Optical spectrum of main-, inter-, and off-pulse emission from the crab pulsar

A dedicated stroboscopic device was used to obtain optical spectra of the Crab pulsar main pulse and interpulse as well as the spectrum of the underlying nebula when the pulsar is turned off. Since the nebular emission is very inhomogeneous, our ability to effectively subtract the nebular background signal is crucial. No spectral lines intrinsic to the pulsar are detected. The main pulse and the interpulse behave as power laws, both with the same dereddened index alpha = +-0.2 +/- 0.1. This value was obtained by subtracting the nebular spectrum at the exact position of the pulsar. The underlying nebula is redder, alpha = -0.4 +/- 0.1. Its emission lines are split into approaching (similar to -1200 km s(-1)) and receding (similar to +600 km s(-1)) components. The strength of the emission line components and the flux in the nebular continuum vary on an arcsecond scale. The nebular line and continuum intensities along the north-south slit are given.