Title:

New results from the MAGNUM telescope on the dust distribution in AGNs



Yuzuru Yoshii
MAGNUM Project P.I.
University of Tokyo

Abstract:

The Multicolor Active Galactic Nuclei Monitoring (MAGNUM) 2-meter
dedicated telescope was commissioned in early 2001 in the University of
Hawaii's LURE Observatory at Haleakala Observatories.

The MAGNUM telescope and camera are operational. Recently we achieved
fully automated, remote controlled operation and we demonstrate the
capabilities of our unique facility for target-of-opportunity
observations, particularly, for monitoring SNs and GRBs shortly after
their discovery.

Since becoming operational, MAGNUM has monitored several tens of AGNs in
the optical (UBVRI) and near-infrared (ZJHK) wave-bands, simultaneously.
To date, the most intense monitoring observations have been made of
several Seyfert 1 galaxies including NGC 4151 and NGC 5548. A delayed
response of light variations in the V band to those in the K band was
detected, and the lag time was precisely measured to within an accuracy of
5-10% by a cross-correlation analysis. The measured lag time is
interpreted as the light-travel time from the central energy source to the
surrounding dust torus, because the K light is emitted from the hot dust
heated by absorption of ultraviolet and optical light from the central
energy source.  Compared with lag measurements of the broad emission lines
in the literature, our results for such dust reverberation indicate that
the broad emission-line region is well within the inner hole of the dust
torus.