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

摘要

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