HUT Observations of the Quasar E1821+64

Details HUT Observations of the Quasar E1821+64 HUT Observations of the Quasar E1821+64

May 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...182.0415l&link_type=abstract

American Astronomical Society, 182nd AAS Meeting, #04.15; Bulletin of the American Astronomical Society, Vol. 25, p.792

Astronomy and Astrophysics

Astronomy

2

Scientific paper

We obtained far-ultraviolet spectra of the quasar E1821+64 using the Hopkins Ultraviolet Telescope during the flight of Astro-1 aboard the space Shuttle Columbia in December 1990. The HUT spectra cover the 912-1860 Angstroms wavelength range with a resolution of ~ 3 Angstroms. In two successive orbits we accumulated 2966 s of high quality data during orbital night. Our spectra extend well past the peak of the blue bump down to a wavelength of 705 Angstroms in the rest frame of this z=0.297 quasar. There is no significant feature or change in spectral shape in the vicinity of the Lyman edge. We model the spectrum with a relativistic accretion disk with black body emissivities computed in the Schwarzschild metric. Our best fit gives a central black hole mass of ~ 13 times 10(8) M_sun accreting mass at a rate of 19 M_sun yr(-1) . This accretion disk spectrum cannot account for the soft X-ray excess observed with ROSAT reported by Kolman et al., nor can Comptonized disk spectra simultaneously match the definite drop in UV flux and the soft X-ray excess. The strength of the soft X-ray excess depends sensitively on the hydrogen column density along the line of sight. From archival HST/FOS spectra we measure a column density using the observed galactic damped Lyalpha profile of 1.8 times 10(20) cm(-2) . This is significantly less than the 4.1 times 10(20) cm(-2) suggested by the Stark et al. survey. For a column density as low as 1.9 times 10(20) cm(-2) , Kolman et al. find that all the soft X-ray flux seen with ROSAT can be attributed to the central star of the nearby planetary nebula K1-16. We suggest that there is no significant soft X-ray excess in E1821+64, consistent with the relatively weak C\ IV and O\ VI emission in our spectra compared to Lyalpha .

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