TITLE: GCN CIRCULAR NUMBER: 40067 SUBJECT: GRB 250404A: Fermi GBM Detection DATE: 25/04/04 19:52:20 GMT FROM: oindabimukherjee@gmail.com
O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 14:19:46.35 UT on 04 April 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250404A (trigger 765469191/250404597).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 123.37, Dec = 34.10 (J2000 degrees, equivalent to J2000 8h 13m, +34d 6'), with a statistical uncertainty of 1.20 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 42 degrees.
The GBM light curve consists of multiple peaks with a duration (T90) of about 91.4 s (50-300 keV). The time-averaged spectrum from T0-3.6 to T0+124.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.10 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 55.7 +/- 0.5 keV.
The event fluence (10-1000 keV) in this time interval is (3.33 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+21 s in the 10-1000 keV band is 12.9 +/- 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/"
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