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K. Iwasawa A. C. Fabian K. Nandra 《Monthly notices of the Royal Astronomical Society》1999,307(3):611-618
We report on simultaneous ASCA and ROSAT observations of the Seyfert galaxy NGC 5548 made during the ASCA Performance Verification phase. Spectral features due to a warm absorber and reflection are clearly seen in the X-ray spectra. We find that the continuum spectral shape differs between the ASCA and ROSAT data sets. The photon-index obtained from the ROSAT PSPC exceeds that from the ASCA SIS ΔΓ≈0.4. The discrepancy is clear even in the 0.5–2 keV energy band over which both detectors are sensitive. The spectra cannot be made consistent by choosing a more complex model. The problem likely lies in the response curve (estimated effective area) of one, or both, detectors. There may be important consequences for a wide range of published results. 相似文献
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A. C. Fabian A. Celotti K. Iwasawa R. G. McMahon C. L. Carilli W. N. Brandt G. Ghisellini I. M. Hook 《Monthly notices of the Royal Astronomical Society》2001,323(2):373-379
We report optical, radio and X-ray observations of a new distant blazar, PMN J0525−3343, at a redshift of 4.4. The X-ray spectrum measured from ASCA and BeppoSAX flattens below a few keV, in a manner similar to the spectra of two other z >4 blazars, GB 1428+4217 ( z =4.72) reported by Boller et al. and RX J1028.6−0844 ( z =4.28) reported by Yuan et al. The spectrum is well fitted by a power-law continuum which either is absorbed or breaks at a few keV. An intrinsic column density corresponding to 2×1023 H‐atoms cm−2 at solar abundance is required by the absorption model. This is however a million times greater than the neutral hydrogen, or dust, column density implied by the optical spectrum, which covers the rest-frame ultraviolet emission of the blazar nucleus. We discuss the problems raised and suggest that, unless there is intrinsic flattening in the spectral distribution of the particles/seed photons producing X-rays via inverse Compton scattering, the most plausible solution is a warm absorber close to the active nucleus. 相似文献
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D. C. Shih K. Iwasawa A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2002,333(3):687-696
We report on an analysis in the 3–10 keV X-ray band of the long 1999 ASCA observation of MCG–6-30-15. The time-averaged broad iron K line is well described by disc emission near a Schwarzschild black hole, confirming the results of earlier analyses on the ASCA 1994 and 1997 data. The time-resolved iron-line profile is remarkably stable over a factor of 3 change in source flux, and the line and continuum fluxes are uncorrelated. Detailed fits to the variable iron-line profile suggest that the active region (parametrized by the best-fitting inner and outer radii of the accretion disc) responsible for iron-line emission actually narrows with increasing flux to a region around 4–5 r g . In contrast with the iron line, the power-law continuum exhibits significant variability during the 1999 observation. Time-resolved spectral analysis reveals a new feature in the well-known photon index (Γ) versus flux correlation: Γ appears to approach a limiting value of Γ∼2.1 at high flux. Two models are proposed to explain both the new feature in the Γ versus flux correlation and the uncorrelated iron-line flux: a phenomenological two power-law model, and the recently proposed 'thundercloud' model of Merloni & Fabian . Both models are capable of reproducing the data well, but because they are poorly constrained by the observed Γ versus flux relation, they cannot at present be tested meaningfully by the data. The various implications and the physical interpretation of these models are discussed. 相似文献
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A. C.Fabian C. S.Crawford K.Iwasawa 《Monthly notices of the Royal Astronomical Society》2002,331(4):L57-L59
We report a Chandra observation of the z =3.395 radio galaxy B2 0902+343. The unresolved X-ray source is centred on the active nucleus. The spectrum is well fitted by a flat power law of photon index of Γ∼1.1 with intrinsic absorption of 8×1022 cm-2 , and an intrinsic 2–10 keV luminosity of 3.3×1045 erg s-1 . More complex models that allow for a steeper spectral index cause the column density and intrinsic luminosity to increase. The data limit any thermal luminosity of the hot magnetized medium, assumed responsible for high Faraday rotation measures seen in the radio source, to less than ∼1045 erg s−1 . 相似文献
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K. Iwasawa G. Matt A.C. Fabian S. Bianchi W.N. Brandt M. Guainazzi T. Murayama Y. Taniguchi 《Monthly notices of the Royal Astronomical Society》2001,326(1):119-125
We report on the BeppoSAX detection of a hard X-ray excess in the X-ray spectrum of the classical high-ionization Seyfert 2 galaxy Tol 0109–383. The X-ray emission of this source observed below 7 keV is dominated by reflection from both cold and ionized gas, as seen in the ASCA data. The excess hard X-ray emission is presumably caused by the central source absorbed by an optically thick obscuring torus with N H ∼2×1024 cm−2 . The strong cold X-ray reflection, if it is produced at the inner surface of the torus, is consistent with the picture where much of the inner nucleus of Tol 0109–383 is exposed to direct view, as indicated by optical and infrared properties. However, the X-ray absorption must occur at small radii in order to hide the central X-ray source but leave the optical high-ionization emission-line region unobscured. This may also be the case for objects such as the Seyfert 1 galaxy Mrk231. 相似文献
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