The density and location of the warm absorber in NGC 3516

Hagai Netzer(School of Physics and Astronomy, Tel Aviv University)

Abstract

We use new Chandra observations and several ASCA observations of NGC 3516 to investigate the spectral variations in this source over a period of 7 years. A comparison of the Chandra observations, when the source was almost at an all-time minimum, and the ASCA 1994 observations, close to the all-time maximum, indicates that the very large change (factor $\sim 20$ at 1 keV) in flux is entirely consistent with a change in ionizing flux seen through a constant column warm-absorber. Intermidiate cases are all fitted by the very same model including an episode of a factor $\sim 2$ flux drop over 60 ks. Our very detailed model allows us to put a strong upper limit on the density of the recombining gas and hence, together with the model parameters, the location of the warm absorber. We find that n > 10⁶ cm^-3 which is the best limit obtained so far on the conditions in the WA gas in AGN. It suggests a location outside but close to the BLR and a thin shell geometry. The analysis of the LETG data shows also a narrow 6.4 keV iron line probably originating in a cold torus.

CATEGORY: ACTIVE GALAXIES AND QUASARS