Eclipsed X-ray Bursts from Magnetar SGR J1935+2154 and the Fireball Measurements

Eclipsed X-ray Bursts from Magnetar SGR J1935+2154 and the Fireball Measurements
Sheng-Lun Xie, A-Ming Chen, Yun-Wei Yu, Shao-Lin Xiong, Hua Feng, Shuang-Nan Zhang, Zi-Gao Dai, Wang-Chen Xue, Ming-Yu Ge, Xiao-Bo Li, Liang-Duan Liu, Jia-Cong Liu, Wen-Jun Tan, Chen-Wei Wang, Shu-Xu Yi, Peng Zhang, Yan-Qiu Zhang, Zhen Zhang, Chao Zheng, Xiao-Ping Zheng
AbstractX-ray bursts from the magnetar can lead to the formation of fireballs trapped by the magnetic field and co-rotating with the star. The fireball emission could occasionally be eclipsed by the magnetar, especially when the burst duration is comparable to the magnetar's spin period. In this work, we discover a peculiar type of burst whose light curve has a plateau-like feature among the long bursts of the magnetar SGR J1935+2154. Based on these bursts, we identified four burst candidates with eclipse-like characteristics. By fitting their light curves with the eclipse fireball model, the viewing angle of the magnetar relative to its spin axis is estimated to be $17^\circ \pm 10^\circ$. The distances from the fireballs to the magnetar are found to be more than five times the magnetar's radius, indicating that the fireballs are suspended in the magnetosphere rather than adhering to the magnetar surface. We also find this configuration is well consistent with the implication of the cyclotron resonance scattering feature in their spectra. Our results suggest that some intermediate X-ray bursts of SGR 1935+2154 may originate from magnetic reconnection within the magnetosphere rather than the starquake.