GCN Circular 41852

Subject

GRB 250917B: Fermi GBM Observation

Event

GRB 250917B

Date

2025-09-17T18:53:07Z (3 days ago)

Edited On

2025-09-17T19:21:37Z (2 days ago)

From

Rushikesh Digambar Sonawane PHD231014 at IISER, TVM <rushikesh23@iisertvm.ac.in>

Edited By

Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Rushikesh sonawane at IISER, TVM <sonawanerushikesh521@gmail.com>

Via

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

"At 06:27:44.33 UT on 17 September 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250917B (trigger 779783269/250917269).
which was also detected by Swift BAT (R. Caputo et al. 2025, GCN 41848Loading...
 
 ).
The Fermi GBM on-ground location is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 48 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 0.2 s (50-300 keV). The time-averaged spectrum
from T0-0.2 to T0+0.3 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1 +/- 0.2 and the cutoff energy,
parameterized as Epeak, is 120 +/- 20 keV.

The event fluence (10-1000 keV) in this time interval is
(3.2 +/- 0.3)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.0 s in the 10-1000 keV band is 24 +/- 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/"