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Satoshi Nakahira, Kazutaka Yamaoka, Mutsumi Sugizaki, Yoshihiro Ueda, Hitoshi Negoro, Ken Ebisawa, Nobuyuki Kawai, Masaru Matsuoka, Hiroshi Tsunemi, Arata Daikyuji, Satoshi Eguchi, Kazuo Hiroi, Ryoji Ishikawa, Masaki Ishiwata, Naoki Isobe, Kazuyoshi Kawasaki, Masashi Kimura, Mitsuhiro Kohama, Tatehiro Mihara, Sho Miyoshi, Mikio Morii, Yujin E. Nakagawa, Motoki Nakajima, Hiroshi Ozawa, Tetsuya Sootome, Kousuke Sugimori, Motoko Suzuki, Hiroshi Tomida, Shiro Ueno, Takayuki Yamamoto, Atsumasa Yoshida, team the MAXI, MAXI GSC Observations of a Spectral State Transition in the Black Hole Candidate XTE J1752–223, Publications of the Astronomical Society of Japan, Volume 62, Issue 5, 25 October 2010, Pages L27–L32, https://doi.org/10.1093/pasj/62.5.L27
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Abstract
We present the first results on the black-hole candidate XTE J1752|$-$|223 from the Gas Slit Camera (GSC) aboard the Monitor of All-sky X-ray Image (MAXI) on the International Space Station. Including the onset of an outburst reported by the Proportional Counter Array aboard the Rossi X-ray Timing Explorer on 2009 October 23, MAXI / GSC has been monitoring this source approximately 10 times per day with high sensitivity in the 2–20 keV band. XTE J1752|$-$|223 was initially in a low / hard state during the first 3 months. An anti-correlated behavior between the 2–4 keV and 4–20 keV bands was observed around 2010 January 20, indicating that the source exhibited a spectral transition to the high / soft state. A transient radio jet may have been ejected when the source was in the intermediate state where the spectrum was roughly explained by a power-law with a photon index of 2.5–3.0. The unusually long period in the initial low / hard state implies a slow variation in the mass-accretion rate, and a dramatic soft X-ray increase may be explained by a sudden appearance of the accretion disk component with a relatively low innermost temperature (0.4–0.7 keV). Such a low temperature might suggest that the maximum accretion rate was just above the critical gas-evaporation rate required for the state transition.