Spectral Index–Flux Density Relation for Quasars

Abstract

THE relation between the mean spectral indices α of extragalactic radio sources and their flux densities S(S∼v^−a) at a frequency of 178 MHz has been obtained from data on the flux densities of all radio sources from the revised 3C catalogue at galactic latitudes |b| ≥ 10° at four frequencies: 86, 178, 750 and 1,400 MHz, measured by the P. N. Lebedev Physical Institute¹, at the University of Cambridge² and at the National Radio Astronomy Observatory³. The analysis assumes a linear relation between the spectral index and the logarithm of the flux densities at 178 MHz. For each of the 247 radio sources, five relations were considered of the form where k corresponds to the different combinations of frequencies from which the spectral index α_k was determined, that is: α₁=α₈₆₋₁₇₈ α₂=α_178−750 α₃=α_750−1,400 α₄=α₈₆₋₇₅₀ α₅=α_86−1,400 The bar in equation (1) means the average over all the radio sources.