MAXI/GSC detection of an X-ray short transient event GRB 210709B/MAXI J1849-237
ATel #14772; M. Nakajima, H. Negoro (Nihon U.), M. Serino (AGU), K. Kobayashi, 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)
on 10 Jul 2021; 10:54 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)
Subjects: X-ray, Gamma Ray, Nova, Transient
The MAXI/GSC nova alert system triggered on a bright uncatalogued X-ray transient source at 22:12 UT on 2021 July 9. Assuming that the source flux was constant over the transit, we obtain the source position at
(R.A., Dec) = (282.394 deg, -23.790 deg) = (18 49 34, -23 47 23) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.36 deg and 0.25 deg, respectively. The roll angle of the long axis from the north direction is 57.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 113+-25 mCrab (4.0-10.0keV, 1 sigma error).
The source was not significant before 20:39 UT, and in the next transit at 1:18 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 vicinity of the galactic center region at (l, b) ~ (11.4 deg, -10.3 deg), it is possible that the source is a galactic transient source. We tentatively name the source MAXI J1849-237.
