Radio Observations of the 1985 Outburst of RS Ophiuchi

The paper reports observations of the first radio source observed in association with a recurrent nova event, the 1985 January 26 outburst of RS Ophiuchi. Measurements at some or all of four VLA frequencies were made at 32 epochs from 1985 February 24 to 1986 January 31, indicating a rapidly evolving spectrum with at least two components. After peaking in flux in early March, the radio source exhibited complex decay at all four frequencies. The radio source was resolved in the early 15 GHz observations, indicating an angular extent expanding at a rate of 0.0015 arcsec (or 0.003 arcsec) per day, corresponding to a velocity of 2100 (or 4200) km/s if the expansion is symmetric (or asymmetric). H I absorption measurements found (2.4 + or - 0.6) x 10 to the 21st hydrogen atoms per sq cm for the line of sight to RS Oph, implying a distance of 1.6 kpc. The rapidly expanding radio source is probably synchrotron emission, and the remnant radio source, dominating during the apparently optically thin decay, may be gyrosynchrotron emission of 300-500 keV electrons radiating in a magnetosphere in the RS Oph binary system.