TITLE: GCN CIRCULAR NUMBER: 35860 SUBJECT: GRB 240303B: Fermi GBM Detection DATE: 24/03/04 15:41:29 GMT FROM: rachel.hamburg@ijclab.in2p3.fr R. Hamburg (CNRS/IN2P3/IJCLab) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 12:18:51.24 UT on 03 March 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240303B (trigger 731161136 / 240303513). The on-ground calculated location is reported in GCN 35850. This burst was also detected by CALET (Nakahira et al., 2024; GCN 35857) and the INTEGRAL SPI-ACS (trigger 10612). The angle from the Fermi LAT boresight is 96 degrees. The GBM light curve consists of a single bright pulse with a duration (T90) of about 5.9 s (50-300 keV). The time-averaged spectrum from T0-1.0 to T0+8.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.33 +/- 0.03 and the cutoff energy, parameterized as Epeak, is 540 +/- 20 keV. A Band function fits the spectrum equally well with Epeak= 510 +/- 20 keV, alpha = -0.30 +/- 0.04 and beta = -3 +/- 0.3. The event fluence (10-1000 keV) in this time interval is (2.31 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3.9 s in the 10-1000 keV band is 18.5 +/- 0.3 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/" View this GCN Circular online at https://gcn.nasa.gov/circulars/35860. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...