Pulsars in the Westerbork Northern Sky Survey

I have searched the Westerbork Northern Sky Survey (WENSS) source list for detections of known ra- dio pulsars. A source with a flux density greater than ve times the local noise level is found near the positions of 25 pulsars. The probability that one out of these 25 sources is a chance coincidence is about 10%. I have looked at the WENSS maps of the non-detected pulsars. A flux den- sity between three and ve times the local noise level is found near the positions of 14 of these non-detected pul- sars. There is a 50 percent probability that (at least) one of these marginal detections is just a noise fluctuation. Fourteen radio pulsars, which according to earlier flux measurements have flux densities above three times the WENSS noise level, are not detected. Of the 39 pulsars detected in the WENSS 19 are also detected in the NRAO VLA Sky Survey (NVSS). By combining the WENSS and NVSS flux densities for these 19 pulsars spectral indices are obtained that dier by up to 50% from the long term averaged values reported in the literature. This aects the reliability of pulsar candidates that are selected on the basis of their WENSS-NVSS spectral index. in this way, while they were missed in regular pulsar sur- veys because their pulses were smeared out in the de- tection process due to their small period and their high dispersion measure. The pulsar population found in this way, may supple- ment the presently known population, since this method has totally dierent selection eects. These eects can be investigated by studying the spectral indices and polari- sation degrees of known pulsars in these continuum ob- servations. The spectral indices are strongly influenced by scintillation. This may cause the flux density of a pulsar to vary by more than 100 percent on time scales of minutes (diractive scintillation) to days (refractive scintillation). In this Paper I search for detections of pulsars in the Westerbork Northern Sky Survey (WENSS), a sur- vey performed at 325 MHz. I compare my results with those from Kaplan et al. (1998) and Han & Tian (1999), who did similar analyses with data from the 1400 MHz NRAO VLA Sky Survey (NVSS). Section 2 describes the WENSS and Sect. 3 describes how the pulsar catalog was correlated with the WENSS source catalog. In Sect. 4 the positions of the non-detected pulsars are searched for flux densities above three times the local noise level. Section 5 discusses the remaining non-correlations. Section 6 com- bines the WENSS results with the NVSS correlation stud- ies to determine the spectral indices and compares these with values reported in other literature. Finally, in Sect. 7 the role of scintillation is discussed.