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Abstract:

The cosmic-ray flux of positrons is measured with high precision by the space-borne particle spectrometer AMS-02. A central open question is the origin of the positron flux above 10 GeV, which exceeds predictions for secondary production by cosmic-ray interactions with the interstellar medium. One leading explanation is that pulsars contribute significantly to this excess, a hypothesis strongly supported by observations of degree-scale TeV gamma-ray halos around several pulsars. These halos, produced by leptons from the pulsar doing inverse Compton scattering with the interstellar radiation fields, provide a powerful tool to study cosmic-ray transport around these sources. These TeV halos appear closely related to X-ray filaments observed around some pulsars, produced by synchrotron emission of the same leptons. In this talk, I will discuss how Galactic pulsars may explain the positron excess, what TeV halos reveal about particle propagation, and how particle-in-cell simulations help interpret these processes.

Luca Orusa is a postdoctoral researcher at Princeton and Columbia University where he focuses on particle acceleration at shocks and pulsar-related phenomena, including TeV halos, X-ray filaments, and the positron excess in cosmic rays.

The McDonald Institute seminar will be held in Stirling 501. A Zoom link is also available and shared via email by the organizers. Please reach out to admin@mcdonaldinstitute.ca for access.