Flicker of extragalactic radio sources at two frequencies

Abstract

Flicker of extragalactic sources was investigated by observing 14 flat and 20 steep spectrum sources at 1410 and 2380 MHz from the Arecibo Observatory on 20 successive days. The rms intensity variation of flat spectrum sources is, on average, higher than for steep spectrum sources. The variations are shown to have contributions on time scales ranging from at least as small as 1 - 2 days to greater than 20 days. The observed ratio of the flicker amplitude (1410:2380 MHz ≈ 1) is not consistent with a simple interpretation in terms of either "slow refractive" or "fast diffractive" interstellar scintillations. If the variations are intrinsic, they imply brightness temperatures in excess of the inverse Compton limit for an incoherent synchrotron source.