TITLE: GCN CIRCULAR NUMBER: 38903 SUBJECT: GRB 250101B: Fermi GBM Observation DATE: 25/01/11 01:26:07 GMT FROM: oindabimukherjee@gmail.com
O. Mukherjee (USRA), S. Bala (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 23:14:12.65 UT on 01 January 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250101B (trigger 757466057/250101968). which was also detected by SVOM/GRM (Zhang et al. 2025, GCN 38793).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 70.87, Dec = -3.25 (J2000 degrees, equivalent to J2000 4h 43m, -3d 15'), with a statistical uncertainty of 3.29 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 49 degrees.
The GBM light curve consists of a single emission episode with two distinct peaks with a duration (T90) of about 4.5 s (50-300 keV). The time-averaged spectrum from T0-1.0 to T0+5.1 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.34 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 146 +/- 7 keV.
The event fluence (10-1000 keV) in this time interval is (2.418 +/- 0.8)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.77 s in the 10-1000 keV band is 5 +/- 0.2 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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