GCN Circular 21518

J. Y. Liao, C. K. Li, M. Y. Ge, Y. Huang, Z. W. Li, S. L. Xiong, Y. Liu,
C. Z. Liu, X. F. 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), F. J. Lu, L. M. Song, H. Y. Wang, 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 GBM trigger time
(T0=2017-08-17 12:41:06.47 UTC) of the short weak bn170817529
(Connaughton 2017, GCN 21506
Not found
 
 
), which is about 2 seconds after the
LIGO trigger of G298048 reported in GCN 21505
Not found
 
 
. This GRB was also
detected by the INTEGRAL/SPI-ACS (Savchenko 2017, GCN 21507
Not found
 
 
).

At T0, both the GBM localization error region and the LHV location area
(reported in GCN 21513
Not found
 
 
) were fully covered by Insight-HXMT
without occultation by the Earth. The incident angle is about 30 deg for
the best GBM location (Ra=190.76 deg, Dec=-39.43 deg), corresponding to
almost the optimum sensitivity of Insight-HXMT to a GRB.

Within T0 +/- 1000 s, no significant excess (SNR > 5) was found
in a search of the Insight-HXMT raw light curves with time scales of
20 ms, 50 ms, 0.2 s and 1 s, respectively. A 3.2 sigma excess is found
2 s before T0, however, consistent with background fluctuations.

With the three typical GRB Band spectral models, integration time of 1 s
and the best GBM localization, the 3-sigma
upper-limits of fluence (0.2 - 5 MeV, incident energy) are reported below:

Band model 1 (alpha=-1.9, beta=-3.7, Ep=70 keV):   1.04e-07 erg cm^-2
Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV):  1.44e-07 erg cm^-2
Band model 3 (alpha=0.0, beta=-1.5, Ep=1000 keV):   2.22e-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 (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.

The analysis results presented above are preliminary; more analysis results
with refined LIGO locations will be reported later.
In addition, Insight-HXMT has initiated a ToO observation to the
GBM location region. ToO observation results will be reported as well.

Insight-HXMT is the first Chinese space X-ray telescope, which was funded
jointly by the China National Space Administration (CNSA) and the Chinese
Academy of Sciences (CAS). More information about it could be found at:
http://www.hxmt.org/index.php/enhome .