LB-1 is a binary system that has drawn great attention since its discovery in 2019.The two components of LB-1 are suggested to be a B-type star plus a black hole (BH).In this paper,we first calculate the wind mass-los...LB-1 is a binary system that has drawn great attention since its discovery in 2019.The two components of LB-1 are suggested to be a B-type star plus a black hole (BH).In this paper,we first calculate the wind mass-loss rate of the B-type star.We then calculate the mass capture rate by the BH,with which as the initial mass accretion rate,we calculate the truncation radius of the accretion disk and the corresponding emergent spectra of the accretion flow(comprising an inner advection-dominated accretion flow (ADAF)+an outer truncated accretion disk) within the framework of the disk evaporation model.It is found that the predicted truncation radius of the accretion disk with appropriate model parameters is consistent with observations inferred from the observed broad H_(α) emission line.The predicted X-ray luminosity is definitely below the estimated upper limits with the sensitivity of the Chandra X-ray Observatory of the X-ray luminosity≈2×10^(31)ergs^(-1),which is also consistent with observations.Finally,we argue that the disk evaporation model can indeed reflect the intrinsic physics of the accretion flow in LB-1,and has potential to be applied to other quiescent BHs in the future.展开更多
X-ray observations play a crucial role in time-domain astronomy.The Einstein Probe(EP),a recently launched X-ray astronomical satellite,emerges as a forefront player in the field of time-domain astronomy and high-ener...X-ray observations play a crucial role in time-domain astronomy.The Einstein Probe(EP),a recently launched X-ray astronomical satellite,emerges as a forefront player in the field of time-domain astronomy and high-energy astrophysics.With a focus on systematic surveys in the soft X-ray band,EP aims to discover high-energy transients and monitor variable sources in the universe.To achieve these objectives,a quick and reliable classification of observed sources is essential.In this study,we developed a machine learning classifier for autonomous source classification using data from the EP-WXT Pathfinder—Lobster Eye Imager for Astronomy(LEIA)and EP-WXT simulations.The proposed Random Forest classifier,built on selected features derived from light curves,energy spectra,and location information,achieves an accuracy of approximately 95%on EP simulation data and 98%on LEIA observational data.The classifier is integrated into the LEIA data processing pipeline,serving as a tool for manual validation and rapid classification during observations.This paper presents an efficient method for the classification of X-ray sources based on single observations,along with implications of most effective features for the task.This work facilitates rapid source classification for the EP mission and also provides valuable insights into feature selection and classification techniques for enhancing the efficiency and accuracy of X-ray source classification that can be adapted to other X-ray telescope data.展开更多
We present the timing and spectral studies of the Be/X-ray binary XTE J1946+274 during its 2018 and 2021 giant outbursts using observations with the SXT and LAXPC instruments on the AstroSat satellite.Unlike the 1998 ...We present the timing and spectral studies of the Be/X-ray binary XTE J1946+274 during its 2018 and 2021 giant outbursts using observations with the SXT and LAXPC instruments on the AstroSat satellite.Unlike the 1998 and 2010 outbursts,where a giant outburst was followed by several low intensity periodic outbursts,the 2018 and 2021 outbursts were single outbursts.The X-ray pulsations are detected over a broad energy band covering 0.5–80 keV from the compact object.We construct the spin evolution history of the pulsar over two decades and find that the pulsar spins-up during the outbursts but switches to spin-down state in the quiescent periods between the outbursts.Energy resolved pulse profiles generated in several bands in 0.5–80 keV show that the pulse shape varies with the energy.The energy spectrum of the pulsar is determined for the 2018 and 2021 outbursts.The best fit spectral models require presence of cyclotron resonant scattering feature at about 43 keV in the energy spectra of both the outbursts.We find indication of possible reversal in the correlation between the cyclotron line energy and luminosity which needs to be ascertained from future observations.Using the best fit spectra the X-ray luminosity of XTE J1946+274 is inferred to be 2.7×10^(37) erg s^(-1) for the 2018 observations and 2.3×10^(37) erg s^(-1) for the 2021 observations.We discuss possible mechanisms which can drive outbursts in this transient Be X-ray binary.展开更多
基金supported by the National Natural Science Foundation of China (grant Nos.12173048,12333004,11988101,and 12273057)the National Key R&D Program of China (No.2023YFA1607903)the support from the K.C.Wong Education Foundation。
文摘LB-1 is a binary system that has drawn great attention since its discovery in 2019.The two components of LB-1 are suggested to be a B-type star plus a black hole (BH).In this paper,we first calculate the wind mass-loss rate of the B-type star.We then calculate the mass capture rate by the BH,with which as the initial mass accretion rate,we calculate the truncation radius of the accretion disk and the corresponding emergent spectra of the accretion flow(comprising an inner advection-dominated accretion flow (ADAF)+an outer truncated accretion disk) within the framework of the disk evaporation model.It is found that the predicted truncation radius of the accretion disk with appropriate model parameters is consistent with observations inferred from the observed broad H_(α) emission line.The predicted X-ray luminosity is definitely below the estimated upper limits with the sensitivity of the Chandra X-ray Observatory of the X-ray luminosity≈2×10^(31)ergs^(-1),which is also consistent with observations.Finally,we argue that the disk evaporation model can indeed reflect the intrinsic physics of the accretion flow in LB-1,and has potential to be applied to other quiescent BHs in the future.
基金supported by the National Key Research and Development Program of China(2022YFF0711500)National Natural Science Foundation of China(NSFC,grant Nos.12373110,12273077,12103070,and 12333004)+3 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(grant Nos.XDA15310300,XDB0550200,XDB0550100,and XDB0550000)supported by China National Astronomical Data Center(NADC)Chinese Virtual Observatory(China-VO)supported by Astronomical Big Data Joint Research Center,cofounded by National Astronomical Observatories,Chinese Academy of Sciences and Alibaba Cloud。
文摘X-ray observations play a crucial role in time-domain astronomy.The Einstein Probe(EP),a recently launched X-ray astronomical satellite,emerges as a forefront player in the field of time-domain astronomy and high-energy astrophysics.With a focus on systematic surveys in the soft X-ray band,EP aims to discover high-energy transients and monitor variable sources in the universe.To achieve these objectives,a quick and reliable classification of observed sources is essential.In this study,we developed a machine learning classifier for autonomous source classification using data from the EP-WXT Pathfinder—Lobster Eye Imager for Astronomy(LEIA)and EP-WXT simulations.The proposed Random Forest classifier,built on selected features derived from light curves,energy spectra,and location information,achieves an accuracy of approximately 95%on EP simulation data and 98%on LEIA observational data.The classifier is integrated into the LEIA data processing pipeline,serving as a tool for manual validation and rapid classification during observations.This paper presents an efficient method for the classification of X-ray sources based on single observations,along with implications of most effective features for the task.This work facilitates rapid source classification for the EP mission and also provides valuable insights into feature selection and classification techniques for enhancing the efficiency and accuracy of X-ray source classification that can be adapted to other X-ray telescope data.
文摘We present the timing and spectral studies of the Be/X-ray binary XTE J1946+274 during its 2018 and 2021 giant outbursts using observations with the SXT and LAXPC instruments on the AstroSat satellite.Unlike the 1998 and 2010 outbursts,where a giant outburst was followed by several low intensity periodic outbursts,the 2018 and 2021 outbursts were single outbursts.The X-ray pulsations are detected over a broad energy band covering 0.5–80 keV from the compact object.We construct the spin evolution history of the pulsar over two decades and find that the pulsar spins-up during the outbursts but switches to spin-down state in the quiescent periods between the outbursts.Energy resolved pulse profiles generated in several bands in 0.5–80 keV show that the pulse shape varies with the energy.The energy spectrum of the pulsar is determined for the 2018 and 2021 outbursts.The best fit spectral models require presence of cyclotron resonant scattering feature at about 43 keV in the energy spectra of both the outbursts.We find indication of possible reversal in the correlation between the cyclotron line energy and luminosity which needs to be ascertained from future observations.Using the best fit spectra the X-ray luminosity of XTE J1946+274 is inferred to be 2.7×10^(37) erg s^(-1) for the 2018 observations and 2.3×10^(37) erg s^(-1) for the 2021 observations.We discuss possible mechanisms which can drive outbursts in this transient Be X-ray binary.
