TITLE: GCN CIRCULAR NUMBER: 39642 SUBJECT: GRB 250309B: Fermi GBM Observation DATE: 25/03/10 00:47:24 GMT FROM: Lorenzo Scotton at UAH lscottongcn@outlook.com
P. McDermott (UCD), P. Veres (UAH) and L. Scotton (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 07:38:30.66 UT on 09 March 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250309B (trigger 763198715/250309318). The Fermi GBM on-ground location was reported in GCN 39635.
The angle from the Fermi LAT boresight is 77 degrees.
The GBM light curve consists of an emission episode with multiple peaks, with a duration (T90) of about 6.4 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+8.192 s is best fit by a Band function with Epeak = 93 +/- 5 keV, alpha = -0.98 +/- 0.06 and beta = -2.40 +/- 0.08.
The event fluence (10-1000 keV) in this time interval is (1.07 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3.8 s in the 10-1000 keV band is 23 +/- 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/"
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