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Titolo:
X-ray spectra of a large sample of quasars with ASCA
Autore:
Reeves, JN; Turner, MJL;
Indirizzi:
Univ Leicester, Dept Phys & Astron, Xray Astron Grp, Leicester LE1 7RH, Leics, England Univ Leicester Leicester Leics England LE1 7RH er LE1 7RH, Leics, England
Titolo Testata:
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
fascicolo: 2, volume: 316, anno: 2000,
pagine: 234 - 248
SICI:
0035-8711(20000801)316:2<234:XSOALS>2.0.ZU;2-X
Fonte:
ISI
Lingua:
ENG
Soggetto:
ACTIVE GALACTIC NUCLEI; SEYFERT-1 GALAXIES; REFLECTION SPECTRA; ACCRETION DISKS; COLD MATTER; RADIO-LOUD; ABSORPTION; EXCESS; QSO;
Keywords:
surveys; galaxies : active; quasars : general; X-rays : general;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
54
Recensione:
Indirizzi per estratti:
Indirizzo: Reeves, JN Univ Leicester, Dept Phys & Astron, Xray Astron Grp, Leicester LE1 7RH, Leics, England Univ Leicester Leicester Leics England LE1 7RH Leics, England
Citazione:
J.N. Reeves e M.J.L. Turner, "X-ray spectra of a large sample of quasars with ASCA", M NOT R AST, 316(2), 2000, pp. 234-248

Abstract

The results from an X-ray spectral analysis of a large sample of quasars, observed with ASCA, are presented. The sample was selected to include all ASCA observations of quasars, with z > 0.05 and M-v < -23.0, available up to1998 January. The data reduction leaves 62 quasars, 35 of which are radio-loud and 27 radio-quiet, suitable for spectral analysis. Differences are found between the radio-quiet quasars (RQQs) and the radio-loud quasars (RLQs): the RLQs have flatter X-ray spectra (Gamma similar to 1.6), with little iron line emission or reflection, and are more X-ray luminous than the softer (Gamma similar to 1.9) RQQs, ill agreement with previous studies. A correlation between Gamma and optical H beta was also found for the radio-quietquasars in this sample, whereby the steepest X-ray spectra tend to be found in those objects with small H beta widths. The correlation is significantat >99 per cent confidence, confirming the well-known trend between Gamma and H beta FWHM in Seyfert Is, but at higher luminosities. Other spectral complexities are observed from this sample. A soft X-ray excess, with blackbody temperatures in the range 100-300 eV, is seen in many low-z radio-quietquasars. In most cases the temperatures are probably too hot to originate directly from the disc and could imply that some reprocessing is involved. Iron K-line emission features are also found in the RQQs, but often from partially ionized material, indeed, in the highest-luminosity RQQs there is neither evidence for iron line emission nor the reflection component expected from disc reflection models. These observations can be explained by an increase in the quasar accretion rate with luminosity. leading to an increasein the ionization state of the surface layers of the disc. The occurrence of ionized or 'warm' absorbers is rare in this sample, with only five detections in low-z objects. However, excess neutral X-ray absorption is found towards several of the high-z predominantly radio-loud, quasars. Although found to increase with quasar redshift, this 'intrinsic' absorption may be associated with radio-loud active galactic nuclei.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 01/10/20 alle ore 07:19:57