J/MNRAS/496/L96 Polarization of LMXB MAXI J1820+070 (Kosenkov+, 2020)
Disc and wind in black hole X-ray binary MAXI J1820+070 observed through
polarized light during its 2018 outburst
Kosenkov I.A., Veledina A., Berdyugin A.V., Kravtsov V., Piirola V.,
Berdyugina S.V., Sakanoi T., Kagitani M., Poutanen J.
<Mon. Not. R. Astron. Soc. 496, L96 (2020)>
=2020MNRAS.496L..96K 2020MNRAS.496L..96K (SIMBAD/NED BibCode)
ADC_Keywords: Polarization ; Binaries, X-ray ; Accretion ; X-ray sources
Keywords: polarisation - stars: black holes -
stars: individual: MAXI J1820+070 - X-rays: binaries
Abstract:
We describe the first complete polarimetric dataset 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, ∼0.15 per cent in B and
V filters, and is likely produced in the irradiated disc. A much
higher polarization, reaching ∼0.5 per cent in V and R filters, at
position angle of ∼25° 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.
Description:
Nightly average observed polarisation degrees (PD) and polarisation
angles (PA), obtained during the 2018 outburst of MAXI J1820+070.
Polarimetric measurements were performed using Dipol-2 polarimeter
(Piirola et al., 2014, Proc. SPIE Conf. Ser. Vol. 9147, p. 91478I)
mounted on the Tohoku 60cm telescope (T60) at Haleakala observatory,
Hawaii. Dipol - 2 is a remotely operated "double - image" CCD
polarimeter, which is capable of recording images in three(BVR)
filters simultaneously. The innovative design of the polarimeter,
where the two orthogonally polarised images of the sky overlap on the
images of the source, allows to completely eliminate the sky
polarisation at an instrumental stage (even if it is variable), and to
achieve unprecedentedly high, up to 10-5, accuracy of target
polarimetric measurements (Piirola 1973A&A....27..383P 1973A&A....27..383P, Berdyugin,
2019, Astrophysics and Space Science Library, Vol. 460, p. 33).
Objects:
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RA (2000) DE Designation(s)
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18 20 21.90 +07 11 07.3 MAXI J1820+070 = ASASSN -18ey
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
j1820pol.dat 75 140 Polarization of MAXIJ1820
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Byte-by-byte Description of file: j1820pol.dat
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Bytes Format Units Label Explanations
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3- 15 F13.4 d JD Julian date
18- 20 A3 --- Filter [BVR] Optical filter
23- 27 A5 --- Phase Outburst phase
30- 35 F6.3 % Q Stokes Q
38- 43 F6.3 % U Stokes U
46- 51 F6.3 % PD Polarisation degree
54- 59 F6.3 % e_PD Polarisation degree error
62- 67 F6.2 deg PA Polarisation angle
70- 75 F6.2 deg e_PA Polaristaion angle error
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Acknowledgements:
Ilia Kosenkov, ilia.kosenkov(at)utu.fi
(End) Ilia Kosenkov [Turku Univ.Finland], Patricia Vannier [CDS] 12-Jun-2020