Strmömgren zones of type II supernovae

Abstract

The emission measures EM in the directions of supernova remnants and pulsars are considered as functions of their ages t. The resulting plot has a well-defined lower boundary, which can be approximated by the expression EMmin∝1/t. The quantity EMmin increases with decreasing age t and does not level off or reach a maximum until t≅500 yr. It is concluded that the bulk of the radiative energy that goes into ionizing and heating the interstellar gas is released at early stages of the supernova remnant’s evolution. We suggest that most of the kinetic energy of the supernova shell is converted into thermal energy and radiated at remnant ages t<100 yr, when the supernova shell, which is expanding at an enormous speed (about 104 km/s), overtakes the shell produced by the presupernova in the supergiant stage. We have estimated the ionization energy E≅1051 erg, diameter L≅60 pc, and electron density N e≅7 cm−3 of the HII regions around the supernovae (the supernova Stromgren zones). A list of objects that can be reliably identified as Stromgren zones of type II supernovae is presented. The plot of pulsar pulse broadening τ as a function of the pulsar age t also has a well-defined lower boundary, for which τ∝t −2 when t≥1000 yr. This suggests that turbulence develops during the first thousand years after the supernova outburst. It is also concluded that turbulence plays an important role in the formation and evolution of the Stromgren zones of type II supernovae.