MAXI/GSC detection of a possible flare from a dMe star YZ CMi

ATel #3211; M. Serino (RIKEN), A. Uzawa, Y. Tsuboi, K. Yamazaki, T. Matsumura (Chuo U.), S. Ueno, H. Tomida, M. Kohama, M. Ishikawa (JAXA), T. Mihara, Y. E. Nakagawa, M. Sugizaki, T. Yamamoto, T. Sootome, M. Matsuoka (RIKEN), N. Kawai, M. Morii, K. Sugimori, R. Usui, T. Toizumi (Tokyo Tech), A. Yoshida, K. Yamaoka, T. Kotani ,S. Nakahira (AGU), H. Tsunemi, M. Kimura, H. Kitayama (Osaka U.), H. Negoro, M. Nakajima, H. Ozawa, F. Suwa (Nihon U.), Y. Ueda, N. Isobe, S. Eguchi, K. Hiroi, M. Shidatsu (Kyoto U.), A. Daikyuji (Miyazaki U.), report on behalf of the MAXI team
on 9 Mar 2011; 05:32 UT
Credential Certification: Yohko Tsuboi (tsuboi@phys.chuo-u.ac.jp)

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MAXI/GSC detected a short X-ray transient at the position of (R.A., Dec) = (+116.06 deg, +3.62 deg) = (07 44 14 ,+03 37 09) (J2000). We obtain a rectangular error box with the following corners:

(R.A., Dec) = (+115.52 deg, +3.95 deg) = (07 42 5, +03 56 57) (J2000) (R.A., Dec) = (+115.78 deg, +4.23 deg) = (07 43 8, +04 13 40) (J2000) (R.A., Dec) = (+116.60 deg, +3.29 deg) = (07 46 24, +03 17 14) (J2000) (R.A., Dec) = (+116.34 deg, +3.01 deg) = (07 45 21, +03 00 36) (J2000)

This error box indicates statistical error with 90 percent confidence level, and there is additional systematic uncertainty of 0.2 deg (90% containment radius). Within the error region, there is a nearby dM4.5e star YZ CMi at a distance of 5.97 pc (Reid & Hawley 2005) with a separation of about 0.1 degree from the best-fit position. The source is an active flare star which has been detected with optical (e.g. Kowalski et al. 2010), UV (e.g. Hawley et al. 2007), and X-ray (e.g. Raassen et al. 2007) bands.

The transient source was detected at the scan transit starting at 2011-03-08 21:31 (UT) (= MJD 55628.897), and decayed to the background level at the next transit (92 min after the detection) with a typical upper limit of 20 mCrab. The source was not detected at this location in the previous orbit (92 min before the detection) at more than a 3-sigma level. The flux at the flare peak in the 4-10 keV band is 200+-40 mCrab. We note that the timescale of the transient is consistent with those in X-ray flares from flare stars. This supports the identification of this transient with YZ CMi. In this case, the peak luminosity during the flare is estimated to be about 1e31 erg/s (4-10 keV), assuming a distance of 6 pc. This X-ray luminosity is among the highest for a flare from dMe stars.

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