MAXI/GSC discovered a new X-ray transient MAXI J1816-195

ATel #15418; H. Negoro (Nihon. U.), M. Serino (AGU), W. Iwakiri (Chuo U.), M. Nakajima, K. Kobayashi, M. Tanaka, Y. Soejima (Nihon U.), T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, J. Kohara (Chuo U.), M. Shidatsu, M. Iwasaki (Ehime U.), N. Kawai, M. Niwano, R. Hosokawa, Y. Imai, N. Ito, Y. Takamatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka, T. Kurihara (JAXA), Y. Ueda, S. Ogawa, K. Setoguchi, T. Yoshitake, K. Inaba (Kyoto U.), H. Tsunemi (Osaka U.), M. Yamauchi, T. Sato, R. Hatsuda, R. Fukuoka, Y. hagiwara, Y. Umeki (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), and M. Sugizaki (NAOC)
on 7 Jun 2022; 15:03 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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The MAXI/GSC detects an uncatalogued X-ray transient source on 2022 June 07. Assuming that the source flux was constant over three transits from 09:51 to 12:57 on June 07, we obtain the source position at
(R.A., Dec) = (274.220 deg, -19.511 deg) = (18 16 52, -19 30 39) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.25 deg and 0.19 deg, respectively. The roll angle of the long axis from the north direction is 169.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scans was 101 +- 15 mCrab (4.0-10.0keV, 1 sigma error).

The X-ray fluxes in six scan observations from 05:12 to 12:57 were almost constant at about 100 mCrab. Unfortunately, MAXI/GSC did not operate normally from 02:18 on June 3 to 04:43 on June 7 because of onboard data processor trouble. Thus, the outburst probably started before 05:12 on June 07.

Since there is no known bright X-ray source in the error region and the nature of the source is still unknown, we tentatively name the source MAXI J1816-195. Followup observations are encouraged to identify this new transient.

Trigger information about MAXI J1816-195