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Jitter Mechanism as a Kind of Coherent Radiation: Constrained by the GRB 221009A Emission at 18 TeV

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arXiv 2023年

作者： Mao, Jirong Wang, Jiancheng Yunnan Observatories Chinese Academy of Sciences Yunnan Province Kunming650011 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 Kunming650011 China

The emission of gamma-ray burst (GRB) 221009A at 18 TeV has been detected by the large high-altitude air shower observatory (LHAASO). We suggest jitter radiation as a possible explanation for the TeV emission for this energetic GRB. In our scenario, the radiation field is linked to the perturbation field, and the perturbation field is dominated by kinetic turbulence. Kinetic turbulence takes a vital role in both magnetic field generation and particle acceleration. The jitter radiation can reach the TeV energy band when we consider either electron cooling or Landau damping. We further suggest that the jitter radiation in the very high-energy band is coherent emission. Our modeling results can be constrained by the observational results of GRB 221009A in the TeV energy band. This radiation mechanism is expected to have wide applications in the high-energy astrophysical research field. © 2023, CC0.

关键词： Gamma rays

The Mass Fractionation of Helium in the Escaping Atmosphere of HD 209458b∗

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arXiv 2023年

作者： Xing, Lei Yan, Dongdong Guo, Jianheng Yunnan Observatories Chinese Academy of Sciences P.0.Box110 Kunming650216 China Yuquan Road Shijingshan District Beijing100049 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.0.Box110 Kunming650216 China

The absorption signals of metastable He in HD 209458b and several other exoplanets can be explained via escaping atmosphere model with a subsolar He/H ratio. The low abundance of helium can be a result of planet formation if there is a small amount of helium in their primordial atmosphere. However, another possibility is that the low He/H ratio is caused by the process of mass fractionation of helium in the atmosphere. In order to investigate the effect of the fractionation in the hydrogen-helium atmosphere, we developed a self-consistent multi-fluid 1D hydrodynamic model based on the well-known open-source MHD code PLUTO. Our simulations show that a lower He/H ratio can be produced spontaneously in the multi-fluid model. We further modeled the transmission spectra of He 10830 lines for HD 209458b in a broad parameter space. The transmission spectrum of the observation can be fitted in the condition of 1.80 times the X-ray and extreme-ultraviolet flux of the quiet Sun. Meanwhile, the ratio of the escaping flux of helium to hydrogen, FHe/FH, is 0.039. Our results indicate that the mass fractionation of helium to hydrogen can naturally interpret the low He/H ratio required by the observation. Thus, in the escaping atmosphere of HD 209458b, decreasing the abundance of helium in the atmosphere is not needed even if its He abundance is similar to that of the Sun. The simulation presented in this work hints that in the escaping atmosphere, mass fractionation can also occur on other exoplanets, which needs to be explored further. © 2023, CC BY-NC-ND.

关键词： Helium

On the Detection and Characterization of Quasiperiodic Oscillations in Astronomical Time Series: Gamma-ray Burst X-ray Light Curves as a Test Case

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arXiv 2024年

作者： Song, Fei-Fan Mao, Jirong Yunnan Observatories Chinese Academy of Sciences Yunnan Province Kunming650011 China University of Chinese Academy of Sciences Beijing100049 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 Kunming650011 China

The study of temporal properties of variable sources can elucidate their physical processes. In this context, we present a critical study comparing three approaches to periodic or quasiperiodic behavior: Gaussian process, power spectrum, and wavelet analysis, using celerite, Lomb-Scargle periodograms, and weighted wavelet-Z transforms, respectively. We use 15 Swift-X-ray Telescope light curves of short gamma-ray bursts (sGRBs) as examples. A comprehensive analysis of two sGRB X-ray light curves is performed. The results reveal the importance of artifacts, largely in the form of false quasiperiodic oscillation signals, possibly introduced by preprocessing (such as detrending) or other aspects of the analysis. The exploration described in this paper can be helpful for future studies of variability in GRBs, active galactic nuclei, and other astronomical sources. Copyright © 2024, The Authors. All rights reserved.

关键词： Z transforms

Investigation of superhumps in SU UMa-type dwarf novae based on the observations of TESS

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arXiv 2024年

作者： Liu, Wei Qian, Shengbang Yunnan Observatories Chinese Academy of Sciences PO Box 110 Kunming650216 China Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China University of Chinese Academy of Sciences No.1 Yanqihu East Rd Huairou District Beijing101408 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences PO Box 110 Kunming650216 China

We report the superhumps analysis of seven SU UMa-type dwarf novae based on the observations of Transiting Exoplanet Survey Satellite (TESS). Superhumps are seen during superoutbursts of SU UMa-type dwarf novae. The month-long data sets of TESS are well suited for studying the variation of superhumps. We selected seven non-eclipsing SU UMa-type dwarf novae with superhumps in which TESS light curves are available and have not yet been studied. The stages A, B, and C of superhumps in superoutbursts were determined by O-C method. The results indicate that not all complete superoutbursts show obvious three stages, such as DT Oct and the second superoutburst of J1730+6247. We calculated the superhump periods for each stage and the mean periods for whole superoutbursts. Taking the stage A superhump method, the mass ratios (M2/M1) were estimated. According to the results, the seven stars are pre-bounce systems with mass ratios ranging from 0.1 to 0.2. By combining the orbital periods and the mean superhump periods, the precession periods were calculated. The results show that the precession periods of the seven SU UMa stars are about 2 days. © 2024, CC BY.

关键词： Stars

Nucleosynthesis in the Innermost Ejecta of Magnetorotational Supernova Explosions in 3-dimensions

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arXiv 2024年

作者： Zha, Shuai Müller, Bernhard Powell, Jade Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China School of Physics and Astronomy Monash University ClaytonVIC3800 Australia Centre for Astrophysics and Supercomputing Swinburne University of Technology HawthornVIC3122 Australia OzGrav: The ARC Centre of Excellence for Gravitational-Wave Discovery HawthornVIC3122 Australia

Core-collapse supernova (CCSN) explosions powered by rotation and magnetic fields present an interesting astrophysical site for nucleosynthesis that potentially contributes to the production of r-process elements. Here we present yields of the innermost ejecta in 3D magnetorotational CCSN models simulated using the CoCoNuT-FMT code. Strong magnetic fields tap the rotational energy of the proto-neutron star and lead to earlier and more energetic (∼ 3 × 1051 erg) explosions than typical neutrino-driven CCSNe. Compared to a reference non-magnetic model, the ejecta in the magnetorotational models have much more neutron-rich components with Ye down to ∼ 0.25. Our post-processing calculations with the reaction network SkyNet show significant production of weak r-process elements up to mass number ∼130. We find negligible differences in the synthesis of heavy elements between two magnetorotational models with different initial field strength of 1010 and 1012 G, in accord with their similar explosion dynamics. The magnetorotational models produce about ∼ 0.19 and 0.14 M☉ of radioactive 56Ni, on the low end of inferred hypernova nickel masses. The yields are publicly available at Zenodo: doi:10.5281/zenodo.10578981 for comparison with stellar abundance patterns, inclusion in modelling galactic chemical evolution, and comparison with other yield calculations. Our results add to the yet restricted corpus of nucleosynthesis yields from 3D magnetorotational supernova simulations and will help quantify yield uncertainties. Copyright © 2024, The Authors. All rights reserved.

关键词： Explosions

AT 2023clx: the Faintest and Closest Optical Tidal Disruption Event Discovered in Nearby Star-forming Galaxy NGC 3799

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arXiv 2023年

作者： Zhu, Jiazheng Jiang, Ning Wang, Tinggui Huang, Shifeng Lin, Zheyu Wang, Yibo Wang, Jian-Guo CAS Key Laboratory for Research in Galaxies and Cosmology Department of Astronomy University of Science and Technology of China Hefei230026 China School of Astronomy and Space Sciences University of Science and Technology of China Hefei230026 China Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatories Kunming650011 China

We report the discovery of a faint optical tidal disruption event (TDE) in the nearby star-forming galaxy NGC 3799. Identification of the TDE is based on its position at the galaxy nucleus, a light curve declining as t−5/3, a blue continuum with an almost constant blackbody temperature of ∼12,000 K, and broad (≈ 15, 000 km s−1) Balmer lines and characteristic He II 4686 Å emission. The light curve of AT 2023clx peaked at an absolute magnitude of −17.16 mag in the g band and a maximum blackbody bolometric luminosity of 4.56 × 1042 erg s−1, making it the faintest TDE discovered to date. With a redshift of 0.01107 and a corresponding luminosity distance of 47.8 Mpc, it is also the closest optical TDE ever discovered to our best knowledge. Furthermore, our analysis of Swift/XRT observations of AT 2023clx yields a very tight 3σ upper limit of 9.53×1039 erg s−1 in the range 0.3–10 keV. AT2023clx, together with very few other faint TDEs such as AT 2020wey, prove that there are probably a large number of faint TDEs yet to be discovered at higher redshifts, which is consistent with the prediction of luminosity functions (LFs). The upcoming deeper optical time-domain surveys, such as the Legacy Survey of Space and Time (LSST) and the Wide-Field Survey Telescope (WFST) will discover more TDEs at even lower luminosities, allowing for a more precise constraint of the low-end of the LF. © 2023, CC BY.

关键词： Luminance

Constraints on Extragalactic Background Light using TeV Observations of BL Lacertae objects

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arXiv 2023年

作者： Qin, Longhua Wang, Jiancheng Gao, Quangui Na, Weiwei Li, Huaizhen Wang, Ao Yang, Chuyuan Yang, Jianping Department of Physics Yuxi Normal University Yunnan Yuxi653100 China Yunnan Observatory Chinese Academy of Sciences Yunnan Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan Kunming650011 China Yunnan Agricultural University Yunnan Kunming650201 China

The extragalactic background light (EBL) in the IR to UV bands partly absorbs very high energy (VHE, E ≥ 100GeV) γ−ray photons travelling over cosmological distances via pair production. In this paper, to get stronger constraints on EBL, we use the deliberate selection of the EBL model and data of five BL Lacs with better statistics and the harder spectra to limit the EBL density and the radiation mechanism of BL Lacs. We constrain the upper limit of the EBL density by fitting the spectral energy distributions (SEDs) of TeV BL Lacs and find that our results are compatible with the published measurement, reaching 50 nWm−2sr−1. We also obtain that the EBL is not necessarily transparent to high VHE photons. We fix the intrinsic spectral index Γi of TeV BL Lacs as 1.0 and 1.5 under observation evidence and model assumption. Comparing the EBL density given by galaxy count and Spitzer observations, we then obtain that 1ES 1101-232 has Γi ≤ 1.0 and 1ES 0229+200 should have Γi not harder than 1.0. We demonstrate that the common radiation assumption of BL Lacs, in which the Γi is softer than 1.5, should be revisited. Furthermore, we propose that the upper EBL density could be given by fitting the hardest energy spectra of TeV BL Lacs. © 2023, CC BY.

关键词： Gamma rays

Absolute parameters and observed flares in the M-type detached eclipsing binary 2MASS J04100497+2931023

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Research in Astronomy and Astrophysics 2021年第5期21卷 130-138页

作者： Gang Meng Li-Yun Zhang Qing-Feng Pi Liu Long Xianming L.Han Misra Prabhakar College of Physics&Guizhou Provincial Key Laboratory of Public Big Data Guizhou UniversityGuiyang 550025China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650011China College of Medicine Guizhou University of Traditional Chinese MedicineGuiyang 550025China Department of Astronomy Beijing Normal UniversityBeijing 100875China Dept.of Physics and Astronomy Butler UniversityIndianapolisIN 46208USA Department of Physics&Astronomy Howard UniversityWashington DC 20059USA

The eclipsing binary 2 MASS J04100497+2931023(J04100497+2931023) is classified its spectral type of M0±2 V on basis of a low-resolution spectral survey by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST). The low-resolution spectra exhibit strong single-peak emission in the Hα line. We obtained the radial velocities of this binary by means of the Cross-Correlation Function method from the LAMOST medium-resolution spectra. Both components of J04100497+2931023 indicate strong emissions in the Hα line. We performed follow-up photometric observations of J04100497+2931023 using the Xinglong 85 cm telescope of National Astronomical Observatories, Chinese Academy of Sciences. We obtained its full light curve in V RI filters. We first determined their absolute parameters from simultaneously radial velocity and light curves by the Wilson-Devinney program. From our new light curves, we detected three flares for the first time, including one convective flare. The amplitudes,durations, energies, and spectral indices of three flares were also determined. J04100497+2931023 was monitored for approximately 29 h, which indicates that the flare rate is 0.1 flare per hour. We conclude that J04100497+2931023 is a low-mass detached eclipsing binary with strong magnetic activity.

关键词： binaries:eclipsing stars:flare star:low-mass stars:J04100497+2931023

Detection of [CI] Emission in Nebular Spectra of a Peculiar TypeIa Supernova 2022pul

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arXiv 2025年

作者： Liu, Jialian Wang, Xiaofeng Yang, Yi Filippenko, Alexei V. Brink, Thomas G. Zheng, WeiKang Zhang, Jujia Li, Gaici Yan, Shengyu Physics Department Tsinghua University Beijing100084 China Purple Mountain Observatory Chinese Academy of Sciences Nanjing210023 China Department of Astronomy University of California BerkeleyCA94720-3411 United States 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

SN 2022pul gains special attention due to its possible origin as a super-Chandrasekhar-mass white dwarf (WD) explosion (also called a 03fg-like Type Ia supernova), which shows prominent [O I], [Ne I], and [Ca II] lines in its late-time spectra taken at ∼+300 days after the time of peak brightness. In this Letter, we present new optical observations of this peculiar object, extending up to over 500 days after peak brightness. In particular, in the t ∼ +515 days spectrum, we identified for the first time the presence of narrow emission from [C I] λλ9824, 9850, which appears asymmetric and quite similar to the accompanied [O I] λ6300 line in strength and profile. Based on the violent merger model that accounts well for previous observations but leaves little carbon in the center of the ejecta, this carbon line can be reproduced by increasing the degree of clumping in the ejecta and setting the carbon mass the same as that of oxygen (∼0.06 Me) in the innermost region (2000 km s−1). In principle, the central carbon could come from the secondary WD if it is ignited when hit by the shock wave of the explosion of the primary WD and explodes as a Ca-rich supernova, whereas pure deflagration of a super-Chandrasekhar-mass WD can account for such unburnt carbon more naturally. Copyright © 2025, The Authors. All rights reserved.

关键词： Supernovae