TITLE: GCN CIRCULAR NUMBER: 23567 SUBJECT: GRB 181225A: Insight-HXMT/HE detection DATE: 18/12/27 14:05:53 GMT FROM: QiBin Yi at IHEP, HXMT Q. B. Yi, C. K. Li, X. B. Li, G. Li, J. Y. Liao, S. L. Xiong, C. Z. Liu, X. F. Li, Z. W. 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), L. M. Song, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team: At 2018-12-25T11:44:10.000 (T0), the Insight-HXMT/HE detected GRB 181225A (trigger ID: HEB181225489) in a routine search of the data, which was also triggered by by AGILE/MCAL (A. Ursi et al.,GCN23560)、 Fermi/LAT (M. Arimoto et al., GCN23561) and Fermi/GBM (S.Poolakkil., GCN23562). The Insight-HXMT/HE light curve mainly consists of multiple pulses with a duration (T90) of 1.23 s measured from T0+0.46 s. The 50-ms peak rate, measured from T0+1.208 s, is 2963.2 cnts/s. The total counts from this burst 2350.8 counts. URL_LC: http://www.hxmt.org/images/GRB/HEB181225489_lc.jpg All measurements above are made with the CsI detectors operating in the GRB mode with the energy range of about 200-3000 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. Insight-HXMT is the first Chinese space X-ray telescope, which was fundedjointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information could be found at: http://www.hxmt.org.