S. Ohm

Escape from Vela X

While the Vela pulsar and its associated nebula are often considered as the archetype of a system powered by a {approx} 10{sup 4} year old isolated neutron star, many features of the spectral energy distribution of this pulsar wind nebula are both puzzling and unusual. Here we develop a model that for the first time relates the main structures in the system, the extended radio nebula (ERN) and the X-ray cocoon through continuous injection of particles with a fixed spectral shape. We argue that diffusive escape of particles from the ERN can explain the steep Fermi-LAT spectrum. In this scenario Vela X should produce a distinct feature in the locally-measured cosmic ray electron spectrum at very high energies. This prediction can be tested in the future using the Cherenkov Telescope Array (CTA). If particles are indeed released early in the evolution of PWNe and can avoid severe adiabatic losses, PWN provide a natural explanation for the rising positron fraction in the local CR spectrum.

Non-thermal emission from pulsar-wind nebulae in starburst galaxies

The recently detected gamma-ray emission from Starburst galaxies is most commonly considered to be diffuse emission arising from strong interactions of accelerated cosmic rays. Mannheim et al. (2012), however, have argued that a population of individual pulsar-wind nebulae (PWNe) could be responsible for the detected TeV emission. Here we show that the Starburst environment plays a critical role in the TeV emission from Starburst PWNe, and perform the first detailed calculations for this scenario. Our approach is based on the measured star-formation rates in the Starburst nuclei of NGC 253 and M 82, assumed pulsar birth periods and a simple model for the injection of non-thermal particles. The two-zone model applied here takes into account the high far-infrared radiation field, and different densities and magnetic fields in the PWNe and the Starburst regions, as well as particle escape. We confirm that PWNe can make a significant contribution to the TeV fluxes, provided that the injection spectrum of particles is rather hard and that the average pulsar birth period is rather short (~35 ms). The PWN contribution should lead to a distinct spectral feature which can be probed by future instruments such as CTA.

ESCAPE FROM VELA X

While the Vela pulsar and its associated nebula are often considered as the archetype of a system powered by a {approx} 10{sup 4} year old isolated neutron star, many features of the spectral energy distribution of this pulsar wind nebula are both puzzling and unusual. Here we develop a model that for the first time relates the main structures in the system, the extended radio nebula (ERN) and the X-ray cocoon through continuous injection of particles with a fixed spectral shape. We argue that diffusive escape of particles from the ERN can explain the steep Fermi-LAT spectrum. In this scenario Vela X should produce a distinct feature in the locally-measured cosmic ray electron spectrum at very high energies. This prediction can be tested in the future using the Cherenkov Telescope Array (CTA). If particles are indeed released early in the evolution of PWNe and can avoid severe adiabatic losses, PWN provide a natural explanation for the rising positron fraction in the local CR spectrum.