Observations of Bow Shocks of Runaway Stars with H.E.S.S

TL;DR

This study systematically searches for very-high-energy gamma-ray emission from bow shocks of runaway stars using H.E.S.S. data, finding no significant emission but setting upper limits to constrain theoretical models.

Contribution

It is the first systematic search for TeV emission from bow shocks of runaway stars using archival H.E.S.S. data.

Findings

No significant gamma-ray emission detected from any candidate.

Upper limits established constrain non-thermal emission models.

Results inform future observational strategies and theoretical developments.

Abstract

Runaway stars form bow shocks by sweeping up interstellar matter in their direction of motion. Theoretical models predict a spectrally wide non-thermal component reaching up to gamma-ray energies at a flux level detectable with current instruments. They were motivated by a detection of non-thermal radio emission from the bow shock of BD$+43^\circ3654$ and a possible detection of non-thermal X-rays from AE Aurigae. A search in the high-energy regime using data from \textit{Fermi}-LAT resulted in flux upper limits for 27 candidates listed in the first E-BOSS catalogue. We perform the first systematic search for TeV emission from bow shocks of runaway stars. Using all available archival H.E.S.S. I data we search for very-high-energy gamma-ray emission at the positions of bow shock candidates listed in the second E-BOSS catalogue. This catalogue comprises 73 bow shock candidates, 32 of which have been observed with the H.E.S.S. telescopes. None of the observed bow shock candidates shows significant emission in the H.E.S.S. energy range. The resulting upper limits are used to constrain current models for non-thermal emission from these objects.