TITLE:   GCN CIRCULAR
NUMBER:  44971
SUBJECT: GRB 260616A: Fermi GBM Observation
DATE:    26/06/18 02:49:59 GMT
FROM:    Matt Godwin <msg0028@uah.edu>

Matt Godwin (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 03:21:54.33 UT on 16 June 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260616A (trigger 803272919/260616140),
which was also detected by Fermi-LAT ( et al. 2026, GCN 44960).
The Fermi GBM on-ground location is consistent with the Fermi-LAT position.

The angle from the Fermi LAT boresight is 111 degrees.

The GBM light curve consists of one long burst with a duration (T90)
of about 69 s (50-300 keV). The time-averaged spectrum
from T0+0.3 to T0+74.1 s is best fit by
a Band function with Epeak = 246 +/- 1 keV,
alpha = -0.63 +/- 0.01, and beta = -2.00 +/- 0.01.

The event fluence (10-1000 keV) in this time interval is
(1.22 +/- 0.02)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+50 s in the 10-1000 keV band is 16.9 +/- 0.4 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/"