TITLE:   GCN CIRCULAR
NUMBER:  24280
SUBJECT: LIGO/Virgo  S190426c: Insight-HXMT/HE observation
DATE:    19/04/27 13:10:14 GMT
FROM:    QiBin Yi at IHEP, HXMT  <yiqb@ihep.ac.cn>

Q.B.Yi, Q. Luo, C. Cai,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 GW trigger time
(T0=2019-04-26 15:21:55 UTC). At T0, about 100% of the LIGO
localization region was covered by the Insight-HXMT without occultation
by the Earth.

Within T0 ���� 100 s, no significant excess events (SNR > 3 sigma) are 
found in a search of the Insight-HXMT/HE raw light curves.

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):
1s: 7.4e-07 erg cm^-2   
10s: 3.9e-06 erg cm^-2 

Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV):
1s: 1.0e-06 erg cm^-2   
10s: 5.6e-06 erg cm^-2

Band model 3 (alpha=-0.0, beta=-1.5, Ep=1000 keV):
1s: 9.6e-07 erg cm^-2  
10s: 5.0e-06 erg cm^-2 

Further analysis will be reported in the following circulars.

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.

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.