All-Moscow Seminar of Astrophysicists
(ASA)
The seminar is supported by the grant of Federal Programm "Integration"
annotation of talk
Джон Кольер (Университет, Лондон)
Измерение постоянной Хаббла по
``освещаемым фонариком'' аккреционным
дискам в AGN
We show how wavelength-dependent time delays between continuum flux
variations of active galactic nuclei (AGNs) can be used to test the
standard black hole--accretion disc paradigm, by measuring the temperature
structure T(R) of the gaseous material surrounding the purported black
hole. Reprocessing of high-energy radiation in a steady-state blackbody
accretion disc with T ~ R-3/4 incurs a wavelength-dependent
light travel time delay tau ~ lambda4/3. The International AGN
Watch multiwavelength monitoring campaign on NGC7469 showed optical
continuum variations lagging behind those in the UV by about 1d at 4800A
and about 2d at 7500A. These UV/optical continuum lags imply a radial
temperature structure T ~ R-3/4, consistent with the classical
accretion disc model, and hence strongly support the existence of a disc in
this system. We assume that the observed time delays are indeed caused by a
classical accretion disc structure, and derive a redshift-independent
luminosity distance to NGC 7469. The luminosity distance allows us to
estimate a Hubble constant of H_0 (cos i / 0.7)1/2 = 42 +/- 9
km/s/Mpc. The interpretation of the observed time delays and spectral
energy distribution in the context of an accretion disc structure requires
further validation. At the same time, efforts to minimize the systematic
uncertainties in our method to derive a more accurate measurement of H_0,
e.g. by obtaining an independent accurate determination of the disc
inclination i or statistical average of a moderate sample of active
galaxies, are required. However, this remains a promising new method of
determining redshift-independent distances to AGNs. (see. MNRAS 302,
L24-L28, 1999)