Binary pulsar B1259-63 spectrum evolution: detailed study
  We studied the radio spectrum of PSR B1259-63 in an unique binary with Be
star LS 2883 and showed that the shape of the spectrum depends on the orbital
phase. We proposed a qualitative model which explains this evolution. We
considered two mechanisms that might influence the observed radio emission:
free-free absorption and cyclotron resonance. Recently published results have
revealed a new aspect in pulsar radio spectra. There were found objects with
turnover at high frequencies in spectra, called gigahertz-peaked spectra (GPS)
pulsars. Most of them adjoin such interesting environments as HII regions or
compact pulsar wind nebulae (PWN). Thus, it is suggested that the turnover
phenomenon is associated with the environment than being related intrinsically
to the radio emission mechanism. Having noticed the apparent resemblance
between the B1259-63 spectrum and the GPS, we suggest that the same mechanisms
should be responsible for both cases. Therefore, the case of B1259-63 can be
treated as a key factor to explain the GPS phenomenon observed for the solitary
pulsars with interesting environments and also another types of spectra (e.g.
with break).
