195 research outputs found
Suzaku observation of the Phoenix galaxy
No full textContext. In recent years, several Seyfert 2 galaxies have beendiscovered that change state when observed in X-rays a few years apart,switching from Compton-thin to reflection-dominated or viceversa.Aims. We observed a member of this class of "Changing-look" sources,the Phoenix galaxy, with Suzaku, with the aim of better understandingthe nature of the variations.Methods. The Suzaku spectrum was analyzed, and the results comparedwith previous ASCA and XMM-Newton observations.Results. The source was caught in a Compton-thin state, as inXMM-Newton, but differently from ASCA. Comparing the Suzaku andXMM-Newton observations, a variation in the column density of theabsorber on a time scale of years is discovered. A similar change, buton much shorter time scales (i.e. ks) may also explain the count-ratevariations during the Suzaku observations. A soft excess is alsopresent, likely due to continuum and line emission from photoionizedcircumnuclear matter
Estimation of Central Black Hole Masses in LowLuminosity Active Galactic Nuclei
No full textAbstract We analyzed six low-luminosity active galactic nuclei (hereafter LLAGNs), which consist of two bright LINERs (low-ionization nuclear emission line region) with broad Hα, and of four bright low-luminosity Seyferts observed by the X-ray satellite ASCA. We examined the time variabilities of these targets, and found that most targets show no significant time variabilities, although these galaxies belong to LLAGNs. By applying Fourier analysis to their light curves in the 2-10 keV band, we obtained the lower limits of their time variability scales, which correspond to their central black hole masses greater than several times 10 6 M . Our result suggests that these LLAGNs are harbors of super-massive black holes, but the emitting powers are only < 1% of the Eddington luminosities of the central engines in the LLAGNs due to their small accretion rates. Since a black hole would grow by mass accretion, it is hard to create such a super-massive black hole under a small accretion rate. Therefore, the mass-accretion rates in the past must have been larger than those at present, and the galaxies have probably been as luminous as QSOs. This will be a hint to find out the cause of the lack of QSOs in the local universe
The thermal analysis of the Hard X-ray Telescope (HXT) and the investigation of the deformation of the mirror foil due to temperature change
No full textEvidence for X-ray flux and spectral modulation by absorption in NGC 6814. 1: The nature of the most rapid variability
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