Speaker
Description
At optical wavelengths, blazar SEDs show a superposition of non-thermal (polarised) emission from the jet, and thermal (unpolarised) emission from the accretion disc, broad-line region, dust torus and host galaxy itself. Due to their variability, the level of polarisation present in blazar emission changes as the non-thermal jet emission becomes more/less prominent. Hence, polarisation studies in blazars provide a direct link to jet activity, as well as a tool to disentangle the different emission components in blazar SEDs. Since 2016, as part of a ToO observation campaign with the Southern African Large Telescope (SALT), a selection of 18 blazars (10 FSRQs, 8 BLLs) have been observed during different states (low/quiescent or high/flaring) to trace the evolution of polarisation in its emission. The optical spectropolarimetry observations cover a wavelength range of λ ≈ 3500Å – 9000Å, with a resolution of R ≈ 170 – 530 (grating PG0300), or R ≈ 670 – 1040 (grating PG0900). The observations provide the optical spectra, and the degree of polarisation and polarisation angle as a function of wavelength. The observations have been complemented by quasi-contemporaneous photometric observations taken with the Las Cumbres Observatory (LCO) to improve flux calibration and study optical light curves. We present an overview of some results for this campaign.
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