TITLE: GCN CIRCULAR NUMBER: 24542 SUBJECT: LIGO/Virgo S190513bm: Insight-HXMT/HE observation DATE: 19/05/14 15:40:38 GMT FROM: Qi Luo at IHEP Q. Luo, C. Cai, Q. B. Yi, S. Xiao, 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, A. M. Zhang, Y. F. Zhang, X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team: Insight-HXMT was taking data normally around the reported LIGO/Virgo S190513bm event (GCN #24522), trigger time T0=2019-05-13 20:54:28.747 UTC. At T0, about 42% of the LIGO localization region was covered by Insight-HXMT without occultation by the Earth. By searching the Insight-HXMT/HE raw light curves within T0 +/- 100 s, we found that there is one excess with a significance of 4.3 sigma from T0 + 8.50 s to T0 + 8.65 s. After an initial investigation, we believe that this signal is very likely due to background fluctutations and thus unrelated to the GW event. Assuming the GW counterpart GRB with three typical GRB Band spectral models, two typical duration timescales(1 s, 10 s) from the peak position of the LIGO-Virgo location probability map, the 5-sigma upper-limits fluence (0.2 - 5 MeV, incident energy) are reported below: Band model 1 (alpha=-1.9, beta=-3.7, Ep=70 keV): 1 s: 2.8e-07 erg cm^-2 10 s: 1.1e-06 erg cm^-2 Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV): 1 s: 4.0e-07 erg cm^-2 10 s: 1.8e-06 erg cm^-2 Band model 3 (alpha=-0.0, beta=-1.5, Ep=1000 keV): 1 s: 5.3e-07 erg cm^-2 10 s: 2.8e-06 erg cm^-2 All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 80-800 keV (deposited 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.