The ultraviolet spectrum and continuum energy distribution of the bright quasar H1821 + 643

view Abstract Citations (33) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Ultraviolet Spectrum and Continuum Energy Distribution of the Bright Quasar H1821+643 Kolman, Michiel ; Halpern, Jules P. ; Shrader, Chris R. ; Filippenko, Alexei V. Abstract We report on the first UV observations of the bright QSO H1821+643. With V = 14.2 mag and z = 0.297, H1821+643 is the second brightest object in the sky at z > 0.1. The IUE data are combined with new optical spectroscopy, and existing infrared and X-ray data, to reveal a strong optical/UV "big bump," which continues past the Lyman limit in the rest frame of the QSO. A possible turnover at the high- frequency side of the UV continuum constrains fits of a thin accretion disk model to a large black hole mass (M ~3 x 10^9^ M_sun_) and high accretion rate (M ~19 M_sun_ yr^-1^), but a small disk size (R_out_/R_in_~12). The shape of the UV continuum was found to be variable, with a hardening of the spectrum when the source was brighter. Because of its location only 3^deg^ from the ecliptic pole, H1821+643 will be an important object for simultaneous UV and soft X- ray monitoring to test for a common origin of the UV bump and soft X- ray excess. Publication: The Astrophysical Journal Pub Date: May 1991 DOI: 10.1086/170022 Bibcode: 1991ApJ...373...57K Keywords: Continuous Radiation; Quasars; Spectral Energy Distribution; Stellar Spectra; Ultraviolet Spectra; Absorption Spectra; Accretion Disks; Emission Spectra; Line Spectra; X Ray Spectra; Astrophysics; QUASARS; SPECTROPHOTOMETRY; ULTRAVIOLET: SPECTRA full text sources ADS | data products SIMBAD (5) NED (1) MAST (1) INES (1)