TITLE: GCN CIRCULAR NUMBER: 40799 SUBJECT: GRB250620C: Fermi GBM Observation DATE: 25/06/20 23:48:00 GMT FROM: oindabimukherjee@gmail.com
O. Mukherjee (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 16:07:09.92 UT on 20 June 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB250620C (trigger 772128434/250620672).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 142.61, Dec = 54.96 (J2000 degrees, equivalent to J2000 9h 30m, +54d 57'), with a statistical uncertainty of 1.00 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]).
The angle from the Fermi LAT boresight is 124 degrees.
The GBM light curve consists of multiple emission episodes with a duration (T90) of about 32 s (50-300 keV). The time-averaged spectrum from T0 to T0+35.7 s is best fit by a Band function with Epeak= 371 +/- 15 keV, alpha = -0.93 +/- 0.02 and beta = -2.6 +/- 0.2.
The event fluence (10-1000 keV) in this time interval is (6.64 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.96 s in the 10-1000 keV band is 50.1 +/- 0.7 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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