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

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 on to a low magnetic field neutron star at close to the Eddington limit. The radio counterpart is highly variable, and was detected in six of 16 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-l and Cir X-l, which usually display an optically thin radio spectrum. Deep wide-field observations indicate an extended structure 3 arcmin 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. © 2007 The Authors. Journal compilation © 2007 RAS.