[vsnet-grb-info 19440] GRB 170527A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21157
SUBJECT: GRB 170527A: Fermi GBM detection
DATE:    17/05/27 20:09:57 GMT
FROM:    C. Michelle Hui at MSFC/Fermi-GBM  <c.m.hui at nasa.gov>

M. Stanbro (UAH), C. M. Hui (NASA/MSFC), C. Meegan (UAH)
and A. von Kienlin (MPE) report on behalf of the Fermi GBM Team:

At 11:31:02.37 UT on 27 May 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170527A (trigger 517577467 / 170527480).

The on-ground calculated location, using the GBM trigger
data, is RA = 195.19 , DEC = +0.94  (J2000 degrees,
equivalent to 13h 00m, +0d 54.0'), with an uncertainty
of 1.00 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 trigger resulted in an Autonomous Repoint Request (ARR)
by the GBM Flight Software owing to the high peak flux of the GRB.
This ARR was accepted and the spacecraft slewed 
to the GBM in-flight location. The initial angle from the 
Fermi LAT boresight is 37.00 degrees.

The GBM light curve shows a sharp peak with multiple sub-structures
with a duration (T90) of about 49.2 s (50-300 keV).
The time-averaged spectrum from T0+1.1 s to T0+50.3 s is 
adequately fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.03 +/- 0.01 and
the cutoff energy, parameterized as Epeak, is 1001.00 +/- 33.50 keV

The event fluence (10-1000 keV) in this time interval is
(8.430 +/- 0.003)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.8 s in the 10-1000 keV band is 
22.19 +/- 0.36 ph/s/cm^2.

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