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Title:
An X-ray survey of quasars using ASCA
Authors:
Reeves, J. N.; Turner, M. J. L.; Ohashi, T.; Kii, T.
Affiliation:
AA(Leicester, Univ.), AB(Leicester, Univ.), AC(Tokyo Metropolitan Univ.), AD(Inst. of Space and Astronautical Science)
Publication:
Royal Astronomical Society, Monthly Notices, vol. 292, p. 468 (MNRAS Homepage)
Publication Date:
12/1997
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
X RAY SOURCES, QUASARS, SATELLITE OBSERVATION, RED SHIFT, ABSORPTION SPECTRA, SPECTRAL RESOLUTION, SPECTRAL SENSITIVITY, GINGA SATELLITE, EXOSAT SATELLITE, POWER SPECTRA, FLUORESCENCE, LINE SPECTRA
Bibliographic Code:
1997MNRAS.292..468R

Abstract

The ASCA (Advanced Satellite for Cosmology and Astrophysics) X-ray observations of 24 quasars, with redshifts greater than 0.05, are presented. The greater sensitivity and spectral resolution of ASCA extend the EXOSAT and Ginga surveys to higher redshifts. Significant intrinsic absorption is observed in some of the high-redshift objects, and a strong correlation is seen between absorption and quasar redshift, significant at greater than 99 percent confidence level. The radio-loud objects in this survey are found, in general, to have flatter X-ray power-law spectra with weak or no iron fluorescence lines. In contrast, the radio-quiet quasars seem to have steeper spectra, with stronger iron lines. The mean photon index of the radio-quiet quasars is found to be 1.93 +/- 0.06, whereas the radio-loud quasars have a mean index of 1.63 +/- 0.04. This corresponds to a significant difference in spectral shape between the radio-loud and radio-quiet quasars, at about the 99 percent significance level, which was not found in the earlier Ginga sample.

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