TITLE: GCN CIRCULAR NUMBER: 38104 SUBJECT: GRB241105A: Fermi GBM Observation of a Short Burst with Extended Emission DATE: 24/11/06 19:06:27 GMT FROM: sumanbala2210@gmail.com

U. Pathak (IITB), O. Mukherjee (USRA), S. Rushikesh (IISER, TVM), S. Bala (USRA), O.J. Roberts (USRA/NASA-MSFC), E. Burns (LSU), P. Veres (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 16:06:04.66 UT on 05 November 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB241105A (trigger 752515569/241105671), which was also detected by Swift/BAT-GUANO (DeLaunay et al. 2024, GCN 38091), GOTO (Julakanti et al. 2024, GCN 38088), Swift-XRT (Kennea et al. 2024, GCN 38098), and SVOM/VT (Qiu et al. 2024, GCN 38099). The spectroscopic redshift of the optical counterpart observered by VLT/FORS2 (Izzo et al. 2024, GCN 38097) is 2.702.

The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position.

The angle from the Fermi LAT boresight is 145 degrees.

The GBM light curve consists of a short single pulse with a duration (T90) of about 1.4 s (50-300 keV) followed by significant extended emission for ~91 (50-300 keV) seconds. The extended emission appears to contain more fluence than the initial spike. The time-averaged spectrum from T0-0.5 to T0+2.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.2 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 702 +/- 278 keV. Considering the redshift of 2.702, and best fit model, we find the isotropic equivalent luminosity Liso = 7.5e+52 erg s-1 (1-10000 keV).

The event fluence (10-1000 keV) in this time interval is (2.8 +/- 0.2)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0-0.19 s in the 10-1000 keV band is 11 +/- 3 ph/s/cm^2.

The total emission (short pulse + extended emission) from T0-2.6 to T0+97 s is best fit by a power law function with photon index -1.42 +/- 0.04. The total fluence (10-1000 keV) in this time interval is (1.1 +/- 0.1)E-05 erg/cm^2. Using z=2.702, we find Eiso = 1.5e+53 erg (1-10000 keV) when fitting the spectrum with a power law function with an exponential high-energy cutoff, with a power-law index of -0.03 +/- 0.4 and cutoff energy, parameterized as Epeak, of 221 +/- 30 keV.

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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