Can runaway O-star bow shocks accelerate particles ?

Séminaire IPAG de Thierry Montmerle (IAP), vendredi 11 octobre 2019 à 9h30, IPAG seminar room

It is well known that supernova remnants (SNR) can accelerate particles. While indirect evidence for acceleration of protons is found in the gamma-ray domain when SNR shocks interact with nearby molecular clouds (pi-0 devay), direct evidence for electron acceleration is found from radio and X-ray observations (synchrotron emission). But SNR are not the only source of shock waves in the Galaxy : the so-called "runaway stars", resulting mainly from ejection from a close binary system or a tight cluster, are known to travel at supersonic velocities (up to 100-200 km/s) across the ISM, thus can be potential sites of particle acceleration as well. Evidence for these new "accelerators" was presented a decade ago for two massive runaway stars, but in spite of many searches in the radio, X-ray and gamma-ray domains since then, no further evidence was found.
We revisit the situation, in particular in the well-publicized case of AE Aur (ejected from the Orion association), by presenting new X-ray (Chandra) and radio (EVLA archive) results. We conclude by theoretical considerations explaining the general lack of evidence for particle acceleration by runaway stars so far.