Fermi Gamma-ray Space Telescope

Investigating the (lack of) gamma-ray emission from superbubbles

Pierrick Martin
(Virginie Slagmolen)


Superbubbles have long been thought as a possible key player in the acceleration of galactic cosmic rays. The many massive stars at their center indeed guarantees the release of large amounts of kinetic energy over relatively short times, hence setting appropriate conditions for efficient shock and/or stochastic acceleration and reacceleration, possibly up to ~PeV energies and beyond. Yet, superbubbles did not show up as a conspicuous source class in the GeV-TeV gamma-ray sky. We aim at assessing whether this paucity can be accounted for from simple assumptions regarding cosmic-ray acceleration and transport. We developed a model for the gamma-ray emission from superbubbles as a result of stochastic release of cosmic rays from supernovae. For a variety of superbubbles and cosmic-ray injection and transport properties, we derived the probability of having gamma-ray emission of a given luminosity and spectrum as a function of superbubble age. We discuss the specific case of superbubble 30 Dor C in the Large Magellanic Cloud, which was claimed to be a TeV-emitting superbubble.