Detection of Radio Emission from Scorpio X-1

Abstract

SOME twenty X-ray sources are now known, among them the well known objects M87 and the Crab nebula. Two X-ray sources (Sco X-1 and Cyg X-2) have been optically identified with previously unknown objects which have a stellar appearance and the characteristics of old novae^1,2. Most X-ray sources remain unidentified, however. Most of them lie at low galactic latitudes, and it seems possible that many are objects similar to Sco X-1. These objects are not prominent at radio wavelengths and previous attempts to detect radio emission from Sco X-1, the strongest X-ray source, have yielded only upper limits to its flux density (refs. 3–5 and Hogg and Johnson quoted in ref. 6). The flux density of Sco X-1 has now been measured as 0.021 ± 0.007 flux units (1 flux unit = 10⁻²⁶ W m⁻² Hz⁻¹) at a wavelength of 4.6 cm. This value is substantially below the previously determined upper limits.