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X-ray Transient detected by MAXI/GSC

ATEL # 2700; R. Usui (Tokyo Tech.), T. Yamamoto (RIKEN), H. Negoro (Nihon U.), K. Kawasaki, S. Ueno, H. Tomida, M. Kohama, M. Ishikawa (JAXA), T. Mihara, Y.E. Nakagawa, M. Sugizaki, M. Suzuki, T. Sootome, M. Matsuoka (RIKEN), N. Kawai, M. Morii, K. Sugimori (Tokyo Tech), A. Yoshida, K. Yamaoka, S. Nakahira (AGU),@ H. Tsunemi, M. Kimura (Osaka U.), M. Nakajima, H. Ozawa, F. Suwa (Nihon U.), Y. Ueda, N. Isobe, S. Eguchi, K. Hiroi (Kyoto U.), A. Daikyuji (Miyazaki U.), A. Uzawa, T. Matsumura, K. Yamazaki (Chuo U.) report on behalf of the MAXI team
on 28 Jun 2010; 17:21 UT
Password Certification: Hitoshi Negoro (

Subjects: X-ray, Transients, Variables, Stars
Referred to by ATEL #: 2701

MAXI/GSC detected a transient X-ray source at the position of (R.A.,Dec) = (272.0 deg, 19.6 deg) = (18 08 00, +19 36 00) (J2000). The positional uncertainty is about 0.2 deg (90% containment radius) including statistical and systematic errors. The source was detected at the 3 scan transits from UT 2010-06-27T08:27 to 2010-06-27T11:31 at the 4-sigma level. We did not detect significant intensity variation among these three scans. The average 4-10 keV flux for the three scans is approximately 25+-6 mCrab. The source was not detected at this location in the previous and following orbits at the more than 3-sigma level, implying that the transient X-ray emission lasted at least 3-6 hours. There are at least two previously catalogued X-ray sources in the error circle, 1RXS J180724.2+194217 and XMMSL1 J180839.4+194432. 1RXS J180724.2+194217 is identified as a variable star HD 347929 with a probable classification of RS CVn type (SIMBAD). We note that the timescale of the transient is consistent with that of X-ray flares from a RS CVn type star, supporting the identification of this transient with 1RXS J180724.2+194217/HD 347929. In this case, the peak luminosity during the flare can be estimated to be about 6.5e31 erg/s (2-10 keV) if the distance to the source is assumed to be 30 pc.

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