GRB 170817B

O.J. Roberts (USRA) and C. Meegan (UAH) report on behalf of 
the Fermi GBM Team:

"At 21:47:34.43 UT on 17 August 2017, the Fermi Gamma-Ray 
Burst Monitor triggered and located GRB 170817B 
(trigger 524699259 / 170817908). The on-ground calculated 
location, using the GBM trigger data, is RA = 83.0, 
DEC = +50.1, with an uncertainty of 3.7 degrees (radius, 
1-sigma containment, statistical only; there is additionally 
a systematic error which we have characterized as a 
core-plus-tail model, with 90% of GRBs having a 3.7 deg error 
and a small tail suffering a larger than 10 deg systematic error. 
[Connaughton et al. 2015, ApJS, 216, 32] ).

The initial angle from the Fermi LAT boresight to
the GBM best location is 90 degrees.

The GBM triggered multiple short unresolvable pulses over a
total duration (T90) of 2.6 s (50-300 keV).
The time-averaged spectrum from T0+0.0 to T0+2.6 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.87 +/- 0.06 and
the cutoff energy, parameterized as Epeak, is 1120 +/- 228 keV

The event fluence (10-1000 keV) in this time interval is
(4.93 +/- 0.16)E-06 erg/cm^2. The 64 ms peak photon flux measured
starting from T0+0.0 s in the 10-1000 keV band
is 10.4 +/- 1.6 ph/s/cm^2.


The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

Z. W. Li, J. Y. Liao, C. K. Li, X. B. Li, S. L. Xiong, 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, X. Ma, 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 2017-08-17T21:47:34.00 (T0),
Insight-HXMT detected GRB 170817B (trigger ID: HEB170817908)
in a routine search of the data, which was also observed by
Fermi/GBM (Roberts et al. 2017, GCN 21540
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 ).

The Insight-HXMT light curve consists of multiple pulses
with a duration (T90) of 2.64 s measured from T0+0.40 s.
The 50-ms peak rate, measured from T0+0.40 s, is 6135.4 cnts/sec.
The total counts from this burst is 5353.1 counts.

URL_LC: http://www.hxmt.org/images/GRB/HEB170817908_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 time-averaged spectrum from T0 to T0+3.60 s is
adequately fit by a Power Law model with spectral index = -1.60 +/- 0.05.
The energy fluence is (1.09 +/- 0.05)E-05 erg/cm^2 in 200 - 5000 keV in
this time interval.

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 .