[vsnet-grb-info 23357] GRB 190823A: MAXI/GSC detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25456
SUBJECT: GRB 190823A: MAXI/GSC detection
DATE:    19/08/23 14:59:48 GMT
FROM:    Motoko Serino at RIKEN/MAXI  <motoko at crab.riken.jp>

W. Iwakiri(Chuo U.), M. Serino(AGU), 
H. Negoro, M. Nakajima, W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.), 
T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN), 
T. Sakamoto,  S. Sugita, H. Nishida, A. Yoshida (AGU), 
Y. Tsuboi,  R. Sasaki, H. Kawai, T. Sato (Chuo U.), 
M. Shidatsu (Ehime U.),
N. Kawai, M. Sugizaki, M. Oeda, K. Shiraishi (Tokyo Tech), 
S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, N.Isobe, R. Shimomukai, M. Tominaga (JAXA), 
Y. Ueda, A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake (Kyoto U.), 
H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), 
M. Yamauchi, S. Iwahori, Y. Kurihara, K. Kurogi, K. Miike (Miyazaki U.), 
T. Kawamuro (NAOJ), 
K. Yamaoka (Nagoya U.),
Y. Kawakubo (LSU)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source 
at 13:30:22 UT on 2019 August 23.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (279.278 deg, -43.439 deg) = (18 37 06, -43 26 19) (J2000)
with a 90% C.L. statistical error of 0.17 deg and an additional systematic uncertainty 
of 0.1 deg (90% containment radius).

Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (280.193, -43.737) deg = (18 40 46, -43 44 13) (J2000)
(R.A., Dec) = (280.285, -43.434) deg = (18 41 08, -43 26 02) (J2000)
(R.A., Dec) = (278.903, -43.205) deg = (18 35 36, -43 12 17) (J2000)
(R.A., Dec) = (278.804, -43.508) deg = (18 35 12, -43 30 28) (J2000) 

The X-ray flux averaged over the scan was 322 +- 29 mCrab
(4.0-10.0keV, 1 sigma error).

There was no significant excess flux in the previous transit at UT 11:57
with an upper limit of 20 mCrab.