Multi-wavelength and Polarisation Studies of Pulsars: the Crab, Vela, and PSR J0205+6449

Abstract

This thesis outlines the findings of a multi-wavelength and polarimetric study of a number of rotation-powered pulsars. Polarisation studies of pulsars are just one example of obtaining insight into the geometry of their emission regions. Such measurements provide observational constraints on the various theoretical models of the pulsar emission mechanism. Hence, it is possible to limit these competing models and find the model that best matches observations. A comparison of the optical light curves to the radio, X-ray, and gamma-ray ones is also important to locate diff erent emission regions in the neutron star magnetosphere. The phase-averaged optical linear polarisation of the Crab nebula and pulsar was measured using observations from the HST/ACS. These findings were then compared to the results of hard-X-ray/soft-gamma -ray polarisation observations of the system using INTEGRAL/IBIS. In both cases it was found that the polarisation position angle (PA) of the pulsar is aligned with its proper-motion and spin-axis. The optical polarisation of the entire inner nebula was mapped out and the polarisation of the inner synchrotron knot and wisps were determined. From this analysis, the knot has been confirmed as the source of the highly polarised o ff-pulse emission seen in phase-resolved studies in the optical and gamma-ray bands. No variation, at the 95% signi cance level, was found in the polarisation of the sources over the period of the HST/ACS observations. The optical linear polarisation of the Vela pulsar was also studied using the HST/ACS. As in the case of the Crab, it was found that the PA of the pulsar is aligned with its proper-motion and spin-axis. Another aim was to search for the optical counterparts to pulsars detected at other wavelengths. To this extent, we used ground-based observations using facilities such as WHT, GTC, INT, and TNG.We used VLT data to search for the optical counterparts to two pulsars, PSR J1357-6429 and PSR J1048-5832, both of which are radio pulsars that have been detected by Fermi. Unfortunately, the optical counterparts of these pulsars were not detected. However, a plausible optical counterpart to one particular pulsar, PSR J0205+6449, was detected using archival observations from Gemini-North. It is located at the centre of the 3C58 pulsar wind nebula (PWN). It has an optical spectral energy distribution (SED) that is pulsar like, with a power law index and FO = 1.9 +/-0.5, and a visual magnitude, i' = 25.5, this is consistent with that estimated via its -ray luminosity (2.63 x 10^34 erg s^-1, F = 1.75+/- 0.68 10^-11 erg cm^2 s^-1) and distance ( 3 kpc) (Abdo et al. 2012).