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GCN Circular 36024

Subject
GRB 240403A: Fermi GBM Detection
Date
2024-04-04T14:27:05Z (16 days ago)
From
rachel.hamburg@ijclab.in2p3.fr
Via
Web form
R. Hamburg (CNRS/IN2P3/IJCLab), S. Dalessi (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 11:57:30.58 UT on 03 April 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 240403A (trigger 733838255/240403498).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 6.5, Dec = -17.3 (J2000 degrees, equivalent to
J2000 +00h 26m, -17d 17'), with a statistical uncertainty of 1.77 degrees.
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 is 62 degrees.

The GBM light curve shows a precursor, a main emission peak 
and third weaker peak, yielding a duration (T90)
of about 35.6 s (50-300 keV). The time-averaged spectrum
from T0-1.2 to T0+76.7 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.11 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 350 +/- 10 keV. 
A Band function also fits well with Epeak = 322 +/- 14 keV,
alpha = -1.08 +/- 0.02, and beta = -2.40 +/- 0.13.

The event fluence (10-1000 keV) in this time interval is
(3.6 +/- 0.4)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+26 s in the 10-1000 keV band is 39.1 +/- 0.4 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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