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Temporal variability and obscuration effects in the X-ray emission of classical nova V339 Delphini (Nova Delphini 2013)

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arXiv 2025年

作者： Pei, Songpeng Ospina, Nataly Zhang, Xiaowan Li, Qiang Ou, Ziwei Yang, Taozhi Cai, Yongzhi School of Physics and Electrical Engineering Liupanshui Normal University Guizhou Liupanshui553004 China Department of Theoretical Physics University Autonoma Madrid Madrid28049 Spain Qiannan Normal University for Nationalities Duyun558000 China Qiannan Key Laboratory of Radio Astronomy Guizhou Province Duyun558000 China Tsung-Dao Lee Institute Shanghai Jiao Tong University Shanghai201210 China Ministry of Education Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter School of Physics Xi’an Jiaotong University Xi’an710049 China Yunnan Observatories Chinese Academy of Sciences Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China

In this study, we present a detailed analysis of public archival soft X-ray data on the classical nova V339 Delphini (Nova Del 2013) during its outburst, obtained using the Chandra High-Resolution Camera Spectrometer (HRC-S) and Low Energy Transmission Grating (LETG), as well as XMM-Newton in 2013. The observations, spanning from day 85.2 to day 112.0 after the optical maximum, capture the nova during its luminous supersoft X-ray source (SSS) phase. The spectra reveal numerous absorption features with blue-shifted velocities ranging from ∼ 724 to ∼ 1474 km s−1, with the majority of lines blue-shifted by approximately 1200 km s−1. We confirm the presence of a short-period modulation of the X-ray flux with a period of approximately 54 seconds, as well as the drift of this period, which was detected on days 97.0 and 112.0 during the outburst with both XMM-Newton and Chandra. This period modulation is transient in nature, with significant variations in amplitude and pulse profile over timescales of a few thousand seconds, likely due to temporary obscuration events that affect the emission from the central hot source. The pulse profiles exhibit substantial deviations from a pure sinusoidal shape, which may be related to the period drift. Additionally, the modulation amplitude shows a possible anti-correlation with the count rates on day 97.0, likely also caused by temporary obscuration events influencing the central source’s emission. Copyright © 2025, The Authors. All rights reserved.

关键词： White dwarfs

Circumstellar Material Ejected Violently by A Massive Star Immediately before its Death

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arXiv 2023年

作者： Zhang, Jujia Lin, Han Wang, Xiaofeng Zhao, Zeyi Li, Liping Liu, Jialian Yan, Shenyu Xiang, Danfeng Wang, Huijuan Bai, Jinming Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Key Laboratory of Radio Astronomy and Technology CAS A20 Datun Road Chaoyang District Beijing100101 China Department of Physics Tsinghua University Beijing100084 China Beijing Planetarium Beijing Academy of Science and Technology Beijing100044 China National Astronomical Observatories CAS Beijing100101 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing101408 China

Type II supernovae represent the most common stellar explosions in the Universe, for which the final stage evolution of their hydrogen-rich massive progenitors towards core-collapse explosion are elusive. The recent explosion of SN 2023ixf in a very nearby galaxy, Messier 101, provides a rare opportunity to explore this longstanding issue. With the timely high-cadence flash spectra taken within 1-5 days after the explosion, we can put stringent constraints on the properties of the surrounding circumstellar material around this supernova. Based on the rapid fading of the narrow emission lines and luminosity/profile of Hα emission at very early times, we estimate that the progenitor of SN 2023ixf lost material at a mass-loss rate M ≈ 6 ×10−4 M☉ a−1 over the last 2-3 years before explosion. This close-by material, moving at a velocity vw ≈ 55 km s−1, accumulates a compact CSM shell at the radius smaller than 7 × 1014 cm from the progenitor. Given the high mass-loss rate and relatively large wind velocity presented here, together with the pre-explosion observations made about two decades ago, the progenitor of SN 2023ixf could be a short-lived yellow hypergiant that evolved from a red supergiant shortly before the explosion. © 2023, CC BY-NC-ND.

关键词： Supernovae

Formation of accreting millisecond X-ray pulsars

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Research in Astronomy and Astrophysics 2019年第8期19卷 45-55页

作者： Xiang He Xiang-Cun Meng Hai-Liang Chen Yunnan Observatories Chinese Academy of SciencesKunming650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming650216China University of Chinese Academy of Sciences Beijing100049China

Accreting millisecond X-ray pulsars(AMXPs) are an important subclass of low-mass X-ray binaries(LMXBs), in which coherent millisecond X-ray pulsations can be observed during outburst *** have dual characteristics of LMXBs and millisecond pulsars, providing a direct confirmation for the recycling scenario. However, their formation is not well understood. In this work, we simulate the evolution of LMXBs with the MESA code to explore the formation and evolution of AMXPs. Based on the binary evolutionary model of LMXBs and the model of accretion disk instability, we find that most of the observed AMXPs can be produced from LMXBs with orbital periods at the onset of Roche lobe overflow close to the bifurcation period and their observed properties can be explained by our models. The AMXPs with main sequence(MS) donors ultimately evolve into AMXPs with extremely low-mass He white dwarf ***, our results indicate that these AMXPs with MS donors are likely to have donor stars near the terminal-age main sequence.

关键词： binaries:close stars:evolution stars:neutron X-ray:binaries

Synchrotron polarization of a hybrid distribution of relativistic thermal and nonthermal electrons in GRB prompt emission

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arXiv 2024年

作者： Cheng, Kangfa Mao, Jirong Zhao, Xiaohong Liu, Hongbang Kole, Merlin Produit, Nicolas Chen, Zhifu School of Mathematics and Physics Guangxi Minzu University Nanning530006 China Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Science Kunming650011 China Center for Astronomical Mega-Science Chinese Academy of Science 20A Datun Road Chaoyang District Beijing100012 China School of Physical Science and Technology Guangxi University Nanning530004 China Space Science Center University of New Hampshire DurhamNH03824 United States Astronomy Department University of Geneva Versoix Switzerland

Synchrotron polarization of relativistic nonthermal electrons in gamma-ray bursts (GRBs) has been widely studied. However, recent numerical simulations of relativistic shocks and magnetic reconnection have found that a more realistic electron distribution consists of a power-law component plus a thermal component, which requires observational validation. In this paper, we investigate synchrotron polarization using a hybrid energy distribution of relativistic thermal and nonthermal electrons within a globally toroidal magnetic field in GRB prompt emission. Our results show that, compared to the case of solely non-thermal electrons, the synchrotron polarization degrees (PDs) in these hybrid electrons can vary widely depending on different parameters and that the PD decreases progressively with frequency in the γ-ray, X-ray, and optical bands. The time-averaged PD spectrum displays a significant bump in the γ-ray and X-ray bands with the PDs higher than ∼ 60% if the thermal peak energy of electrons is much smaller than the conjunctive energy of electrons between the thermal and non-thermal distribution. The high synchrotron PD ( 60%) in the γ-ray and X-ray bands, which generally can not be produced by solely non-thermal electrons with typical power-law slopes, can be achieved by the hybrid electrons and primarily originates from the exponential decay part of the thermal component. Moreover, this model can roughly explain the PDs and spectral properties of some GRBs, where GRB 110301A with a high PD ((Equation presented)) may be potential evidence for the existence of relativistic thermal electrons. Copyright © 2024, The Authors. All rights reserved.

关键词： Gamma rays

Deep search for gamma-ray emission from the accreting X-ray pulsar 1A 0535+262

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arXiv 2023年

作者： Hou, X. Zhang, W. Torres, D.F. Ji, L. Li, J. Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Campus UAB Barcelona08193 Spain Barcelona08034 Spain BarcelonaE-08010 Spain School of Physics and Astronomy Sun Yat-Sen University Zhuhai519082 China CAS Key Laboratory for Research in Galaxies and Cosmology Department of Astronomy University of Science and Technology of China Hefei China School of Astronomy and Space Science University of Science and Technology of China Hefei China

Binary systems are a well-established subclass of gamma-ray sources. The high mass X-ray binary pulsar 1A 0535+262 has been considered to be a possible gamma-ray emitter for a long time, although former gamma-ray searches using Fermi-LAT and VERITAS data resulted in upper limits only. We aim at a deep search for gammaray emission and pulsations from 1A 0535+262 using more than 13 years of FermiLAT data. The analysis was performed for both the whole Fermi-LAT data set, as well as for the X-ray outbursts that 1A 0535+262 has experienced since the launch of Fermi. Various X-ray observations have been used to generate the ephemeris for the pulsation search. We also investigate the long-term gamma-ray flux variability and perform orbital phase-resolved analysis for the outbursts. We did not detect any steady or pulsed gamma-ray emission from 1A 0535+262 during the whole Fermi-LAT mission span or its X-ray outbursts. We thus derived the deepest gamma-ray luminosity upper limits to date at the 95% confidence level to be around (2.3−4.7)×1032 erg s−1 depending on different spectral indices assumed, which results in a ratio of Lγ to LX (2−150 keV) being (1.9−3.9)×10−6 Copyright © 2023, The Authors. All rights reserved.

关键词： Gamma rays

A New Stellar Spectral Feature Extraction Method Based on Two-dimensional Fourier Spectrum Image and Its Application in the Stellar Spectral Classification Based on Deep Network

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Chinese Astronomy and Astrophysics 2020年第3期44卷 334-344页

作者： Jing-min, ZHANG Chen-ye, M.A. Lu, Wang Li-ting, Du Ting-ting, X.U. Lin-pin, Ai Wei-hong, Z.H.O.U. School of Mathematics and Computer Sciences Yunnan Minzu University Kunming 650500 School of Economics and Business Administration Yunnan Vocational and Technical Collage of Agriculture Kunming 650031 School of Physics and Electronic Engineering Guangzhou University Guangzhou510006 Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming 650011

The classification of celestial spectra is one of the important contents of astronomical research. The key is to select and extract the most effective feature for classification from spectra data. In this paper, we propose a new feature extraction method for astronomical spectra based on two-dimensional Fourier spectrum image, and apply the method to the classification study of LAMOST (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope) stellar spectral data. The spectra data are from LAMOST Data Release 5 (DR5). We select 30000 F, G, and K types of spectra data. The short-time Fourier transform (STFT) is used to transform the one-dimensional spectra data into two-dimensional Fourier spectrum images. We classify and test these two-dimensional Fourier spectrum images with a module based on deep convolution network, and the classification accuracy rate is 92.90%. The experimental result shows that the LAMOST stellar spectra data can be transformed into the two-dimensional Fourier spectrum images by the STFT. These spectral images inform new features, and build a new feature space, which is effective for classification. The method is a fully new attempt in spectra classification, which has certainly a pioneering significance for the classification and mining of massive celestial spectra. © 2020

关键词： Methods: data analysis Stars: fundamental parameters techniques: spectral analysis

Multiwavelength Polarization Observations of Mrk 501

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arXiv 2024年

作者： Hu, Xin-Ke Yu, Yu-Wei Zhang, Jin Wang, Xiang-Gao Patra, Kishore C. Brink, Thomas G. Zheng, Wei-Kang Wang, Qi Kong, De-Feng Chen, Liang-Jun Zhou, Ji-Wang Cao, Jia-Xin Lu, Ming-Xuan Zhou, Zi-Min Wei, Yi-Ning Huang, Xin-Bo Li, Xing-Lin Lou, Hao Mao, Ji-Rong Liang, En-Wei Filippenko, Alexei V. Guangxi Key Laboratory for Relativistic Astrophysics School of Physical Science and Technology Guangxi University Nanning530004 China School of Physics Beijing Institute of Technology Beijing100081 China Department of Astronomy University of California BerkeleyCA94720-3411 United States Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China

Mrk 501 is a prototypical high-synchrotron-peaked blazar (HBL) and serves as one of the primary targets for the Imaging X-ray Polarimetry Explorer (IXPE). In this study, we report X-ray polarization measurements of Mrk 501 based on six IXPE observations. The detection of X-ray polarization at a confidence level exceeding 99% is achieved in four out of the six observations conducted across the entire energy range (2–8 keV) of IXPE. The maximum polarization degree (ΠX) is measured to be 15.8% ± 2.8%, accompanied by a polarization angle (ψX) of 98.0◦ ± 5.1◦ at a confidence level of 5.6σ. During the remaining two observations, only an upper limit of ΠX X. The chromatic behavior of Π and the consistent values of ψ across different frequencies from X-rays to radio waves, along with the agreement between ψ and jet position angle, strongly support the interpretation of the energy-stratified model with shock-accelerated particles in the jet of Mrk 501. Additionally, the possibility of the presence of a global helical magnetic field in the jet of Mrk 501 is discussed. Copyright © 2024, The Authors. All rights reserved.

关键词： Active Galactic Nuclei

Multi-epoch spectroscopy of Mg II broad absorption line transitions

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arXiv 2021年

作者： Yi, Weimin Timlin, John Yunnan Observatories Kunming650216 China Department of Astronomy & Astrophysics The Pennsylvania State University 525 Davey Lab University ParkPA16802 United States Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China

Built upon a sample of 134 quasars that was dedicated to a systematic study of Mg ii-BAL variability from Yi et al. (2019a), we investigate these quasars showing Mg ii-BAL disappearance or emergence with the aid of at least three epoch optical spectra sampled more than 15 yr in the observed frame. We identified 3/3 quasars undergoing pristine/tentative BAL transformations. The incidence of pristine BAL transformations in the sample is therefore derived to be 2.2+2−122%, consistent with that of high-ionization BAL transformations from the literature. Adopting an average Mg ii-BAL disappearance timescale of rest-frame 6.89 yr among the six quasars, the average characteristic lifetime of Mg ii BALs in the sample is constrained to be >160 yr along our line of sight. There is a diversity of BAL-profile variability observed in the six quasars, probably reflecting a variety of mechanisms at work. Our investigations of Mg ii-BAL transitions, combined with observational studies of BAL transitions from the literature, imply an overall FeLoBAL/LoBAL→HiBAL/non-BAL transformation sequence along with a decrease in reddening. This sequence is consistent with the evacuation models for the origin of commonly seen blue quasars, in which LoBAL quasars are in a shorted-lived, blowout phase. © 2021, CC BY-NC-SA.

关键词： Galaxies

r-process Abundance Patterns in the Globular Cluster M92

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arXiv 2023年

作者： Kirby, Evan N. Ji, Alexander P. Kovalev, Mikhail Department of Physics and Astronomy University of Notre Dame 225 Nieuwland Science Hall Notre DameIN46556 United States Department of Astronomy & Astrophysics University of Chicago 5640 S Ellis Avenue ChicagoIL60637 United States Kavli Institute for Cosmological Physics University of Chicago ChicagoIL60637 United States Yunnan Observatories China Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China

Whereas light element abundance variations are a hallmark of globular clusters, there is little evidence for variation in neutron-capture elements. A significant exception is M15, which shows a star-to-star dispersion in neutron-capture abundances of at least one order of magnitude. The literature contains evidence both for and against a neutron-capture dispersion in M92. We conducted an analysis of archival Keck/HIRES spectra of 35 stars in M92, 29 of which are giants, which we use exclusively for our conclusions. M92 conforms to the light element abundance variations typical of massive clusters. Like other globular clusters, its neutron-capture abundances were generated by the r-process. We confirm a star-to-star dispersion in the r-process. Unlike M15, the dispersion is limited to "first-generation" (low Na, high Mg) stars, and the dispersion is smaller for Sr, Y, and Zr than for Ba and the lanthanides. This is the first detection of a relation between light element and neutron-capture abundances in a globular cluster. We propose that a source of the main r-process polluted the cluster shortly before or concurrently with the first generation of star formation. The heavier r-process abundances were inhomogeneously distributed while the first-generation stars were forming. The second-generation stars formed after several crossing times (∼ 0.8 Myr);hence, the second generation shows no r-process dispersion. This scenario imposes a minimum temporal separation of 0.8 Myr between the first and second generations. © 2023, CC BY-NC-SA.

关键词： Stars