[vsnet-grb-info 28047] GRB 210607A/MAXI J1733-222: MAXI/GSC detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30150
SUBJECT: GRB 210607A/MAXI J1733-222: MAXI/GSC detection
DATE:    21/06/08 00:12:49 GMT
FROM:    Hitoshi Negoro at Nihon U  <negoro.hitoshi at nihon-u.ac.jp>

K. Kobayashi, H. Negoro (Nihon U.), M. Serino (AGU), M. Nakajima,  K. Asakura, K. Seino (Nihon U.), 
T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, K. Komachi, A. Yoshida (AGU),
Y. Tsuboi, W. Iwakiri, H. Kawai, Y. Okamoto, S. Kitakoga (Chuo U.), M. Shidatsu (Ehime U.),
N. Kawai, 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, Y. Nonaka, T. Sato, R. Hatsuda, R. Fukuoka (Miyazaki U.), T. Kawamuro (UDP/NAOJ),
K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC) 
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered on an X-ray transient source at 19:43:06 UT on 2021 June 7.
Assuming that the source flux was constant over the transit, we obtain the source position at
(R.A., Dec) = (263.367 deg, -22.279 deg) = (17 33 28, -22 16 44) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.56 deg and 0.53 deg, respectively. 
The roll angle of the long axis from the north direction is 69.0 deg counterclockwise. 
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 59 +- 21 mCrab
(4.0-10.0keV, 1 sigma error).

There was no significant excess flux in the previous transit at 18:10 UT and in the next transit 
at 21:16 UT with an upper limit of 20 mCrab for each.

Since the source showed a soft X-ray spectrum and no significant time variations during the scan 
and the source is located in the galactic bulge region at (l, b) ~ (4.2 deg, 5.8 deg),  it is possible 
that the source is a galactic transient source. We tentatively name the source MAXI J1733-222.