SPECTROPHOTOMETRY OF THE CRAB PULSAR

The first high quality optical spectrum of the Crab Pulsar is presente d. 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 scan ter data, the power law spectral index arising from our observations i s much more precise than anything available so far. Moreover, using th e same data integrated over the V band, as well as new images of the f ield, 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 ob tain a decrease of 0.008 mag/yr +/- 0.004 to be compared with the theo retical 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.