University of Minnesota
School of Physics & Astronomy

MN Institute for Astrophysics Colloquium

Friday, September 27th 2019
2:30 pm:
Speaker: Patrick Wilcox, University of Minnesota
Subject: Observation of Pulsar Wind Nebula DA 495 at Very High Energies Using VERITAS

The constant flux of cosmic rays that bombard Earth from within our own galaxy are understood to come from both shell-type supernova remnants and pulsar wind nebulae (PWNe). Since we cannot directly trace the charged cosmic rays to their source, we must rely on multiwavelength study of these objects to help us understand the conditions within. The generation of very energetic particles also leads to very energetic emission processes, and as such, gamma-ray emission is key to understanding and identifying the types of cosmic rays that are generated by these extreme astrophysical laboratories; studies which cannot be done at lower-energies alone. DA 495 was recently identified as a TeV source and was observed for about 70 hours with the Very Energetic Radiation Imaging Telescope Array System (VERITAS), a TeV gamma-ray observatory located in Southern Arizona. Radio observations of DA 495 indicate that it is nearby (~1kpc) "Crab-like" PWN with unusually strong (~mG) magnetic fields throughout the nebula. Even though PWN are often TeV gamma-ray sources, the strong magnetic fields made it an unlikely candidate for detection at TeV energies since it would be expected that the highest energy particles would quickly “burn off” in the strong fields and be unable to generate TeV gamma rays through inverse-Compton scattering. For this study, TeV results are combined with radio and X-ray spectral information to allow for detailed astrophysical modeling of the region that allows for both leptonic and hadronic emission scenarios to be evaluated. Hadronic scenarios instill doubt on the pure PWN interpretation and favor a previously undetected shell-type remnant being present.

In this colloquium, I will discuss how TeV gamma rays are detected from the ground using VERITAS and how we use can use the results to model the particle populations at the source of cosmic ray generating objects within our galaxy. Further, I will put DA 495 into context with its over 50 year observational history, and show how the mystery of the strong magnetic fields deepens with the observations made by VERITAS and how they could be solved using future gamma-ray observatories.

Faculty Host: Lucy Fortson

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