TITLE:   GCN CIRCULAR
NUMBER:  28244
SUBJECT: GRB 200809B: Fermi GBM detection
DATE:    20/08/10 17:48:07 GMT
FROM:    Rachel Dunwoody at UCD  <rachel.dunwoody@ucdconnect.ie>

R. Dunwoody (UCD), C. Fletcher (USRA), J. Mangan (UCD) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 15:41:27.13 UT on 09 August 2020, the Fermi Gamma-Ray Burst Monitor
(GBM)
triggered and located GRB 200809B (trigger 618680492 / 200809654)
which was also detected by the Swift/BAT-GUANO (Tohuvavohu et al. 2020, GCN
28237)
The Fermi GBM Final Real-time Localization (GCN 28236) is consistent with
the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 111
degrees.

This burst was also independently detected by MAXI/GSC (GCN 28240)
and AstroSat CZTI (GCN 28238).

The GBM light curve consists of a single peak
with a duration (T90) of about 17 s (50-300 keV).
The time-averaged spectrum from T0 s to T0+17.6 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.5 +/- 0.3 and
the cutoff energy, parameterized as Epeak, is 682 +/- 246 keV.


The event fluence (10-1000 keV) in this time interval is
(3.717 +/- 0.387)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.13 s in the 10-1000 keV band
is 4.7 +/- 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/"