arXiv subjects

Chiho Matsumoto

Publications and source records attributed to Chiho Matsumoto.

4 recordsLinked to original sources

arXiv2006

Suzaku observations of the hard X-ray variability of MCG-6-30-15: the effects of strong gravity around a Kerr black hole

Suzaku has, for the first time, enabled the hard X-ray variability of the Seyfert 1 galaxy MCG-6-30-15 to be measured. The variability in the 14-45 keV band, which is dominated by a strong reflection hump, is quenched relative to that at a few keV. This directly demonstrates that the whole reflection spectrum is much less variable than the power-law continuum. The broadband spectral variability can be decomposed into two components - a highly variable power-law and constant reflection - as previously inferred from other observations in the 2-10 keV band. The strong reflection and high iron abundance give rise to a strong broad iron line, which requires the inner disc radius to be at about 2 gravitational radii. Our results are consistent with the predictions of the light bending model which invokes the very strong gravitational effects expected very close to a rapidly spinning black hole.

astro-ph↗

arXiv2004

An XMM-Newton Observation of the Seyfert 2 Galaxy NGC 6300. I. The Nucleus

We present results from a half-day observation by XMM-Newton of the nucleus of the nearby Seyfert 2 galaxy NGC 6300. The X-ray spectrum of the nucleus consists of a heavily absorbed hard component dominating the 3--10 keV band and a soft component seen in the 0.2--2 keV band. In the hard band, the spectrum is well fitted by a power-law model with photon index of 1.83+/-0.08 attenuated by a Compton-thin absorber (N_H \simeq 2.2 x 10^{23} cm^{-2}). A narrow iron line is detected at 6.43_{-0.02}^{+0.01} keV with an equivalent width of ~150 eV; the line velocity width is marginally resolved to be σ~60eV. The soft emission can be modeled as a power-law and may be emission scattered by surrounding plasma. Rapid and high-amplitude variability is observed in the hard X-ray band, whereas both the iron line and the soft emission show no significant variability. It is suggested that the nucleus has experienced an overall long-term trend of decreasing hard X-ray intensity on a timescale of years. We discuss the origins of the spectral components.

astro-ph↗

arXiv2003

A Chandra HETGS observation of the Narrow-line Seyfert 1 galaxy Ark 564

We present results from a 50 ks observation of the narrow-line Seyfert 1 galaxy Ark 564 with the Chandra HETGS. The spectra above 2 keV are modeled by a power-law with a photon-index of 2.56+/-0.06. We confirm the presence of the soft excess below about 1.5 keV. If we fit the excess with blackbody model, the best-fit temperature is 0.124 keV. Ark 564 has been reported to show a peculiar emission line-like feature at 1 keV in various observations using lower resolution detectors, and the Chandra grating spectroscopy rules out an origin of blends of several narrow emission lines. We detect an edge-like feature at 0.712 keV in the source rest frame. The preferred interpretation of this feature is combination of the O VII K-edge and a number of L-absorption lines from slightly ionized iron, which suggests a warm absorber with ionization parameter xi~1 and N_H ~ 10^21 cm^-2. These properties are roughly consistent with those of the UV absorber. We also detect narrow absorption lines of O VII, O VIII, Ne IX, Ne X, and Mg XI at the systemic velocity. From these lines, a second warm absorber having log xi ~ 2 and N_H ~ 10^21 cm^-2 is required.

astro-ph↗

arXiv2002

A Chandra Observation of the Luminous NLS1 1H 0707-495

We present preliminary results from a long Chandra HETG observation of the luminous Narrow-line Seyfert 1 galaxy 1H 0707-495. We find a complex X-ray spectrum comprised of a two-component continuum with superimposed emission and absorption lines. The short time scale X-ray variability is different than observed in other AGN: the soft X-rays vary markedly less than the hard X-rays. This behavior is similar to that of high-state Galactic black holes. We also investigated the long time scale variability, and discovered an apparent bimodal flux distribution. We postulate that the bimodality is the signature of the radiation pressure instability, and note that this instability may be expected in luminous NLS1s.

astro-ph↗