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GCN Circular 33515

Subject
GRB 230320B: Fermi GBM Observation
Date
2023-03-24T21:32:11Z (a year ago)
From
Sarah Dalessi at UAH <sd0104@uah.edu>
S. Dalessi (UAH), C. Fletcher (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 21:12:25 UT on 20 March 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 230320B (trigger 701039550/230320884).
which was also detected by AstroSat (P K. Navaneeth et al. 2023, GCN
33492), Swift/BAT-GUANO (S. Ronchini et al. 2023, GCN 33499) CALET (T.
Tamura et al. 2023, GCN 33501), and GRBAlpha (M. Dafcikova et al.
2023, GCN 33503).

The on-ground calculated location, using the GBM trigger
data, is RA = 28.11, DEC = 68.88 (J2000 degrees,
equivalent to 01 h 52 m,  68 d 53��� ), with a statistical uncertainty
of 2.6 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 is 140 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 15 s (50-300 keV). The time-averaged spectrum
from T0+0.003 to T0+15.616 s is best fit by a power law function with
an exponential
high-energy cutoff.The power law index is -0.30 +/- 0.09 and
the cutoff energy, parameterized as Epeak = 186 +/- 8 keV.

The event fluence (10-1000 keV) in this time interval is
(1.02 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0 s in the 10-1000 keV band is 12.7 +/- 0.6 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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