RoboPol : the optical polarization of gamma-ray-loud and gamma-ray-quiet blazars

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This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Authors

Date

2016-12

Department

Metsähovi Radio Observatory
Department of Radio Science and Engineering

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Mcode

Degree programme

Language

en

Pages

16

Series

Monthly Notices of the Royal Astronomical Society, Volume 463, issue 3, pp. 3365-3380

Abstract

We present average R-band optopolarimetric data, as well as variability parameters, from the first and second RoboPol observing season. We investigate whether gamma-ray-loud and gamma-ray-quiet blazars exhibit systematic differences in their optical polarization properties. We find that gamma-ray-loud blazars have a systematically higher polarization fraction (0.092) than gamma-ray-quiet blazars (0.031), with the hypothesis of the two samples being drawn from the same distribution of polarization fractions being rejected at the 3σ level. We have not found any evidence that this discrepancy is related to differences inthe redshift distribution, rest-frame R-band luminosity density, or the source classification. The median polarization fraction versus synchrotron-peak-frequency plot shows an envelope implying that high-synchrotron-peaked sources have a smaller range of median polarization fractions concentrated around lower values. Our gamma-ray-quiet sources show similar median polarization fractions although they are all low-synchrotron-peaked. We also find that the randomness of the polarization angle depends on the synchrotron peak frequency. For high-synchrotron-peaked sources, it tends to concentrate around preferred directions while for low-synchrotron-peaked sources, it is more variable and less likely to have a preferred direction. We propose a scenario which mediates efficient particle acceleration in shocks and increases the helical B-field component immediately downstream of the shock.

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Keywords

polarization, galaxies: active, galaxies: jets, galaxies: nuclei

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DOI

10.1093/mnras/stw2217

Citation

Angelakis, E, Hovatta, T, Blinov, D, Pavlidou, V, Kiehlmann, S, Myserlis, I, Böttcher, M, Mao, P, Panopoulou, G V, Liodakis, I, King, O G, Baloković, M, Kus, A, Kylafis, N, Mahabal, A, Marecki, A, Paleologou, E, Papadakis, I, Papamastorakis, I, Pazderski, E, Pearson, T J, Prabhudesai, S, Ramaprakash, A N, Readhead, A C S, Reig, P, Tassis, K, Urry, M & Zensus, J A 2016, 'RoboPol : the optical polarization of gamma-ray-loud and gamma-ray-quiet blazars', Monthly Notices of the Royal Astronomical Society, vol. 463, no. 3, pp. 3365-3380. https://doi.org/10.1093/mnras/stw2217

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https://urn.fi/URN:NBN:fi:aalto-201703283228

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[article-cris] Sähkötekniikan korkeakoulu / ELEC