The integrated radio spectrum of Virgo A

Abstract

The flux density of the radio galaxy Virgo A has been measured at 38 and 151.5 MHz. These measurements and published flux densities at 59 other frequencies from 5.6 MHz to 857 GHz are used to obtain a fit to the frequency dependence of the logarithm of the flux density in the form of a second-order polynomial of the logarithm of the frequency,

\(S_\nu ^{Vir A} [Jy] = 1224.4(\nu [MHz]/150)^{ - 0.817 + 0.007\log (\nu [MHz]/150)} .\)

This spectrum, which has a small positive curvature, agrees slightly better with the observed flux densities than a purely power-lawspectrumwith the spectral index 0.793±0.003 and S_{150 [MHz]}^{Vir A} = 1187±23 Jy. The relative errors in using the power-law spectrum instead of this spectrum with its small, positive curvature lie in the range (−5.2−1.6)% for frequencies from 70 MHz to 857 GHz. The expected peak frequency of the spectrum of Virgo A is estimated.