X-ray properties of the Parkes sample of flat-spectrum radio sources: dust in radio-loud quasars?

Siebert, J., Brinkmann, W., Drinkwater, M. J., Yuan, W., Francis, P. J., Peterson, B. A. and Webster, R. L. (1998) X-ray properties of the Parkes sample of flat-spectrum radio sources: dust in radio-loud quasars?. Monthly Notices of The Royal Astronomical Society, 301 1: 261-279. doi:10.1046/j.1365-8711.1998.02019.x

Author Siebert, J.
Brinkmann, W.
Drinkwater, M. J.
Yuan, W.
Francis, P. J.
Peterson, B. A.
Webster, R. L.
Title X-ray properties of the Parkes sample of flat-spectrum radio sources: dust in radio-loud quasars?
Journal name Monthly Notices of The Royal Astronomical Society   Check publisher's open access policy
ISSN 0035-8711
Publication date 1998
Sub-type Article (original research)
DOI 10.1046/j.1365-8711.1998.02019.x
Open Access Status DOI
Volume 301
Issue 1
Start page 261
End page 279
Total pages 19
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Language eng
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 photon index 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 continua among 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 expected for 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 some of the radio-loud quasars with red optical continua.
Keyword Astronomy & Astrophysics
Dust, Extinction
Bl Lacertae Objects
Alpha Absorption
Sky Survey
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Physical Sciences Publications
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Citation counts: TR Web of Science Citation Count  Cited 35 times in Thomson Reuters Web of Science Article | Citations
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Created: Mon, 13 Aug 2007, 10:50:04 EST