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arXiv 2025年

作者： Peng, J.Q. Zhang, S. Chen, Y.P. Kong, L.D. Wang, P.J. Zhang, S.N. Shui, Q.C. Ji, L. Zhang, G.B. Yan, Z. Tao, L. Qu, J.L. Ge, M.Y. Yu, Z.L. Li, J. Chang, Z. Li, Z.S. Zhang, P. Xiao, Y.X. Zhao, S.J. Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing100049 China University of Chinese Academy of Sciences Chinese Academy of Sciences Beijing100049 China Institute für Astronomie und Astrophysik Kepler Center for Astro and Particle Physics Eberhard Karls Universität Sand 1 TübingenD-72076 Germany School of Physics and Astronomy Sun Yat-Sen University Zhuhai519082 China Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution Celestial Objects Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China 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 Science University of Science and Technology of China Hefei230026 China Key Laboratory of Stars and Interstellar Medium Xiangtan University Hunan Xiangtan411105 China College of Science China Three Gorges University Yichang443002 China Center for Astronomy and Space Sciences China Three Gorges University Yichang443002 China

Context. Thermonuclear bursts, also known as type-I X-ray bursts, result from unstable nuclear burning of H/He accreted to the surface of neutron stars, lasting from tens of seconds to hundreds of seconds. Thermonuclear bursts have an important impact on accretion environments around the neutron stars, such as their disks and corona, and are therefore a subject of extensive research. Thermonuclear bursts can be used as probes to gain a deeper understanding of the properties of their disks and corona. Aims. By analyzing the data from Insight-HXMT and NICER, we can determine the evolution of the significance of the hard shortage in 4U 1636–536 with its spectral state, as well as the evolution of the fraction of deficit with energy. Additionally, we investigate the possible geometry and evolution of the corona in 4U 1636–536 by combining our findings with the results of spectral analysis. Methods. Extracting the light curves from the Insight-HXMT LE, ME, and HE data and subtracting their pre-burst emission allows us to estimate the significance of the hard shortages during the bursts. By fitting the spectra, the correlation between the persistent spectral parameters and the significance of the hard shortages can be established. The bursts are then grouped according to the spectral state in which they occurred, and the significance of the hard shortages is estimated. These in turn help to investigate the evolution of the fraction of deficit with energy. Results. We find that during the soft state, the significance of possible hard X-ray shortage in bursts is almost zero. However, in the hard state, some bursts exhibit significant shortages (>3 σ), while others do not. We attempt to establish a correlation between the significance of the hard X-ray shortage and the spectral parameters, but the data quality and the limited number of bursts prevent us from finding a strong correlation. For bursts with insignificant shortages in the soft state, their fraction of the deficit

关键词： Stars

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Long-term evolution of surviving companion stars of Type Iax supernovae

arXiv

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arXiv 2020年

作者： Liu, Zheng-Wei Zeng, Yaotian 396 Yangfangwang Guandu District Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China Center for Astronomical Mega-Science CAS Beijing100012 China University of Chinese Academy of Science Beijing100012 China

The nature of the progenitors and explosion mechanism of Type Iax supernovae (SNe Iax) remain a mystery. The single-degenerate (SD) systems that involve the incomplete pure deflagration explosions of near-Chandrasekhar-mass white dwarfs (WDs) have recently been proposed for producing SNe Iax, in which non-degenerate companions are expected to survive from SN explosions. In this work we concentrate on the main-sequence (MS) donor SD progenitor systems. By mapping the computed companion models from three-dimensional hydrodynamical simulations of ejecta-companion interaction into a one-dimensional stellar evolution code MESA, we investigate the long-term appearance and observational signatures of surviving MS companions of SNe Iax by tracing their post-impact evolution. Depending on different MS companion models, it is found that the shocked surviving companion stars can significantly expand and evolve to be more luminous (5–500 L☉) for a time-scale of 10–104 yr. Comparing with the late-time light curve of an observed SN Iax (SN 2005hk), it is suggested that surviving MS companions of SNe Iax would expect to be visible about 1000 d after the explosion when SN itself has been faded. Copyright © 2020, The Authors. All rights reserved.

关键词： Explosions

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Synchrotron Circular Polarization in Gamma-Ray Burst Prompt Optical Emission: Relativistic Thermal Electron Contribution

arXiv

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arXiv 2025年

作者： Cheng, Kangfa Mao, Jirong Zhao, Xiaohong Liu, Hongbang Chen, Zhegeng Yu, Gaojin Chen, Zhifu Guangxi Key Laboratory for Relativistic Astrophysics School of Physical Science and Technology Guangxi University Nanning530004 China School of Physics and Electronic Information 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

Synchrotron circular polarization of a non-thermal power-law electron distribution in gamma-ray bursts (GRBs) has been studied. However, some numerical simulations have shown that the resulting distribution of electrons is a combination of a thermal component and a non-thermal power-law component. In this paper, we investigate synchrotron circular polarization using such a hybrid energy distribution of relativistic thermal and nonthermal electrons within a globally toroidal magnetic field in GRB prompt optical emission. Our results show that compared to the solely nonthermal electron model, the synchrotron circular polarization degree (PD) in the hybrid electron model can vary widely in the optical band, depending on different parameters. The lower the electron temperature, the higher the circular PD. The time-averaged circular PD in the hybrid electron model can be higher than ∼ 1% when the electron temperature is as low as ∼ 1010 K, while in the solely nonthermal electron model is usually lower than ∼ 1%. We further calculate the radiative transfer of the circular and linear polarization in the optical band. Our results show that both of the circular and linear PDs decrease with the increase of optical depth, but the linear PDs decline faster than the circular PDs. To further examine the physical mechanisms of both radiation and particle acceleration, we expect that instruments will be capable of measuring the circular polarization of GRB prompt optical emission in the future. Copyright © 2025, The Authors. All rights reserved.

关键词： Circular polarization

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FAST discovery of an extremely radio-faint millisecond pulsar from the Fermi-LAT unassociated source 3FGL J0318.1+0252

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Science China(Physics,Mechanics & Astronomy) 2021年第12期64卷 10-17页

作者： Pei Wang Di Li Colin J.Clark Pablo M.Saz Parkinson Xian Hou Weiwei Zhu Lei Qian Youling Yue Zhichen Pan Zhijie Liu Xuhong Yu Shanping You Xiaoyao Xie Qijun Zhi Hui Zhang Jumei Yao Jun Yan Chengmin Zhang Kwok Lung Fan Paul S.Ray Matthew Kerr David A.Smith Peter F.Michelson Elizabeth C.Ferrara David J.Thompson Zhiqiang Shen Na Wang FAST&Fermi-LAT Collaboration CAS Key Laboratory of FAST National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China Jodrell Bank Centre for Astrophysics Department of Physics and AstronomyUniversity of ManchesterManchester M139PLUK Department of Physics and Laboratory for Space Research University of Hong KongHong Kong 999077China Santa Cruz Institute for Particle Physics University of CaliforniaSanta Cruz CA 95064USA Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China School of Computer Science and Technology Key Laboratory of Information and Computing Guizhou ProvinceGuizhou Normal UniversityGuiyang 550001China School of Physics and Electronic Science Guizhou Normal UniversityGuiyang 550001China Physics Department Stanford UniversityStanford CA 94305USA UMCP/CRESST/GSFC NASAGreenbeltMaryland MD 20771USA GSFC NASAGreenbeltMaryland MD 20771USA Centre d’´Etudes Nucl´eaires de Bordeaux Gradignan IN2P3/CNRSUniversit´e BordeauxGradignan 33175France Space Science Division U.S.Naval Research LaboratoryWashington DC 20375-5352USA Shanghai Astronomical Observatory Chinese Academy of SciencesShanghai 200030China Xinjiang Astronomical Observatory Urumqi 830011China Department of Physics University of MarylandCollege Park MD 20742USA NAOC-UKZN Computational Astrophysics Centre University of KwaZulu-NatalDurban 4000South Africa 不详

High sensitivity radio searches of unassociated γ-ray sources have proven to be an effective way of finding new pulsars. Using the Five-hundred-meter Aperture Spherical radio Telescope(FAST) during its commissioning phase, we have carried out a number of targeted deep searches of Fermi Large Area Telescope(LAT) γ-ray sources. On February 27, 2018 we discovered an isolated millisecond pulsar(MSP), PSR J0318+0253, coincident with the unassociated γ-ray source 3 FGL J0318.1+0252. PSR J0318+0253 has a spin period of 5.19 ms, a dispersion measure(DM) of 26 pc cm-3 corresponding to a DM distance of about 1.3 kpc, and a period-averaged flux density of(~11±2) μJy at L-band(1.05-1.45 GHz). Among all high energy MSPs, PSR J0318+0253 is the faintest ever detected in radio bands, by a factor of at least ~4 in terms of L-band fluxes. With the aid of the radio ephemeris, an analysis of 9.6 years of Fermi-LAT data revealed that PSR J0318+0253 also displays strong γ-ray pulsations. Follow-up observations carried out by both Arecibo and FAST suggest a likely spectral turn-over around 350 MHz. This is the first result from the collaboration between FAST and the Fermi-LAT teams as well as the first confirmed new MSP discovery by FAST, raising hopes for the detection of many more MSPs. Such discoveries will make a significant contribution to our understanding of the neutron star zoo while potentially contributing to the future detection of gravitational waves, via pulsar timing array(PTA) experiments.

关键词： FAST pulsar radio gamma rays

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A long-period pre-ELM system discovered from LAMOST medium-resolution survey

arXiv

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arXiv 2022年

作者： Zhang, Zhi-Xiang Zheng, Ling-Lin Gu, Wei-Min Sun, Mouyuan Yi, Tuan Shi, Jian-Rong Wang, Song Bai, Zhong-Rui Zhang, Hao-Tong Cui, Wen-Yuan Wang, Junfeng Wu, Jianfeng Li, Xiang-Dong Shao, Yong Lu, Kai-Xing Bai, Yu Li, Chunqian Fu, Jin-Bo Liu, Jifeng Department of Astronomy Xiamen University Fujian Xiamen361005 China Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100012 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing100049 China Department of Physics Hebei Normal University Shijiazhuang050024 China Department of Astronomy Nanjing University Nanjing210023 China Key laboratory of Modern Astronomy and Astrophysics Nanjing University Ministry of Education Nanjing210023 China Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China WHU-NAOC Joint Center for Astronomy Wuhan University Wuhan430072 China

We present LAMOST J041920.07+072545.4 (hereafter J0419), a close binary consisting of a bloated extremely low mass pre-white dwarf (pre-ELM WD) and a compact object with an orbital period of 0.607189 days. The large-amplitude ellipsoidal variations and the evident Balmer and He I emission lines suggest a filled Roche lobe and ongoing mass transfer. No outburst events were detected in the 15 years of monitoring of J0419, indicating a very low mass transfer rate. The temperature of the pre-ELM, Teff = 5793+124−133 K, is cooler than the known ELMs, but hotter than most CV donors. Combining the mean density within the Roche lobe and the radius constrained from our SED fitting, we obtain the mass of the pre-ELM, M1 = 0.176 ± 0.014 Mo. The joint fitting of light and radial velocity curves yields an inclination angle of i = 66.5+1.4−1.7 degrees, corresponding to the compact object mass of M2 = 1.09 ± 0.05 Mo. The very bloated pre-ELM has a smaller surface gravity (log g = 3.9 ± 0.01, R1 = 0.78 ± 0.02 Ro) than the known ELMs or pre-ELMs. The temperature and the luminosity (Lbol = 0.62+0.11−0.10. Lo) of J0419 are close to the main sequence, which makes the selection of such systems through the HR diagram inefficient. Based on the evolutionary model, the relatively long period and small log g indicate that J0419 could be close to the "bifurcation period" in the orbit evolution, which makes J0419 to be a unique source to connect ELM/pre-ELM WD systems, wide binaries and cataclysmic variables. Copyright © 2022, The Authors. All rights reserved.

关键词： Mass transfer

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Distinguishing super-Nyquist frequencies via their temporal variation in γ Doradus stars from continuous photometry

arXiv

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arXiv 2024年

作者： Wang, Xuan Zong, Weikai Ma, Xiao-Yu Charpinet, Stéphane Wu, Tao Wang, Haotian Institute for Frontiers in Astronomy and Astrophysics Beijing Normal University Beijing102206 China School of Physics and Astronomy Beijing Normal University Beijing100875 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Institute Université de Liège Allée du 6 Août 19C Liège4000 Belgium IRAP CNRS UPS CNES Université de Toulouse 14 av. Edouard Belin Toulouse31400 France Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects 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 University of Chinese Academy of Sciences Beijing100049 China Institute of Astronomy KU Leuven Celestijnenlaan 200D Leuven3001 Belgium

As mixed with real pulsations, the reflection of super-Nyquist frequencies (SNFs) pose a threat to asteroseismic properties. Although SNFs have been studied in several pulsating stars, a systematic survey remains scarcely explored. Here we propose a method to identify SNFs from Kepler and TESS photometry by characterizing their periodic frequency modulations using a sliding Fourier transform. After analyzing long cadence photometry in the Kepler legacy, we have identified 304 SNFs in 56 stars from 45607 frequencies in ∼ 600 γ Doradus stars, corresponding to a fraction of approximately 0.67% and 9.2%, respectively. Most SNFs are detected in the frequency range of pressure mode over 120 µHz and the fraction of SNF detection increases as frequency up to ∼ 7%. We barely found two potential SNFs mixed with gravity modes in two γ Doradus stars. These findings indicate that SNFs have a negligible impact on the global seismic properties, such as those derived from period spacing in γ Doradus stars. However, we stress that SNFs must be carefully and systematically examined by this method in other pulsating stars, particularly δ Scuti and hot B subdwarf stars, to establish a solid foundation for precise asteroseismolgy of various types of pulsators. Copyright © 2024, The Authors. All rights reserved.

关键词： Photometry

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Hemispheric Distribution of Solar Active Regions During Solar Cycles 23-25

arXiv

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arXiv 2025年

作者： Liu, Yuxia Xu, Tingting Wan, Miao Deng, Linhua Zhao, Xinhua Qi, Shiyang Xiang, Nanbin Zhou, Weihong School of Mathematics and Computer Science Yunnan Minzu University Yunnan Kunming650504 China State Key Laboratory of Space Weather National Space Science Center Chinese Academy of Sciences Beijing100190 China Sichuan Chengdu610041 China College of Science Henan Agricultural University Henan Zhengzhou450002 China Yunnan Observatories Chinese Academy of Sciences Yunnan Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Yunnan Kunming650216 China

Solar active regions (ARs) are crucial for understanding the long-term evolution of solar activities and predicting eruptive phenomena, including solar flares and coronal mass ejections. However, the cycle-dependent properties in the north-south asymmetry of ARs have not been fully understood. In this study, we investigate the hemispheric distribution of ARs from Carrington Rotation 1909 to 2278 (between 1996 May and 2023 November) by using three parameters that describe the magnetic field distribution of ARs: number, area, and flux. The main findings are as follows: (1) The three AR parameters show significant hemispheric asymmetry in cycles 23-25. The strong correlation between AR area and flux indicates that they can better reflect the intrinsic properties of solar magnetic field. (2) The correlation between sunspot activity and AR parameters varies in the two hemispheres across the different cycles. The AR parameters provide additional information for the variations in sunspot activity, which can better predict the intensity and cyclical changes of solar activity. (3) The variation in the fitting slope sign of the asymmetry index for AR parameters reflects periodic changes in hemispheric ARs, providing valuable insights into the activity of other stars. (4) Both the dominant hemisphere and the cumulative trend of AR parameters display a cycle-dependent behavior. Moreover, the trend variations of AR area and flux are similar, reflecting the long-term evolutionary characteristics of solar magnetic field. Our analysis results are relevant for understanding the hemispheric coupling of solar magnetic activity and its cyclic evolutionary patterns. Copyright © 2025, The Authors. All rights reserved.

关键词： Aspherics

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Minute-cadence Observations of the LAMOST Fields with the TMTS: III. Statistic Study of the Flare Stars from the First Two Years

arXiv

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arXiv 2023年

作者： Liu, Qichun Lin, Jie Wang, Xiaofeng Gu, Shenghong Shi, Jianrong Zhang, Liyun Xi, Gaobo Mo, Jun Cai, Yongzhi Chen, Liyang Chen, Zhihao Guo, Fangzhou Jiang, Xiaojun Li, Gaici Li, Wenxiong Lin, Han Lin, Weili Liu, Jialian Miao, Cheng Ma, Xiaoran Peng, Haowei Xiang, Danfeng Yan, Shengyu Zhang, Jicheng Zhang, Xinhan Physics Department Tsinghua Center for Astrophysics Tsinghua University Beijing100084 China Beijing Planetarium Beijing Academy of Science and Technology Beijing100044 China Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China CAS Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing100101 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing100049 China College of Physics College of Big Data and Information Engineering Guizhou University Guiyang550025 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China The School of Physics and Astronomy Tel Aviv University Tel Aviv69978 Israel Department of Astronomy Beijing Normal University Beijing100875 China

Tsinghua University-Ma Huateng Telescopes for Survey (TMTS) aims to detect fast-evolving transients in the Universe, which has led to the discovery of thousands of short-period variables and eclipsing binaries since 2020. In this paper, we present the observed properties of 125 flare stars identified by TMTS within the first two years, with an attempt to constrain their eruption physics. As expected, most of these flares were recorded in late-type red stars with GBP − GRP > 2.0 mag;however, the flares associated with bluer stars tend to be on average more energetic and have broader profiles. The peak flux (Fpeak) of the flare is found to depend strongly on the equivalent duration (ED) of the energy release, i.e., Fpeak ∝ ED0.72±0.04, which is consistent with results derived from the Kepler and Evryscope samples. This relation is likely related to the magnetic loop emission, while, for the more popular non-thermal electron heating model, a specific time evolution may be required to generate this relation. We notice that flares produced by hotter stars have a flatter Fpeak ∝ ED relation compared to that from cooler stars. This is related to the statistical discrepancy in light-curve shape of flare events with different colors. In spectra from LAMOST, we find that flare stars have apparently stronger Hα emission than inactive stars, especially at the low temperature end, suggesting that chromospheric activity plays an important role in producing flares. On the other hand, the subclass with frequent flares is found to show Hα emission of similar strength in its spectra to that recorded with only a single flare but similar effective temperature, implying that the chromospheric activity may not be the only trigger for eruptions. Copyright © 2023, The Authors. All rights reserved.

关键词： Stars

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The formation of neutron star systems through accretion-induced collapse in white-dwarf binaries

arXiv

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arXiv 2020年

作者： Wang, Bo Liu, Dongdong 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 Beijing100012 China University of Chinese Academy of Sciences Beijing100049 China

The accretion-induced collapse (AIC) scenario was proposed 40 years ago as an evolutionary end state of oxygen-neon white-dwarfs (ONe WDs), linking them to the formation of neutron star (NS) systems. However, there has been no direct detection of any AIC event so far, even though there exists a lot of indirect observational evidence. Meanwhile, the evolutionary pathways resulting in NS formation through AIC are still not well investigated. In this article, we review recent studies on the two classic progenitor models of AIC events, i.e., the single-degenerate model (including the ONe WD+MS/RG/He star channels and the CO WD+He star channel) and the doubledegenerate model (including the double CO WD channel, the double ONe WD channel and the ONe WD+CO WD channel). Recent progress on these progenitor models is reviewed, including the evolutionary scenarios leading to AIC events, the initial parameter space for producingAIC events, and the related objects (e.g., the pre-AIC systems and the post-AIC systems). For the single-degenerate model, the pre-AIC systems (i.e., the progenitor systems of AIC events) could potentially be identified as supersoft X-ray sources, symbiotics and cataclysmic variables (such as classical novae, recurrent novae, Ne novae and He novae) in the observations, whereas the post-AIC systems (i.e., NS systems) could potentially be identified as low-/intermediate-massX-ray binaries, and the resulting low-/intermediate-mass binary pulsars, most notably millisecond pulsars. For the doubledegenerate model, the pre-AIC systems are close double WDs with short orbital periods, whereas the post-AIC systems are single isolated NSs that may correspond to a specific kind of NSs with peculiar *** also review the predicted rates of AIC events, the mass distribution of NSs produced via AIC, and the gravitationalwave (GW) signals from double WDs that are potential GW sources in the Galaxy in the context of future spacebased GW detectors, such as LISA, T

关键词： White dwarfs

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Probing the Shock Breakout Signal of SN 2024ggi from the Transformation of Early Flash Spectroscopy

arXiv

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arXiv 2024年

作者： Zhang, Jujia Dessart, Luc Wang, Xiaofeng Zhai, Qian Yang, Yi Li, Liping Lin, Han Valerin, Giorgio Cai, Yongzhi Guo, Zhen Wang, Lingzhi Zhao, Zeyi Wang, Zhenyu Yan, Shengyu Kunming650216 China International Centre of Supernovae Yunnan Key Laboratory Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650216 China Institut d’Astrophysique de Paris CNRS-Sorbonne Université 98 bis boulevard Arago ParisF-75014 France Physics Department Tsinghua University Beijing100084 China Department of Astronomy University of California BerkeleyCA94720-3411 United States INAF-Osservatorio Astronomico di Padova Vicolo dell’Osservatorio 5 Padova35122 Italy Instituto de Física y Astronomía Universidad de Valparaíso ave. Gran Bretaña 1111 Casilla 5030 Valparaíso Chile Centre for Astrophysics Research University of Hertfordshire HatfieldAL10 9AB United Kingdom Millennium Institute of Astrophysics Nuncio Monseñor Sotero Sanz 100 Of. 104 Providencia Santiago Chile National Astronomical Observatories CAS Beijing China

We present early-time, hour-to-day cadence spectroscopy of the nearby type II supernova (SN II) 2024ggi, which was discovered at a phase when the SN shock just emerged from the red-supergiant (RSG) progenitor star. Over the first few days after the first light, SN 2024ggi exhibited prominent narrow emission lines formed through intense and persistent photoionization of the nearby circumstellar material (CSM). In the first 63 hours, spectral lines of He, C, N, and O revealed a rapid rise in ionization, as a result of the progressive sweeping-up of the CSM by the shock. The duration of the IIn-like spectra indicates a dense and relatively confined CSM distribution extending up to ∼ 4 × 1014 cm. Spectral modeling reveals a CSM mass loss rate at this region exceeding 5× 10−3 M☉ yr−1 is required to reproduce low-ionization emissions, which dramatically exceeds that of an RSG. Analyzing Hα emission shift implies the velocity of the unshocked outer CSM to be between 20 and 40 km s−1, matching the typical wind velocity of an RSG. The differences between the inner and outer layers of the CSM and an RSG progenitor highlight a complex mass loss history before the explosion of SN 2024ggi. © 2024, CC BY.

关键词： Supernovae

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