Search for particle acceleration in two massive Wolf-Rayet stars using uGMRT observations

TL;DR

This study used uGMRT observations to search for non-thermal radio emission from two Wolf-Rayet stars, constraining their mass-loss rates and binary properties, but found no detectable emission indicating limited particle acceleration activity.

Contribution

First uGMRT observations of WR 114 and WR 142 at low frequencies, setting new upper limits on their radio emission and constraining their binary separation and mass-loss rates.

Findings

No detection of radio emission from WR 114 and WR 142.

Mass-loss rate of WR 114 constrained to less than 10^-5 M_sun/yr.

Binary separation likely greater than 70 AU for WR 114 and 20 AU for WR 142.

Abstract

Large wind kinetic power of Wolf-Rayet (WR) stars make them ideal targets in low radio frequencies to search for non-thermal emission due to relativistic particle acceleration. In this paper, we present observations of two WR stars, WR 114 and WR 142, in Band 4 (550-950 MHz) and Band 5 (1050-1450 MHz) using the upgraded Giant Meterwave Radio Telescope (uGMRT). Neither star is detected in the observed frequency bands, nor extended emission associated with them. The upper limit to the free-free radio emission from the stellar wind enables us to constrain the mass-loss rate of WR 114 to $\lesssim \rm 10^{-5}\,M_{ \odot}\,yr^{-1}$; this is a factor three smaller than previously estimated using spectroscopic modelling. If we further assume that the WR stars are binaries, the non-detection of synchrotron emission from the putative wind collision region implies that the stars are either in very wide binary systems away from periastron, or that the stars are in close binary systems with an orbital separation $<70$ AU for WR 114 and $<20$ AU for WR 142. The non-detection of low-frequency radio emission from these two systems thus provides evidence that narrows their nature, though it does not rule them out as bonafide particle-accelerating colliding-wind binaries.