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MAXI/GSC detection of a hard X-ray SMC transient MAXI J0057-720

ATel #5925; K. Suzuki, H. Negoro (Nihon U.), M. Sugizaki (RIKEN), Y. Ogawa (Miyazaki U.) S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, M. Serino, M. Morii, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN), N. Kawai, R. Usui, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Nakano, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, M. Sasaki (Osaka U.), M. Nakajima, H. Sakakibara, K. Fukushima, T. Onodera (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, M. Higa (Chuo U.), M. Yamauchi, K. Yoshidome, H. Yamada (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team
on 27 Feb 2014; 03:47 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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

Referred to by ATel #: 5930, 9348

MAXI/GSC has detected a hard X-ray transient toward the Small Magellanic Cloud. The 2-20 keV light curve shows that the source flux has almost linearly increased since November, 2013, and the recent flux is approximately 15 mCrab. The centroid source position on the GSC image, obtained from December 1, 2013 to February 22, 2014, is (R.A., Dec)=(14.40, -72.03) with a typical error of 0.2 deg.

The position is not consistent with any recently reported SMC pulsars, IGR J00569-7226 (ATel #5547, #5553), RX J0059.2-7138 (ATel #5756, #5766), Swift J010745.0-772740 (ATel #5778), nor IGR J01217-7257 (ATel #5806). We also note that RX J0059.2-7138 is also recognized on the same image, implying that this new transient is different from RX J0059.2-7138.

Previously known X-ray sources, for instance, AX J0058-720 (IAU Circular #6853) and RX J0056.4-7159 are positionally consistent with this new transient. Currently, a possibility of a previously unknown transient can not be exclude Hence we tentatively name the source MAXI J0057-720.

Followup observations are encouraged.