MAXI /GSC detection of a new X-ray transient MAXI J0903-531

ATel #14555; K. Yamaoka (Nagoya U.), H. Negoro (Nihon U.), M. Serino (AGU), M. Nakajima, 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, R. Sasaki, H. Kawai, Y. Okamoto, S. Kitakoga (Chuo U.), M. Shidatsu (Ehime U.), N. Kawai, R. Adachi, 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, K. Kurogi, K. Miike (Miyazaki U.), T. Kawamuro (UDP/NAOJ), Y. Kawakubo (LSU), M. Sugizaki (NAOC) report on behalf of the MAXI team:
on 16 Apr 2021; 08:02 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 nova alert system triggered a bright uncatalogued X-ray transient source at 04:33 UT on 2021 April 14. Assuming that the source flux was constant over 41 transits from 17:18 on April 13th, we obtain the source position at

(R.A., Dec) = (135.898 deg, -53.132 deg) = (09 03 35, -53 07 55) (J2000)

with a statistical 90% C.L. elliptical error region with long and short radii of 0.53 deg and 0.4 deg, respectively. The roll angle of long axis from the north direction is 96.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scans was 16+/-5 mCrab (4.0-10.0keV, 1 sigma error). There are signs that the source flux is gradually increasing from a week ago. Since there is no bright catalogued X-ray source in the error region, we tentatively name the source MAXI J0903-531.

Follow-up observations are strongly encouraged to clarify the nature of this source.

Trigger Information about MAXI J0903-531