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GCN Circular 31689

Subject
GRB 220305A: Fermi GBM observation
Date
2022-03-05T23:40:22Z (2 years ago)
From
Joe Mangan at UCD <joseph.mangan@ucdconnect.ie>
R. Dunwoody (UCD), J. Mangan (UCD) and C.Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 11:33:20.48 UT on 05 March 2022, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 220305A (trigger 668172805 / 220305481).

The on-ground calculated location, using the GBM trigger
data, is RA = 174, DEC = -34 (J2000 degrees,
equivalent to 11 h 36 m, -34 d 00 '), with a statistical uncertainty
of 1.5 degrees.

The angle from the Fermi LAT boresight at the GBM trigger time is 35 degrees.

The GBM light curve consists of three emission episodes, the most
prominent occurring around T0+50s, with a duration (T90) of about
172.8 s (50-300 keV).

The time-averaged spectrum for the first emission episode, from
T0-12.3 to T0+12.3, is best fit by a power law function with an
exponential high-energy cutoff. The power law index is -0.6 +/- 0.5
and the cutoff energy, parameterized as Epeak, is 60.9 +/- 9.1 keV.
The event fluence (10-1000 keV) in this time interval is (6.8 +/-
0.8)E-07 erg/cm^2.

The time-averaged spectrum for the second emission episode, from
T0+39.9 to T0+60.4, is best fit by a Band function with Epeak = 320.7
+/- 35.7 keV, alpha = -0.9 +/- 0.1, and beta = -1.9 +/- 0.1. The event
fluence (10-1000 keV) in this time interval is (1.78 +/- 0.03)E-05.

The time-averaged spectrum for the third emission episode, from
T0+164.9 to T0+193.5, is best fit by a power law function with an
exponential high-energy cutoff. The power law index is -1.3 +/- 0.1
and the cutoff energy, parameterized as Epeak, is 205.2 +/- 42.8 keV.
The event fluence (10-1000 keV) in this time interval is(3.5 +/-
0.3)E-06 erg/cm^2.

The 1-sec peak photon flux measured starting from T0+49.6 s in the
10-1000 keV band is 19.5 +/- 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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