[vsnet-grb-info 27670] GRB 210406B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29773
SUBJECT: GRB 210406B: Fermi GBM detection
DATE:    21/04/08 14:53:07 GMT
FROM:    Christian Malacaria at NASA-MSFC/USRA  <cmalacaria at usra.edu>

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

"At 22:46:05.23 UT on 6 April 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 210406B (trigger 639441970 / 210406949).

The on-ground calculated location, using the GBM trigger
data, is RA = 6.58, DEC = 19.58 (J2000 degrees,
equivalent to 00 h 26 m, 19 d 34 '), with an uncertainty of 1.5 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 at the GBM trigger time is 83 degrees.

The GBM light curve consists of a long GRB with three
distinct peaks and with a duration (T90) of about 20 s (50-300 keV).
The spectrum shows a marked hard to soft evolution throughout the burst.
The time-averaged spectrum from T0+1.5 s to T0+20.9 s is
best fit by a Band function with Epeak = 53.4 +/- 0.7 keV,
alpha = -1.16 +/- 0.02, and beta = -3.06 +/- 0.09 .

The event fluence (10-1000 keV) in this time interval is
(2.423 +/- 0.027)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+10.7 s in the 10-1000 keV band
is 29.7 +/- 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/"