Physics
Scientific paper
Sep 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...192.8503r&link_type=abstract
American Astronomical Society, 192nd AAS Meeting, #85.03; Bulletin of the American Astronomical Society, Vol. 30, p.1158
Physics
Scientific paper
Most BL Lacs are believed to be low-luminosity Fanaroff-Riley class I radio galaxies (FR-1s) whose jet axes are oriented towards the observer such that their emission is dominated by relativistically-boosted synchrotron and inverse-Compton emission, making them ideal laboratories for understanding the physics of beaming and relativistic jet propogation. Currently there are only two statistically-complete samples of BL Lacs: the radio-selected 1Jy sample (RBLs) and the X-ray-selected EMSS sample (XBLs). While once extremely rare, new X-ray and radio surveys are increasing the number of known BL Lacs dramatically, creating an impetus to understand their nature. In the unified model both RBLs and XBLs are believed to be beamed FR-1s and that XBLs are either viewed farther from the jet axis than RBLs. Alternatively, it has been suggested that their difference lies not in orientation but in the high-energy cutoff in their energy distributions, where XBLs and RBLs represent a single family of objects with a smooth energy distribution followed by a sharp cutoff. For RBLs this cutoff occurs in the near-IR/optical and for XBLs this cutoff is at UV/X-ray or higher energies. Padovani & Giommi have argued against the unified model on the basis that the radio structure of XBLs is more core dominated than predicted. However, their conclusions are drawn from VLA observations of a subset of the EMSS sample which includes only the brighter radio sources (Perlman & Stocke); a subset which, due to Doppler boosting, is biased towards more core-dominated sources. To eliminate this bias we have completed deep, 20cm observations with the VLA of the remaining objects in the EMSS sample. We will present these observations as well as discuss their implications for both the unified and energy-cutoff models for BL Lacs. These results will also be used to constrain beaming parameters for the XBL population.
Rector Travis A.
Stocke John T.
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