Suzaku observations of M 82 X-l: Detection of a curved hard X-Ray spectrum

Ryohei Miyawaki, Kazuo Makishima, Shin'ya Yamada, Poshak Gandhi, Tsunefumi Mizuno, Aya Kubota, Takeshi G. Tsuru, Hironori Matsumoto

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Abstract

A report is presented on Suzaku observations of the ultra-luminous X-ray source X-l in the starburst galaxy M 82, made three times in 2005 October for an exposure of ̃ 30 ks each. The XIS signals from a region of radius 3' around the nucleus defined a 2-10keV flux of 2.1 × 10 -11 erg s -1 cm -2 attributable to point sources. The 3.2-10keV 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 ̃20keV, at a 12-20keV flux of 4.4 × 10 -12erg s -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-l, 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) × 10 40 erg s -1. These results are interpreted as Comptonized emission from a black hole of 100-200 solar masses, radiating roughly at the Eddington luminosity.

Original languageEnglish
JournalPublications of the Astronomical Society of Japan
Volume61
Issue numberSUPPL. 1
Publication statusPublished - 2009

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Keywords

  • Balck hole physics
  • Galaxies: Individual (M 82)
  • X-rays: Stars

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Miyawaki, R., Makishima, K., Yamada, S., Gandhi, P., Mizuno, T., Kubota, A., ... Matsumoto, H. (2009). Suzaku observations of M 82 X-l: Detection of a curved hard X-Ray spectrum. Publications of the Astronomical Society of Japan, 61(SUPPL. 1).