[vsnet-grb-info 27461] Konus-Wind detection of GRB 210222A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29564
SUBJECT: Konus-Wind detection of GRB 210222A
DATE:    21/02/24 15:02:52 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred at mail.ioffe.ru>

D. Frederiks, S. Golenetskii, A.Lysenko, D. Svinkin,
A. Ridnaya, A. Tsvetkova,  M. Ulanov, and T. Cline, report:

The long GRB 210222A (MAXI/GSC detection: Nakajima et al., GCN 29543;
CALET Gamma-Ray Burst Monitor detection: Marrocchesi et al., GCN 29553)
was detected by Konus-Wind (KW) in the waiting mode starting from
~T0 = 57443.990 (15:57:23.990) UT (or ~2 minutes before the MAXI trigger).

A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band
reveals a ~30 sigma count rate increase over background in the interval
from ~T0 to ~T0+177 s.
The KW light curve of this burst is available
at http://www.ioffe.ru/LEA/GRBs/GRB210222A/

Modeling the KW 3-channel time-integrated spectrum
(measured from T0+0.115 s to T0+176.755 s)
by a power law with exponential cutoff (CPL) model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.33(-0.11,+0.15) and Ep = 317(-72,+108) keV.

A CPL fit to the spectrum near the peak count rate,
measured from T0+0.115 s to T0+14.835 s, gives
alpha -0.48(-0.14,+0.15), and Ep of 375(-40,+40) keV.

In the 10 keV -10 MeV band, the total burst fluence is (4.2 ± 0.6)x10^-5 erg/cm^2,
and the 2.944 s peak energy flux is (9.3 ± 0.8)x10^-7 erg/cm^2.

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.