First Unambiguous X-Ray Detection of R Aquarii

The authors report coordinated ultraviolet and X-ray observations of the symbiotic Mira R Aqr obtained with IUE and EXOSAT in 1985 June and December at phases 0.0 and 0.5 of the Mira light curve. They have detected with the Low-Energy EXOSAT detector a weak X-ray flux of 5.4 and 4.6×10^-3 counts s^-1 at the two epochs, respectively. The source is probably soft, with a 0.2 - 1 keV luminosity of 0.8 - 1.0×10³⁰erg s^-1. An IUE image of the jet obtained in 1985 December shows high-temperature lines of N V and He II stronger than in an exposure of the star. It is argued that the X-rays are mostly emitted from the jet. Possible radiation mechanisms of the X-ray source in R Aqr are considered.