Fermi Gamma-ray Space Telescope

The study of magnetic field direction in blazar jets by identifying optical outbursts using the l1 trend filter.

M. Uemura
Y. Tanaka, H. Akitaya, R. Itoh, K. Shiki

Abstract:

We investigated a systematic relationship between the position angle (P.A.) of optical polarization of the outburst component and that of radio jets in blazars. In the optically thin domain, P.A. is perpendicular to the direction of magnetic field. Hence, we can study the universal field structure in the jet by investigating a correlation between P.A. of the outburst component and the direction of radio jets. However, it is difficult to uniquely identify the outburst components because blazars show very irregular variations. Here, we identified optical outbursts of blazars using the l1 trend filter and the wavelet analysis. The l1 trend filter is a filtering method to estimate the turning points of time-series data. We used the optical polarimetric data observed with Kanata telescope in Hiroshima, Japan. Our targets consist of approximately 40 FSRQs and BL Lacs. The observation period is approximately six years (2008 to 2014). As a result, we identified approximately 450 outbursts and their P.A. We compared them with the position angles of radio jets which were referred from the public VLBA data. We surveyed the distribution of the angular difference between P.A. and radio jets, and found no deviation from a uniform distribution. We obtained similar results even for each individual object. In this study, we also report the characteristics of the?polarization position angle in terms of gamma-ray loud or quiet outbursts using the public data of Fermi LAT.