X-ray observations of pulsar wind nebulae: The nature of pulsar winds and their environment
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Date
2020-03-31
Authors
Guest, Benson
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Abstract
Pulsar wind nebulae (PWNe) are non-thermal bubbles blown by the relativistic winds of rapidly rotating neutron stars. They are formed in the cavity evacuated by the explosion of a core collapse supernova, and depending on their evolutionary stage may appear as a region of hard X-ray emission within a shell of million degree gas, or be the only visible remains of the cataclysmic event. With deep observations and spatially resolved X-ray spectroscopy, we probe the environment surrounding PWNe of different ages to search for the missing emission predicted from shock heated gas. We examine the properties of the relativistic winds and compare our results with diffusion models and hydrodynamic simulations. In the process of creating consistent spectral maps of PWNe we discover variability in archival Chandra data, opening a new window for observations and theory to explore. We present the deepest Chandra study of G21.5-0.9, finding faint thermal emission embedded in the primarily non-thermal limb-brightened shell. In analysing the synchrotron emission from the PWN, we find an adequate fit with a spatially averaged diffusion model to describe the transport of the wind through the nebula.
Unlike the limb-brightened shell previously revealed in G21.5-0.9 with sufficient observation time, the missing shell in CTB 87 remains hidden despite a deep XMM-Newton observation. We constrain the ambient density and favour expansion into a low density bubble. We attribute the morphology to an interaction of the wind with a reverse shock due to the motion of the pulsar within a ~20 kyr old remnant. We present the first X-ray spectral map of this remnant, and find a good agreement with a simulated map. While merging or simultaneously fitting observations separated by extended periods of time will improve statistics, it may also hide unknown variability. We discover significant spectral variability in G21.5-0.9, 3C58, and Kes 75, and marginal evidence of variability in G11.2-0.3 and G54.1+0.3 to be confirmed with future observations.
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Astrophysics, Astronomy