TITLE:   GCN CIRCULAR
NUMBER:  33689
SUBJECT: GRB 230426A: Fermi GBM Detection
DATE:    23/04/27 15:03:34 GMT
FROM:    Joshua Wood at NASA/MSFC <joshua.r.wood@nasa.gov>

J. Wood (NASA/MSFC) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 20:28:59.97 UT on 26 April 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 230426A (trigger 704233744/230426853)
which was also detected by AstroSat CZTI (P K. Navaneeth et al. 2023, GCN 33686).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 38.53, Dec = -82.40 (J2000 degrees, equivalent to
J2000 2h 34m, -82d 24'), with a statistical uncertainty of 1.00 degrees.
(radius, 1-sigma containment, statistical only; there is additionally a
systematic error which we have characterized as a mixture of two Gaussians,
one with a radius of 1.8 degrees (52% contribution) and one with a radius
of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]).

The angle from the Fermi LAT boresight is 49 degrees.

The GBM light curve consists of multiple pulses with a duration (T90)
of about 25.9 s (50-300 keV). The time-averaged spectrum
from T0+8.2 to T0+35.8 s is best fit by
a Band function with Epeak = 77 +/- 2 keV,
alpha = -1.34 +/- 0.02, and beta = -2.38 +/- 0.03.

The event fluence (10-1000 keV) in this time interval is
(5.21 +/- 0.04)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+23 s in the 10-1000 keV band is 66.6 +/- 0.7 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/"