The Square Kilometre Array (SKA)

Abstract:

We estimate the bispectrum of the Very Small Array data from the compact and extended configuration observations released in 2002 December, and compare our results with those obtained from Gaussian simulations. There is a slight excess of large bispectrum values for two individual fields, but this does not appear when the fields are combined. Given our expected level of residual point sources, we do not expect these to be the source of the discrepancy. Using the compact configuration data, we put an upper limit of 5400 on the value of F NL, the non-linear coupling parameter, at 95 per cent confidence. We test our bispectrum estimator using non-Gaussian simulations with a known bispectrum, and recover the input values.

Abstract:

In most pulsars, the circularly polarized component, Stokes V, is weak in the average pulse profiles. By forming the average profile of |V| from single pulses we can distinguish between pulsars where V is weak in the individual pulses and those where large V of variable handedness is observed from one pulse to the other. We show how |V| profiles depend on the signal-to-noise ratio of V in the single pulses and demonstrate that it is possible to simulate the observed, broad distributions of V by assuming a model where |V| is distributed around a mean value and the handedness of V is permitted to change randomly. The |V| enhanced profiles of 1.3 pulsars are shown, five observed at 1.41 GHz and eight observed at 4.85 GHz, to complement the set in Karastergiou et al. (2003b). It is argued that the degree of circular polarization in the single pulses is related to the orthogonal polarization mode phenomenon and not to the classification of the pulse components as cone or core.