the finite-temperature proton–neutron relativistic quasiparticle random-phase approximation. We explore a variety of astrophysical conditions and find that the effect on the abundance pattern is significant in hot and moderately neutron-rich conditions such as are expected in magnetorotational supernovae. Accelerated β-decay rates also increase the heating rate in the early phase, resulting in an additional modification of the final abundance pattern.
{"title":"Effect of Finite-temperature β-decay Rates on the Rapid Neutron Capture Process","authors":"Yukiya Saito, Ante Ravlić, Pranav Nalamwar and Rebecca Surman","doi":"10.3847/1538-4357/ae52f3","DOIUrl":"https://doi.org/10.3847/1538-4357/ae52f3","url":null,"abstract":"β-decay is known to play an essential role in the rapid neutron capture process (r-process) during (n, γ) ↔ (γ, n) equilibrium and freeze-out when the neutron-rich nuclei decay back to stability. Recent systematic theoretical studies on β-decay at finite temperature indicated that under hot conditions (T ∼ 10 GK), a significant acceleration of β-decay rates is expected, especially for nuclei near stability. This corresponds to the early stage of the r-process. In this study, we investigate the effect of the β-decays in finite temperature using the rates calculated with the finite-temperature proton–neutron relativistic quasiparticle random-phase approximation. We explore a variety of astrophysical conditions and find that the effect on the abundance pattern is significant in hot and moderately neutron-rich conditions such as are expected in magnetorotational supernovae. Accelerated β-decay rates also increase the heating rate in the early phase, resulting in an additional modification of the final abundance pattern.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147625674","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}
Pub Date : 2026-04-06DOI: 10.3847/1538-4357/ae53de
Rui-Qi Huang, Xin-Ke Hu, Yu-Wei Yu, Ji-Shun Lian and Jin Zhang
We present a comprehensive analysis of the 17 yr Fermi-LAT observational data of Mrk 421 to investigate the spectral variations in the γ-ray bands. The light curve of the source in the 0.1–1000 GeV band with a 14 day time bin exhibits significant variability at a confidence level exceeding 5σ, which is accompanied by spectral variation, displaying a harder-when-brighter behavior. Moreover, its flux variation can reach up to 1 order of magnitude within 1 day, with a daily flux up to (1.19 ± 0.84) × 10−8 erg cm−2 s−1 on MJD 56152. The 17 yr integrated spectrum of Mrk 421 necessitates a complex model for explanation, whereas its time-resolved spectra over 1 day or several-day time intervals can be well fitted by a power-law model. We propose that the complex spectral shape of the 17 yr integrated spectrum stems from the superposition of different spectral shapes in different flux states. By generating the GeV spectra that are simultaneously observed with the archived TeV observations and constructing the combined GeV–TeV spectra, we find that some combined GeV–TeV spectral shapes clearly imply different radiation origins for the GeV and TeV emissions, challenging the one-zone leptonic model. It is found that the flux follows a lognormal distribution, while the photon spectral index distributions can be well fitted by either a lognormal or a Gaussian function. The possible nature of the γ-ray variability in Mrk 421 is discussed.
{"title":"Spectral Variations of γ-Rays in Mrk 421","authors":"Rui-Qi Huang, Xin-Ke Hu, Yu-Wei Yu, Ji-Shun Lian and Jin Zhang","doi":"10.3847/1538-4357/ae53de","DOIUrl":"https://doi.org/10.3847/1538-4357/ae53de","url":null,"abstract":"We present a comprehensive analysis of the 17 yr Fermi-LAT observational data of Mrk 421 to investigate the spectral variations in the γ-ray bands. The light curve of the source in the 0.1–1000 GeV band with a 14 day time bin exhibits significant variability at a confidence level exceeding 5σ, which is accompanied by spectral variation, displaying a harder-when-brighter behavior. Moreover, its flux variation can reach up to 1 order of magnitude within 1 day, with a daily flux up to (1.19 ± 0.84) × 10−8 erg cm−2 s−1 on MJD 56152. The 17 yr integrated spectrum of Mrk 421 necessitates a complex model for explanation, whereas its time-resolved spectra over 1 day or several-day time intervals can be well fitted by a power-law model. We propose that the complex spectral shape of the 17 yr integrated spectrum stems from the superposition of different spectral shapes in different flux states. By generating the GeV spectra that are simultaneously observed with the archived TeV observations and constructing the combined GeV–TeV spectra, we find that some combined GeV–TeV spectral shapes clearly imply different radiation origins for the GeV and TeV emissions, challenging the one-zone leptonic model. It is found that the flux follows a lognormal distribution, while the photon spectral index distributions can be well fitted by either a lognormal or a Gaussian function. The possible nature of the γ-ray variability in Mrk 421 is discussed.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"43 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147625684","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}
Pub Date : 2026-04-06DOI: 10.3847/1538-4357/ae4e18
Tomoharu Oka, Ryo Ariyama and Tatsuya Kotani
We report the detection of a molecular cloud, CO+40.05–2.40, positionally coincident with the “heartbeating” GeV source Fermi J1913+0515 at the northern boundary of the SS 433/W50 system. Millimeter and submillimeter spectroscopy with the Nobeyama 45 m Telescope and the James Clerk Maxwell Telescope shows that the cloud has physical properties typical of quiescent dark clouds in the Galactic disk, with no evidence of shock heating or enhanced excitation. We examine possible high-energy emission mechanisms and find that the observed GeV luminosity cannot be accounted for by electron bremsstrahlung or hadronic interactions driven by relativistic particles originating from SS 433 under reasonable energetic assumptions. As an alternative, we propose that the gamma rays may arise from a compact object embedded within the cloud and powered by Bondi-type accretion. In this framework, the reported heartbeat-like variability may reflect periodic modulation of the accretion flow by density waves induced by the precessing equatorial outflow of SS 433.
{"title":"Detection of a Molecular Cloud toward the Heartbeating Gamma-Ray Source near the Microquasar SS 433","authors":"Tomoharu Oka, Ryo Ariyama and Tatsuya Kotani","doi":"10.3847/1538-4357/ae4e18","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4e18","url":null,"abstract":"We report the detection of a molecular cloud, CO+40.05–2.40, positionally coincident with the “heartbeating” GeV source Fermi J1913+0515 at the northern boundary of the SS 433/W50 system. Millimeter and submillimeter spectroscopy with the Nobeyama 45 m Telescope and the James Clerk Maxwell Telescope shows that the cloud has physical properties typical of quiescent dark clouds in the Galactic disk, with no evidence of shock heating or enhanced excitation. We examine possible high-energy emission mechanisms and find that the observed GeV luminosity cannot be accounted for by electron bremsstrahlung or hadronic interactions driven by relativistic particles originating from SS 433 under reasonable energetic assumptions. As an alternative, we propose that the gamma rays may arise from a compact object embedded within the cloud and powered by Bondi-type accretion. In this framework, the reported heartbeat-like variability may reflect periodic modulation of the accretion flow by density waves induced by the precessing equatorial outflow of SS 433.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"76 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147625627","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}
Pub Date : 2026-04-06DOI: 10.3847/1538-4357/ae4d19
Shing-Chi Leung, Henry Yerdon, Seth Walther, Ken’ichi Nomoto and Aurora Simionescu
The Perseus Cluster has been precisely measured by the legacy Hitomi telescope on the Si-group (Si, S, Ar, Ca) and Fe-group elements (Cr, Mn, Ni). These element abundance ratios provide insight into the typical behavior of supernovae. In Leung et al., we presented new massive star explosion models at various metallicity, assuming spherical explosions. We show that while the fitting is improved, some features (e.g., Ni/Fe) remain to be improved. In this article, we extend our calculation to an aspherical explosion using the jet-induced explosion mechanism. The detailed pre- and postexplosion chemical profiles are calculated with a large postprocessing network to capture the production of odd-number elements (V, Mn, Cu) and iron-group elements. We further explore how the jet-driven explosions create the diversity of models which could be compatible with the observed diversity in terms of 56Ni mass versus ejecta mass, Ti–V relation, and stellar abundances. Finally, we apply the new collapsar models in the Galactic Chemical Evolution context. We study how the Galactic stars, including the Zn-enriched star HE 1327–2326, can put constraints on the relative rates of collapsar and some of its model parameters. We show that collapsar could lead to significant changes in some elements, e.g., Zn. Our study shows that the collapsar is a necessary component to explain multiple elemental trends observed in the Milky Way Galaxy.
{"title":"Revisiting the Perseus Cluster. III. Role of Aspherical Explosions on Its Chemical Composition and Extension to Metal-poor Stars and Galaxies","authors":"Shing-Chi Leung, Henry Yerdon, Seth Walther, Ken’ichi Nomoto and Aurora Simionescu","doi":"10.3847/1538-4357/ae4d19","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4d19","url":null,"abstract":"The Perseus Cluster has been precisely measured by the legacy Hitomi telescope on the Si-group (Si, S, Ar, Ca) and Fe-group elements (Cr, Mn, Ni). These element abundance ratios provide insight into the typical behavior of supernovae. In Leung et al., we presented new massive star explosion models at various metallicity, assuming spherical explosions. We show that while the fitting is improved, some features (e.g., Ni/Fe) remain to be improved. In this article, we extend our calculation to an aspherical explosion using the jet-induced explosion mechanism. The detailed pre- and postexplosion chemical profiles are calculated with a large postprocessing network to capture the production of odd-number elements (V, Mn, Cu) and iron-group elements. We further explore how the jet-driven explosions create the diversity of models which could be compatible with the observed diversity in terms of 56Ni mass versus ejecta mass, Ti–V relation, and stellar abundances. Finally, we apply the new collapsar models in the Galactic Chemical Evolution context. We study how the Galactic stars, including the Zn-enriched star HE 1327–2326, can put constraints on the relative rates of collapsar and some of its model parameters. We show that collapsar could lead to significant changes in some elements, e.g., Zn. Our study shows that the collapsar is a necessary component to explain multiple elemental trends observed in the Milky Way Galaxy.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"19 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147625620","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}
Pub Date : 2026-04-06DOI: 10.3847/1538-4357/ae5183
Hanya Pan, Astrid M. Veronig, Rui Liu, Yuncong Li and Tingyu Gou
Supra-arcade downflows (SADs)—dark, tadpole-like, sunward-moving structures observed above post-flare loops—are considered key signatures of magnetic reconnection in solar eruptions. However, their physical origin and connection to reconnection dynamics remain controversial. In particular, their connection to hard X-ray (HXR) emission has been elusive, as they are predominantly observed during the flare decay phase. In this study, we investigate SADs that occurred during the late decay phase of a long-duration M6.7 flare on 2022 August 22 and their relationship with HXR emission, observed by the Solar Dynamics Observatory and Solar Orbiter. While thermal HXR emission dominates most of the decay phase, a significant nonthermal HXR enhancement with an electron power-law index of δ ≈ 2.5 coincides temporally with the appearance of SADs. Notably, we identify a nonthermal HXR source spatially associated with a well-defined SAD interacting with a supra-arcade spike. This spatiotemporal correlation—reported for the first time during the late decay phase—substantiates the association between SADs and ongoing magnetic reconnection. With the kink wave phase speed (≈400 km s−1) derived from spike oscillations and the density and temperature derived from a differential emission measure analysis, we estimate that the local magnetic field strength is in the range of 1.9–3.4 G, and the plasma β in the spike is on the order of unity. This analysis provides new insights into the physical nature of the supra-arcade structures and highlights the role of the magnetic field in their generation and evolution.
超拱桥下流（SADs）——在耀斑后环上观察到的黑暗的、蝌蚪状的、向太阳移动的结构——被认为是太阳爆发中磁重联的关键特征。然而，它们的物理起源和与重联动力学的联系仍然存在争议。特别是，它们与硬x射线（HXR）发射的联系一直难以捉摸，因为它们主要是在耀斑衰变阶段观察到的。在这项研究中，我们研究了在2022年8月22日发生的长时间M6.7耀斑的衰变后期阶段发生的SADs及其与太阳动力学观测站和太阳轨道飞行器观测到的HXR发射的关系。虽然热HXR辐射在大部分衰变阶段占主导地位，但电子幂律指数δ≈2.5的非热HXR显著增强与SADs的出现在时间上一致。值得注意的是，我们确定了一个非热HXR源在空间上与一个定义明确的SAD与一个超级街机尖峰相互作用有关。这种时空相关性首次在衰变后期被报道，证实了SADs与正在进行的磁重联之间的联系。利用尖峰振荡得到的扭结波相速度（≈400 km s−1）和差分发射测量分析得到的密度和温度，我们估计局部磁场强度在1.9 ~ 3.4 G之间，尖峰中的等离子体β在一个数量级上。这一分析为超级拱廊结构的物理性质提供了新的见解，并强调了磁场在其产生和演变中的作用。
{"title":"Nonthermal X-Ray Emission Associated with Supra-arcade Downflows in the Late Decay Phase of a Solar Flare","authors":"Hanya Pan, Astrid M. Veronig, Rui Liu, Yuncong Li and Tingyu Gou","doi":"10.3847/1538-4357/ae5183","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5183","url":null,"abstract":"Supra-arcade downflows (SADs)—dark, tadpole-like, sunward-moving structures observed above post-flare loops—are considered key signatures of magnetic reconnection in solar eruptions. However, their physical origin and connection to reconnection dynamics remain controversial. In particular, their connection to hard X-ray (HXR) emission has been elusive, as they are predominantly observed during the flare decay phase. In this study, we investigate SADs that occurred during the late decay phase of a long-duration M6.7 flare on 2022 August 22 and their relationship with HXR emission, observed by the Solar Dynamics Observatory and Solar Orbiter. While thermal HXR emission dominates most of the decay phase, a significant nonthermal HXR enhancement with an electron power-law index of δ ≈ 2.5 coincides temporally with the appearance of SADs. Notably, we identify a nonthermal HXR source spatially associated with a well-defined SAD interacting with a supra-arcade spike. This spatiotemporal correlation—reported for the first time during the late decay phase—substantiates the association between SADs and ongoing magnetic reconnection. With the kink wave phase speed (≈400 km s−1) derived from spike oscillations and the density and temperature derived from a differential emission measure analysis, we estimate that the local magnetic field strength is in the range of 1.9–3.4 G, and the plasma β in the spike is on the order of unity. This analysis provides new insights into the physical nature of the supra-arcade structures and highlights the role of the magnetic field in their generation and evolution.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"43 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147625622","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}
Pub Date : 2026-04-06DOI: 10.3847/1538-4357/ae5184
Ramiz Aktar, Kuo-Chuan Pan and Toru Okuda
We perform 3D radiation-relativistic magnetohydrodynamic (3D Rad-RMHD) simulations of accretion flows around spinning active galactic nuclei. Our study focuses on the magnetically arrested disk (MAD) state, adopting a single-temperature model that includes bremsstrahlung opacity as the sole radiation process while varying the black hole spin from nonspinning to rapidly spinning cases. We find that the MAD state persists across all spin values, as demonstrated by the normalized magnetic flux at the horizon and the physically motivated spatially averaged plasma beta. The overall flow dynamics remain qualitatively similar for all spin models in 3D flow, suggesting that black hole spin has minimal influence on the accretion dynamics. In addition, we conduct postprocessing using a two-temperature model to calculate the luminosities from synchrotron and bremsstrahlung radiation. We find that the total radiation luminosity is significantly higher than the luminosities from synchrotron and bremsstrahlung. This finding highlights the influence of radiation on the dynamics of the accretion flow. Our analysis shows that the electron temperature is significantly high in the jet region, regardless of spin. We further find that the temporal evolution of both radiative and synchrotron luminosities exhibits qualitatively similar behavior across all spin values. Finally, our results indicate that black hole spin has minimal impact on the spectral energy distribution in MAD state accretion flows.
{"title":"3D Global Relativistic Radiation Magnetohydrodynamics of Magnetically Arrested Disk Accretion Flows in Active Galactic Nuclei","authors":"Ramiz Aktar, Kuo-Chuan Pan and Toru Okuda","doi":"10.3847/1538-4357/ae5184","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5184","url":null,"abstract":"We perform 3D radiation-relativistic magnetohydrodynamic (3D Rad-RMHD) simulations of accretion flows around spinning active galactic nuclei. Our study focuses on the magnetically arrested disk (MAD) state, adopting a single-temperature model that includes bremsstrahlung opacity as the sole radiation process while varying the black hole spin from nonspinning to rapidly spinning cases. We find that the MAD state persists across all spin values, as demonstrated by the normalized magnetic flux at the horizon and the physically motivated spatially averaged plasma beta. The overall flow dynamics remain qualitatively similar for all spin models in 3D flow, suggesting that black hole spin has minimal influence on the accretion dynamics. In addition, we conduct postprocessing using a two-temperature model to calculate the luminosities from synchrotron and bremsstrahlung radiation. We find that the total radiation luminosity is significantly higher than the luminosities from synchrotron and bremsstrahlung. This finding highlights the influence of radiation on the dynamics of the accretion flow. Our analysis shows that the electron temperature is significantly high in the jet region, regardless of spin. We further find that the temporal evolution of both radiative and synchrotron luminosities exhibits qualitatively similar behavior across all spin values. Finally, our results indicate that black hole spin has minimal impact on the spectral energy distribution in MAD state accretion flows.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"37 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147625623","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}
Pub Date : 2026-04-06DOI: 10.3847/1538-4357/ae5222
Meghna Sitaram, Hui Li, Yong Zheng, Greg L. Bryan, Mary Putman, Aaron Smith and Rahul Kannan
Isolated star-forming galaxies require inflows of fresh gas from the surrounding medium to sustain episodes of star formation over time. However, there are very few direct detections of accretion onto external galaxies. Studies in absorption can only observe along limited sightlines, while those in emission can have difficulty distinguishing inflowing gas in the foreground of the galactic disk from similarly Doppler-shifted outflowing gas in the background. We explore the possibility of using the Balmer decrement (Hα/Hβ) in low-inclination systems as a diagnostic for disentangling the flow geometry in disk-like galaxies. We leverage mock spatial–spectral observations of an isolated Milky Way–mass galaxy simulated using the radiation-hydrodynamics code AREPO-RT and post-processed with the Monte Carlo radiative transfer code COLT. We find that gas components located in front of the disk exhibit systematically lower Balmer decrements than gas embedded in or behind the disk, with a mean front–back offset of Δ(Hα/Hβ) ≈ –0.14. The ability to differentiate between the disk and far-side components is limited by the extremely clumpy, multiphase dust distribution along the line of sight introducing substantial scatter. Overall, the results provide a useful observational diagnostic of inflow and outflow in dusty face-on galaxies.
{"title":"Identifying Signatures of Inflow onto Face-on Galaxies Using the Balmer Decrement","authors":"Meghna Sitaram, Hui Li, Yong Zheng, Greg L. Bryan, Mary Putman, Aaron Smith and Rahul Kannan","doi":"10.3847/1538-4357/ae5222","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5222","url":null,"abstract":"Isolated star-forming galaxies require inflows of fresh gas from the surrounding medium to sustain episodes of star formation over time. However, there are very few direct detections of accretion onto external galaxies. Studies in absorption can only observe along limited sightlines, while those in emission can have difficulty distinguishing inflowing gas in the foreground of the galactic disk from similarly Doppler-shifted outflowing gas in the background. We explore the possibility of using the Balmer decrement (Hα/Hβ) in low-inclination systems as a diagnostic for disentangling the flow geometry in disk-like galaxies. We leverage mock spatial–spectral observations of an isolated Milky Way–mass galaxy simulated using the radiation-hydrodynamics code AREPO-RT and post-processed with the Monte Carlo radiative transfer code COLT. We find that gas components located in front of the disk exhibit systematically lower Balmer decrements than gas embedded in or behind the disk, with a mean front–back offset of Δ(Hα/Hβ) ≈ –0.14. The ability to differentiate between the disk and far-side components is limited by the extremely clumpy, multiphase dust distribution along the line of sight introducing substantial scatter. Overall, the results provide a useful observational diagnostic of inflow and outflow in dusty face-on galaxies.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147625625","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}
Pub Date : 2026-04-06DOI: 10.3847/1538-4357/ae50ee
Tyler R. Hinrichs, Patrick S. Kamieneski, Rogier A. Windhorst, Seth H. Cohen, Brenda L. Frye, Timothy Carleton, Massimo Pascale, Jose M. Diego, Rolf A. Jansen, Jessica Berkheimer, Nathan J. Adams, Christopher J. Conselice, Simon P. Driver, Nicholas Foo, Nikhil Garuda, Nimish P. Hathi, Rachel Honor, Anton M. Koekemoer, Rafael Ortiz III, Marta Reina-Campos, Aaron S. G. Robotham, Jake S. Summers, Haojing Yan and William E. Harris
Although the James Webb Space Telescope has received much attention for its ability to search deeper into the cosmos than ever before, it also enhances our capability to study objects closer to us in the Universe. We apply a methodology of subtracting intracluster light from the PLCK G165.7+67.0 (G165; z = 0.35) cluster, revealing a population of unresolved pointlike sources including globular clusters (GCs). By applying a fitting algorithm in color space used to select galaxy cluster members, we uncover over 900 GC candidates from our point-source sample. We also identify candidates by estimating the contribution of interlopers to the point-source sample, yielding an estimate of 793 ± 83 GC candidates. We find the color-selected sources to be approximately spatially correlated with the intracluster light and lensing mass of the cluster. The observed luminosity function of the sources shows a turnover point fainter than the completeness limit, so we use fixed-parameter curve-fitting models to predict a k-corrected turnover point in the range −9.4 mag ≤ MF200W ≤ −10.7 mag, although we predict the expected k-corrected turnover point should be closer to −7.7 mag ≤ MF200W ≤ −8.4 mag. We discuss the dynamical state of this disturbed galaxy cluster with a bimodal mass distribution using the spatial distribution of GC candidates and find that the radial profiles of our color-selected GC candidates are very consistent with the lensing-derived surface mass density at >50 kpc.
{"title":"Hidden in Plain Sight: Searching for Globular Clusters within JWST Observations of the PLCK G165.7+67.0 Galaxy Cluster","authors":"Tyler R. Hinrichs, Patrick S. Kamieneski, Rogier A. Windhorst, Seth H. Cohen, Brenda L. Frye, Timothy Carleton, Massimo Pascale, Jose M. Diego, Rolf A. Jansen, Jessica Berkheimer, Nathan J. Adams, Christopher J. Conselice, Simon P. Driver, Nicholas Foo, Nikhil Garuda, Nimish P. Hathi, Rachel Honor, Anton M. Koekemoer, Rafael Ortiz III, Marta Reina-Campos, Aaron S. G. Robotham, Jake S. Summers, Haojing Yan and William E. Harris","doi":"10.3847/1538-4357/ae50ee","DOIUrl":"https://doi.org/10.3847/1538-4357/ae50ee","url":null,"abstract":"Although the James Webb Space Telescope has received much attention for its ability to search deeper into the cosmos than ever before, it also enhances our capability to study objects closer to us in the Universe. We apply a methodology of subtracting intracluster light from the PLCK G165.7+67.0 (G165; z = 0.35) cluster, revealing a population of unresolved pointlike sources including globular clusters (GCs). By applying a fitting algorithm in color space used to select galaxy cluster members, we uncover over 900 GC candidates from our point-source sample. We also identify candidates by estimating the contribution of interlopers to the point-source sample, yielding an estimate of 793 ± 83 GC candidates. We find the color-selected sources to be approximately spatially correlated with the intracluster light and lensing mass of the cluster. The observed luminosity function of the sources shows a turnover point fainter than the completeness limit, so we use fixed-parameter curve-fitting models to predict a k-corrected turnover point in the range −9.4 mag ≤ MF200W ≤ −10.7 mag, although we predict the expected k-corrected turnover point should be closer to −7.7 mag ≤ MF200W ≤ −8.4 mag. We discuss the dynamical state of this disturbed galaxy cluster with a bimodal mass distribution using the spatial distribution of GC candidates and find that the radial profiles of our color-selected GC candidates are very consistent with the lensing-derived surface mass density at >50 kpc.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147625621","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}
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