Optical polarization of high-energy BL Lac objects

Understand

We investigate the optical polarization properties of high-energy BL Lac objects using data from the RoboPol blazar monitoring program and the Nordic Optical Telescope.

• We wish to understand if there are differences in the BL Lac objects that are detected with the current-generation TeV instruments compared to those that have not yet been detected.
• The mean polarization fraction of the TeV-detected BL Lacs is 5% while the non-TeV sources show a higher mean polarization fraction of 7%.
• This difference in polarization fraction disappears when the dilution by the unpolarized light of the host galaxy is accounted for.