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Kazushi Iwasawa

Publications and source records attributed to Kazushi Iwasawa.

75 records · Page 5Linked to original sources

The XMM-Newton view of Mrk3 and IXO30

We present the analysis of the XMM-Newton EPIC pn spectrum of the Seyfert 2 galaxy, Mrk3. We confirm that the source is dominated by a pure Compton reflection component and an iron K$α$ line, both produced as reflection from a Compton-thick torus, likely responsible also for the large column density which is pierced by the primary powerlaw only at high energies. A low inclination angle and an iron underabundance, suggested by the amount of reflection and the depth of the iron edge, are consistent with the iron K$α$ line EW with respect to the Compton reflection component. Moreover, the iron line width, if interpreted in terms of Doppler broadening due to the Keplerian rotation of the torus, puts an estimate to the inner radius of the latter, $r=0.6^{+1.3}_{-0.3} \sin^2{i}$ pc. Finally, two different photoionised reflectors are needed to take into account a large number of soft X-ray emission lines from N, O, Ne, Mg, Si, Fe L and the FeXXV emission line. RGS spectra show that the soft X-ray spectrum is dominated by emission lines, while the underlying continuum is best fitted by an unabsorbed powerlaw with the same photon index of the primary continuum, produced as reflection by a photoionised material with a column density of a few $10^{22}$ cm$^{-2}$. We also present the first X-ray spectrum of ROSAT source IXO30, which shows a huge iron line and is well represented either by an absorbed powerlaw or bremsstrahlung emission. Its spectral properties point to a likely identification in terms of a weak Galactic Cataclysmic Variable, but the lack of any optical counterpart precludes excluding other possibilities, like an ULX at the distance of Mrk3.

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The circumnuclear X-ray reflectors in NGC 1068 and the Circinus Galaxy

The ASCA and BeppoSAX spectra of the Circinus Galaxy and NGC 1068 are analysed and compared with photoionization models based on cloudy. In the case of Circinus, a single, mildly ionized reflector can account for the line spectrum, while in NGC 1068 at least three different reflectors (with different ionization states) are needed. We suggest that the reflector in Circinus, and the low ionized one in NGC1068 are the inner and visible part of the material responsible for the X-ray absorption. With this assumption, we estimate for the inner radius of the absorber a value of 0.2 pc for Circinus and of a few parsecs for NGC 1068.

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NGC 7582: The Prototype Narrow-Line X-ray Galaxy

NGC 7582 is a candidate prototype of the Narrow Line X-ray Galaxies (NLXGs) found in deep X-ray surveys. An ASCA observation shows the hard (> 3 keV) X-ray continuum of NGC 7582 drops 40% in ~6 ks, implying an AGN, while the soft band (< 3 keV) does not drop in concert with the hard continuum, requiring a separate component. The X-ray spectrum of NGC 7582 also shows a clear 0.5-2 keV soft (kT = 0.8 (+0.9,-0.3) keV or Gamma = 2.4 +/- 0.6; L(X) = 6 x 10**40 ergs s**-1) low--energy component, in addition to a heavily absorbed [N(H) = (6 +/- 2)\times 10**22 cm**-2 ] and variable 2-10 keV power law [Gamma = 0.7 (+0.3,-0.4); L(X) = (1.7-2.3) x 10**42 ergs s**-1]. This is one of the flattest 2-10 keV slopes in any AGN observed with ASCA. (The ROSAT HRI image of NGC 7582 further suggests extent to the SE.) These observations make it clear that the hard X-ray emission of NGC 7582, the most "narrow-line" of the NLXGs, is associated with an AGN. The strong suggestion is that all NLXGs are obscured AGNs, as hypothesized to explain the X-ray background spectral paradox. The separate soft X-ray component makes NGC 7582 (and by extension other NLXGs) detectable as a ROSAT source.

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