Polarimetric Study of GRS 1915+105: Estimation of Interstellar Polarization Component

TL;DR

This study analyzes near-infrared polarimetry of GRS 1915+105 and surrounding field stars to estimate the interstellar polarization component, concluding that interstellar dust dominates the observed polarization in the NIR band.

Contribution

It provides new polarimetric measurements of field stars around GRS 1915+105, clarifying the interstellar polarization contribution in the NIR band.

Findings

Interstellar clouds beyond 4 kpc cause significant polarization.

Polarization from interstellar dust aligns with that of GRS 1915+105.

Jet-origin synchrotron polarization is minor in NIR during 2019-2023.

Abstract

GRS 1915+105 is a well-known X-ray binary system composed of a black hole with a low-mass companion star and is recognized for emitting relativistic jets. Imazato et al. (2021) performed extensive polarimetry in a near-infrared (NIR) Ks band from 2019 April through December when GRS 1915+105 experienced an X-ray low luminous state and found almost stable polarization of P=2.42% +/- 0.08%. We performed NIR polarimetry of the field stars around GRS 1915+105 in 2023 April and October, and found that the field stars that are not listed in Gaia DR3 and StarHorse2 catalogues show well aligned polarization that is consistent with GRS 1915+105' s polarization. Those suggest that the interstellar clouds existing beyond 4 kpc causes the large interstellar extinction and that the polarization the GRS 1915+105 is mostly originated from the magnetically aligned dust grains within the clouds. Therefore, the jet-origin synchrotron radiation polarization would have given only minor contribution in the NIR band in 2019 Apr-Dec.