Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...396..504b&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 396, no. 2, Sept. 10, 1992, p. 504-509. Research supported by CNRS.
Astronomy and Astrophysics
Astronomy
17
Quasars, X Ray Astronomy, X Ray Spectra, Background Radiation, Extragalactic Radio Sources, Spaceborne Astronomy
Scientific paper
Observations of the quasar 3C 273 with the Sigma imaging telescope on board the Granat satellite on four occasions during 1990 for a total exposure time of 62 hr are reported. Comparison of the observations indicates a marginally significant flux variation (3 sigma) of a factor of about 2 on a time scale a short as 41 days. This is the first suggestion of a short time variation at hard X-ray frequencies, and it agrees very well with similar measurements in soft X-rays. The combined data of the first two pointings are well fitted by a power law of photon index of about 1.5 up to about 500 keV with no evidence for a break of steepening in the spectrum. Two sigma upper limits obtained by Sigma at the location of the low-luminosity quasar 0241 + 62 suggest a softer X-ray spectrum for this object. The implications of the Sigma results with respect to astrophysical processes in quasars and their contribution to the cosmic diffuse background are discussed.
Ballet Jean
Bassani Loredana
Bouchet Laurent
Chulkov I.
Churazov Eugene
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