Optical polarisation variability of narrow line Seyfert 1 galaxies

TL;DR

This study monitors optical polarisation in ten narrow line Seyfert 1 galaxies, revealing significant variability and potential long rotations of the polarisation plane, suggesting intrinsic magnetic field evolution.

Contribution

It introduces a method to evaluate the likelihood that polarisation variability is due to intrinsic evolution rather than noise in NLSy1 galaxies.

Findings

Significant polarisation variability observed in all well-sampled cases.

Candidate long rotations of the polarisation plane identified.

Intrinsic evolution of the EVPA is more probable than noise.

Abstract

We have monitored the R-band optical linear polarisation of ten jetted NLSy1 galaxies with the aim to quantify their variability and search for candidate long rotation of the polarisation plane. In all cases for which adequate datasets are available we observe significant variability of both the polarisation fraction and angle. In the best-sampled cases we identify candidate long rotations of the polarisation plane. We present an approach that assesses the probability that the observed phenomenology is the result of pure noise. We conclude that although this possibility cannot be excluded it is much more likely that the EVPA undergoes an intrinsic evolution. We compute the most probable parameters of the intrinsic event which forecasts events consistent with the observations. In one case we find that the EVPA shows a preferred direction which, however, does not imply any dominance of a toroidal or poloidal component of the magnetic field at those scales.