On the Interpretation of Radio-Source Spectra and the Evolution of Radio Galaxies and Quasi-Stellar Sources

view Abstract Citations (130) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Interpretation of Radio-Source Spectra and the Evolution of Radio Galaxies and Quasi-Stellar Sources Kellermann, K. I. Abstract It is known that radio galaxies and quasi-stellar sources (QSS) have spectral indices ranging from about -0.2 to - 1.3 with a strong concentration near -0.75 to -080. It is shown here that this distribution may be readily explained if relativistic electrons which have an initial energy distribution N(E) = KE-1 5 - ` are injected into a magnetic field in a series of recurring bursts. Then at low frequencies, where electron energy losses due to synchrotron radiation and the inverse Compton effect are not important, the spectral index, a, is equal to its initial value of - 0.25. At intermediate frequencies, the time scale for electron energy losses is longer than the period between bursts and the injection can be considered to be quasi-continuous. The spectrum is thus in equilibrium since the electron energy losses are balanced by the injection of new particles. The spectral index is then steeper by and becomes -0.75, which is close to that observed for the majority of sources. At higher frequencies where radiation losses steepen the spectrum, the limiting index becomes -1.33, in good agreement with the observed cutoff near -1.3 in the spectral index distribution. If the source is observed soon after an outburst of relativistic particles, the high-frequency spectrum is dominated by the young electrons that have not yet decayed. The large positive curvature observed at centimeter wavelength in the spectra of several QSS and in NGC 1275, and the rapid variations in the radio and optical luminosity reported for these sources is interpreted as evidence of a recent injection of relativistic electrons. In some of these cases the density of particles is sufficiently great that the source is optically thick down to centimeter wavelengths, and the flux density increases rapidly with increasing frequency. Additional sources which do not have low-frequency components, such as Parkes 1934-63, might be discovered by an independent survey made at centimeter wavelengths. Publication: The Astrophysical Journal Pub Date: December 1966 DOI: 10.1086/148940 Bibcode: 1966ApJ...146..621K full text sources ADS | data products SIMBAD (8) NED (4)