GCN Circular 41420
Subject
GRB 250818C: Fermi GBM Final Real-time Localization
Event
Date
2025-08-18T23:26:54Z (8 days ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB
At 23:16:23 UT on 18 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250818C (trigger 777251788.512804 / 250818970).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 203.8, Dec = 74.7 (J2000 degrees, equivalent to J2000 13h 35m, 74d 42'), with a statistical uncertainty of 1.0 degrees.
The angle from the Fermi LAT boresight is 0.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250818970/quicklook/glg_skymap_all_bn250818970.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250818970/quicklook/glg_healpix_all_bn250818970.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250818970/quicklook/glg_lc_medres34_bn250818970.gif