MAXI/GSC detection of renewed activity of the short X-ray transient MAXI J1957+032

ATel #9565; H. Negoro (Nihon U.), R. Sasaki (Chuo U.), H. Tomida, S. Ueno, S. Nakahira, M. Ishikawa, Y. Sugawara (JAXA), T. Mihara, M. Sugizaki, M. Serino, W. Iwakiri, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, N. Isobe, S. Sugita, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara, S. Harita, Y. Muraki (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), H. Tsunemi, R. Shomura (Osaka U.), M. Nakajima, K. Tanaka, T. Masumitsu, T. Kawase (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori, A. Tanimoto (Kyoto U.), Y. Tsuboi, Y. Nakamura (Chuo U.), M. Yamauchi, K. Furuya (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. E. Nakagawa (JAMSTEC)
on 29 Sep 2016; 16:18 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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At 08:19 UT on 2016 September 29, the MAXI/GSC nova-alert system triggered on a faint X-ray source positionally consistent with MAXI J1957+032. MAXI/GSC data show that the 4-10 keV X-ray flux started to increase around the beginning of Sep. 29, and the flux averaged over 4 scan transits from 00:36 to 05:14 on the same day was 0.039 +/- 0.012 photons/s/cm2 (~ 33 mCrab).

MAXI J1957+032 was discovered on 2015 May 11 (ATel #7504), and also known as IGRJ19566+0326 (ATel #7506). The source also exhibited renewed activity on 2015 Oct. 6 (ATel #8143, #8146), and 2016 Jan. 7 (ATel #8529). In the previous activities, the source showed relatively rapid decay in X-ray flux on timescales of hours or days (e.g., ATel #7520). This is the 4th detection of this source, but the nature of the source is still unknown, although optical followup observations were performed (ATel #7524, #8149, #8197). Thus, we strongly encourage multiwavelength follow-up observations of this source.

Swift/XRT followup observations are planned. We thank Neil Gehrels and the Swift team for scheduling ToO observations.

MAXI public data for MAXI J1957+032