SALT Spectropolarimetric Pipeline Comparisons
J. Cooper* and B. van Soelen
*: corresponding author
Full text: pdf
Pre-published on: December 06, 2023
Published on: December 27, 2023
Abstract
Blazars are active galactic nuclei (AGN) with jets aligned very closely to our line of sight. The optical emission of blazars is often dominated by the polarised, non-thermal emission arising in the jets, with an underlying unpolarised, thermal emission component arising from the host galaxy, dusty torus, and accretion disk components.

Coupled with multi-wavelength observations, optical spectropolarimetry of blazars during both flaring and quiescent states can be used to disentangle the polarised and unpolarised components in their spectral energy distributions, providing better constraints for the non-thermal particle distribution. To this end, spectropolarimetry of blazars during different states of activity was taken with the Southern African Large Telescope (SALT) using the Robert Stobie Spectrograph (RSS). For RSS spectropolarimetry, reductions are performed using the \textsc{polsalt} pipeline. In order to streamline the spectropolarimetric reductions, we have implemented supplementary interactive tools which provides additional wavelength calibration to improve the accuracy of the wavelength calibration for the O & E beam.

Here we present a brief overview of the tools and the results for Hiltner 652, a spectropolarimetric standard, as well as results for the blazars 3C 279. The reduced, PQ and PU, Stokes parameters of Hiltner 652 show no major deviation from previously published results which reassures us that there is no interference introduced into the Stokes parameter calculations when wavelength calibrations are handled by our supplementary tools. The 60009000 Å range of 3C 279 shows a notable dip in the normalized spectrum during a period of flaring when compared to epochs of enhanced activity. The degree of polarisation for 3C 279 of 13.2%, 9.5%, and 21.2% for the epochs 2017 March 28, 2017 March 31, and 2017 May 17, respectively, remains fairly constant across the observed wavelength ranges while still varying with the blazars' state of quiescence or flaring.
DOI: https://doi.org/10.22323/1.426.0056
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