TITLE: GCN CIRCULAR NUMBER: 37509 SUBJECT: GRB 240913C: Fermi GBM detection DATE: 24/09/14 18:00:44 GMT FROM: Elisabetta Bissaldi at Politecnico and INFN Bari elisabetta.bissaldi@ba.infn.it

E. Bissaldi (Politecnico and INFN Bari) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:

"At 11:42:36.12 UT on 13 September 2024, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 240913C (trigger 747920561 / 240913488), which was also detected by the Einstein Probe (GCN #37492, #37493).

The on-ground calculated location, using the GBM trigger data, is RA = 14.6, DEC = 12.3 (J2000 degrees, equivalent to 00h 58m, 12d 18'), with a statistical uncertainty of 3.8 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error [Connaughton et al. 2015, ApJS, 216, 32] ).

The angle from the Fermi LAT boresight at the GBM trigger time is 104 degrees.

The GBM light curve consists of a bright peak with a duration (T90) of about 6.3 s (50-300 keV). The time-averaged spectrum from T0-1.3 s to T0+3.8 s is best fit by a Band function with Epeak = 68 +/- 6 keV, alpha = 0.08 +/- 0.23, and beta = -2.41 +/- 0.12.

The event fluence (10-1000 keV) in this time interval is (2.35 +/- 0.01)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.26 s in the 10-1000 keV band is 15.1 +/- 2.6 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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