X-ray spectrum of NP0532

Abstract

THERE is a change in the X-ray spectral index of the Crab pulsar NP0532 near 10 keV (refs 1 and 2). We here examine this in a more quantitative fashion than before, using most of the available published data, together with some unpublished data (Table 1). The pulsed fraction is the ratio of the pulsed radiation to total radiation; data published as the ratio of the pulsed to unpulsed components have been duly corrected. The unpulsed reference level has been determined according to Ducros et al.³ and where other workers have used a significantly different convention, these data have been corrected. We believe that all data (31 points), can be validly compared. Other results, not considered here^2,4,5, are generally in agreement with the data we have used. The use of the pulsed fraction as the basic spectral quantity allows the low energy spectrum to be treated independently of interstellar absorption because it is the same for both the pulsed and unpulsed components.