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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.
Pulsar wind nebulae (PWNe), nebulae harbouring a rotation-powered neutron star that was born in a supernova, provide opportunities to study highly relativistic pulsar winds and their interaction with the surrounding medium. Particularly interesting are PWNe that do not show any sign of the expected surrounding SNR shell and were thought to be born in subenergetic explosions or with unusual progenitors. The detection of a shell around one such PWN suggested that shells are indeed produced but may be faint due to unseen shocked ejecta, a low density environment, and/or a young age that has not yet allowed the shell to brighten and become visible. Here, by using observational X-ray data from modern telescopes with excellent spatial and energy resolution (Chandra and XMM-Newton), we target PWNe that do not have prominent SNR shells, and are known to be in varied environments, to further explore the characteristics of this growing, but poorly explored, class of PWNe. By combining imaging and spectroscopic results, we study the morphology of the PWNe, search for thermal emission from shock-heated material, investigate the energetics of the nebulae, and search for candidates for the neutron stars powering the nebulae. We find that while the faint shell surrounding G21.5-0.9 can be explained as a young PWN evolving in a low density medium, CTB 87 (G74.9+1.2) appears to be in an advanced stage of evolution, and G63.7+1.1 appears to be both in an advanced stage of evolution and in a dense environment. By performing spatially resolved spectroscopy, we have shown how the spectral characteristics vary across the PWNe, and note that more data will place better constraints on possible thermal emission in these remnants. The imaging portion of these studies has revealed intriguing large-scale morphologies for CTB 87 and G63.7+1.1, as well as a torus-jet structure in CTB 87 and neutron star candidates in both CTB 87 and G63.7+1.1. We conclude that both CTB 87 and G63.7+1.1 are likely interacting with the supernova remnant reverse shock, and CTB 87 may be additionally influenced by the motion of its neutron star.
I analyze filament G359.97-0.038 by incorporating broad-band morphological and spectral data from radio (5.5 and 8.3 GHz) and X-ray data with NuSTAR data. I conclude that it is not a PWN but more likely the result of an interaction between the Sgr A East remnant and the nearby molecular cloud. Lastly I observe the filament G0.13-0.11, likely a PWN elongated by the ram pressure from the nearby Radio Arc.
In view of the current and forthcoming observational data on pulsar wind nebulae, this book offers an assessment of the theoretical state of the art of modelling them. The expert authors also review the observational status of the field and provide an outlook for future developments. During the last few years, significant progress on the study of pulsar wind nebulae (PWNe) has been attained both from a theoretical and an observational perspective, perhaps focusing on the closest, more energetic, and best studied nebula: the Crab, which appears in the cover. Now, the number of TeV detected PWNe is similar to the number of characterized nebulae observed at other frequencies over decades of observations. And in just a few years, the Cherenkov Telescope Array will increase this number to several hundreds, actually providing an essentially complete account of TeV emitting PWNe in the Galaxy. At the other end of the multi-frequency spectrum, the SKA and its pathfinder instruments, will reveal thousands of new pulsars, and map in exquisite detail the radiation surrounding them for several hundreds of nebulae. By carefully reviewing the state of the art in pulsar nebula research this book prepares scientists and PhD students for future work and progress in the field.
Pulsars -- Pulsar wind nebulae -- Supernova remnants -- Gamma rays -- Non-thermal radiation mechanisms -- Neutron stars -- X-rays -- Multi-wavelength astronomy -- Astroparticle physics -- Numerical methods.
Energetic particles streaming out from rapidly spinning neutron stars radiate across the electromagnetic spectrum, creating a pulsar wind nebula (PWN). Many PWNe are spatially resolved in the radio, X-ray, and even gamma-ray wavebands, and thereby provide an excellent laboratory to study not only pulsar winds and dynamics, but also shock processes, magnetic field evolution, and particle transport. Single-zone spectral energy distribution (SED) models have long been used to study the global properties of PWNe, but to fully take advantage of high spatial resolution data one must move beyond these simple models. Supported by multiple X-ray PWN observations, we describe multi-zone time-dependent SED model fitting, with particular emphasis on the spatial variations within nebulae. The SED model constrains the wind velocity profile, magnetic field profile, age and spin-down history of the central pulsar, and the PWN injection spectrum. These constraints are of great value to the study of the gamma-ray pulsar population, and to investigations of particle acceleration and the cosmic ray spectrum. The large size of many PWNe in the very high energy gamma-ray (TeV) regime is indicative of significant particle transport over the pulsar lifetime, and in the case study of HESS J1825-137 we find that rapid diffusion of high energy particles is required to match the multi-wavelength data.