Spectral energy distributions and high-energy emission of BL Lac type objects

Abstract

Based on identifications from the Veron and Quasars.org catalogs, we determine the optical-to-X-ray spectral indices for a sample of 201 BL Lac type objects (BLLs) and search for trends in the distribution of these indices of the sources detected in high-energy bands. We find that EGRET-detected sources are low-energy peaked and that the positional correlation with the arrival directions of ultra-high-energy cosmic rays from the previously studied AGASA, Yakutsk and High Resolution Fly's Eye samples is dominated by low-energy-peaked BLLs.