A dedicated stroboscopic device was used to obtain optical spectra of the Crab main–pulse and inter–pulse as well as the spectrum of the underlying nebula when the pulsar is turned off .
As 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 inter-pulse behave as power laws , both with the same de-reddened index \alpha = +0.2 \pm 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 \pm 0.1 .
Its emission lines are split into approaching ( \sim - 1200 km/s ) and receding ( \sim + 600 km/s ) components .
The strength of emission line components and the flux in nebular continuum vary on arcsec scale .
The nebular line and continuum intensities along the N-S slit are given .