Bibcode
Russell, D. M.; Shahbaz, T.; Lewis, F.; Gallo, E.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 463, Issue 3, p.2680-2689
Advertised on:
12
2016
Número de citas
14
Número de citas referidas
13
Descripción
We present near-infrared polarimetric observations of the black hole
X-ray binaries Swift J1357.2-0933 and A0620-00. In both sources, recent
studies have demonstrated the presence of variable infrared synchrotron
emission in quiescence, most likely from weak compact jets. For Swift
J1357.2-0933, we find that the synchrotron emission is polarized at a
level of 8.0 ± 2.5 per cent (a 3.2σ detection of intrinsic
polarization). The mean magnitude and rms variability of the flux
(fractional rms of 19-24 per cent in KS band) agree with
previous observations. These properties imply a continuously launched
(stable on long time-scales), highly variable (on short time-scales) jet
in the Swift J1357.2-0933 system in quiescence, which has a moderately
tangled magnetic field close to the base of the jet. We find that for
A0620-00, there are likely to be three components to the
optical-infrared polarization; interstellar dust along the line of
sight, scattering within the system, and an additional source that
changes the polarization position angle in the reddest (H and
KS) wavebands. We interpret this as a stronger contribution
of synchrotron emission, and by subtracting the line-of-sight
polarization, we measure an excess of ˜1.25 ± 0.28 per cent
polarization and a position angle of the magnetic field vector that is
consistent with being parallel with the axis of the resolved radio jet.
These results imply that weak jets in low-luminosity accreting systems
have magnetic fields which possess similarly tangled fields compared to
the more luminous, hard state jets in X-ray binaries.