TITLE:   GCN CIRCULAR
NUMBER:  31734
SUBJECT: Fermi GBM Detection of GRB 220308A
DATE:    22/03/10 20:42:33 GMT
FROM:    Cori Fletcher at USRA  <cfletcher@usra.edu>

C. Fletcher (USRA), O. J. Roberts (USRA) and J. Wood (NASA/MSFC) report on behalf of the Fermi-GBM Team:

Swift/BAT-GUANO detected GRB 220308A at 05:43:08 UT (GCN 31716), which was also detected by INTEGRAL/SPI-ACS (trig#9761), IPN (GCN 31715), Konus-Wind (GCN 31723), CGBM (GCN 31719), and AGILE (GCN 31733).

The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals identified a transient most significantly on the 2.048 s consistent with GRB 220308A. The GBM targeted search location is RA=350.6, DEC = 4.7 (J2000 degrees, equivalent to 23 h 22 m, 04 d 42'), with an approximate 68% error radius of 10.6 degrees (statistical plus a core-plus-tail systematic model, with 77% of GRBs having a 2.4 deg error and the remaining fraction having a 10.9 deg error.)

The time-averaged spectrum (using a T0 of 2022-03-08T05:43:00 UT) from T0+8.000 s to T0+28.480 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is  -1.0 +/- 0.0 and the cutoff energy, parameterized as Epeak = 1371 +/- 26 keV. The event fluence (10-1000 keV) in this time interval is (1.53 +/- 0.05)E-04 erg/cm^2.

There was a Fermi-GBM onboard trigger of a gamma-ray burst (GRB 220308B, GCN 31726) approximately 460 s before  GRB 220308A, however, we do not believe these two events to be related.

The spectral analysis results presented above are preliminary.

[1] Goldstein et al. 2019 arXiv:1903.12597