The variable radio counterpart and possible large-scale jet of the new Z-source XTE J1701-462

TL;DR

This study reports on radio observations of the new Z-source XTE J1701-462, revealing a highly variable radio counterpart, a possible large-scale jet, and insights into its accretion behavior and radio/X-ray coupling.

Contribution

First detailed radio study of XTE J1701-462, identifying a variable radio counterpart and potential large-scale jet linked to the source.

Findings

Radio counterpart detected in 6 of 16 observations

Radio spectrum is unusually flat or inverted

Possible large-scale jet aligned with the X-ray binary

Abstract

We report radio observations, made with the Australia Telescope Compact Array, of the X-ray transient XTE J1701-462. This system has been classified as a new `Z' source, displaying characteristic patterns of behaviour probably associated with accretion onto a low magnetic field neutron star at close to the Eddington limit. The radio counterpart is highly variable, and was detected in six of sixteen observations over the period 2006 January -- April. The coupling of radio emission to X-ray state, despite limited sampling, appears to be similar to that of other `Z' sources, in that there is no radio emission on the flaring branch. The mean radio and X-ray luminosities are consistent with the other Z sources for a distance of 5--15 kpc. The radio spectrum is unusually flat, or even inverted, in contrast to the related sources, Sco X-1 and Cir X-1, which usually display an optically thin radio spectrum. Deep wide-field observations indicate an extended structure three arcminutes to the south which is aligned with the X-ray binary. This seems to represent a significant overdensity of radio sources for the field and so, although a background source remains a strong possibility, we consider it plausible that this is a large-scale jet associated with XTE J1701-462.