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MAXI/GSC discovery of a new soft X-ray transient MAXI J1421-613

ATel #5750; Y. Morooka, Y. Ogawa (Miyazaki U.), H. Negoro (Nihon U.), M. Serino (RIKEN), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, M. Sugizaki, M. Morii, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN), N. Kawai, R. Usui, K. Ishikawa, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Nakano, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, M. Sasaki, D. Uchida (Osaka U.), M. Nakajima, H. Sakakibara, K. Fukushima, T. Onodera, K. Suzuki (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, M. Higa, A. Kawagoe (Chuo U.), M. Yamauchi, K. Yoshidome, H. Yamada (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team
on 9 Jan 2014; 23:53 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

Subjects: X-ray, Binary, Black Hole, Cataclysmic Variable, Neutron Star, Transient, Pulsar

Referred to by ATel #: 5751, 5759, 5765, 5780, 5802, 5894

The MAXI/GSC nova alert system triggered an uncatalogued X-ray transient source at 01:13:07 UT on 2014-01-09. Assuming that the source flux was constant over the transit, we obtain the source position at

(R.A., Dec) = (215.413 deg, -61.345 deg) = (14 21 39, -61 20 41) (J2000)

with a statistical 90% C.L. elliptical error region with long and short radii of 0.55 deg and 0.39 deg respectively. The roll angle of the long axis from the north direction is 118.0 deg counterclockwise. There is an additional systematic uncertainty of 0.2 deg (90% containment radius).

MAXI scanned the region only a few times a day in recent days, but count excesses in the 2-4 keV and 4-10 keV bands had been recognized since the beginning of Jan. 7th. The 4-10 keV X-ray flux averaged over 4 scan transits from 23:40 on Jan. 8th to 04:18 on Jan. 9th was 40+-11 mCrab.

We tentatively name the source MAXI J1421-613. Followup observations are strongly encouraged to reveal the nature of the source.