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The UV Properties of I Zw 1
Ari Laor
IZw1 is the prototype narrow line quasar. This type of AGNs show a number of common peculiar characteristics whose physical origin is not yet well understood. Here, I review the re…
The Ionizing Continuum of Quasars
Ari Laor
The ionizing continuum shape of quasars is generally not directly observable, but indirect arguments, based on photoionization models and thin accretion disk models suggest that it…
The PG X-Ray QSO Sample: Links among X-ray, UV & Optical Spectra
Beverley J. Wills, M. S. Brotherton, A. Laor +3
A unique, essentially complete sample of 22 QSOs, with high quality soft X-ray spectra from ROSAT, as well as HST and optical spectrophotometry from below Ly-alpha to above H-alpha…
On Quasar Masses and Quasar Host Galaxies
Ari Laor
The mass of massive black holes in quasar cores can be deduced using the typical velocities of Hb-emitting clouds in the Broad Line Region (BLR) and the size of this region. Howeve…
The variability properties of X-ray steep and X-ray flat quasars
Fabrizio Fiore, Ari Laor, Martin Elvis +2
We have studied the variability of 6 low redshift, radio quiet `PG' quasars on three timescales (days, weeks, and months) using the ROSAT HRI. The quasars were chosen to lie at the…
A Note on the Viability of Gaseous Ionization in Active Galaxies by Fast Shocks
Ari Laor
Observational evidence suggest that shocks may affect the spatial and velocity distributions of gas in the NLR/ENLR of some active galaxies. It thus seemed plausible that shocks ma…
Are AGN Broad Emission Lines Formed by Discrete Clouds? --- Analysis of Keck High Resolution Spectroscopy of NGC 4151
Nahum Arav, Thomas A. Barlow, Ari Laor +2
We search for a direct signature of discrete ''clouds'' in the broad line region (BLR) of the Seyfert galaxy NGC 4151. For this purpose we apply cross correlation (CC) analysis to…