Study of emission from the bow shocks of runaway massive stars at radio frequencies

Bow shocks from runaway massive stars can accelerate particles up to relativistic energies, making them excellent laboratories for studying different types of emission and their interaction with the interstellar medium those stars are passing through. Not many studies have been done in the radio frequencies regarding the thermal and non-thermal emission of bow shocks from runaway massive stars. The pioneering study made by Benaglia et al. 2010, where BD+43 3654 was successfully observed with the Very Large Array at 1.42 and 4.86 GHz, reignated the need for further investigation of bow shocks in the radio frequencies, as traces of both thermal and non-thermal emission were found. Following their example, we repeated the experiment in higher radio frequencies of 4--12 GHz to determine the nature of the emission of BD+43 3654 even further (Moutzouri et al. 2022). In addition, we observed, at the same frequencies, a sample of 23 more sources that were found to be bow shock candidates (e.g. Kobulnicky et al. 2016), in order to compare our findings with the BD+43 3654 and establish whether or not non-thermal emission is common in such sources and in what way. What is more, we developed 3D simulations of the stellar wind of massive runaway stars using Magnetohydrodynamics and the PhotoIonization of Nebula (PION) code. We compare our results with previous 2D Hydrodynamic simulations (Green et al. 2019) as well as X-ray observations and their synthetic counterpart (Green et al. 2022). In this work, we present our findings in detail.