Intrinsic variability and field statistics for pulsars B1641-45 and B0950+08

Abstract

The ‘burstiness’ and time variability of pulsars B1641–45 and B0950+08 are investigated by calculating and fitting the field statistics as a function of pulse phase. Pulsar B1641–45 has a simple average profile with minimal evidence for microstructure, while B0950+08 has a complicated pulse profile with strong microstructure and multiple active components. Detailed fitting shows that the primary emission from both pulsars corresponds to lognormal statistics, consistent with stochastic growth theory (SGT) and implying the radiation is generated by a linear micro-instability (either directly or via linear mode conversion). Evidence exists for multiple emission components, with the lognormal parameters and overall field statistics varying with phase. A Gaussian-distributed secondary component for both pulsars, which increases towards the peak in the average profile, may be the result of scattering by density irregularities or multiple superposed subsources. Weak evidence exists for B0950+08 that a non-linear decay process limits the highest fields in a restricted phase domain. Non-linear processes (e.g. modulational instability and wave collapse) and self-organized criticality (SOC), which typically yield power-law statistics, are viable only under stringent conditions: suitably ensemble averaged they must yield lognormal statistics. These conclusions are very similar to those for the Vela pulsar (B0833–45), suggesting they are applicable to many pulsars. Giant micropulses, precursor and diffuse emissions are identified for B0950+08. They are distinguished from each other and the normal pulsar emission by changes with phase bin of the functional form of the field statistics and the rarity and phase localization of signals. This brings to four the number of pulsars with giant micropulses, all with very similar characteristics: their statistics are most consistent with non-linear wave collapse. Precursor emissions are best interpreted in terms of local enhancements of the normal pulsar emission, while interpretations for diffuse emissions are poorly constrained. The strongly similar field statistics for normal pulsar emission and giant micropulses for the Vela pulsar (B0833–45), B1641–45 and B0950+08 suggest that these properties and their theoretical implications are widely applicable to pulsars.