TITLE:   GCN CIRCULAR
NUMBER:  30199
SUBJECT: GRB 210610B: Fermi GBM detection
DATE:    21/06/11 14:50:39 GMT
FROM:    Christian Malacaria at NASA-MSFC/USRA  <cmalacaria@usra.edu>

C. Malacaria (USRA) and B. Hristov (UAH)
report on behalf of the Fermi GBM Team:

At 19:51:05.05 UT on the 10th of June 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 210610B (trigger 645047470 / 210610827),
which was also detected by Swift (Page et al. 2021, GCN 30170).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 63 degrees.

The GBM light curve shows of 3 major peaks
with a duration (T90) of about 55 s (50-300 keV).
Spectral evolution is clear throughout the burst, 
therefore we report the spectrum of the brightest peak.
The time-averaged spectrum of the first peak from T0+25.6s to T0+28.7 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.28 +/- 0.03 and
the cutoff energy, parameterized as Epeak, is 414.3 +/- 11.7 keV.

The event fluence (10-1000 keV) in this time interval is
(1.73 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+30.1 s in the 10-1000 keV band
is 27.4 +/- 0.3 ph/s/cm^2.


The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/