A1 Refereed original research article in a scientific journal
Disc and wind in black hole X-ray binary MAXI J1820+070 observed through polarized light during its 2018 outburst
Authors: Kosenkov IA, Veledina A, Berdyugin AV, Kravtsov V, Piirola V, Berdyugina SV, Sakanoi T, Kagitani M, Poutanen J
Publisher: OXFORD UNIV PRESS
Publication year: 2020
Journal: Monthly Notices of the Royal Astronomical Society
Journal name in source: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Journal acronym: MON NOT R ASTRON SOC
Volume: 496
Issue: 1
First page : L96
Last page: L100
Number of pages: 5
ISSN: 0035-8711
eISSN: 1365-2966
DOI: https://doi.org/10.1093/mnrasl/slaa096
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/49109635
We describe the first complete polarimetric data set of the entire outburst of a low-mass black hole X-ray binary system and discuss the constraints for geometry and radiative mechanisms it imposes. During the decaying hard state, when the optical flux is dominated by the non-thermal component, the observed polarization is consistent with the interstellar values in all filters. During the soft state, the intrinsic polarization of the source is small, similar to 0.15 per cent in B and V filters, and is likely produced in the irradiated disc. A much higher polarization, reaching similar to 0.5 per cent in V and R filters, at a position angle of similar to 25 degrees observed in the rising hard state coincides in time with the detection of winds in the system. This angle coincides with the position angle of the jet. The detected optical polarization is best explained by scattering of the non-thermal (hot flow or jet base) radiation in an equatorial wind.
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