High-precision optical polarimetry of the accreting black hole V404 Cyg during the 2015 June outburst

Abstract

Our simultaneous three-colour (BV R) polarimetric observations of the low-mass black hole Xray binary V404 Cyg show a small but statistically significant change of polarization degree (∆p ∼ 1 per cent) between the outburst in June 2015 and the quiescence. The polarization of V404 Cyg in the quiescent state agrees within the errors with that of the visually close (1. 4) companion (p R = 7.3 ± 0.1 per cent), indicating that it is predominantly of interstellar origin. The polarization pattern of the surrounding field stars supports this conclusion. From the observed variable polarization during the outburst we show that polarization degree of the intrinsic component peaks in the V -band, p V = 1.1 ± 0.1 per cent, at the polarization position angle of θ V = −7 • ± 2 • , which is consistent in all three passbands. We detect significant variations in the position angle of the intrinsic polarization in R band from −30 • to ∼ 0 • during the outburst peak. The observed wavelength dependence of the intrinsic polarization does not support non-thermal synchrotron emission from a jet as a plausible mechanism, but is in better agreement with the combined effect of electron (Thomson) scattering and absorption in a flattened plasma envelope or outflow surrounding the illuminating source. Alternatively, the polarization signal can be produced by scattering of the disc radiation in a mildly relativistic polar outflow. The position angle of the intrinsic polarization, nearly parallel to the jet direction (i.e. perpendicular to the accretion disc plane), is in agreement with these interpretations.

Evolving optical polarisation of the black hole X-ray binary MAXI J1820+070

“…To more accurately estimate the contribution from the ISM polarisation to that observed from MAXI J1820+070, we studied polarisation of the field stars. This method of estimating the ISM polarisation in the source direction has been shown to give sufficiently accurate results (Kosenkov et al 2017). The resulting measurements for nearby field stars are given in Table 2.…”

“…ized to some extent (see the discussion in Veledina et al 2013;Kosenkov et al 2017). In the soft state, the outer parts of the standard accretion disc irradiated by the X-ray emission from the compact object likely dominate the optical flux (see e.g.…”

Polarimetry and spectroscopy of the “oxygen flaring” DQ Herculis-like nova: V5668 Sagittarii (2015)

“…Description of the polarimeter design is given by (Piirola et al 2014). Detailed descriptions of the observational routine and data reduction procedure can be found in Kosenkov et al (2017).…”

Polarization and Spectral Energy Distribution in OJ 287 during the 2016/17 Outbursts

“…In this figure we also plotted data reported in Valtonen et al 2016 [10] and new measurements taken in 2016/17 season in the R filter with the Dipol-2 polarimeter on the T60 telescope in Maui, Hawaii. Detailed description of the observation routine and data reduction procedure for Dipol-2 can be found in Kosenkov et al 2017 [16]. Except for the December 2015 flare (marked by the red vertical line), for which the polarization degree was at the level of 0.1 or below, the subsequent brightenings were highly polarized.…”