Heidelberg 2022 – scientific programme

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T: Fachverband Teilchenphysik

T 73: Cosmic Ray 4

T 73.8: Talk

Wednesday, March 23, 2022, 18:00–18:15, T-H32

Can superbubbles accelerate PeV protons? — •Thibault Vieu and Brian Reville — Max-Planck-Institut für Kernphysik, Postfach 10 39 80, 69029 Heidelberg, Germany

The local cosmic-ray spectrum and recent gamma-ray observations suggest the existence of Galactic sources able to accelerate protons up to at least several PeV. These sources are still to be identified. Standard scenarios of particle acceleration at isolated supernova remnants struggle to reach PeV bands. However, most massive stars are not isolated but clustered. Clustered stars heat their surrounding medium, which inflates a cavity called a superbubble. In the superbubble, the stellar feedback creates multiple shocks, a turbulent environment, and amplifies the magnetic fields. These are ideal conditions for particle acceleration and superbubbles have long been thought to accelerate PeV protons. While it is indeed expected that an extended and strongly turbulent source could accelerate protons up to tens of PeV, it is yet unclear how the different acceleration processes can act collectively in superbubbles.

In this work we estimate the maximum energy of protons accelerated in superbubbles, considering various detailed scenarios. We derive under which circumstances PeV protons are expected. The forward shock of the superbubble barely accelerates particles up to 100 TeV. Supernova remnants expanding in the interior, or the collective wind termination shock which forms around a compact cluster, barely accelerate PeV protons. We show that protons of several PeV are only expected within loose and extended stellar clusters.