Radiation from Vela-Like Pulsars Near the Death Line

Abstract

Radiation of both the outer gaps and the neutron star surface is considered for a Vela-like pulsar near the death line. It is shown that if such a pulsar is close enough to the death line, its optical, UV and X-ray emission has to increase. Using results of this consideration, it is argued that Geminga is not a close relative of Vela-like pulsars. The outer gap model of Geminga in which the main part of the outer gap volume operates as a Vela-like generator of $\gamma$-rays is ruled out. A Vela-like mechanism of $\gamma$-ray generation can operate only in a small region of the outer gap of Geminga. The length of this region along the magnetic field is an order of magnitude smaller than the outer gap dimensions. In the magnetosphere of Geminga the main mechanism of $\gamma$-ray generation at $\sim 10 - 10^4$ MeV is curvature radiation and not the synchrotron radiation as it was assumed for Vela-like pulsars.