著者
Mizuno Tsunefumi Miyawaki Ryohei Ebisawa Ken KUBOTA Aya MIYAMOTO Masao WINTER Lisa M. UEDA Yoshihiro ISOBE Naoki DEWANGAN Gulab C. DONE Chris GRIFFITHS Richard E. HABA Yoshito KOKUBUN Motohide KOTOKU Jun'ichi MAKISHIMA Kazuo MATSUSHITA Kyoko MUSHOTZKY Richard F. NAMIKI Masaaki PETRE Robert TAKAHASHI Hiromitsu TAMAGAWA Toru TERASHIMA Yuichi
出版者
日本天文学会
雑誌
PASJ : publications of the Astronomical Society of Japan (ISSN:00046264)
巻号頁・発行日
vol.59, no.1, pp.S257-S267, 2007-01-31
参考文献数
56
被引用文献数
2

Two ultraluminous X-ray sources (ULXs) in the nearby Sb galaxy NGC 1313, named X-1 and X-2, were observed with Suzaku on 2005 September 15. During the observation for a net exposure of 28 ks (but over a gross time span of 90 ks), both objects varied in intensity by about 50%. The 0.4–10 keV X-ray luminosities of X-1 and X-2 were measured as 2.5×1040 ergs-1 and 5.8×1039 ergs-1, respectively, with the former exhibiting the highest ever reported for this ULX. The spectrum of X-1 can be explained by the sum of a strong and variable powerlaw component with a high-energy cutoff, and a stable multicolor blackbody with an innermost disk temperature of ∼ 0.2keV. These results suggest that X-1 was in a "very high" state, where disk emission is strongly Comptonized. The absorber within NGC 1313 toward X-1 is suggested to have a subsolar oxygen abundance. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor blackbody model with an innermost disk temperature of 1.2–1.3 keV, and becomes flatter as the source becomes brighter. Hence, X-2 is interpreted to be in a slim-disk state. These results suggest that the two ULXs have black hole masses of some dozens to a few hundred of solar masses.