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GECAM discovery of a peculiar magnetar X-ray burst (MXB 221120) from SGR J1935+2154 associated with a fast radio burst

Wen-Jun Tan, Yue Wang, Chen-Wei Wang, Shao-Lin Xiong, Xiao-Bo Li, Shuang-Nan Zhang, Ce Cai, Wang-Chen Xue, Peng Zhang, Bo-Bing Wu, Zheng-Hua An, Ming Gao, Ming-Yu Ge, Ke Gong, Dong-Ya Guo, Hao-Xuan Guo, Long-Fei Hao, Yue Huang, Yu-Xiang Huang, Ke-Jia Lee, Bing Li, Kui-Cheng Li, Xin-Qiao Li, Jia-Cong Liu, Xiao-Jing Liu, Ya-Qing Liu, Xiang Ma, Wen-Xi Peng, Rui Qiao, Yang-Zhao Ren, Li-Ming Song, Xi-Lei Sun, Jin Wang, Jin-Zhou Wang, Ping Wang, Xiang-Yang Wen, Shuo Xiao, Lun-Sheng Xie, Heng Xu, Sheng Yang, Shu-Xu Yi, Qi-bin Yi, Zheng-Hang Yu, Li-Da Zhang, Fan Zhang, Hong-Mei Zhang, Jin-Peng Zhang, Yan-Qiu Zhang, Zhen Zhang, Xiao-Yun Zhao, Yi Zhao, Chao Zheng, Shi-Jie Zheng

Abstract

Fast radio bursts (FRBs) are enigmatic cosmic transients of millisecond duration observed in the radio band. The identification of FRB-associated magnetar X-ray bursts (MXBs) from galactic magnetar SGR J1935+2154 suggests that at least a fraction of FRBs can be produced from magnetar activity. However, the sample size of FRB-associated MXBs is still very small. Here we report a bright and peculiar FRB-associated MXB from SGR J1935+2154 detected by GECAM on November 20, 2022, dubbed MXB 221120. We find that both temporal and spectral properties of MXB 221120 exhibit distinctive features. Its light curve could be generally described by a single FRED function with superposition of several narrow pulses. Interestingly, we identify a possible QPO feature with center frequency of ~18 Hz in this MXB. The time-integrated spectrum is best fitted by a blackbody model with temperature (kT ) of 18.6 keV, rendering it the first thermal spectrum FRB-associated MXB from SGR J1935+2154. Compared to other MXBs with single emission episode, MXB 221120 has longer duration and higher blackbody temperature, making it an outlier in the burst sample. These results indicate that MXB 221120 may be produced by a special mechanism with extreme physical conditions.

GECAM discovery of a peculiar magnetar X-ray burst (MXB 221120) from SGR J1935+2154 associated with a fast radio burst

Abstract

Fast radio bursts (FRBs) are enigmatic cosmic transients of millisecond duration observed in the radio band. The identification of FRB-associated magnetar X-ray bursts (MXBs) from galactic magnetar SGR J1935+2154 suggests that at least a fraction of FRBs can be produced from magnetar activity. However, the sample size of FRB-associated MXBs is still very small. Here we report a bright and peculiar FRB-associated MXB from SGR J1935+2154 detected by GECAM on November 20, 2022, dubbed MXB 221120. We find that both temporal and spectral properties of MXB 221120 exhibit distinctive features. Its light curve could be generally described by a single FRED function with superposition of several narrow pulses. Interestingly, we identify a possible QPO feature with center frequency of ~18 Hz in this MXB. The time-integrated spectrum is best fitted by a blackbody model with temperature (kT ) of 18.6 keV, rendering it the first thermal spectrum FRB-associated MXB from SGR J1935+2154. Compared to other MXBs with single emission episode, MXB 221120 has longer duration and higher blackbody temperature, making it an outlier in the burst sample. These results indicate that MXB 221120 may be produced by a special mechanism with extreme physical conditions.

Paper Structure

This paper contains 10 sections, 5 equations, 4 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Observation and data reduction
  3. Data analyses and results
  4. Temporal analysis
  5. Light curve fitting
  6. QPO search
  7. Spectral analysis
  8. MXB sample comparison
  9. Discussion
  10. Summary

Figures (4)

  • Figure 1: a, Light curve in 10 ms resolution and duration ($T_{90}$). The red dashed line in top panel represents the background level. The blue shadow region in lower panel represents the background range. b, Light curves in different energy bands observed by GECAM-B. c, Light curve fitting with FRED function. The light curve and FRED profile is plotted in top panel, and the residuals are plotted in lower panel.
  • Figure 2: QPO searching of MXB 221120.a, $Z_{1}^{2}$ periodogram of MXB 221120 during the time interval of -0.1 s to 0.1 s. The red dashed line represents the false alarm probability of 0.1$\%$ level. b, Phase folding light curve of MXB 221120 with the best detected frequency.
  • Figure 3: The best spectrum fitting of MXB 221120.
  • Figure 4: Several properties of MXB 221120 in sample distribution.a, The position of duration ($T_{90}$) and burst fluence in sample of FRED MXBs and ERCOD MXBs. The solid lines represent the power-law fitting of the data and the dashed lines represent the 1 $\sigma$ error region. b, The position of rise time and decay time in sample of FRED MXBs and ERCOD MXBs. The gray dotted lines indicate the ratio between rise time and decay time. c, The position of $kT$ and flux in sample of FRED MXBs and ERCOD MXBs. d, The position of $\alpha$ and $E_{\rm p}$ in Fermi/GBM sample. e, The position of $kT$ and BB area in Fermi/GBM sample. The solid lines represent the power-law fitting of the data and the dashed lines represent the 1 $\sigma$ error region. f, The position of fluence in Fermi/GBM sample. In a-c, the sample is obtained from ercod. In d-f, the sample is obtained from GBM_catalog_2021_SepGBM_catalog_2022_JanGBM_catalog_2022_Oct