MAXI GSC and SSC detection of a soft X-ray transient near SMC: XRF 111111A / MAXI J0158-744

ATel #3756; M. Kimura (Osaka U.), H. Tomida (JAXA), T. Sootome, M. Serino, T. Mihara,(RIKEN), M. Morii (Tokyo Tech), M. Matsuoka, M. Sugizaki, S. Nakahira, T. Yamamoto (RIKEN), S. Ueno, M. Kohama, M. Ishikawa (JAXA), N. Kawai, K. Sugimori, R. Usui, T. Toizumi, Y. Aoki, S. Song (Tokyo Tech), A. Yoshida, K. Yamaoka (AGU), H. Tsunemi, H. Kitayama (Osaka U.), H. Negoro, M. Nakajima, F. Suwa (Nihon U.), Y. Ueda, K. Hiroi, M. Shidatsu (Kyoto U.), Y. Tsuboi, T. Matsumura, K. Yamazaki (Chuo U.) report on behalf of the MAXI team
on 11 Nov 2011; 08:20 UT
Credential Certification: Motoko Suzuki (motoko@crab.riken.jp)

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MAXI/GSC triggered a bright uncatalogued X-ray transient source at UT 2011-11-11T05:05:59. The source is extremely soft and most of the flux is emitted below 4keV. Assuming that the source flux was constant over the transit, we obtain the source position at
(R.A., Dec) = (+29.5 deg, -74.4 deg) = (01 58 03, -74 24 01)(J2000)
with a 90% C.L. statistical error of 0.42 deg. There is additional systematic uncertainty of 0.1 deg (90% containment radius). This position is in the outskirts of SMC.
The preliminary flux of the transient source was 400 mCrab (2-4 keV), and that corresponds to the luminosity of 6.4 × 10³⁸ erg s^-1 (distance of SMC 61.3kpc is assumed). The hardness ratio gives the blackbody temperature of about 0.4 keV. This source is also detected by SSC with the flux of 1 Crab (0.7-7 keV).
There was no significant detection at the transit location in the previous and the next orbit (92 min before and after the detection) with an upper limit of 20 mCrab. There is no known bright X-ray source at the detected position. There are at least four super soft sources known in SMC, and any of them does not match this transient.
Follow-up observations are encouraged.