Burst forest from SGR 1935+2154 as detected with NICER
George Younes, Tolga Güver, Teruaki Enoto, Zaven Arzoumanian, Keith C. Gendreau, Chin‐Ping Hu, Paul S. Ray, C. Kouveliotou, Sébastien Guillot, Wynn C. G. Ho, E. C. Ferrara, Christian Malacaria
Abstract
Following reports of substantial bursting activity from the magnetar SGR 1935+2154 (e.g., GCN #27657, Barthelmy et al.; GCN #27661, Nakahira et al.), we initiated a series of DDT observations with NICER. The first observation started at 00:40:58.000 UTC of 2020-04-28 UTC and lasted approximately 1 ks. The NICER light curve (1 - 9 keV; 4 ms time resolution) shows a large number of typical magnetar short bursts. Assuming that bursts separated by more than 200 ms are distinct, we identify over 100 bursts during this observation. The burst with the brightest peak is detected at 00:46:21.2 UTC. This burst lasted approximately 200 ms, and reached a peak count rate of about 140k counts/second. Assuming a typical magnetar spectrum at soft energies consisting of a black-body with a temperature of 4 keV, and a hydrogen column density towards the source of about 3e22 /cm2 (Israel et al. 2016, MNRAS, 457, 3448; Younes et al. 2017, ApJ, 847, 85), we estimate a 4 ms peak flux for this burst of about 2.7e-6 erg/s/cm2 (1 - 9 keV). We caution that this value is affected by deadtime and other saturation effects, which may be substantial given the large count rate during burst peaks.