TITLE: GCN CIRCULAR NUMBER: 39882 SUBJECT: GRB 250327A: Fermi GBM observation DATE: 25/03/27 14:52:00 GMT FROM: Andreas von Kienlin at MPE azk@mpe.mpg.de

A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team:

"At 07:30:06.33 UT on 27 March 2025, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 250327A (trigger 764753411 / 250327313), which was also detected by the Swift/BAT (Parsotan et al. 2025, GCN 39877). The Fermi GBM Final Real-time Localization (GCN 39876) is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 47 degrees.

The GBM light curve shows a structured emission episode with a duration (T90) of about 160 s (50-300 keV). The time-averaged spectrum from T0-1.024s to T0+90.114s is best fit by a Band function with Epeak = 480 +/- 50 keV, alpha = -1.08 +/- 0.03, and beta = -2.14 +/- 0.15.

The event fluence (10-1000 keV) in this time interval is (2.97 +/- 0.07)E-05 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+0.704 s in the 10-1000 keV band is 5.08 +/- 0.23 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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