The Size of a Quasar's Accretion Disk Derived from an Eclipse

Details The Size of a Quasar's Accretion Disk Derived from an Eclipse The Size of a Quasar's Accretion Disk Derived from an Eclipse

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006head....9.0715p&link_type=abstract

American Astronomical Society, HEAD meeting #9, #7.15; Bulletin of the American Astronomical Society, Vol. 38, p.351

Astronomy and Astrophysics

Astronomy

Scientific paper

The prodigious energies generated by active galactic nuclei are believed to be produced by the accretion of large quantities of matter into a supermassive black hole. Most of the energy radiated by the accretion disk is believed to come out in the ultraviolet, and originates within 50 gravitational radii of the black hole. Here we report the results of 12 low-resolution Hubble Space Telescope spectra of the Quasar 3C 279, taken at irregular intervals over a period of six months. During these observations, we observed an absorption feature near the center of the Ly-alpha line, which appeared only in the 7 spectra taken 10-23 April 2002. We interpret this as the passage of a single obscuring cloud across the accretion disk, moving predominantly in the transverse direction. This simple geometry allows a direct measurement of the UV-emitting region of 3C 279's accretion disk. Assuming a transverse velocity of 1000 km/s, typical of narrow-line clouds, we derive a characteristic radius of 23 AU (23 Rg for a 10^8 solar mass black hole) for 3C 279's UV emission region. We discuss the physical conditions in the eclipsing cloud, as well as implicatoins for AGN and accretion disk models. We also discuss the implications of the lack of any overall variability in the emission line parameters.

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