TITLE:   GCN CIRCULAR
NUMBER:  29246
SUBJECT: GRB 210104A: Fermi GBM detection
DATE:    21/01/04 22:13:38 GMT
FROM:    Christian Malacaria at NASA-MSFC/USRA  <cmalacaria@usra.edu>

C. Malacaria (NASA-MSFC/USRA), C. Fletcher (USRA) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 11:26:59.87 UT on 04 January 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 210104A (trigger 631452424 / 210104477).
which was also detected by the Swift/BAT (Troja et al. 2021, GCN 29233)
The Fermi GBM Final Real-time Localization (GCN 29232) is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 134 degrees.

The GBM light curve roughly consists of three separated peaks
with a duration (T90) of about 32 s (50-300 keV).
The time-averaged spectrum of each peak is best fit by 
a power law function with an exponential high-energy cutoff.
For the first peak, from T0-3.1 s to T0+9.2 s, 
the power law index is -1.2 +/- 0.1 and
the cutoff energy, parameterized as Epeak, is 155 +/- 21 keV.
For the second peak, from T0+16.4 s to T0+22.5 s, 
the power law index is -0.92 +/- 0.1 and Epeak is 245 +/- 23 keV.
For the third peak, from T0+24.6 s to T0+33.8 s,
the power law index is -1.1 +/- 0.1 and Epeak is 199 +/- 14 keV.

The event fluence values (10-1000 keV) in the first, second and third time interval are
(4.004 +/- 0.270)E-06, (5.350 +/- 0.246)E-06 and 
(8.266 +/- 0.276)E-06 erg/cm^2, respectively. 
The 1-sec peak photon flux measured
starting from T0+19.7 s in the 10-1000 keV band
is 17.2 +/- 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/"