Diameter of PKS 1514-24 (AP Lib)

Abstract

THE radio source PKS 1514-24, which is identified with the optical object AP Lib^1,2, has aroused considerable interest because of its apparent similarity with the peculiar object BL Lac (VRO 42.22.01). BL Lac exhibits optical and radio variability, the optical variations showing time scales as small as 2 min^3,4. There is evidence to show that there are optical variations⁵ in AP Lib but no radio variation has been detected⁶. The radio variations of BL Lac indicate the presence of an extremely compact radio source which has been confirmed by VLBI measurements⁷. If the source AP Lib is similar to BL Lac it is likely that it too has a compact component. Its flat spectrum¹ also suggests the presence of a small diameter component. The best estimate of the diameter of AP Lib available at present is from the lunar occultation observations at Ooty² which indicate that most of the radio emission originates in a component of diameter ≤0.7 arc s. We have observed interplanetary scintillations of AP Lib and find the existence of a compact component having a diameter ≤ 0.035 arc s.