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IXPE and multi-wavelength observations of blazar PG 1553+113 reveal an orphan optical polarization swing

Middei, R; Perri, M; Puccetti, S; Wu, K; Zane, S; Turolla, R; (2023) IXPE and multi-wavelength observations of blazar PG 1553+113 reveal an orphan optical polarization swing. The Astrophysical Journal Letters , 953 , Article L28. Green open access

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Abstract

The lower energy peak of the spectral energy distribution of blazars has commonly been ascribed to synchrotron radiation from relativistic particles in the jets. Despite the consensus regarding jet emission processes, the particle acceleration mechanism is still debated. Here, we present the first X-ray polarization observations of PG 1553+113, a high-synchrotron-peak blazar observed by the Imaging X-ray Polarimetry Explorer (IXPE). We detect an X-ray polarization degree of (10 ± 2)% X-ray polarization in PG 1553+113 3 along an electric-vector position angle of ψX = 86◦ ± 8 ◦ . At the same time, the radio and optical polarization degrees are lower by a factor of ∼3. During our IXPE pointing, we observed the first orphan optical polarization swing of the IXPE era, as the optical angle of PG 1553+113 underwent a smooth monotonic rotation by about 125◦ , with a rate of ∼17 degree per day. We do not find evidence of a similar rotation in either radio or X-rays, which suggests that the X-ray and optically emitting regions are separate or, at most, partially co-spatial. Our spectro-polarimetric results provide further evidence that the steady-state X-ray emission in blazars originates in a shock-accelerated and energy-stratified electron population.

Type: Article
Title: IXPE and multi-wavelength observations of blazar PG 1553+113 reveal an orphan optical polarization swing
Open access status: An open access version is available from UCL Discovery
Publisher version: https://doi.org/10.3847/2041-8213/acec3e
Language: English
Additional information: This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third-party material in this article are included in the Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
Keywords: Acceleration of particles, black hole physics, polarization, radiation mechanisms: nonthermal, galaxies: active, galaxies: jets
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10174558
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