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GCN Circular 34885

GRB 231024A: Fermi GBM Observation
2023-10-25T19:47:00Z (7 months ago)
Lorenzo Scotton at UAH <>
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L. Scotton (UAH), O.J. Roberts (USRA/NASA-MSFC), C. Fletcher (USRA),
E. Burns (LSU) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 13:20:34.42 UT on 24 October 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 231024A (trigger 719846439/231024556). This trigger 
was later followed up by GOTO (Gompertz et al. 2023, GCN 34878), 
LCOGT and ZTF (Iglesias-López et al. 2023, GCN 34881), 
and X-shooter (Saccardi et al. 2023, GCN 34882) identifying 
a candidate afterglow (AT2023vuc/GOTO23baj) and suggested it was the counterpart.

The Fermi GBM Final Localization was reported in GCN 34876.

The angle from the Fermi LAT boresight is 89 degrees.

The GBM light curve consists of a single peak  
with a duration (T90) of about 0.05s. The time-averaged spectrum
from T0-0.064 to T0+0.064 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.76 +/- 0.26 and the cutoff energy,
parameterized as Epeak, is 516 +/- 202 keV. 
A Band function fits the spectrum equally well with
Epeak = 519 +/- 203 keV, alpha = -0.75 +/- 0.26 and beta = -8.82 +/- 0.01.

The event fluence (10-1000 keV) in this time interval is
(2.9 +/- 0.4)E-07 erg/cm^2. The 64-msec peak photon flux measured
starting from T0-0.06 s in the 10-1000 keV band is 8 +/- 1 ph/s/cm^2.

Due to the large GBM localization error radius of 12.6 degrees, 
as reported in GCN 34876, we are currently unable to confirm or deny 
the association between GRB 231024A and AT2023vuc/GOTO23baj.
However, considered the spectroscopic classification of the optical transient 
as an early supernova we expect it to be unrelated to the gamma-ray trigger. 
The alignment in time and space is likely coincidental, in part due 
to the large localization region.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:"
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