Catalogo Articoli (Spogli Riviste)

OPAC HELP

Titolo:
GINGA OBSERVATIONS OF THE X-RAY-SPECTRA OF QUASARS
Autore:
LAWSON AJ; TURNER MJL;
Indirizzi:
UNIV SOUTHAMPTON,DEPT PHYS,HIGHFIELD SOUTHAMPTON SO17 1BJ HANTS ENGLAND UNIV LEICESTER,DEPT PHYS & ASTRON LEICESTER LE1 7RH LEICS ENGLAND
Titolo Testata:
Monthly Notices of the Royal Astronomical Society
fascicolo: 4, volume: 288, anno: 1997,
pagine: 920 - 944
SICI:
0035-8711(1997)288:4<920:GOOTXO>2.0.ZU;2-O
Fonte:
ISI
Lingua:
ENG
Soggetto:
ACTIVE GALACTIC NUCLEI; HIGH-REDSHIFT QUASARS; RADIO-EMISSION; COLD MATTER; SEYFERT-GALAXIES; ENERGY-DISTRIBUTIONS; COMPLETE SAMPLE; WARM ABSORBER; VARIABILITY; LINE;
Keywords:
GALAXIES, ACTIVE; QUASARS, GENERAL; RADIO CONTINUUM, GALAXIES; X-RAYS, GALAXIES;
Tipo documento:
Review
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
108
Recensione:
Indirizzi per estratti:
Citazione:
A.J. Lawson e M.J.L. Turner, "GINGA OBSERVATIONS OF THE X-RAY-SPECTRA OF QUASARS", Monthly Notices of the Royal Astronomical Society, 288(4), 1997, pp. 920-944

Abstract

An analysis of observations of 50 radio-loud and radio-quiet quasars made by the X-ray satellite Ginga is presented. The spectra are the most accurate and sensitive yet obtained in the 2-20 keV band, and provide a unique opportunity to study the X-ray emission from these faint, although highly luminous, objects. The properties of the hard X-ray continuum are compatible with those of previous quasar surveys, with a highly significant variation of observed spectral indices which is unlikely to be due either to the radio heterogeneity of the sample or to spectral variability. The spectral variability shows no direct link to changes in luminosity. The spectra of the radio-quiet quasars are generally consistent with those of Seyfert galaxies, in support of currentunification schemes; and there is also some evidence for the presenceof Compton reflection and ionized absorption. However, a comparatively high percentage of quasars with soft spectra indicates that these features are unlikely to be present in ail radio-quiet quasars. A comparison with recent ASCA observations of distant radio-quiet sources suggests that we may be seeing the start of a spectral transition between the low-luminosity Seyfert galaxies and these more powerful distant objects. It is shown for the first time that there is a definite range in the spectral index of radio-loud objects. Whether or not this is a direct indication of differing physical parameters in the nuclei of these objects is not known. It is possible that it is indirectly due to the observed relationship between radio core dominance and spectral index which has also been seen using the Einstein observatory. This relationship can be explained using a two-component beaming model, which also provides an explanation for the measured iron line strengths of theradio-loud objects.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 18/09/20 alle ore 09:06:30