VRO 42 22 01: a Variable Source with Circular Polarization

Abstract

THE radio source VRO 42 22 01 was recently identified with a variable stellar object, BL Lac (ref. 1), and we have obtained results which show that the source is radio variable and probably circularly polarized. Since September 1967, a 2,695 MHz receiver has been in operation at the Nancay radiotelescope. It allows simultaneous measurements of flux densities with electric vectors at position angles 0° (V) and 90° (H), and of the products, in phase and through a quarter-wavelength delay, of the two corresponding voltages. It is thus possible to determine the complete polarization, linear or circular, of the most intense sources. One of the programmes in progress with this receiver is the measurement of flux variations for known variable sources, and of possible polarization variations. The radio source VRO 42 22 01 was included in that programme. This source has a flux density at 610.5 MHz of S₆₁₀ = 4.0 flux units (ref. 2) (1 flux umt = 10⁻²⁶ W/m⁻² Hz⁻¹), but it does not appear in the 4C catalogue³, so S₁₇₈<2.0 flux units. Its flux density was measured at 1,417 MHz by Williams, and Stewart⁴, who give S₁₄₁₇ = 7.3 flux units. Its radio spectrum resembles that of the variable components of well known radio sources.