GCN Circular 21919

Y. F. Zhang, S. L. Xiong, J. Y. Liao, C. K. Li, X. B. Li, C. Z. Liu,
X. F. Li, Z. W. Li, Z. Chang, X. F. Lu, J. L. Zhao, A. M. 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:

During the commissioning phase, at 2017-09-21T00:43:37.00 (T0),
Insight-HXMT/HE detected GRB 170921C (trigger ID: HEB170921030)
with a significance of 12 sigma in a routine search of the data,
which is also detected by Fermi/GBM subthreshold trigger
(trig time: 2017-09-21T00:43:37.18).

The Insight-HXMT light curve mainly consists of a single pulse
with a duration (T90) of 1.2 s measured from T0-0.27 s.
The 500-ms peak rate, measured from T0+0.06 s, is 1220.3 cnts/sec.
The total counts from this burst is 1247.3 counts.

URL_LC: http://www.hxmt.org/images/GRB/HEB170921030_lc.jpg

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;
final results will be published elsewhere.

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 .

[GCN OPS NOTE(26sep17):  The name was changed from "21A" to "21C".]