Discovery of Radio Emission from Transient Anomalous X - ray Pulsar XTE J 1810 − 197

We report the first detection of radio emission from any anomalous X-ray pulsar (AXP). Data from the Very Large Array (VLA) MAGPIS survey with angular resolution 6 reveals a point-source of flux density 4.5± 0.5 mJy at 1.4 GHz at the precise location of the 5.54 s pulsar XTE J1810−197. This is greater than upper limits from all other AXPs and from quiescent states of soft gammaray repeaters (SGRs). The detection was made in 2004 January, 1 year after the discovery of XTE J1810−197 during its only known outburst. Additional VLA observations both before and after the outburst yield only upper limits that are comparable to or larger than the single detection, neither supporting nor ruling out a decaying radio afterglow related to the X-ray turn-on. Another hypothesis is that, unlike the other AXPs and SGRs, XTE J1810−197 may power a radio synchrotron nebula by the interaction of its particle wind with a moderately dense environment that was not evacuated by previous activity from this least luminous, in X-rays, of the known magnetars. Subject headings: pulsars: general — pulsars: individual (XTE J1810−197, AX J1844.8−0256) — radio continuum: stars — X-rays: stars Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027; jules,[email protected] Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027; [email protected] Physics Department, University of California, 1 Shields Avenue, Davis, CA 95616; and Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA 94550; [email protected] Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218; [email protected]