A Large X-Ray Flare from a Single Weak-Lined T Tauri Star TWA-7 Detected with MAXI GSC
Isobe, Naoki; Yamaoka, Kazutaka; Nakagawa, Yujin E.; Yoshida, Atsumasa; Ueda, Yoshihiro; Ebisawa, Ken; Kawai, Nobuyuki; Shidatsu, Megumi; Tomida, Hiroshi; Tsuboi, Yohko; Tsunemi, Hiroshi; Kimura, Masashi; Mihara, Tatehiro; Nakajima, Motoki; Sugizaki, Mutsumi; Morii, Mikio; Hiroi, Kazuo; Eguchi, Satoshi; Matsuoka, Masaru; Ishikawa, Masaki; Kitayama, Hiroki; Kohama, Mitsuhiro; Matsumura, Takanori; Nakahira, Satoshi; Negoro, Hitoshi; Serino, Motoko; Sootome, Tetsuya; Sugimori, Kousuke; Suwa, Fumitoshi; Ueno, Shiro; Usui, Ryuichi; Yamamoto, Takayuki; Yamazaki, Kyohei; Kotani, Taro; Uzawa, Akiko; Daikyuji, Arata; Kawasaki, Kazuyoshi; Ozawa, Hiroshi
Japan
Abstract
We present a large X-ray flare from a nearby weak-lined T Tauri star TWA-7 detected with the Gas Slit Camera (GSC) on the Monitor of All-sky X-ray Image (MAXI). The GSC captured X-ray flaring from TWA-7 with a flux of 3 $\times$ 10 $^{-9}\ $ erg cm $^{-2}\ $ s $^{-1}$ in 2-20 keV band during the scan transit starting at 2010-09-07 18:24:30 (UT). The estimated X-ray luminosity at the scan in the energy band is 3 $\times$ 10 $^{32}\ $ erg s $^{-1}$ , indicating that the event is among the largest X-ray flares from T Tauri stars. Since MAXI GSC monitors a target only during a scan transit of about a minute per 92 min orbital cycle, the luminosity at the flare peak might have been higher than that detected. At the scan transit, we observed a high X-ray-to-bolometric luminosity ratio, log $\ L_{\rm X}/L_{\rm bol}$$=$$-$ 0.1 $^{+0.2}_{-0.3}$ ; i.e., the X-ray luminosity is comparable to the bolometric luminosity. Since TWA-7 has neither an accreting disk nor a binary companion, the observed event implies that none of those are essential to generate such big flares in T Tauri stars.