Galactic Supernova Remnants: Radio Evolution and Population Characteristics

Abstract

Shell SNRs show a systematic gradient of radio surface brightness normal to the galactic plane, and a measured scale height for this effect has been obtained. The progenitor distribution and birth rate are significantly modified when allowance is made for this effect. The galactic height dependence of radio surface brightness satisfactorily accounts for the otherwise anomalous highlatitude SNR AD 1006. It also provides a crucial clue to the origin of the radio emission, suggesting that the interstellar magnetic field is dominant over internally generated fields in shell SNRs. Recently we have independently reached the same conclusion from a consideration of the cumulative number count of shell SNRs.