Probing cosmic ray escape from \eta\ Carinae

Abstract

The binary stellar system $\eta$ Carinae is one of very few established astrophysical hadron accelerators. It seems likely that at least some fraction of the accelerated particles escape from the system. Copious target material for hadronic interactions and associated $\gamma$-ray emission exists on a wide range of spatial scales outside the binary system. This material creates a unique opportunity to trace the propagation of particles into the interstellar medium. Here we analyse $\gamma$-ray data from Fermi-LAT of $\eta$ Carinae and surrounding molecular clouds and investigate the many different scales on which escaping particles may interact and produce $\gamma$-rays. We find that interactions of escaping cosmic rays from $\eta$ Carinae in the wind region and the Homunculus Nebula could produce a significant contribution to the $\gamma$-ray emission associated with the system. Furthermore, we detect excess emission from the surrounding molecular clouds. The derived radial cosmic-ray excess profile is consistent with a steady injection of cosmic rays by a central source. However, this would require a higher flux of escaping cosmic rays from $\eta$ Carinae than provided by our model. Therefore it is likely that additional cosmic ray sources contribute to the hadronic $\gamma$-ray emission from the clouds.