Discovery of Radio Emission from the Transient Anomalous X-Ray Pulsar XTE J1810-197

Abstract

We report the first detection of radio emission from anyanomalous X-ray pulsar (AXP). Data from the Very Large Array (VLA)Multi-Array Galactic Plane Imaging Survey with angular resolution of 6"reveal a point source of flux density 4.5+/-0.5 mJy at 1.4 GHz atthe precise location of the 5.54 s pulsar XTE J1810-197. This isgreater than upper limits from all other AXPs and from quiescent statesof soft gamma-ray repeaters (SGRs). The detection was made in 2004January, 1 year after the discovery of XTE J1810-197 during its onlyknown outburst. Additional VLA observations both before and after theoutburst yield only upper limits that are comparable to or larger thanthe single detection, neither supporting nor ruling out a decayingradio afterglow related to the X-ray turn-on. Another hypothesisis that, unlike the other AXPs and SGRs, XTE J1810-197 may power aradio synchrotron nebula by the interaction of its particle wind witha moderately dense environment that was not evacuated by previousactivity from this least luminous, in X-rays, of the known magnetars.