The effect of synchrotron absorption on the observed radio luminosities of pulsars

Propagation of radio waves through the flow of an ultrarelativistic magnetized plasma of pulsar magnetospheres is considered. It is known that, for the parameters typical of pulsar plasma, cyclotron absorption of radio emission is efficient and the absorbing particles easily acquire relativistic gyration. The character of synchrotron absorption, i.e. absorption by relativistically gyrating particles, can differ from that known for cyclotron absorption. It is shown that the particle pitch angles rapidly become comparable to the angle of incidence of the resonant radiation in the laboratory frame, ψ∼θ . Further, synchrotron absorption occurs in the regime θ−ψ≪θ . The resonant frequency decreases with distance because of the magnetic field strength decrease. It is found that only the highest frequencies, ≳10 GHz , suffer absorption by the particles with ψ≪θ , whereas radiation over the remaining part of the radio frequency range is subject to synchrotron absorption in the regime θ−ψ≪θ . It is the latter process that can affect the observed radio luminosities of pulsars. The optical depth to the synchrotron absorption in the limit θ−ψ≪θ appears to be much less than that previously known for the limit ψ≪θ . For long‐period pulsars, P ∼ 1 s , the effect of synchrotron absorption at θ−ψ≪θ is found to be negligible, whereas for short‐period ones, P ≲ 0.1 s , the absorption depth can be of order unity. Now the escape of radio waves from pulsar magnetospheres can be explained without any additional assumptions. At the same time, synchrotron absorption is suggested to underlie the marked distinction in the energetic characteristics of short‐period and long‐period pulsars proved by a number of conclusions of pulsar statistics.