MAXI/GSC detection of a possible bright X-ray flare from the BL Lac 2FGL J1931.1+0938

ATel #6174; K. Yamaoka (Nagoya U.), H. Negoro (Nihon U.), S. Nakahira (JAXA), M. Serino (RIKEN), M. Nakajima, K. Fukushima, T. Onodera, K. Suzuki, M. Fujita, T. Namba, F. Honda (Nihon U.), T. Mihara, M. Sugizaki, M. Morii, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN), S. Ueno, H. Tomida, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, D. Uchida (Osaka U.), Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, A. Kawagoe (Chuo U.), M. Yamauchi, Y. Morooka (Miyazaki U.), report on behalf of the MAXI team:
on 27 May 2014; 10:59 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Kazutaka Yamaoka (yamaoka@stelab.nagoya-u.ac.jp)

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The MAXI/GSC nova alert system triggered an X-ray transient source at 18:09:36 UT on 2014-05-26 (Trigger ID: 6803626528, tentative name MAXI J1932+091). Assuming that the source flux was constant over the transit, we obtain the source position at

(R.A., Dec) = (293.169 deg, 9.227 deg) = (19 32 40, +09 13 37) (J2000)

with a statistical 90% C.L. elliptical error region with long and short radii of 0.42 deg and 0.38 deg respectively. The roll angle of the long axis from the north direction is 7.0 deg counter-clockwise. There is an additional systematic uncertainty of 0.2 deg (90% containment radius). The position is marginally consistent with BL Lac 2FGL J1931.1+0938, but we cannot rule out a possibility of a new MAXI source.

The MAXI/GSC light curve suggests a 3-5 hours long flaring behavior in the 2-10 keV flux of 34+/-15, 47+/-17, 38+/-14 mCrab over the three transits at 10:25, 11:57, and 15:03 UT, respectively, and is currently declined to an undetectable level. If the source originates from 2FGL J1931.1+0938, the flux level during this flare is larger by a factor of 3-4 than that previously reported in ATel #5943.

Swift XRT follow-up observations are planned. Multi-wavelength observations are strongly encouraged.