The population of small-scale brightenings observed across broad regions of the quiet-Sun (QS) corona shows coherent strong periodicities of ≈5 minutes and amplitudes of 20% to 30% of the mean. The periodicity is in the total number of detected brightenings, their creation rate, and their mean lifetime. Atmospheric Imaging Assembly/Solar Dynamics Observatory extreme-ultraviolet data spanning 2 hr shows that the periodicity is significant across broad areas of the QS. The periodicities are strong in the hotter 171 Å (300 s period) and 193 Å (340 s period) channels, but absent from the upper chromospheric 304 Å channel, although periodicities are present in the 304 Å channel in other datasets. The density of brightenings is highest above the photospheric network, with the network concentration becoming increasingly pronounced in the hotter channels. An extended study of 11 QS datasets spanning several years shows that these periodic modulations are common, with most periodicities found in the 4 to 6 minutes range. The time profiles of area and brightness for most brightenings show a gradual, nonimpulsive onset inconsistent with local reconnection, and the brightenings are more likely to appear first in the 171 Å channel, then in the hotter 193 Å channel. This suggests that the most plausible formation mechanism is wave or shock dissipation at or near the transition region, likely connected to spicule activity. This heating is modulated by photospheric p-modes and drives the production of transient brightenings in the QS upper chromosphere, transition region, and low corona.
在安静太阳（QS）日冕的广大区域观测到的小范围增亮显示出约5分钟的相干强周期性，振幅为平均值的20%至30%。周期性体现在探测到的亮度的总数、产生速率和平均寿命上。大气成像组件/太阳动力学观测站2小时的极紫外数据表明，在QS的广大地区，周期性是显著的。在较热的171 Å （300 s周期）和193 Å （340 s周期）通道中周期性很强，而在色球上部的304 Å通道中不存在周期性，尽管在其他数据集中304 Å通道中存在周期性。在光球网络上方，增亮密度最高，在较热的通道中，网络浓度越来越明显。对11个QS数据集的扩展研究表明，这些周期性调制是常见的，大多数周期在4到6分钟的范围内。大多数增亮的面积和亮度的时间分布显示出一个渐进的、非脉冲的开始，与局部重联不一致，而且增亮更有可能首先出现在171 Å通道，然后出现在更热的193 Å通道。这表明，最合理的形成机制是在过渡区或附近的波或激波耗散，可能与针状体活动有关。这种加热由光球p模调制，并驱动QS色球上层、过渡区和低日冕的瞬态增亮产生。
{"title":"Five-minute Periodicities in the Population of Solar Coronal Brightenings","authors":"Huw Morgan, Yeghiazar Taroyan, Harshita Gandhi, Llŷr Humphries and Shaktivel Pillai","doi":"10.3847/1538-4357/ae3e89","DOIUrl":"https://doi.org/10.3847/1538-4357/ae3e89","url":null,"abstract":"The population of small-scale brightenings observed across broad regions of the quiet-Sun (QS) corona shows coherent strong periodicities of ≈5 minutes and amplitudes of 20% to 30% of the mean. The periodicity is in the total number of detected brightenings, their creation rate, and their mean lifetime. Atmospheric Imaging Assembly/Solar Dynamics Observatory extreme-ultraviolet data spanning 2 hr shows that the periodicity is significant across broad areas of the QS. The periodicities are strong in the hotter 171 Å (300 s period) and 193 Å (340 s period) channels, but absent from the upper chromospheric 304 Å channel, although periodicities are present in the 304 Å channel in other datasets. The density of brightenings is highest above the photospheric network, with the network concentration becoming increasingly pronounced in the hotter channels. An extended study of 11 QS datasets spanning several years shows that these periodic modulations are common, with most periodicities found in the 4 to 6 minutes range. The time profiles of area and brightness for most brightenings show a gradual, nonimpulsive onset inconsistent with local reconnection, and the brightenings are more likely to appear first in the 171 Å channel, then in the hotter 193 Å channel. This suggests that the most plausible formation mechanism is wave or shock dissipation at or near the transition region, likely connected to spicule activity. This heating is modulated by photospheric p-modes and drives the production of transient brightenings in the QS upper chromosphere, transition region, and low corona.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"46 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147360925","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 : 2026-03-06DOI: 10.3847/1538-4357/ae4228
Brandon J. Lazard, Nicholas A. Featherstone and Jonathan M. Aurnou
Convection is ubiquitous in stellar and planetary interiors, where it likely plays an integral role in the generation of magnetic fields. As the interiors of these objects remain hidden from direct observation, numerical models of convection are an important tool in the study of astrophysical dynamos. In such models, unrealistically large values of the viscous (ν) and thermal (κ) diffusivities are routinely used as an ad hoc representation of the effects of subgrid-scale turbulence, which is otherwise too small to resolve numerically. However, the functional forms of these diffusion coefficients can vary greatly between studies, complicating efforts to compare between results and against observations. We explore this issue by considering a series of nonrotating, nonmagnetic, solar-like convection models with varying radial functions for the diffusivities and differing boundary conditions. We find that the bulk kinetic energy scales similarly regardless of the diffusivity parameterization. This scaling is consistent with a freefall scaling, wherein viscosity plays a subdominant role in the force balance. We do not, however, observe such diffusion-free behavior in the convective heat transport. Our results also indicate that the functional form adopted for the diffusion coefficients can impact the distribution of turbulence within the convective shell. These results suggest that some care should be taken when comparing solar convection models directly against helioseismic observations.
{"title":"The Effects of Radially Varying Diffusivities on Stellar Convection Zone Dynamics","authors":"Brandon J. Lazard, Nicholas A. Featherstone and Jonathan M. Aurnou","doi":"10.3847/1538-4357/ae4228","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4228","url":null,"abstract":"Convection is ubiquitous in stellar and planetary interiors, where it likely plays an integral role in the generation of magnetic fields. As the interiors of these objects remain hidden from direct observation, numerical models of convection are an important tool in the study of astrophysical dynamos. In such models, unrealistically large values of the viscous (ν) and thermal (κ) diffusivities are routinely used as an ad hoc representation of the effects of subgrid-scale turbulence, which is otherwise too small to resolve numerically. However, the functional forms of these diffusion coefficients can vary greatly between studies, complicating efforts to compare between results and against observations. We explore this issue by considering a series of nonrotating, nonmagnetic, solar-like convection models with varying radial functions for the diffusivities and differing boundary conditions. We find that the bulk kinetic energy scales similarly regardless of the diffusivity parameterization. This scaling is consistent with a freefall scaling, wherein viscosity plays a subdominant role in the force balance. We do not, however, observe such diffusion-free behavior in the convective heat transport. Our results also indicate that the functional form adopted for the diffusion coefficients can impact the distribution of turbulence within the convective shell. These results suggest that some care should be taken when comparing solar convection models directly against helioseismic observations.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147360929","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 : 2026-03-06DOI: 10.3847/1538-4357/ae4358
Lachlan Passenger, Sharan Banagiri, Eric Thrane, Paul D. Lasky, Angela Borchers, Maya Fishbach and Claire S. Ye
The binary black hole merger GW231123 is both the most massive gravitational-wave event observed and has the highest component spins measured to date. The dimensionless spins of the more massive (primary) and less massive (secondary) black holes are measured to be and (90% credible intervals), respectively. Its large mass and extremal spins are challenging to explain through standard binary stellar physics, though a flurry of hypothetical scenarios have been proposed. Hierarchical assembly—i.e., mergers of black holes that are themselves formed from previous generations of mergers—is generally a promising way to explain massive and rapidly spinning black holes. Here, we investigate the possibility that GW231123 was assembled hierarchically in a dense star cluster as the merger of two second-generation black holes. Taking the inferred spin values at face value, we find that it is possible (p ≈ 5%) that a compact binary with component spins like GW231123 could form in a cluster from hierarchical assembly.
{"title":"Is GW231123 a Hierarchical Merger?","authors":"Lachlan Passenger, Sharan Banagiri, Eric Thrane, Paul D. Lasky, Angela Borchers, Maya Fishbach and Claire S. Ye","doi":"10.3847/1538-4357/ae4358","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4358","url":null,"abstract":"The binary black hole merger GW231123 is both the most massive gravitational-wave event observed and has the highest component spins measured to date. The dimensionless spins of the more massive (primary) and less massive (secondary) black holes are measured to be and (90% credible intervals), respectively. Its large mass and extremal spins are challenging to explain through standard binary stellar physics, though a flurry of hypothetical scenarios have been proposed. Hierarchical assembly—i.e., mergers of black holes that are themselves formed from previous generations of mergers—is generally a promising way to explain massive and rapidly spinning black holes. Here, we investigate the possibility that GW231123 was assembled hierarchically in a dense star cluster as the merger of two second-generation black holes. Taking the inferred spin values at face value, we find that it is possible (p ≈ 5%) that a compact binary with component spins like GW231123 could form in a cluster from hierarchical assembly.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147360934","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 : 2026-03-06DOI: 10.3847/1538-4357/ae3f9a
Ana Sofía M. Uzsoy, Andrew K. Saydjari, Arjun Dey, Anand Raichoor, Douglas P. Finkbeiner, Eric Gawiser, Kyoung-Soo Lee, Steven Ahlen, Davide Bianchi, David Brooks, Todd Claybaugh, Andrei Cuceu, Axel de la Macorra, Peter Doel, Andreu Font-Ribera, Jaime E. Forero-Romero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Gaston Gutierrez, Mustapha Ishak, Robert Kehoe, David Kirkby, Anthony Kremin, Martin Landriau, Laurent Le Guillou, Aaron Meisner, Ramon Miquel, John Moustakas, Nathalie Palanque-Delabrouille, Francisco Prada, Ignasi Pérez-Ràfols, Graziano Rossi, Eusebio Sanchez, David Schlegel, Michael Schubnell, Hee-Jong Seo, David Sprayberry, Gregory Tarlé, Benjamin Alan Weaver and Hu Zou
Lyα emitters (LAEs) are valuable high-redshift cosmological probes traditionally identified using specialized narrowband photometric surveys. In ground-based spectroscopy, it can be difficult to distinguish the sharp LAE peak from residual sky emission lines using automated methods, leading to misclassified redshifts. We present a Bayesian spectral component separation technique to automatically determine spectroscopic redshifts for LAEs while marginalizing over sky residuals. We use visually inspected spectra of LAEs obtained using the Dark Energy Spectroscopic Instrument (DESI) to create a data-driven prior and can determine redshift by jointly inferring sky residual, LAE, and residual components for each individual spectrum. We demonstrate this method on 881 spectroscopically observed z = 2–4 DESI LAE candidate spectra and determine their redshifts with >90% accuracy when validated against visually inspected redshifts. Using the Δχ2 value from our pipeline as a proxy for detection confidence, we then explore potential survey design choices and implications for targeting LAEs with medium-band photometry. This method allows for scalability and accuracy in determining redshifts from DESI spectra, and the results provide recommendations for LAE targeting in anticipation of future high-redshift spectroscopic surveys.
{"title":"Bayesian Component Separation for DESI LAE Automated Spectroscopic Redshifts and Photometric Targeting","authors":"Ana Sofía M. Uzsoy, Andrew K. Saydjari, Arjun Dey, Anand Raichoor, Douglas P. Finkbeiner, Eric Gawiser, Kyoung-Soo Lee, Steven Ahlen, Davide Bianchi, David Brooks, Todd Claybaugh, Andrei Cuceu, Axel de la Macorra, Peter Doel, Andreu Font-Ribera, Jaime E. Forero-Romero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Gaston Gutierrez, Mustapha Ishak, Robert Kehoe, David Kirkby, Anthony Kremin, Martin Landriau, Laurent Le Guillou, Aaron Meisner, Ramon Miquel, John Moustakas, Nathalie Palanque-Delabrouille, Francisco Prada, Ignasi Pérez-Ràfols, Graziano Rossi, Eusebio Sanchez, David Schlegel, Michael Schubnell, Hee-Jong Seo, David Sprayberry, Gregory Tarlé, Benjamin Alan Weaver and Hu Zou","doi":"10.3847/1538-4357/ae3f9a","DOIUrl":"https://doi.org/10.3847/1538-4357/ae3f9a","url":null,"abstract":"Lyα emitters (LAEs) are valuable high-redshift cosmological probes traditionally identified using specialized narrowband photometric surveys. In ground-based spectroscopy, it can be difficult to distinguish the sharp LAE peak from residual sky emission lines using automated methods, leading to misclassified redshifts. We present a Bayesian spectral component separation technique to automatically determine spectroscopic redshifts for LAEs while marginalizing over sky residuals. We use visually inspected spectra of LAEs obtained using the Dark Energy Spectroscopic Instrument (DESI) to create a data-driven prior and can determine redshift by jointly inferring sky residual, LAE, and residual components for each individual spectrum. We demonstrate this method on 881 spectroscopically observed z = 2–4 DESI LAE candidate spectra and determine their redshifts with >90% accuracy when validated against visually inspected redshifts. Using the Δχ2 value from our pipeline as a proxy for detection confidence, we then explore potential survey design choices and implications for targeting LAEs with medium-band photometry. This method allows for scalability and accuracy in determining redshifts from DESI spectra, and the results provide recommendations for LAE targeting in anticipation of future high-redshift spectroscopic surveys.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147360926","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 : 2026-03-06DOI: 10.3847/1538-4357/ae40f4
Lucas A. Tarr, N. Dylan Kee, James E. Leake, Mark G. Linton and Peter W. Schuck
Solar eruptions arise from instabilities or loss of equilibria in the solar atmosphere, but routinely inferring the precise magnetic and plasma properties that lead to eruptions is not currently practical using synoptic solar observations. Data-driven simulations offer an appealing alternative. We test our boundary data-driven magnetohydrodynamic (MHD) approach, based on the method of characteristics, on a simulation that includes full MHD, a stratified atmosphere, and the emergence of a model solar magnetic active region, from the photosphere upward. The data-driven simulation is tested against a larger, ab initio “Ground Truth” simulation that extends downward into the convection zone. Our data-driven simulation accurately reproduces the dynamic emergence of the active region above the photosphere, the formation of key topological features throughout the corona, and the subsequent eruption of mass and magnetic field. The total emerged energy matches to better than one percent, the ratio of emerged to eruptive energy is ≈2%, and the actual values of each energy term agree to within 10% between the two cases. Crucially, the data injection cadence, when properly scaled, matches the cadence of synoptic observations of the Sun’s surface magnetic field, and is 3–4 orders of magnitude longer than the inherent CFL time step of the simulations. The stability of the code and fidelity of the results over an entire active region lifetime, from emergence to eruption, strongly suggest that our method will produce reliable results when driven using solar synoptic observations from existing and anticipated ground- and spaced-based observatories.
{"title":"Simulating the Photospheric to Coronal Plasma Using Magnetohydrodynamic Characteristics. III. Validation Including Gravity, Flux Emergence, and an Eruption","authors":"Lucas A. Tarr, N. Dylan Kee, James E. Leake, Mark G. Linton and Peter W. Schuck","doi":"10.3847/1538-4357/ae40f4","DOIUrl":"https://doi.org/10.3847/1538-4357/ae40f4","url":null,"abstract":"Solar eruptions arise from instabilities or loss of equilibria in the solar atmosphere, but routinely inferring the precise magnetic and plasma properties that lead to eruptions is not currently practical using synoptic solar observations. Data-driven simulations offer an appealing alternative. We test our boundary data-driven magnetohydrodynamic (MHD) approach, based on the method of characteristics, on a simulation that includes full MHD, a stratified atmosphere, and the emergence of a model solar magnetic active region, from the photosphere upward. The data-driven simulation is tested against a larger, ab initio “Ground Truth” simulation that extends downward into the convection zone. Our data-driven simulation accurately reproduces the dynamic emergence of the active region above the photosphere, the formation of key topological features throughout the corona, and the subsequent eruption of mass and magnetic field. The total emerged energy matches to better than one percent, the ratio of emerged to eruptive energy is ≈2%, and the actual values of each energy term agree to within 10% between the two cases. Crucially, the data injection cadence, when properly scaled, matches the cadence of synoptic observations of the Sun’s surface magnetic field, and is 3–4 orders of magnitude longer than the inherent CFL time step of the simulations. The stability of the code and fidelity of the results over an entire active region lifetime, from emergence to eruption, strongly suggest that our method will produce reliable results when driven using solar synoptic observations from existing and anticipated ground- and spaced-based observatories.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"15 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147360927","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 : 2026-03-06DOI: 10.3847/1538-4357/ae42c4
R. Moradi, C. W. Wang, E. S. Yorgancioglu and S. N. Zhang
We introduce the accretion-modulated internal shock model as a possible framework for explaining the observational properties of long gamma-ray burst (GRB) prompt emission. In this scenario, the envelope of the prompt light curve follows the time-dependent mass-supply history to the central engine, associated with stellar collapse and, where applicable, fallback accretion, whose early time onset can be approximated by and which subsequently may decay as , producing a photon count rate with a single fast-rise-exponential-decay (FRED)-like profile. In general, the prompt-emission envelope is regulated by a time-dependent mass supply to the central engine, while internal shocks produce the rapid variability. Since we only aim to introduce this framework here, we focus on the simplest single-FRED shape of the prompt emission profiles, while more complex cases involving multiple episodes and interacting shocks will be explored in forthcoming studies. The model indicates correlations between spectral evolution, FRED-pulse narrowing at high energies, and the mass-supply–controlled envelope. Stochastic Lorentz-factor variations of ejected mass- or rate-driven shells, superimposed on the accretion-modulated envelope, explain the coexistence of smooth global trends and irregular short-timescale features, such as the widths of individual pulses in long GRB light curves, offering diagnostic tools for probing the inner engine activity.
{"title":"An Accretion-Modulated Internal Shock Model for Long GRBs","authors":"R. Moradi, C. W. Wang, E. S. Yorgancioglu and S. N. Zhang","doi":"10.3847/1538-4357/ae42c4","DOIUrl":"https://doi.org/10.3847/1538-4357/ae42c4","url":null,"abstract":"We introduce the accretion-modulated internal shock model as a possible framework for explaining the observational properties of long gamma-ray burst (GRB) prompt emission. In this scenario, the envelope of the prompt light curve follows the time-dependent mass-supply history to the central engine, associated with stellar collapse and, where applicable, fallback accretion, whose early time onset can be approximated by and which subsequently may decay as , producing a photon count rate with a single fast-rise-exponential-decay (FRED)-like profile. In general, the prompt-emission envelope is regulated by a time-dependent mass supply to the central engine, while internal shocks produce the rapid variability. Since we only aim to introduce this framework here, we focus on the simplest single-FRED shape of the prompt emission profiles, while more complex cases involving multiple episodes and interacting shocks will be explored in forthcoming studies. The model indicates correlations between spectral evolution, FRED-pulse narrowing at high energies, and the mass-supply–controlled envelope. Stochastic Lorentz-factor variations of ejected mass- or rate-driven shells, superimposed on the accretion-modulated envelope, explain the coexistence of smooth global trends and irregular short-timescale features, such as the widths of individual pulses in long GRB light curves, offering diagnostic tools for probing the inner engine activity.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"75 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147360931","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 : 2026-03-06DOI: 10.3847/1538-4357/ae41b1
Run-Duo Liang, Wen-Xiong Li, Liang-Duan Liu, Ken W. Smith, Stephen J. Smartt, Qin-Yu Wu, Niu Li, Arne Rau, Ling-Zhi Wang, Armin Rest, Ning-Chen Sun, Franz E. Bauer, Ezequiel Treister, Jia-Sheng Huang, Jennifer Chacón, Seán J. Brennan, Matt Nicholl, Ting-Wan Chen, Amar Aryan, Sheng Yang, Albert K.H. Kong, Sofia Rest, Qi-Nan Wang, James H. Gillanders, Dong-Yue Li, An Li, Jun Yang, Qing-Chang Zhao, Hui Sun, Yun-Fei Xu, Zhi-Xing Ling, Thomas J. L. de Boer, Ken C. Chambers, Chien-Cheng Lin, Thomas B. Lowe, Eugene A. Magnier, Richard J. Wainscoat, J. Quirola-Vásquez, Xiao-Feng Wang, Samaporn Tinyanont, Jing-Wei Hu, He-Yang Liu, Hua-Qing Cheng, Hao-Wei Peng, Chen Zhang, Dong-Hua Zhao, Mao-Hai Huang, Yong Chen, Shu-Mei Jia, Cheng-Kui Li, Ju Guan, Chen-Zhou Cui, Yuan Liu and Weimin Yuan
Extragalactic fast X-ray transients (eFXTs) represent a rapidly growing class of high-energy phenomena, whose physical origins remain poorly understood. With its wide-field, sensitive all-sky monitoring, the Einstein Probe (EP) has greatly increased the discovery rate of eFXTs. The search for and identification of the optical counterparts of eFXTs are vital for understanding their classification and constraining their physical origin. Yet, a considerable fraction of eFXTs still lack secure classifications due to the absence of timely follow-up observations. We carry out a systematic search of publicly available optical survey data and transient databases (including the Zwicky Transient Facility and the Transient Name Server) for optical counterparts to eFXT candidates detected by EP. In this paper, we describe our ongoing program and report the first results. Specifically, we identified the eFXT EP240506a to be associated with a UV/optical counterpart, AT 2024ofs. Spectroscopy of its host galaxy with the Very Large Telescope yields a redshift of z = 0.120 ± 0.002. By combining archival survey data with early-time multiwavelength observations, we find that the luminosity and light-curve evolution of AT 2024ofs are consistent with a core-collapse supernova origin. From detectability simulations, we estimate a local event rate density for EP240506a-like events, and completeness-corrected rate of about 36–78 yr−1 Gpc−3 for EP-detected X-ray transients associated with supernovae. Our results demonstrate the potential of EP to uncover prompt high-energy emission from core-collapse supernovae and underscore the critical importance of timely follow-up of future eFXT events.
{"title":"An Archival Optical Counterpart Search for Extragalactic Fast X-Ray Transients Discovered by Einstein Probe","authors":"Run-Duo Liang, Wen-Xiong Li, Liang-Duan Liu, Ken W. Smith, Stephen J. Smartt, Qin-Yu Wu, Niu Li, Arne Rau, Ling-Zhi Wang, Armin Rest, Ning-Chen Sun, Franz E. Bauer, Ezequiel Treister, Jia-Sheng Huang, Jennifer Chacón, Seán J. Brennan, Matt Nicholl, Ting-Wan Chen, Amar Aryan, Sheng Yang, Albert K.H. Kong, Sofia Rest, Qi-Nan Wang, James H. Gillanders, Dong-Yue Li, An Li, Jun Yang, Qing-Chang Zhao, Hui Sun, Yun-Fei Xu, Zhi-Xing Ling, Thomas J. L. de Boer, Ken C. Chambers, Chien-Cheng Lin, Thomas B. Lowe, Eugene A. Magnier, Richard J. Wainscoat, J. Quirola-Vásquez, Xiao-Feng Wang, Samaporn Tinyanont, Jing-Wei Hu, He-Yang Liu, Hua-Qing Cheng, Hao-Wei Peng, Chen Zhang, Dong-Hua Zhao, Mao-Hai Huang, Yong Chen, Shu-Mei Jia, Cheng-Kui Li, Ju Guan, Chen-Zhou Cui, Yuan Liu and Weimin Yuan","doi":"10.3847/1538-4357/ae41b1","DOIUrl":"https://doi.org/10.3847/1538-4357/ae41b1","url":null,"abstract":"Extragalactic fast X-ray transients (eFXTs) represent a rapidly growing class of high-energy phenomena, whose physical origins remain poorly understood. With its wide-field, sensitive all-sky monitoring, the Einstein Probe (EP) has greatly increased the discovery rate of eFXTs. The search for and identification of the optical counterparts of eFXTs are vital for understanding their classification and constraining their physical origin. Yet, a considerable fraction of eFXTs still lack secure classifications due to the absence of timely follow-up observations. We carry out a systematic search of publicly available optical survey data and transient databases (including the Zwicky Transient Facility and the Transient Name Server) for optical counterparts to eFXT candidates detected by EP. In this paper, we describe our ongoing program and report the first results. Specifically, we identified the eFXT EP240506a to be associated with a UV/optical counterpart, AT 2024ofs. Spectroscopy of its host galaxy with the Very Large Telescope yields a redshift of z = 0.120 ± 0.002. By combining archival survey data with early-time multiwavelength observations, we find that the luminosity and light-curve evolution of AT 2024ofs are consistent with a core-collapse supernova origin. From detectability simulations, we estimate a local event rate density for EP240506a-like events, and completeness-corrected rate of about 36–78 yr−1 Gpc−3 for EP-detected X-ray transients associated with supernovae. Our results demonstrate the potential of EP to uncover prompt high-energy emission from core-collapse supernovae and underscore the critical importance of timely follow-up of future eFXT events.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"199 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147360928","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 : 2026-03-05DOI: 10.3847/1538-4357/ae4696
Kritti Sharma, Vikram Ravi, Liam Connor, Elisabeth Krause, Pranjal R. S. and Dhayaa Anbajagane
Fast radio bursts (FRBs) have emerged as powerful probes of baryonic matter in the Universe, offering constraints on cosmological and feedback parameters through their extragalactic dispersion measure–redshift (DMexgal–z) relation. However, the observed FRB population is shaped by complex selection effects arising from instrument sensitivity, DM-dependent search efficiency, and FRB source population redshift evolution. In this work, we quantify the impact of such observational and population selection effects on cosmological inference derived from the conditional distribution p(DMexgal∣z). Using forward-modeled FRB population simulations, we explore progressively realistic survey scenarios incorporating redshift evolution, luminosity function, and instrument DM selection function. To enable rapid likelihood evaluations, we build a neural network emulator for the variance in cosmic DM, σ2[DMcosmic(z)], trained on 5 × 104 baryonification halo model simulations, achieving ≤4% accuracy up to z = 4. We demonstrate that while redshift- and DM-dependent selection effects substantially alter the joint distribution p(DM, z), they have a negligible impact on the conditional distribution p(DMexgal∣z) for current sample sizes. The parameter biases are ≲0.8σ for 102 FRBs, indicating that conditional analyses are robust for present surveys. However, depending on the survey DM-dependent search efficiency, these biases may exceed 3σ for 104 FRBs, thus implying that explicit modeling of selection effects will be essential for next-generation samples.
{"title":"Quantifying the Impact of Selection Effects on FRB DM–z Relation Cosmological Inference","authors":"Kritti Sharma, Vikram Ravi, Liam Connor, Elisabeth Krause, Pranjal R. S. and Dhayaa Anbajagane","doi":"10.3847/1538-4357/ae4696","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4696","url":null,"abstract":"Fast radio bursts (FRBs) have emerged as powerful probes of baryonic matter in the Universe, offering constraints on cosmological and feedback parameters through their extragalactic dispersion measure–redshift (DMexgal–z) relation. However, the observed FRB population is shaped by complex selection effects arising from instrument sensitivity, DM-dependent search efficiency, and FRB source population redshift evolution. In this work, we quantify the impact of such observational and population selection effects on cosmological inference derived from the conditional distribution p(DMexgal∣z). Using forward-modeled FRB population simulations, we explore progressively realistic survey scenarios incorporating redshift evolution, luminosity function, and instrument DM selection function. To enable rapid likelihood evaluations, we build a neural network emulator for the variance in cosmic DM, σ2[DMcosmic(z)], trained on 5 × 104 baryonification halo model simulations, achieving ≤4% accuracy up to z = 4. We demonstrate that while redshift- and DM-dependent selection effects substantially alter the joint distribution p(DM, z), they have a negligible impact on the conditional distribution p(DMexgal∣z) for current sample sizes. The parameter biases are ≲0.8σ for 102 FRBs, indicating that conditional analyses are robust for present surveys. However, depending on the survey DM-dependent search efficiency, these biases may exceed 3σ for 104 FRBs, thus implying that explicit modeling of selection effects will be essential for next-generation samples.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"55 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147358762","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 : 2026-03-05DOI: 10.3847/1538-4357/ae3d33
Vishal Gajjar and Grayce C. Brown
Narrowband radio technosignatures can be significantly modulated by the host star’s exoplanetary interplanetary medium (Exo-IPM), where turbulence in stellar winds and coronal mass ejections (CMEs) imprint spectral broadening. We present a novel framework that maps isotropic wind properties, turbulence strength, observing frequency, and geometry to the spectral broadening of narrowband technosignatures. Anchored to what is likely the largest compilation of empirical spectral-broadening measurements from solar-system spacecraft, we validate and derive a robust radial dependence of spectral broadening from the host star. For Sun-like stars, wind speeds and turbulence strengths are constrained directly from empirical measurements, while for M-dwarfs, these properties are scaled from solar values. Applied to a simulated 1 GHz survey of the nearest 106 stars across orbital properties, orientation, stellar population, and Exo-IPM conditions, the survival function indicates that ∼70% of systems produce >1 Hz and >30% produce >10 Hz of broadening, disproportionately affecting M-dwarf systems, which constitute ∼75% of the stellar population. At 100 MHz, the effects are even more pronounced, with >60% of systems exhibiting >100 Hz of spectral broadening. Although the probability of encountering a CME during a typical technosignature observation is low (<3%), nearly all such encounters induce additional broadening by several orders of magnitude (>103 Hz). This redistribution of power from the expected intrinsic δ-like line into Lorentzian wings suppresses the peak signal-to-noise ratio targeted by standard narrowband pipelines, biasing sensitivity limits and plausibly contributing to the persistent “Great Silence” in narrowband radio technosignature searches over the past several decades.
{"title":"Exo–IPM Scattering as a Hidden Gatekeeper of Narrowband Technosignatures","authors":"Vishal Gajjar and Grayce C. Brown","doi":"10.3847/1538-4357/ae3d33","DOIUrl":"https://doi.org/10.3847/1538-4357/ae3d33","url":null,"abstract":"Narrowband radio technosignatures can be significantly modulated by the host star’s exoplanetary interplanetary medium (Exo-IPM), where turbulence in stellar winds and coronal mass ejections (CMEs) imprint spectral broadening. We present a novel framework that maps isotropic wind properties, turbulence strength, observing frequency, and geometry to the spectral broadening of narrowband technosignatures. Anchored to what is likely the largest compilation of empirical spectral-broadening measurements from solar-system spacecraft, we validate and derive a robust radial dependence of spectral broadening from the host star. For Sun-like stars, wind speeds and turbulence strengths are constrained directly from empirical measurements, while for M-dwarfs, these properties are scaled from solar values. Applied to a simulated 1 GHz survey of the nearest 106 stars across orbital properties, orientation, stellar population, and Exo-IPM conditions, the survival function indicates that ∼70% of systems produce >1 Hz and >30% produce >10 Hz of broadening, disproportionately affecting M-dwarf systems, which constitute ∼75% of the stellar population. At 100 MHz, the effects are even more pronounced, with >60% of systems exhibiting >100 Hz of spectral broadening. Although the probability of encountering a CME during a typical technosignature observation is low (<3%), nearly all such encounters induce additional broadening by several orders of magnitude (>103 Hz). This redistribution of power from the expected intrinsic δ-like line into Lorentzian wings suppresses the peak signal-to-noise ratio targeted by standard narrowband pipelines, biasing sensitivity limits and plausibly contributing to the persistent “Great Silence” in narrowband radio technosignature searches over the past several decades.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147358968","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 : 2026-03-05DOI: 10.3847/1538-4357/ae4489
Chun Huang
X-ray pulse-profile modeling of millisecond pulsars offers a direct route to measuring neutron star masses and radii, thereby constraining the dense-matter equation of state. However, standard analyses typically rely on ad hoc hotspot parameterizations rather than self-consistent physical models. While connecting surface heating directly to the magnetospheric geometry provides a more natural physical pathway, computing global magnetospheric solutions is too computationally expensive to perform on-the-fly during parameter inference. In this work, we bridge this gap by deriving fully analytic, first-principles expressions for surface return currents in mixed dipole–quadrupole magnetospheres. Working within force-free electrodynamics, we generalize the field-aligned current invariant Λ, the crucial scalar that maps the far-zone magnetic structure to the near-zone heating rate, from the standard dipole approximation to arbitrary quadrupolar configurations. We demonstrate that even when the quadrupole component is subdominant in the far zone (the mixing regime), using a dipole-based heating prescription fails to capture the significant enhancement or suppression of the return-current density on the polar cap. Our consistent quadrupole-aware framework reveals that these multipolar currents redistribute the surface heating, leading to systematic discrepancies in predicted pulse profiles that are amplified by atmosphere beaming and can reach ∼30% near pulse peaks. These results provide a rigorous analytic foundation for mapping global magnetic geometry to surface heating in multipolar magnetospheres, enabling physically consistent inference beyond the idealized dipole approximation.
{"title":"First-principles Polar-cap Currents in Multipolar Pulsar Magnetospheres","authors":"Chun Huang","doi":"10.3847/1538-4357/ae4489","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4489","url":null,"abstract":"X-ray pulse-profile modeling of millisecond pulsars offers a direct route to measuring neutron star masses and radii, thereby constraining the dense-matter equation of state. However, standard analyses typically rely on ad hoc hotspot parameterizations rather than self-consistent physical models. While connecting surface heating directly to the magnetospheric geometry provides a more natural physical pathway, computing global magnetospheric solutions is too computationally expensive to perform on-the-fly during parameter inference. In this work, we bridge this gap by deriving fully analytic, first-principles expressions for surface return currents in mixed dipole–quadrupole magnetospheres. Working within force-free electrodynamics, we generalize the field-aligned current invariant Λ, the crucial scalar that maps the far-zone magnetic structure to the near-zone heating rate, from the standard dipole approximation to arbitrary quadrupolar configurations. We demonstrate that even when the quadrupole component is subdominant in the far zone (the mixing regime), using a dipole-based heating prescription fails to capture the significant enhancement or suppression of the return-current density on the polar cap. Our consistent quadrupole-aware framework reveals that these multipolar currents redistribute the surface heating, leading to systematic discrepancies in predicted pulse profiles that are amplified by atmosphere beaming and can reach ∼30% near pulse peaks. These results provide a rigorous analytic foundation for mapping global magnetic geometry to surface heating in multipolar magnetospheres, enabling physically consistent inference beyond the idealized dipole approximation.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"44 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147358977","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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