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MAXI/GSC detection of a possible X-ray flaring activity from XTE J1739-302/IGR 17391-3021 or a new X-ray transient MAXI J1739-301

ATel #6900; H. Negoro (Nihon U.), S. Nakahira, S. Ueno, H. Tomida, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, M. Sugizaki, M. Serino, M. Morii, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN), N. Kawai, Y. Tachibana, T. Yoshii (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, D. Uchida (Osaka U.), M. Nakajima, K. Fukushima, T. Onodera, K. Suzuki, M. Fujita, F. Honda, T. Namba (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, A. Kawagoe (Chuo U.), M. Yamauchi, Y. Morooka, D. Itoh (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team:
on 11 Jan 2015; 17:04 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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

At 04:08 UT on 11 January 2015, MAXI/GSC detected a short-term X-ray enhancement from the position at
(R.A., Dec) = (264.825 deg, -30.106 deg) = (17 39 17, -30 06 21) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.23 deg and 0.21 deg, respectively, if we assumed a constant source flux over the transit. The roll angle of long axis from the north direction is 39.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius).

The error region marginally includes the position of the SFXT XTE J1739-302/IGR 17391-3021 (e.g., Romano et al. 2009, MNRAS, 399, p2021, Bodaghee et al. 2011, ApJ, 727, p59), which exhibited the latest outburst in 11 February 2011 (Romano et al. ATel. #3182). Since the position is near the Galactic center region, (l, b) = (358.28, 0.56), a possibility of a new transient can not be excluded, and we tentatively name the source MAXI J1739-301 (in the MAXI New-transient ML, No.139, we referred as J1740-304).

The X-ray flux averaged over the scan transit at 04:08 was 200 +- 32 mCrab (4-10keV, 1 sigma error). There was no significant excess flux in previous transits before UT 02:35 with an upper limit of 20 mCrab. There is a slight, but not significant soft excess after the detection.

The GSC spectrum obtained over the scan transit at 04:08 can be described by an absorbed power-law model with the photon index of 1.4 +/- 0.5 and the absorption column of (1.9+/-3.9)e22, or a blackbody model with the temperature of kT = 2.3 +/- 0.3 keV (the absorption is not necessary).

The observed properties, the short-term enhancement, the flux, and the hard spectrum, are all similar to those obtained by the Swift observations of XTE J1739-302 in 2011 (Romano et al. 2012, MSAIS 21, p210). Thus, XTE J1739-302 is a probable candidate of this source. The followup observations are encouraged.