[vsnet-grb-info 22443] LIGO/Virgo S190513bm: Insight-HXMT/HE observation

[GCN Circulars]

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  <luoqi at ihep.ac.cn>

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.