TITLE:   GCN CIRCULAR
NUMBER:  30147
SUBJECT: GRB 210606B: Fermi GBM detection
DATE:    21/06/07 22:12:01 GMT
FROM:    Christian Malacaria at NASA-MSFC/USRA  <cmalacaria@usra.edu>

C. Malacaria (USRA) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 22:40:25.32 UT on 6 June 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 210606B (trigger 644712030 / 210606945).
This burst was also independently detected by INTEGRAL SPI-ACS,
GECAM (GCN 30138) and AGILE (GCN 30142).

The on-ground calculated location, using the GBM trigger
data, is RA = 87.48, DEC = -18.41 (J2000 degrees,
equivalent to 05 h 49 m, -18 d 24 '), with a statistical uncertainty
of 1.20 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 at the GBM trigger time is 82 degrees.

The GBM light curve consists of three main peaks
taking place about 40 s after the initial trigger,
plus one weaker peak showing 250 s after the initial trigger.
The full event has a duration (T90) of about 244 s (50-300 keV).

The time-averaged spectrum from T0+42 s to T0+52 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.04 +/- 0.01 and
the cutoff energy, parameterized as Epeak, is 397 +/- 13 keV.
A Band function fits the spectrum equally well
with Epeak= 394 +/- 14 keV, alpha = -1.04 +/- 0.01 and beta = -3.7 +/- 1.5 .

The event fluence (10-1000 keV) in this time interval is
(3.45 +/- 0.04)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+49 s in the 10-1000 keV band
is 35.6 +/- 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/"