TITLE: GCN CIRCULAR NUMBER: 39003 SUBJECT: GRB 250119B: Fermi GBM Observation DATE: 25/01/20 16:45:38 GMT FROM: Utkarsh Pathak at IIT Bombay utkarshpathak.07@gmail.com

U. Pathak (IITB), R. Sonawane (IISER, TVM), and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 08:27:01.67 UT on 19 January 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250119B (trigger 758968026/250119352) which was also detected by INTEGRAL/SPI-ACS (Barria et al. 2025, GCN 38997).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 306.74, Dec = 21.23 (J2000 degrees, equivalent to J2000 20h 26m, +21d 13'), 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 106 degrees.

The GBM light curve consists of two emission episodes with multiple spikes for a duration (T90) of about 255.5 s (50-300 keV). The time-averaged spectrum from T0-4 to T0+300 s is best fit by a Band function with Epeak = 297 +/- 14 keV, alpha = -0.98 +/- 0.02, and beta = -2.6 +/- 0.2.

The event fluence (10-1000 keV) in this time interval is (9.2 +/- 0.1)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+44 s in the 10-1000 keV band is 17.6 +/- 0.4 ph/s/cm^2.

A power law function with an exponential high-energy cutoff fits the spectrum equally well with Epeak= 314 +/- 11 keV, and alpha = -0.99 +/- 0.02.

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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