Abstract
We present results taken from a study aiming at detecting the emission from relativistic particles jets in neutron star-low mass X-ray binaries using optical polarimetric observations. First, we focus on a polarimetric study performed on the persistent LMXB 4U 0614+091. Once corrected for interstellar effects, we measured an intrinsic linear polarization in the r-band of ~3% at a 3σ confidence level. This is in-line with the observation of an infrared excess in the spectral energy distribution (SED) of the source, reported in a previous work, which the authors linked to the optically thin synchrotron emission of a jet. We then present a study performed on the transitional millisecond pulsar PSR J1023+0038 during quiescence. We measured a linear polarization of 1.09 ± 0.27% and 0.90 ± 0.17% in the V and R bands, respectively. The phase-resolved polarimetric curve of the source in the R-band reveals a hint of a sinusoidal modulation at the source orbital period. The NIR -optical SED of the system did not suggest the presence of a jet. We conclude that the optical linear polarization observed for PSR J1023+0038 is possibly due to Thomson scattering with electrons in the disc, as also suggested by the hint of the modulation of the R-band linear polarization at the system orbital period.
Highlights
Low mass X-ray binaries (LMXBs) are binary systems that typically host a compact object, that can be either a neutron star (NS) or a stellar-mass black hole (BH), and a companion star, that is normally a main sequence low mass star (M < M )
The system 4U 0614+091 is an ultra-compact X-ray binary (UCXB) candidate, i.e., a LMXB with short orbital period, which causes the density of the companion star to be higher than the typical density of main sequence stars
Right panel: NIR– optical contemporaneous spectral energy distribution (SED) of J1023 obtained in this work; the NIR–X-rays SED of J1023 reported in [23] is represented, with superimposed the fit with a model made by the companion star, the accretion disc and the shock emission powered by the neutron star (NS)
Summary
Low mass X-ray binaries (LMXBs) are binary systems that typically host a compact object, that can be either a neutron star (NS) or a stellar-mass black hole (BH), and a companion star, that is normally a main sequence low mass star (M < M ). The case is strong that there is a significant contribution of the jet in the NIR-optical regime of LMXBs. This contribution is typically detectable in the spectral energy distribution (SED) of the systems as an infrared excess with respect to the multi-colour black body of the accretion disc.
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