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Ryohei Miyawaki, Kazuo Makishima, Shin’ya Yamada, Poshak Gandhi, Tsunefumi Mizuno, Aya Kubota, Takeshi G. Tsuru, Hironori Matsumoto, Suzaku Observations of M 82 X-1 : Detection of a Curved Hard X-Ray Spectrum, Publications of the Astronomical Society of Japan, Volume 61, Issue sp1, 30 January 2009, Pages S263–s278, https://doi.org/10.1093/pasj/61.sp1.S263
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Abstract
A report is presented on Suzaku observations of the ultra-luminous X-ray source X-1 in the starburst galaxy M 82, made three times in 2005 October for an exposure of |$\sim$|30 ks each. The XIS signals from a region of radius 3|$^\prime$| around the nucleus defined a 2–10 keV flux of 2.1|$\times$|10|$^{-11}$|ergs|$^{-1}$|cm|$^{-2}$| attributable to point sources. The 3.2–10 keV spectrum was slightly more convex than a power-law with a photon index of 1.7. In all observations, the HXD also detected signals from M 82 up to |$\sim$|20 keV, at a 12-20 keV flux of 4.4|$\times$|10|$^{-12}$|ergs|$^{-1}$|cm|$^{-2}$|. The HXD spectrum was steeper than that of the XIS. The XIS and HXD spectra can be jointly reproduced by a cutoff power-law model, or similar curved models. Of the detected wide-band signals, 1|$/$|3 to 2|$/$|3 are attributable to X-1, while the remainder to other discrete sources in M 82. Regardless of the modeling of these contaminants, the spectrum attributable to X-1 is more curved than a power-law, with a bolometric luminosity of (1.5–3)|$\times$|10|$^{40}$|ergs|$^{-1}$|. These results are interpreted as Comptonized emission from a black hole of 100–200 solar masses, radiating roughly at the Eddington luminosity.
