Suzaku discovery of a hard component varying independently of the power-law emission in MCG-6-30-15

Hirofumi Noda, Kazuo Makishima, Yuuichi Uehara, Shin'Ya Yamada, Kazuhiro Nakazawa

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18 Citations (Scopus)


Focusing on hard X-ray variability, we reanalyzed Suzaku data of the Type I Seyfert galaxy MCG-6-30-15 obtained in 2006. Intensity-sorted spectroscopy and a principal-component analysis consistently revealed a very hard component that varies independently of the dominant power-law emission. Although the exact nature of this hard component has not yet been identified, it can be modeled as a power-law with a photon index of ∼2 affected by a partial covering absorption, or as a thermal Comptonization emission with a relatively large optical depth. When this component is included in the fitting model, the time-averaged 2.5-55 keV spectrum of MCG-6-30-15 can be reproduced successfully by invoking a mildly broadened iron line with its emission region located at ≥8 times the gravitational radii from the central black hole, and a moderate reflection with a covering fraction of ∼3.4π. This result implies that the solution of a highly spinning black hole in MCG-6-30-15, obtained byMiniutti et al. (2007, PASJ, 59, S315) using the same Suzaku data as ours, is a model-dependent result.

Original languageEnglish
Pages (from-to)449-458
Number of pages10
JournalPublications of the Astronomical Society of Japan
Issue number2
Publication statusPublished - 2011 Apr 25
Externally publishedYes


  • Active-galaxies
  • Galaxies
  • Individual (MCG-6-30-15)-galaxies
  • Seyfert-X-rays

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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