TITLE: GCN CIRCULAR NUMBER: 21739 SUBJECT: GRB 170826B: Insight-HXMT detection DATE: 17/08/29 03:49:05 GMT FROM: Zhengwei Li at IHEP Z. W. Li, J. Y. Liao, C. K. Li, X. B. Li, S. L. Xiong, C. Z. Liu, X. F. Li, Z. Chang, X. F. Lu, J. L. Zhao, A. M. Zhang, Y. F. Zhang, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, H. Y. Wang, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team: During the commissioning phase, at 2017-08-26T19:38:58.00 (T0), Insight-HXMT detected GRB 170826B (trigger ID: HEB170826818) in a routine search of the data, which was also observed by Fermi/GBM (Poolakkil et al, GCN Circ.21717). The Insight-HXMT light curve consists of multiple pulses with a duration (T90) of 10.12 s measured from T0-0.46s. The 500-ms peak rate, measured from T0-0.46 s, is 2948.6 cnts/sec. The total counts from this burst is 23373.3 counts. URL_LC: http://www.hxmt.org/images/GRB/HEB170826818_lc.jpg All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 80-800 keV (record energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. The time-averaged spectrum from T0-1.00 to T0+9.00 s is adequately fit by a Power Law model with spectral index = -2.03 +/- 0.04 . The energy fluence is (1.46 +/- 0.06)E-05 erg/cm^2 in 200 - 5000 keV in this time interval. The analysis results presented above are preliminary; final results will be published elsewhere. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org/index.php/enhome. -- Sincerely Yours, Zhengwei Li, Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing China TEL:15210983070 E-mail:lizw@ihep.ac.cn