A Study of Dynamical and Emission Variabilities in Pulsars

A Study of Dynamical and Emission Variabilities in Pulsars Andrew D. Seymour Pulsars are rapidly rotating highly magnetized neutron stars thought to have been formed in the core-collapse supernova of massive stars. Ever since their discovery, pulsars have shown complex behaviors. This is certainly true for their emission mechanism, which is still not fully understood. This is primarily because of the abrupt changes that appear in the pulse profile. Recent discoveries have shown that these emission changes effect the spin dynamics, particularly the spin-down rate. This indicates that pulsar emissions are even more complex than previously thought. The goal of this thesis is to apply new analysis techniques to help shed light on the pulsar emission problem. Over the past decade, it has become apparent that a class of ‘bursting pulsars’ exist with the discovery of PSR J1752+2359 and PSR J1938+2213. In these pulsars, a sharp increase in the emission intensity is observed that then tends to systematically drop-off from pulse-to-pulse. We describe the discovery of such a relationship in high-sensitivity observations of the young (characteristic age of 90, 000 yrs) 0.33 s pulsar B0611+22 at both 327 MHz and 1400 MHz with the Arecibo observatory. While it was previously shown that B0611+22 has mode-switching properties, the data presented here show that this pulsar emits bursts with characteristic time-scales of several hundred seconds. At 327 MHz, the pulsar shows steady behavior in one emission mode which is enhanced by bursting emission slightly offset in pulse phase from this steady emission. Contrastingly at 1400 MHz, the two modes appear to behave in a competing operation while still offset in phase. Using a fluctuation spectrum analysis, we also investigate each mode independently for sub-pulse drifting. Neither emission mode (i.e. during bursts or persistent emission) shows the presence of the drifting sub-pulse phenomenon. While further examples of this behavior and studies at different wavelengths are required, it appears that this phenomenon may be quite common among the pulsar population. Until now, PSR J1752+2359 is the only one of the three bursting pulsars that has not been accompanied by a lower energy level normal emission mode. Rather, it has appeared to null between bursting events. We have been able to show through the pulse-energy distribution that PSR J1752+2359 does indeed have a normal mode with a peak flux at 0.17±0.03 mJy with a pulse energy of 1.0±0.1 μJy-s. It is also shown that PSR J1752+2359 presents no evidence for the drifting sub-pulse phenomenon in either emission mode. This is consistent with what has been seen in PSR B0611+22. We also present techniques that searched for chaotic behaviors within the spin dynamics of 17 pulsars. These techniques allow us to re-sample the original spin-down rate estimates without losing structural information, and to search for evidence of a strange attractor within these frequency derivative time series. We demonstrate the effectiveness of our methods by applying them to a component of the Lorenz and Rössler attractors that were sampled with similar cadence to the pulsar time series. Our measurements of correlation dimension and Lyapunov exponent show that the underlying behavior appears to be driven by a strange attractor with approximately three governing non-linear differential equations. This is particularly apparent in the case of PSR B1828−11 where a correlation dimension of 2.06± 0.03 and a Lyapunov exponent of (4.0± 0.3)× 10−4 inverse days were measured. These results provide an additional diagnostic for testing future models of this behavior. Lastly, we introduce future plans to further improve our understanding of the bursting phenomena and spin-down rate changes seen here. Simultaneous observations at different frequencies will help determine how a burst is propagating through different emission regions. Along with this, a recent analogous discovery to bursting implies that bursting events may be accompanied by X-ray changes. Scheduled X-ray observations will soon determine if this is true. As data sets cover even larger amounts of time, the non-linear analysis will improve and can be utilized to test theoretical models. We also present data provided by Andrew Lyne that hints at a connection between bursting and spin-down changes.