Multiwavelength observations of the quasar Q 1821 + 643 during the ROSAT All Sky Survey

Details Multiwavelength observations of the quasar Q 1821 + 643 during the ROSAT All Sky Survey Multiwavelength observations of the quasar Q 1821 + 643 during the ROSAT All Sky Survey

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...266..183u&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 266, no. 1, p. 183-189.

Astronomy and Astrophysics

Astronomy

6

Quasars, Sky Surveys (Astronomy), Spaceborne Astronomy, Astronomical Spectroscopy, Bremsstrahlung, Light Curve, Rosat Mission, X Ray Spectra

Scientific paper

Temporal variations of the flux in the optical, UV, soft X-ray and medium X-ray ranges occur in most AGN studied, but no general correlation has emerged between the variations in these different energy ranges. Because of its high ecliptic latitude the radio-quiet quasar Q 1821 + 643 was surveyed for 37 days by ROSAT during the ROSAT All Sky Survey, thereby providing the rare opportunity for repeated simultaneous observations of a bright quasar in the X-ray, ultraviolet and optical ranges. The first result is that no flux variation by more than 10 percent has been detected during the 37 d period of visibility in the range (0.1-2.4) keV, and no variation by more than 5 percent has been detected in the UV and optical ranges. This indicates a steady state of the emission mechanisms during this period. The most interesting result is that the fit of the soft X-ray spectrum of Q 1821 + 643 and of 3 C 273 (a flat radio spectrum quasar of similar optical luminosity) obtained during the ROSAT Survey with a thermal bremsstrahlung indicates a definitely lower temperature for Q 1821 + 643 than for 3 C 273 (kT = 73 and 173 eV respectively).

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