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Vacuum Breakdown near a Black Hole Charged by Hypercritical Accretion
A. Treves, R. Turolla
We consider a black hole accreting spherically from the surrounding medium. If accretion produces a luminosity close to the Eddington limit the hole acquires a net charge so that e…
HST snapshot imaging of BL Lac objects
R. Falomo, C. Megan Urry, Riccardo Scarpa +2
Snapshot images of about 100 BL Lac objects were obtained with WFPC2 on HST. Sources from various samples, in the redshift range 0.05 to 1.2, were observed and 61 resolved (51 with…
Science with IUE and the Growth of an Astrophysical Group in Milan: from X-Ray Binaries to AGN
Renato Falomo, Laura Maraschi, Elena Pian +1
The contribution of an astrophysics group based in Milan to the science with the IUE satellite during its almost 20 years lifetime has focussed on high energy sources, of both gala…
Fast X-ray Variability of PKS 2155-304: A Cross Correlation Analysis
A. Treves, Y. H. Zhang, A. Celotti +7
PKS 2155-304 is one of the prototypes of BL Lac objects. Its spectral energy distribution is known from the radio to the TeV band and has two peaks, one in the soft X-rays and the…
BeppoSAX Observations of the BL Lac Object Mkn 501 in an Intermediate State
Elena Pian, Eliana Palazzi, Lucio Chiappetti +8
The BL Lac object Mkn 501 was observed with the BeppoSAX satellite at three epochs in April-May 1998, simultaneously with the Whipple and HEGRA Cherenkov telescopes. The X-ray spec…
BeppoSAX Observations of PKS 2155-304 during an active Gamma-ray State
L. Maraschi, L. Chiappetti, F. Tavecchio +8
PKS 2155-304 was observed with BeppoSAX in November 1997 for 64 ksec (total elapsed time 33.5 hours) and, for the first time, simultaneously in gamma-rays with EGRET on board the C…
Ultraviolet Isotropic Emission from the Blazar 3C 279
E. Pian, A. Koratkar, L. Maraschi +7
Archival IUE SWP and HST FOS spectra show the presence of a relatively strong, broad Lyman alpha emission line superposed onto the UV spectral continuum of the blazar 3C 279. As op…
BeppoSAX Observations of the TeV Blazar Mkn 421
G. Fossati, L. Chiappetti
The blazar Mkn 421 has been observed, as part of the AO1 Core Program, five times from 2 to 7 May 1997. In the LECS+MECS energy band the spectrum shows convex curvature, well repre…
The elusiveness of old neutron stars
M. Colpi, R. Turolla, S. Zane +1
Old neutron stars (ONSs) which have radiated away their internal and rotational energy may still shine if accreting the interstellar medium. Despite their large number, only two pr…