The structure of the central disk of NGC 1068: a clumpy disk model

NGC 1068 is one of the best studied Seyfert II galaxies, for which the blackhole mass has been determined from the Doppler velocities of water maser. We show that the standard $\alpha$-disk model of NGC 1068 gives disk mass between the radii of 0.65 pc and 1.1 pc (the region from which water maser emission is detected) to be about 7x10$^7$ M$_\odot$ (for $\alpha=0.1$), more than four times the blackhole mass, and a Toomre Q-parameter for the disk is $\sim$0.001. This disk is therefore highly self-gravitating and is subject to large-amplitude density fluctuations. We conclude that the standard $\alpha$-viscosity description for the structure of the accretion disk is invalid for NGC 1068. In this paper we develop a new model for the accretion disk. The disk is considered to be composed of gravitationally bound clumps; accretion in this clumped disk model arises because of gravitational interaction of clumps with each other and the dynamical frictional drag exerted on clumps from the stars in the central region of the galaxy. The clumped disk model provides a self-consistent description of the observations of NGC 1068. The computed temperature and density are within the allowed parameter range for water maser emission, and the rotational velocity in the disk falls off as $r^{-0.35}$.Comment: To appear in Ap

Anomaluos RR Lyrae (V-I)_0 colors in Baade's Window

We compare (V-I)_0-(V-K)_0 color-color and (V-I)_0-log P period-color diagrams for Baade's Window and local RRab Lyrae stars. We find that for a fixed log P the Baade's Window RR Lyrae stars are ~0.17 magnitudes redder in (V-I)_0 than the local RR Lyrae stars. We also show that there is no such effect observed in (V-K)_0. We argue that an extinction misestimate towards Baade's Window is not a plausible explanation of the discrepancy. Unlike Baade's Window RR Lyrae stars, the local ones follow a black-body color-color relation and are well approximated by theoretical models. We test two parameters, metallicity and surface gravity, and find that their effects are too small to explain the (V-I)_0 discrepancy between the two groups of stars. We do not provide any explanation for the anomalous (V-I)_0 behavior of the Baade's Window RR Lyrae stars. We note that a similar effect for clump giant stars has been recently reported by Paczynski and we caution that RR Lyrae stars and clump giants, often used as standard candles, can be subject to the same type of systematics.Comment: 10 pages, 7 figures, submitted to Ap

The Ulysses Supplement to the BATSE 3B Catalog of Cosmic Gamma-Ray Bursts

We present Interplanetary Network localization information for 218 gamma-ray bursts in the 3rd BATSE catalog, obtained by analyzing the arrival times of these bursts at the Ulysses and Compton Gamma-Ray Observatory (CGRO) spacecraft. For any given burst observed by these two spacecraft, arrival time analysis (or "triangulation") results in an annulus of possible arrival directions whose half-width varies between 7 arcseconds and 32 arcminutes, depending on the intensity and time history of the burst, and the distance of the Ulysses spacecraft from Earth. This annulus generally intersects the BATSE error circle, resulting in an average reduction of the error box area of a factor of 30.Comment: Accepted for publication in the Astrophysical Journal Supplemen