Astronomy and Astrophysics, volume 311, 384-392 (1996/7-2)
ROSAT observations of BL Lacertae objects.
LAMER G., BRUNNER H. and STAUBERT R.
Abstract (from CDS):
We present soft X-ray spectra of 74 BL Lacertae objects observed with the PSPC detector on board of the ROSAT satellite. The sample contains all BL Lac objects detected during the pointed observation phase as a target or serendipitously. We have investigated the soft X-ray and broad band spectral properties and discuss the consequences for the X-ray emission processes. For the first time a clear dependence of the X-ray spectral steepness on the radio to X-ray spectral energy distribution is found: αrxand αxare correlated in the X-ray selected (XBL) subsample and anticorrelated in the radio selected (RBL) subsample. The objects with intermediate αrxvalues thus do have the steepest soft X-ray spectra. Simulated PSPC spectra based on a set of simple two component multifrequency spectra are in good agreement with the measurements and suggest a broad range of synchrotron cutoff energies. We have calculated synchrotron self-Compton beaming factors for a subsample of radio bright objects and find a correlation of the beaming factors δICwith αrxand αx. The most extreme RBL objects are very similar to flat spectrum radio quasars in all their broad band and X-ray properties.
galaxies: active - BL Lacertae objects: general - radio continuuum: galaxies - X-rays: galaxies
VizieR on-line data:
<Available at CDS (J/A+A/311/384): table2 table3>