Collaborative Research: Unidentified Galactic TeV Sources: Neutron Star Connection

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Dr. Kargaltsev (University of Florida) and Dr. Pavlov (Pennsylvania State University) will undertake a systematic analysis of the multiwavelength properties of a new population of unidentified extended TeV (teraelectron volt) sources recently discovered by the HESS (High Energy Stereoscopic System) gamma-ray observatory. TeV emission is a tracer of the cosmic ray acceleration sites in objects such as supernova remnants, high-mass binaries, and young, magnetized neutron stars. Therefore, the study of TeV sources allows one to learn not only about these objects but also about the most energetic processes in our Galaxy. In the framework of this project archival X-ray, infrared, optical and radio data will be collected and reduced, and the multiwavelength properties of each of the 35-40 extended TeV sources will be analyzed. Particular attention will be paid to the environments of these TeV sources because the presence of dense clouds or locally enhanced infrared radiation background can be intimately linked to the TeV properties and can provide a key to understanding the nature of the TeV source. Once put together as a convenient public on-line database, the multiwavelength data will facilitate meaningful tests of the emission models. In particular, for a large subset of unidentified TeV sources that are found near young energetic pulsars, the connection between the two will be tested by fitting their multiwavelength properties to the pulsar wind models developed as part of the project. The multi-zone models will trace the evolution of the pulsar wind properties out to large distances from the pulsar, taking into account the radiative and expansion losses and allowing for both leptonic and hadronic wind components. The model output will include the spatially-resolved and integrated multiwavelength spectra for pulsar wind nebulae (PWNe) of various ages and energetics, which will be compared with the data collected. By fitting the models to the data, it will be possible to infer the properties of the relic pulsar winds (e.g., energetics, particle density, magnetization) and check whether or not such winds can be produced by neighboring pulsars. The connection would imply that (1) most of the extended galactic TeV sources are indeed relic PWNe even though in many cases no pulsar has been identified yet, (2) relic PWNe are most prominent in gamma-rays and can have a much larger spatial extent than previously thought based on observations at lower frequencies, and (3) pulsars and PWNe are efficient factories of cosmic rays that influence the structure and evolution of our Galaxy and its constituents. The project will naturally integrate the fundamental research and education by involving graduate and undergraduate students at two universities in the cutting-edge, multiwavelength research in high-energy astrophysics. It will also serve as a start-up for a High Energy Astrophysics group at the Department of Astronomy in the University of Florida. The project will provide a unique on-line database of multi-wavelength properties of newly discovered TeV sources, which will be useful for the broad astrophysical community. The results of the project will be presented to the general public through popular lectures and image exhibitions at the outreach events held at both universities (e.g., the Penn State In-Service Workshops in Astronomy for middle- and high-school science teachers).