Spectrophotometry of the Crab pulsar

The first high quality optical spectrum of the Crab Pulsar is presented. The pulsar shows a flat, featureless, continuum which, in the range 4900 - 7000 Angstrom, is well fitted by a power law with alpha = -0.1 +/- 0.01. While in agreement with previous results based on much scanter data, the power law spectral index arising from our observations is much more precise than anything available so far. Moreover, using the same data integrated over the V band, as well as new images of the field, we try to assess the secular decrease of the pulsar's luminosity. No firm conclusion can be drawn for the data available so far. We obtain a decrease of 0.008 mag/yr +/- 0.004 to be compared with the theoretical rate predicted by the Pacini's law (similar to 0.005 mag/yr). In parallel, the velocity structures of the nebula emission lines have been studied, finding no evidence for an high velocity halo.