Unpulsed optical emission from the crab pulsar

Based on observations of the Crab pulsar using the TRIFFID high-speed imaging photometer in the UBV bands using the Special Astrophysical Observatory's 6 m telescope in the Russian Caucasus, we report the detection of pronounced emission during the so-called off phase of emission. Following de-extinction, this unpulsed component of emission is shown to be consistent with a power law with an exponent of alpha = -0.60 +/- 0.37, the uncertainty being dominated by the error associated with the independent CCD photometry used to reference the TRIFFID data. This suggests a steeper power-law form than that reported elsewhere in the literature for the total integrated spectrum, which is essentially hat with alpha similar to 0.1, although the difference in this case is only significant at the less than or equal to 2 sigma level. Deeper reference integrated and TRIFFID phase-resolved photometry, in these bands in conjunction with further observations in the UV and R region, would constrain this fit further.