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MAXI/GSC detects a possible outburst of Be/X-ray binary LS V +44 17

ATEL # 2527; M. Morii, N. Kawai, K. Sugimori (Tokyo Tech), S. Nakahira, A. Yoshida, K. Yamaoka (AGU), M. Sugizaki, T. Mihara, M.Kohama, Y.E. Nakagawa, T. Yamamoto, T. Saotome (RIKEN), H. Negoro, M. Nakajima, S. Miyoshi, H. Ozawa, R. Ishiwata (Nihon U.), H. Tomida, M. Matsuoka, K. Kawasaki, S. Ueno, M. Suzuki, M. Ishikawa (JAXA), H. Tsunemi, M. Kimura (Osaka U.), Y. Ueda, N. Isobe, S. Eguchi, K. Hiroi (Kyoto U.), A. Daikyuji (Miyazaki U.), A. Uzawa, T. Matsumura, K. Yamazaki (Chuo U.), on behalf of the MAXI team
on 31 Mar 2010; 20:36 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Nobuyuki Kawai (nkawai@phys.titech.ac.jp)

Subjects: X-ray, Binaries, Neutron Stars, Transients
Referred to by ATEL #: 2537

MAXI/GSC detected brightening of an X-ray source at a position consistent with LS V +44 17 (also known as BSD 24-491, RX J0440.9+4431), a Be/X-ray binary with 202 s pulse period (Reig and Roche 1999, MNRAS 306, 100). The best-fit position of the detected source is estimated using eight scans between 2010-03-31 02:10:23 and 09:48:47 (UT) as

(R.A.,Dec) = (70.35 +-0.24 deg, 44.39 +-0.09 deg) = (04 41 24, 44 23 24) (J2000)

The quoted errors are 1-sigma statistical, and there is additional systematic uncertainty of 0.2 deg (90% containment radius). The source has been detected since 2010-03-28 (UT) with a significance above 4 sigma. The brightening probably had started prior to the detection. The daily flux was 25+-19, 28+-10, 39+-6, 36+-7, and 65+-7 mCrab (1.5-10 keV) on each day from 2010-03-26 to 2010-03-30 (average from 0H to 0H UT, errors represent 1-sigma statistical uncertainties).

MAXI/GSC also detected a short bright X-ray transient at a scan transit from 2010-03-31T00:39:30 to 00:39:42. The transient emission lasted at least for 12 seconds within the 50 second long triangular transit response of MAXI/GSC. Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners:

(R.A., Dec) = (+70.40 deg, +45.41 deg) = (04 41 36, +45 24 47) (J2000)
(R.A., Dec) = (+69.42 deg, +44.79 deg) = (04 37 41, +44 47 21) (J2000)
(R.A., Dec) = (+71.60 deg, +42.99 deg) = (04 46 24, +42 59 30) (J2000)
(R.A., Dec) = (+72.56 deg, +43.60 deg) = (04 50 15, +43 36 16) (J2000)

This error box contains the position of the brightening source reported above tentatively identified as LS V +44 17. The peak flux of the short transient event was at least 240 +-75 mCrab in the 4-10 keV band.

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