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Titolo:
X-ray properties of the Parkes sample of flat-spectrum radio sources: dustin radio-loud quasars?
Autore:
Siebert, J; Brinkmann, W; Drinkwater, MJ; Yuan, W; Francis, PJ; Peterson, BA; Webster, RL;
Indirizzi:
Max Planck Inst Extraterr Phys, D-85740 Garching, Germany Max Planck Inst Extraterr Phys Garching Germany D-85740 arching, Germany Univ New S Wales, Sch Phys, Sydney, NSW 2052, Australia Univ New S Wales Sydney NSW Australia 2052 s, Sydney, NSW 2052, Australia AustralianAustraliav, Mt Stromlo & Siding Spring Observ, Weston, ACT 2611,Australian Natl Univ Weston ACT Australia 2611 Observ, Weston, ACT 2611, Univ Melbourne, Sch Phys, Parkville, Vic 3052, Australia Univ Melbourne Parkville Vic Australia 3052 arkville, Vic 3052, Australia
Titolo Testata:
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
fascicolo: 1, volume: 301, anno: 1998,
pagine: 261 - 279
SICI:
0035-8711(19981121)301:1<261:XPOTPS>2.0.ZU;2-F
Fonte:
ISI
Lingua:
ENG
Soggetto:
BL LACERTAE OBJECTS; ALPHA ABSORPTION; SKY SURVEY; H-I; GALAXIES; CATALOG; SYSTEMS;
Keywords:
dust, extinction; galaxies : active; quasars : general; X-rays : galaxies;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
63
Recensione:
Indirizzi per estratti:
Indirizzo: Siebert, J Max Planck Inst Extraterr Phys, Giessenbachstr, D-85740 Garching, Germany Max Planck Inst Extraterr Phys Giessenbachstr Garching Germany D-85740
Citazione:
J. Siebert et al., "X-ray properties of the Parkes sample of flat-spectrum radio sources: dustin radio-loud quasars?", M NOT R AST, 301(1), 1998, pp. 261-279

Abstract

We investigate the X-ray properties of the Parkes sample of Bat-spectrum radio sources using data from the ROSAT All-Sky Survey and archival pointed PSPC observations. In total, 163 of the 323 sources are detected. For the remaining 160 sources, 2 sigma upper limits to the X-ray flux are derived. We present power-law photon indices in the 0.1-2.4 keV energy band for 115 sources, which were determined either with a hardness ratio technique or from direct fits to pointed PSPC data if a sufficient number of photons were available. The average photon index is <Gamma > = 1.95(-0.12)(+0.13) for flat-spectrum radio-loud quasars, <Gamma > = 1.70(-0.24)(+0.23) for galaxies, and <Gamma > = 2.40(-0.31)(+0.12) for BL Lac objects. The soft X-ray photonindex is correlated with redshift and with radio spectral index in the sense that sources at high redshift and/or with flat (or inverted) radio spectra have flatter X-ray spectra on average. The results are in accord with orientation-dependent unification schemes for radio-loud active galactic nuclei. Webster et al. discovered many sources with unusually red optical continuaamong the quasars of this sample, and interpreted this result in terms of extinction by dust. Although the X-ray spectra in general do not show excess absorption, we find that low-redshift optically red quasars have significantly lower soft X-ray luminosities on average than objects with blue optical continua. The difference disappears for higher redshifts, as is expectedfor intrinsic absorption by cold gas associated with the dust. In addition, the scatter in log(f(x)/f(o)) is consistent with the observed optical extinction, contrary to previous claims based on optically or X-ray selected samples. Although alternative explanations for the red optical continua cannot be excluded with the present X-ray data, we note that the observed X-ray properties are consistent with the idea that dust plays an important role in someof the radio-loud quasars with red optical continua.

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Documento generato il 22/10/14 alle ore 09:57:49