[Show abstract][Hide abstract] ABSTRACT: 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 gtrsim8 times the gravitational radii from the central black hole, and a moderate reflection with a covering fraction of ˜3.4pi. This result implies that the solution of a highly spinning black hole in MCG -6-30-15, obtained by Miniutti et al. (2007, PASJ, 59, S315) using the same Suzaku data as ours, is a model-dependent result.
Publications- Astronomical Society of Japan 04/2011; 63:449-458. · 2.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The wide-band Suzaku spectra of the black hole (BH) binary GX 339–4, acquired in 2007 February during the Very High state, were reanalyzed. Effects of event pileup (significant within ~3' of the image center) and telemetry saturation of the X-ray Imaging Spectrometer (XIS) data were carefully considered. The source was detected up to ~300 keV, with an unabsorbed 0.5-200 keV luminosity of 3.8 × 1038 erg s–1 at 8 kpc. The spectrum can be approximated by a power law of photon index 2.7, with a mild soft excess and a hard X-ray hump. When using the XIS data outside 2' of the image center, the Fe K line appeared extremely broad, suggesting a high BH spin as already reported by Miller et al. based on the same Suzaku data and other CCD data. When the XIS data accumulation is further limited to >3' to avoid event pileup, the Fe K profile becomes narrower, and a marginally better solution appears which suggests that the inner disk radius is 5-14 times the gravitational radius (1σ), though a maximally spinning BH is still allowed by the data at the 90% confidence level. Consistently, the optically thick accretion disk is inferred to be truncated at a radius 5-32 times the gravitational radius. Thus, the Suzaku data allow an alternative explanation without invoking a rapidly spinning BH. This inference is further supported by the disk radius measured previously in the High/Soft state.
The Astrophysical Journal 12/2009; 707(2):L109. · 6.28 Impact Factor