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Gaussian process modeling Fermi-LAT γ-ray blazar variability: A sample of blazars with γ-ray quasi-periodicities

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arXiv 2020年

作者： Yang, Shenbang Yan, Dahai Zhang, Pengfei Dai, Benzhong Zhang, Li School of Physics and Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatory Chinese Academy of Sciences Kunming650011 China

Blazar variability may be driven by stochastic processes. On the other hand, quasi-periodic oscillation (QPO) behaviors are recently reported to be detected in Fermi-LAT data of blazars. However, the significances of these QPO signals given by traditional Fourier-like methods are still questioned. We analyze γ-ray light curves of the QPO blazars with two Gaussian process methods, CARMA and celerite, to examine the appropriateness of Gaussian processes for characterizing γ-ray light curves of blazars and the existence of the reported QPOs. We collect a sample of 27 blazars with possible γ-ray periodicity and generate their ∼ 11 years Fermi-LAT light curves. We apply the Gaussian process models to the γ-ray light curves, and build their intrinsic power spectral densities (PSDs). The results show that in general the γ-ray light curves can be characterized by CARMA and celerite models, indicating that γ-ray variabilities of blazars are essentially Gaussian processes. The resulting PSDs are generally the red noise shapes with slopes between −0.6 and −1.7. Possible evidence for the γ-ray QPOs in PKS 0537−441 and PG 1553+113 are found in the Gaussian process modelings. © 2020, CC BY.

关键词： Gamma rays

SN 2014C: a metamorphic supernova exploded in the intricate and hydrogen-rich surroundings

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arXiv 2024年

作者： Zhai, Qian Zhang, Jujia Lin, Weili Mazzali, Paolo Pian, Elena Benetti, Stefano Tomasella, Lina Liu, Jialian Li, Liping Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Department of Astronomy Xiamen University Fujian Xiamen361005 China Tsinghua University Beijing100084 China Astrophysics Research Institute Liverpool John Moores University Liverpool Science Park 146 Brownlow Hill LiverpoolL3 5RF United Kingdom Max-Planck-Institut für Astrophysik Karl-Schwarzschild Straße 1 Garching85748 Germany INAF Astrophysics and Space Science Observatory Via P. Gobetti 101 Bologna40129 Italy INAF Osservatorio Astronomico di Padova Vicolo dell’Osservatorio 5 PadovaI-35122 Italy

We present photometric and spectroscopic observations of supernova (SN) 2014C, primarily emphasizing the initial month after the explosion at approximately daily intervals. During this time, it was classified as a Type Ib SN exhibiting a notably higher peak luminosity (Lpeak ≈ 4.3 × 1042erg s−1), a faster rise to brightness (trise ≈ 11.6 d), and a more gradual dimming (∆mV15 ≈ 0.48 mag) compared to typical SNe Ib. Analysis of the velocity evolution over the first ∼ 20 days after the explosion supports the view that the absorption near 6200Å is due to high-velocity Hα in the outer layers of the ejecta, indicating the presence of a small amount of hydrogen in the envelope of progenitor before the explosion. Assuming the peak luminosity is entirely attributed to radioactive decay, we estimate that 0.14 M☉ of 56Ni was synthesized in the explosion. However, this amount of nickel could no longer maintain observed brightness approximately ten days after peak luminosity, suggesting additional energy sources beyond radioactive decay. This supplementary energy likely originates from interaction with the circumstellar medium (CSM). Consequently, the timing of the SN-CSM interaction in SN 2014C may occur much earlier than the emergence of IIn-like features during the nebular phase. © 2024, CC BY.

关键词： Supernovae

Asteroseismic investigation on KIC 10526294 to probe convective core overshoot mixing

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arXiv 2023年

作者： Zhang, Qian-Sheng Li, Yan Wu, Tao Jiang, Chen 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 University of Chinese Academy of Sciences Beijing100049 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Institute of Theoretical Physics Shanxi University Taiyuan030006 China Max-Planck-Institut für Sonnensystemforschung Justus-von-Liebig-Weg 3 GöttingenD-37077 Germany

In the overshoot mixing model with an exponentially decreasing diffusion coefficient, the initial value of the diffusion coefficient plays a crucial role. According to the turbulent convective mixing model, the characteristic length of convection in the convection zone differs from that in the overshoot region, resulting in a rapid decrease of the diffusion coefficient near the convective boundary. To investigate this quick decrease, we conducted an asteroseismic study on the intermediate-mass SPB star KIC 10526294. We generated stellar models with varied input parameters, including the overshoot parameters, and compared the resulting stellar oscillation periods with observations. To mitigate the potential issue arising from large steps in the stellar parameters and stellar age, we employed a comprehensive interpolation scheme for the stellar oscillatory frequencies, considering all stellar parameters and stellar age. Our analysis revealed that the quick decreasing of the diffusion coefficient has discernible effects on the stellar oscillations and a quick decrease with 4 magnitude orders shows the best oscillatory frequencies compared with the observations. This provides weak evidence in support of the prediction made by the turbulent convective mixing model. Furthermore, we examined the residuals of the oscillation periods and discovered a potential association between abundance anomalies in the buoyancy frequency profile and the oscillation-like patterns observed in the residuals. © 2023, CC BY.

关键词： Diffusion

TYC∼2990-127-1: an Algol-type SB2 binary system of subgiant and red giant with a probable ongoing mass-transfer

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arXiv 2022年

作者： Kovalev, Mikhail Li, Zhenwei Zhang, Xiaobin Li, Jiangdan Chen, Xuefei Han, Zhanwen Yunnan Observatories China Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China Max Planck Institute for Astronomy Heidelberg D-69117 Germany Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100012 China University of the Chinese Academy of Sciences Yuquan Road 19 Shijingshan Block Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China

We present a study of the spectroscopic binary TYC 2990-127-1 from the LAMOST survey. We use full-spectrum fitting to derive radial velocities and spectral parameters. The high mass ratio indicates that the system underwent mass transfer in the past. We compute the orbital solution and find that it is a very close sub-giant/red giant pair on circular orbit, slightly inclined to the sky-plane. Fitting of the TESS photometrical data confirms this and suggests an inclination of i ∼ 39.8◦. The light curve and spectrum around Hα show signs of irregular variability, which supports ongoing mass transfer. The binary evolution simulations suggest that the binary may experience non-conservative mass transfer with accretion efficiency 0.3, and the binary will enter into common envelope phase in the subsequent evolution. The remnant product after the ejection of common envelope may be a detached double helium white dwarf (He WD) or a merger. Copyright © 2022, The Authors. All rights reserved.

关键词： Mass transfer

The statistical properties of early-type stars from LAMOST DR8

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arXiv 2022年

作者： Guo, Yanjun Liu, Chao Wang, Luqian Wang, Jinliang Zhang, Bo Ji, Kaifan Han, ZhanWen Chen, XueFei Yunnan observatories Chinese Academy of Sciences P.O. Box 110 Kunming650011 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing100049 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.O. Box 110 Kunming650216 China Key Laboratory of Space Astronomy and Technology National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China

Context. Massive binary stars play a crucial role in many astrophysical fields. Investigating the statistical properties of massive binary stars is essential to trace the formation of massive stars and constrain the evolution of stellar populations. However, no consensus has been achieved on the statistical properties of massive binary stars, mainly due to the lack of a large and homogeneous sample of spectroscopic observations. Aims. We study the intrinsic binary fraction fbin and distributions of mass ratio f(q) and orbital period f(P) of early-type stars (comprised of O-, B-, and A-type stars) and investigate their dependences on effective temperature Teff, stellar metallicity [M/H], and the projection velocity v sin i, based on the homogeneous spectroscopic sample from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release Eight (DR8). Methods. We collected 886 early-type stars, each with more than six observations from the LAMOST DR8, and divided the sample into subgroups based on their derived effective temperature (Teff), metallicity ([M/H]), and projected rotational velocity (v sin i). Radial velocity measurements were archived from a prior study. A set of Monte Carlo simulations, following distributions of f(P) ∝ Pπ and f(q) ∝ qγ were applied to the observed binary fraction to correct for any observational biases. The uncertainties of the derived results induced by the sample size and observation frequency are examined systematically. Results. We found that fbin increases with increasing Teff. For stars in groups of B8-A, B4-B7, O-B3, the binary fractions are fbin = 48% ± 10%, 60% ± 10%, and 76% ± 10%, respectively. The binary fraction is positively correlated with metallicity for spectra in the sample, with derived values of fbin = 44% ± 10%, 60% ± 10%, and 72% ± 10% for spectra with metallicity ranges of [M/H]bin have constant values of ∼50%. It seems that the binary population is relatively evenly distributed over a wide rang

关键词： Monte Carlo methods

Hot subdwarfs from the surviving companions of the white dwarf + main-sequence channel of type Ia supernovae

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arXiv 2021年

作者： Meng, Xiang-Cun Luo, Yang-Ping Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Department of Astronomy China West Normal University Nanchong637002 China

Some surviving companions of type Ia supernovae (SNe Ia) from the white-dwarf + main-sequence (WD + MS) channel may evolve to hot subdwarfs. In this paper, we preformed stellar evolution calculations for surviving companions of close WD +MS systems in the spin-up/spin-downmodel and the canonical non-rotatingmodel to map out the initial parameter spaces in the orbital period - secondary mass plane in which the surviving companions can evolve to hot subdwarfs. Based on these results, we carried out a series of binary population synthesis calculation to obtain the Galactic birth rate of the hot subdwarfs from the WD + MS channel, which is 2.3 - 6 × 10-4yr-1for the spin-up/spin-down model and 0.7 - 3 × 10-4yr-1for the canonical non-rotating model. We also show the distributions of some integral properties of the hot subdwarfs, e.g. the mass and the space velocity, for different models. In addition, comparing our results with the observations of the intermediate helium-rich (iHe-rich) hot subdwarfs, the hot subdwarfs from the WD + MS channel may explain some observational features of the iHe-rich hot subdwarfs, especially for those from the spin-up/spin-down model. Although we expect that the SN Ia channel can only contribute a small fraction of the iHe-rich hot subdwarf population, some of these may help to explain cases with unusual kinematics. Copyright © 2021, The Authors. All rights reserved.

关键词： White dwarfs

Astrometric observations of a near-Earth object using the image fusion technique

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arXiv 2021年

作者： Zhang, Yigong Wang, Jiancheng Su, Jie Cheng, Xiangming Zhang, Zhenjun Yunnan Astronomical Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China University of Chinese Academy of Sciences Beijing100049 China Anyang institute of technology Anyang455000 China

The precise astrometric observation of small near-Earth objects (NEOs) is an important observational research topic in the astrometric discipline, which greatly promotes multidisciplinary research, such as the origin and evolution of the solar system, the detection and early warning of small NEOs, and deep-space navigation. The characteristics of small NEOs, such as faintness and fast moving speed, restrict the accuracy and precision of their astrometric observations. In the paper, we present a method to improve the accurate and precise astrometric positions of NEOs based on image fusion technique. The noise analysis and astrometric test from the observed images of the open cluster M23 are given. Using the image fusion technique, we obtain the sets of superimposed images and original images containing reference stars and moving targets respectively. The final fused image set includes background stars with high signal-to-noise ratios and ideal NEO images simultaneously and avoids the saturation of background stars. Using the fused images, we can reduce the influence of telescope tracking and NEO ephemeris errors on astrometric observations, and our results indicate that the accuracy and precision of NEO Eros astrometry are improved obviously after we choose suitable image fuse mode. Copyright © 2021, The Authors. All rights reserved.

关键词： Stars

AT2021aeuk: A Repeating Partial Tidal Disruption Event Candidate in a Narrow-line Seyfert 1 Galaxy

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arXiv 2025年

作者： Sun, Jingbo Guo, Hengxiao Gu, Minfeng Li, Ya-Ping Chen, Yongjun González-Buitrago, D. Wang, Jian-Guo Li, Sha-Sha Feng, Hai-Cheng Xiong, Dingrong Wang, Yanan Yuan, Qi Jin, Jun-Jie Zhang, Wenda Deng, Hongping Zhang, Minghao Shanghai Astronomical Observatory Chinese Academy of Sciences 80 Nandan Road Shanghai200030 China University of Chinese Academy of Sciences 19A Yuquan Road Beijing100049 China Universidad Nacional Autónoma de México Instituto de Astronomía AP 106 BC Ensenada22860 Mexico Department of Physics and Astronomy 4129 Frederick Reines Hall University of California IrvineCA92697-4575 United States Yunnan Observatories Chinese Academy of Sciences Yunnan Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan Kunming650011 China National Astronomical Observatories Chinese Academy of Sciences 20A Datun Road Beijing100101 China Changchun Observatory National Astronomical Observatories Chinese Academy of Sciences Changchun130117 China

A black hole (BH) can tear apart a star that ventures within its tidal radius, producing a luminous flare as the stellar debris falls back, known as a tidal disruption event (TDE). While TDEs in quiescent galaxies are relatively well understood, identifying TDEs in active galactic nuclei (AGN) still remains a significant challenge. We present the discovery of AT2021aeuk, a transient exhibiting dual flares within around three years in a narrow-line Seyfert 1 galaxy. Multi-wavelength observations triggered during the second flare in 2023 revealed an extraordinary X-ray V-shaped light curve, strongly anti-correlated with the optical light curve and accompanied by a lag of ∼40 days. This behavior is inconsistent with both supernova and pure AGN origins. In addition, a new broad component emerges in the Balmer lines during the second flare, showing a clear reverberation signal to the continuum variation. We propose that the dual-flare may be linked to a repeating partial TDE (rpTDE), where the second flare results from a collision between the TDE stream and the inner accretion disk, triggering an optical flare while simultaneously partially destroying the X-ray corona. However, other mechanisms, such as a stellar-mass BH (sBH) merger within an accretion disk, could produce similar phenomena, which we cannot entirely rule out. The Vera C. Rubin Observatory will be a powerful tool for further investigating the nature of such events in the future. Copyright © 2025, The Authors. All rights reserved.

关键词： Active Galactic Nuclei

Broadening and redward asymmetry of Hα line profiles observed by LAMOST during a stellar flare on an M-type star

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arXiv 2022年

作者： Wu, Yuchuan Chen, Hechao Tian, Hui Zhang, Liyun Shi, Jianrong He, Han Lu, Hongpeng Xu, Yu Wang, Haifeng School of Earth and Space Sciences Peking University Beijing100871 China National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China College of Physics Guizhou University Guiyang550025 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China CAS Key Laboratory of Solar Activity National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China University of Chinese Academy of Sciences Beijing100049 China GEPI Observatoire de Paris Université PSL CNRS Place Jules Janssen 92195 Meudon France

Stellar flares are characterized by sudden enhancement of electromagnetic radiation in stellar atmospheres. So far much of our understanding of stellar flares comes from photometric observations, from which plasma motions in flare regions could not be detected. From the spectroscopic data of LAMOST DR7, we have found one stellar flare that is characterized by an impulsive increase followed by a gradual decrease in the Hα line intensity on an M4-type star, and the total energy radiated through Hα is estimated to be on the order of 1033 erg. The Hα line appears to have a Voigt profile during the flare, which is likely caused by Stark pressure broadening due to the dramatic increase of electron density and/or opacity broadening due to the occurrence of strong non-thermal heating. Obvious enhancement has been identified at the red wing of the Hα line profile after the impulsive increase of the Hα line intensity. The red wing enhancement corresponds to plasma moving away from the Earth at a velocity of 100−200 km s−1. According to the current knowledge of solar flares, this red wing enhancement may originate from: (1) flare-driven coronal rain, (2) chromospheric condensation, or (3) a filament/prominence eruption that either with a non-radial backward propagation or with strong magnetic suppression. The total mass of the moving plasma is estimated to be on the order of 1015 kg. © 2022, CC BY.

关键词： Stars