MAXI/GSC refined analysis of SGR 1935+2154

ATel #9191; M. Sugizaki (RIKEN), S. Ueno, H. Tomida, S. Nakahira, M. Ishikawa, Y. Sugawara (JAXA), Y. E. Nakagawa (JAMSTEC), T. Mihara, M. Serino, W. Iwakiri, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, N. Isobe, S. Sugita, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), H. Tsunemi, R. Shomura (Osaka U.), H. Negoro, M. Nakajima, K. Tanaka, T. Masumitsu, T. Kawase (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori, A. Tanimoto (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), M. Yamauchi, K. Furuya (Miyazaki U.), K. Yamaoka (Nagoya U.)
on 25 Jun 2016; 14:23 UT
Credential Certification: Mutsumi Sugizaki (sugizaki@riken.jp)

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We performed refined analysis of MAXI/GSC data for the short burst from SGR 1935+2154 that appeared at 2016 June 20, 15:16:35 (UT) (Sugita et al. GCN Circ. 19545). The event was simultaneously detected by Fermi GBM (Younes et al. GCN Circ. 19546), and the recent short-burst activities in this source were observed by Swift BAT (Burrows et al. GCN Circ. 19556).

The MAXI/GSC light curve revealed that a short spike with a duration of 0.3 sec started at 15:16:34.8 (UT) when the GSC had been scanning the field including SGR 1935+2154 from 15:15:25 to 15:17:28. The two GSC units, GSC_0 and GSC_6, which detected the short burst, were under a non-standard operation at that time, because they had shown some significant degradation. The GSC_0 counter is working under continued gas leak and the GSC_6 counter has a couple of malfunction anodes. Therefore, we performed the spectral analysis with a tentative response function which is just under the calibration process.

The 2-30 keV GSC spectrum averaged over the 0.3-sec short burst was fitted with a blackbody model, together with photoelectric absorption of which equivalent hydrogen column density is fixed to the Galactic value of 1.27×10²² cm^-2 (Burrows et al. GCN Circ. 19556). The fit is accepted with the reduced chi squared, 1.36 for 33 degree of freedom. The blackbody temperature of kT = 3.5 ± 0.4 keV and the normalization represented by the source radius of R = 48 ± 7 km, assuming the source distance of 10 kpc, are obtained as the best-fit value and the 90 % statistical uncertainty. Due to the calibration uncertainty, the normalization of the blackbody radiation is expected to have an additional error by ~30%.