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Observations of TeV gamma rays enable investigation of extreme, high-energy astrophysical environments. Of the identied TeV sources within the Galaxy, the largest number are pulsar wind nebulae (PWNe), formed by the shocked wind of relativistic leptons emitted by a pulsar and conned by the surrounding medium, with broadband emission arising from synchrotron and inverse Compton mechanisms. PWNe exhibit a wide range of morphologies as a result of a complex evolution, depending on the properties of the parent pulsar and conning medium. This work describes the discovery of gamma-ray emission from the PWN within the supernova remnant (SNR) CTA 1 by the VERITAS telescope array. By imaging the Cherenkov light from gamma-ray induced atmospheric showers, VERITAS revealed an extended TeV nebula surrounding the pulsar PSR J0007+7303. Comparison of the observed properties with known PWN, along with a one-zone model, suggests a recent interaction with the SNR reverse shock and allows for an estimate of the average nebular magnetic eld strength. No signicant energy-dependent morphology is seen. A multi-zone, cylindrically symmetric model is created to investigate tailed-out PWN morphology, accounting for multiple mechanisms for particle transport and cooling. The model is applied to the CTA 1 data, with a limited search of the parameter space performed to t the observed spectrum and extent. Possible improvements to the model performance are discussed.
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.