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MAXI/GSC detection of a possible flare from TWA-7

ATEL # 2836; M. Morii (Tokyo Tech), Y. Tsuboi, A. Uzawa, K. Yamazaki, K. Matsumura (Chuo U.), K. Kawasaki, S. Ueno, H. Tomida, M. Kohama, M. Ishikawa (JAXA), T. Mihara, Y.E. Nakagawa, M. Sugizaki, M. Serino, T. Yamamoto, T. Sootome, M. Matsuoka (RIKEN), N. Kawai, K. Sugimori, R. Usui (Tokyo Tech), A. Yoshida, K. Yamaoka, S. Nakahira (AGU), H. Tsunemi, M. Kimura (Osaka U.), H. Negoro, M. Nakajima H. Ozawa, F. Suwa (Nihon U.), Y. Ueda, N. Isobe, S. Eguchi, K. Hiroi (Kyoto U.), A. Daikyuji (Miyazaki U.), report on behalf of the MAXI team
on 9 Sep 2010; 3:33 UT
Password Certification: Mikio Morii (morii@hp.phys.titech.ac.jp)

Subjects: X-ray, Transients, Variables, Stars

MAXI/GSC detected a short X-ray transient at the position of (R.A., Dec) = (+160.86 deg, -33.68 deg) = (10 43 27, -33 40 53)(J2000). We obtain a rectangular error box with the following corners: (R.A., Dec) = (+161.09 deg, -34.13 deg) = (10 44 22, -34 07 49)(J2000) (R.A., Dec) = (+160.23 deg, -33.68 deg) = (10 40 55, -33 40 54)(J2000) (R.A., Dec) = (+160.63 deg, -33.23 deg) = (10 42 32, -33 13 44)(J2000) (R.A., Dec) = (+161.49 deg, -33.68 deg) = (10 45 58, -33 40 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). Only one X-ray source is present in the ROSAT bright catalog in this error region with a separation of about 0.2 degree from the best-fit position. The source is a T Tauri star TWA-7, which is a member of TW Hya association, one of the nearest groups of young co-moving stars with the age of 1-10 Myr. The transient source was detected at the scan transit starting at UT 2010-09-07 18:24:30, and decayed with an e-folding time of 2+-1 hours. 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 2-10 keV band is about 100 mCrab. We note that the timescale of the transient is consistent with that in X-ray flares from a T Tauri star. This supports the identification of this transient with TWA-7. In this case, the peak luminosity during the flare is estimated to be about 1e33 erg/s (2-10 keV), assuming a distance of 55 pc. This X-ray luminosity is among the highest for a flare from T Tauri stars.

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