A New Model for the Width of the Broad Emission Lines in AGN: The Role of the Accretion Rate

We present a model which relates the Broad Emission Line Regions of AGN to the accretion mechanism. Based on the Keplerian assumption for the high velocity clouds of the gas responsible for the production of the Broad Emission Lines, we identify that gas with an outflowing disk/coronal wind forms a stabilized Shakura-Sunyaev accretion disk. We show that in the framework of this picture the observed range of H-beta FWHM from Broad Line to Narrow Line type 1 AGN, is well reproduced as a function of the accretion rate.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho

Ubiquitous variability of X-ray absorbing column densities in Seyfert 2 Galaxies

We present a study of the variations in the absorbing column density of 25 X-ray defined Seyfert 2 galaxies, as inferred from hard X-ray observations, on timescales from months to several years. We show that a significant variation of N$_H$ (from 20% to 80%) is observed in almost all (22/25) the sources with multiple X-ray observations, although X-ray absorption never vanishes. For a subsample of 11 sources observed at least five times the typical variation time, as defined by a structure function, is less than one year for both heavily absorbed (nH ~ 10^23 cm^(-2)) and moderately absorbed (nH ~ 10^22 cm^(-2)) sources. These variations rule out the simplest version of the unified models, based on a homogeneous obscuring torus, and suggest the presence of clumpy circumnuclear material on a scale well below a parsec. We propose a modification of the torus model in which an overabundance of slightly dusty BELR clouds obscures the BELR. The BELR needs, like the torus, to have an axisymmetric structure. This model is closely related to that of Elvis (2000) for type 1 AGN. For lightly obscured AGN (nH ~ 10^22 cm^(-2)) the structure function shows an increase at a timescale of $\sim$5 yr, indicating a second absorber, most probably on a 5-10 pc scale associated with the host galaxy.Comment: 34 pages, 8 figures, accepted for publication in the Astrophysical Journa

The 2-10 keV emission properties of PSR B1937+21

We present the results of a BeppoSAX observation of the fastest pulsar known: PSR B1937+21. The ~ 200 ks observation (78.5 (34) ks MECS (LECS) exposure times) allowed us to investigate with high statistical significance both the spectral properties and the pulse profile shape. The absorbed power law spectral model gave a photon index of ~ 1.7 and N_H ~ 2.3 x 10^22 cm^-2. These values explain both a) the ROSAT non-detection and b) the deviant estimate of a photon index of ~ 0.8 obtained by ASCA. The pulse profile appears, for the first time, clearly double peaked with the main component much stronger than the other. The statistical significance is 10 sigma (main peak) and 5 sigma (secondary peak). The 1.6-10 keV pulsed fraction is consistent with 100%; only in the 1.6-4 keV band there is a ~ 2 sigma indication for a DC component. The secondary peak is detected significantly only for energies above 3 / 4 keV. The unabsorbed (2-10 keV) flux is F_2-10 = 3.7 x 10^-13 erg cm^-2 s^-1, implying a luminosity of L_X = 4.6 x 10^31 Theta (d/3.6 kpc)^2 erg s^-1 and an X-ray efficiency of eta = 4 x 10^-5 Theta, where Theta is the solid angle spanned by the emission beam. These results are in agreement with those obtained by ASCA.Comment: 4 pages, 4 figures, 2 tables. To appear in the Proceedings of the 270. WE-Heraeus Seminar on Neutron Stars, Pulsars and Supernova Remnants, Jan. 21-25, 2002, Physikzentrum Bad Honnef, eds W. Becker, H. Lesch & J. Truemper. Proceedings are available as MPE-Report 27

Broad band spectral properties of Seyfert 1 galaxies observed with BeppoSAX

We will present some results on the broad--band observations of BeppoSAX of the bright Seyfert galaxies NGC 4151 and NGC 5548.Comment: 5 pages, 4 figures, Proc. of the 32 COSPAR Ass., Session E1.1 "Broad Band X-Ray Spectra of Cosmic Sources, ed.s K. Makishima, L. Piro, T. Takahashi, Advances in Space Research, in pres