GRB 210222A

M. Nakajima (Nihon U.), M. Serino (AGU), Y. Kawakubo (LSU),
H. Negoro, M. Aoki, K. Kobayashi, R. Takagi, K. Asakura, K. Seino (Nihon U.),
T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN),
T. Sakamoto, S. Sugita, H. Nishida, K. Komachi, A. Yoshida (AGU),
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, Y. Okamoto, S. Kitakoga (Chuo U.),
M. Shidatsu (Ehime U.),
N. Kawai, R. Adachi, M. Niwano, R. Hosokawa (Tokyo Tech),
S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka (JAXA),
Y. Ueda, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake, Y. Goto, R. Uematsu (Kyoto U.),
H. Tsunemi (Osaka U.),
M. Yamauchi, K. Kurogi, K. Miike (Miyazaki U.),
T. Kawamuro (UDP/NAOJ),
K. Yamaoka (Nagoya U.),
M. Sugizaki (NAOC)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray 
transient source at 2021-02-22T15:59:19 UT.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (353.129 deg, -29.464 deg) = (23 32 30, -29 27 50) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.11 deg and 0.04 deg, respectively.
The roll angle of long axis from the north direction is 90.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 389 +- 38 mCrab
(4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at 14:26 UT
with an upper limit of 20 mCrab.

P. S. Marrocchesi (U of Siena),
A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU),
Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN),
Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC),
M. L. Cherry (LSU), S. Ricciarini (U of Florence),
and the CALET collaboration:

At 15:57:23.469 UTC on 22 February 2021, the CALET Gamma-ray Burst
Monitor (CGBM) triggered on long GRB 210222A
(http://cgbm.calet.jp/cgbm_trigger/flight/1298044600/),
which was also detected by the MAXI/GSC at T0(CGBM)+116 s
(Nakajima et al., GCN Circ. 29543
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 ).
The burst signal was seen by all CGBM detectors.

The burst light curve shows a FRED-like pulse which starts at T+0.6 sec,
peaks at T+7.5 sec, and ends at T+87.3 sec. The T90 and T50 durations
measured by the SGM data are 71.4 +- 11.5 sec and 33.5 +- 4.4 sec
(40-1000 keV), respectively.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1298044600/

The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at the Waseda University.

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
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 ;
CALET Gamma-Ray Burst Monitor detection: Marrocchesi et al., GCN 29553
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 )
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.