AN EXPANDING SHELL AND SYNCHROTRON JET IN RS OPHIUCHI

We report high-resolution radio imaging of the recurrent nova RS Ophiuchi (RS Oph) during the first month of the 2006 outburst, using the Very Long Baseline Array (VLBA). Observations made on days 20.8 and 26.8 of the outburst show a synchrotron-emitting partial shell that is much brighter to the east than to the west. Assuming that the broad component of the infrared lines corresponds to the outermost part of the shell seen by the VLBA, the distance to the source is 2: 45 +/- 0: 4 kpc. The circular shape and spectral indices of the shell emission challenge simple models for the radio structure immediately after the outburst. The second epoch also shows an additional, resolved, synchrotron-emitting component well to the east of the shell. Its inferred velocity is comparable to the escape speed from the surface of a high-mass white dwarf. This component was not seen in the first epoch. Its appearance may be related to the outflow reaching the edge of the nebula created by the red giant wind, which had been refilling the void left by the last outburst in 1985. This eastern component is likely related to the jets previously seen in this and other symbiotic stars, and it represents the earliest clear detection of such a jet, as well as the best case yet for synchrotron emission from a white dwarf jet.