TITLE: GCN CIRCULAR NUMBER: 41890 SUBJECT: GRB 250919A: Fermi GBM Observation DATE: 25/09/19 18:56:13 GMT FROM: oindabimukherjee@gmail.com O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 00:28:52.28 UT on 19 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250919A (trigger 779934537/250919020) which was also detected by Fermi-LAT ( A. Holzmann Airasca et al. 2025, GCN 41884), SVOM-GRM (Chen-Wei Wang et al. 2025, GCN 41882), Swift-XRT (J.P. Osborne et al., 2025, GCN 41885), EP-WXT (Y.F. Liang et al. 2025, GCN 41879), Swift-UVOT (S.R. Oates et al. 2025, GCN 41886), Gemini/GMOS-S spectroscopic redshift z = 1.145 (A. J. Levan et al. 2025, GCN 41883) The Fermi GBM on-ground location is consistent with the position measured by other instruments. The angle from the Fermi LAT boresight is 56 degrees. The GBM light curve consists of a very bright emission episode, followed by a fainter second emission episode, with a total duration (T90) of about 129.3 s (50-300 keV). The time-averaged spectrum from T0+3 to T0+190 s is best fit by a Band function with Epeak = 476 +/- 6 keV, alpha = -0.88 +/- 0.01, and beta = -2.39 +/- 0.04. The event fluence (10-1000 keV) in this time interval is (4.36 +/- 0.002)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+33 s in the 10-1000 keV band is 115.2 +/- 0.7 ph/s/cm^2. The time-averaged spectrum of the main pulse from T0+3 to T0+58 s is best fit by a Band function with Epeak = 475 +/- 5 keV, alpha = -0.7 +/- 0.01, and beta = -2.38 +/- 0.03. The event fluence (10-1000 keV) in this time interval is (2.56 +/- 0.01)E-04 erg/cm^2. The time-averaged spectrum of the second pulse from T0+111 to T0+190 s is best fit by a Band function with Epeak = 220 +/- 12 keV, alpha = -1.12 +/- 0.02, and beta = -1.93 +/- 0.03. The event fluence (10-1000 keV) in this time interval is (5.77 +/- 0.05)E-05 erg/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/" View this GCN Circular online at https://gcn.nasa.gov/circulars/41890. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...