Discovery of the linear energy dependence of the spectral lag of X-ray bursts from SGR J1935+2154. Issue 4 (22nd March 2023)

• Record Type: Journal Article
• Authors: Xiao, Shuo; Tuo, You-Li; Zhang, Shuang-Nan; Xiong, Shao-Lin; Lin, Lin; Zhang, Yan-Qiu; Wang, Yue; Xue, Wang-Chen; Cai, Ce; Gao, He; Li, Cheng-Kui; Li, Xiao-Bo; Zheng, Chao; Liu, Jia-Cong; Wang, Ping; Wang, Jin; Peng, Wen-Xi; Liu, Cong-Zhan; Li, Xin-Qiao; Wen, Xiang-Yang; An, Zheng-Hua; Song, Li-Ming; Zheng, Shi-Jie; Zhang, Fan; Dong, Ai-Jun; Xie, Wei; Feng, Jian-Chao; Ma, Qing-Bo; Wang, De-Hua; Luo, Xi-Hong; Dang, Shi-Jun; Shang, Lun-Hua; Zhi, Qi-Jun; Li, Ti-Pei;
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 521:Issue 4(2023)
• Page Start: 5308
• Page End: 5333
• Publication Date: 2023-03-22
• Subjects: stars: magnetars; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stad885
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Spectral lag of the low-energy photons with respect to the high-energy ones is a common astrophysical phenomenon (such as gamma-ray bursts and the Crab Pulsar) and may serve as a key probe to the underlying radiation mechanism. However, spectral lag in keV range of the magnetar bursts has not been systematically studied yet. In this work, we perform a detailed spectral lag analysis with the Li et al.'s Cross-Correlation Function (Li-CCF) method for SGR J1935+2154 bursts observed by Insight - Hard X-ray Modulation Telescope ( HXMT ), Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor ( GECAM ), and Fermi /Gamma-ray Burst Monitor (GBM) from 2014 July to 2022 January. We discover that the spectral lags of about 61 per cent (non-zero significance >1σ) bursts from SGR J1935+2154 are linearly dependent on the photon energy ( E ) with t lag ( E ) = α( E /keV) + C, which may be explained by a linear change of the temperature of the blackbody-emitting plasma with time. The distribution of the slope (α) approximately follows a Gaussian function with mean and standard deviation of 0.02 ms keV −1 (i.e. high-energy photons arrive earlier) and 0.02 ms keV −1, respectively. We also find that the distribution can be well fitted with three Gaussians with mean values of ∼−10.009, 0.013, and 0.039 ms keV −1, which may correspond to different origins of the bursts. These spectral lag features may have important implications on the magnetar bursts.