MAXI/GSC detection of a new soft X-ray transient MAXI J1810-222
ATel #12254; H. Negoro, M. Nakajima, A. Sakamaki, W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.), T. Mihara, S. Nakahira, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, T. Hashimoto, A. Yoshida (AGU), N. Kawai, M. Sugizaki, Y. Tachibana, K. Morita (Tokyo Tech), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai, T. Midooka (JAXA), Y. Ueda, A. Tanimoto, T. Morita, S. Yamada, S. Ogawa (Kyoto U.), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, K. Hidaka, S. Iwahori (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), M. Shidatsu (Ehime U.) report on behalf of the MAXI team:
on 1 Dec 2018; 14:45 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)
Subjects: X-ray, Black Hole, Neutron Star, Transient
Referred to by ATel #: 12264, 12283, 12487, 12496, 12521, 12910, 13540, 16025, 16129, 16136, 16154
We report the MAXI/GSC detection of a soft X-ray transient MAXI J1820-222. The source is seen on GSC images at least on 29th and 30th November 2018 only in the 2-4 keV band. The 2-4 keV X-ray flux is about 20-40 mCrab. No significant time variations are recognized.
Assuming that the source flux was constant over the transit, we obtain the source position at
(R.A., Dec) = (272.732 deg, -22.280 deg) = (18 10 55, -22 16 48) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.32 deg and 0.26 deg, respectively. The roll angle of the long axis from the north direction is 108.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
There is no bright catalogued X-ray source in the error region except for a few ROSAT X-ray sources, e.g., 1RXS J181011.5-222515 (13.3 arcmin apart), 1RXS J181026.5-223424 (18.9 arcmin). This transient has an unusually soft X-ray spectrum and a duration of more than 1 day, suggesting that the source is a LMXB hosting a neutron star or black hole in the soft state. Other possibilities, however, can not be excluded, and we tentatively name the source MAXI J1810-222.
Followup observations are strongly encouraged though the source is currently close to the sun (~25 deg).
Transient Information on MAXI J1810-222