Non-thermal emission from Pulsar-Wind Nebulae in Starburst Galaxies

TL;DR

This paper investigates how pulsar-wind nebulae in starburst galaxies contribute to observed gamma-ray emissions, emphasizing the environment's role and providing detailed models to predict their impact on TeV fluxes.

Contribution

It presents the first detailed calculations showing the significant role of starburst environments in PWN TeV emission, considering various physical factors and particle injection spectra.

Findings

PWNe can significantly contribute to TeV gamma-ray fluxes in starburst galaxies.

A hard particle injection spectrum and short pulsar birth periods (~35 ms) are required.

Future observations like CTA can test the predicted spectral features.

Abstract

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.