TITLE:   GCN CIRCULAR
NUMBER:  26569
SUBJECT: LIGO/Virgo S191216ap: Upper limits from Insight-HXMT/HE observations
DATE:    19/12/23 14:58:42 GMT
FROM:    Qi Luo at IHEP  <luoqi@ihep.ac.cn>

Q. Luo, Y. G. Zheng, C. Cai, S. Xiao, Q. B. Yi, 
Y. Huang, C. K. Li, G. Li, X. B. 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 
S191216ap GW event (GCN #26454). At the GW trigger time 
2019-12-16T21:33:38.473 UTC (denoted as T0), 0.96% of the GW 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 center 
of the GW location probability map (RA=288.6 deg, DEC=61.1 deg)
without occultation by the Earth, 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:   5.8e-08 erg cm^-2
10 s:  1.9e-07 erg cm^-2

Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV):
1 s:   1.0e-07 erg cm^-2
10 s:  3.4e-07 erg cm^-2

Band model 3 (alpha=-0.0, beta=-1.5, Ep=1000 keV):
1 s:   2.7e-07 erg cm^-2
10 s:  1.1e-06 erg cm^-2

Futhermore, from T0-15 minutes to T0+21 minutes, both the IceCube counterpart 
neutrino candidate (GCN #26450) and the HAWC sub-threshold event (GCN #26472) 
were invisible to Insight-HXMT due to the Earth shielding. 

Assuming that the counterpart GRB comes from the HAWC location 
(RA=323.5 deg, DEC=5.2 deg), we estimated 5-sigma upper-limits 
(0.2 - 5 MeV, incident energy) of the extended emission of this GRB 
at 2019-12-16T21:55:00.000 UTC (T0+1281.527 s) as follows: 

Band model 1 (alpha=-1.9, beta=-3.7, Ep=70 keV):
1 s:   2.0e-08 erg cm^-2 
10 s:  1.0e-07 erg cm^-2

Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV):
1 s:   3.5e-08 erg cm^-2
10 s:  1.7e-07 erg cm^-2

Band model 3 (alpha=-0.0, beta=-1.5, Ep=1000 keV):
1 s:   1.5e-07 erg cm^-2
10 s:  5.6e-07 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 spacecraft.