Evidence for quasi-periodic oscillations in the optical polarization of the blazar PKS 2155-304

Abstract

Evidence for the presence of quasi-periodic oscillations (QPOs) in the optical polarization of the blazar PKS 2155-304, during a period of enhanced gamma-ray brightness, is presented. The periodogram of the polarized flux revealed the existence of a prominent peak at T ~ 13 min, detected at >99.7 per cent significance, and T ~ 30 min, which was nominally significant at >99 per cent. This is the first evidence of QPOs in the polarization of an active galactic nucleus, potentially opening up a new avenue of studying this phenomenon.