| Abstract: | Spectral energy distributions (SEDs) and radio continuum spectra are
presented for a northern sample of 104 extragalactic radio sources, based on
the Planck Early Release Compact Source Catalog (ERCSC) and simultaneous
multifrequency data. The nine Planck frequencies, from 30 to 857 GHz, are
complemented by a set of simultaneous observations ranging from radio to
gamma-rays. This is the first extensive frequency coverage in the radio and
millimetre domains for an essentially complete sample of extragalactic radio
sources, and it shows how the individual shocks, each in their own phase of
development, moving in the relativistic jet, shape the radio spectra. The SEDs
presented in this paper were fitted with second and third degree polynomials to
estimate the frequencies of the synchrotron and inverse Compton (IC) peaks, and
the spectral indices of low and high frequency radio data, including the Planck
ERCSC data, were calculated. SED modelling methods are discussed, with an
emphasis on proper, physical modelling of the synchrotron bump using multiple
components. Planck ERCSC data also suggest that the original accelerated
electron energy spectrum could be much harder than commonly thought, with
power-law index s around 1.5 instead of the canonical 2.5. The implications of
this for the acceleration mechanisms effective in blazar shocks are discussed. |
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