X-ray Observations of Bow Shocks around Runaway O Stars. The case of $\zeta$ Oph and BD+43$^{\circ}$3654

TL;DR

This study used X-ray observations to investigate non-thermal emissions from bow shocks around runaway stars, finding thermal emission near $$ Oph and questioning previous non-thermal detections for BD+43$^{\u00b0}$3654.

Contribution

First X-ray observational analysis of bow shocks around runaway stars, providing insights into their thermal and non-thermal emission properties.

Findings

No non-thermal X-ray emission detected at bow shocks.

Diffuse thermal emission observed near $$ Oph with plasma temperature ~2 million K.

Results support radiation-hydrodynamic models of bow shock emissions.

Abstract

Non-thermal radiation has been predicted within bow shocks around runaway stars by recent theoretical works. We present X-ray observations towards the runaway stars $\zeta$ Oph (Chandra and Suzaku) and BD+43$^{\circ}$3654 (XMM-Newton) to search for the presence of non-thermal X-ray emission. We found no evidence of non-thermal emission spatially coincident with the bow shocks, nonetheless, diffuse emission is detected in the vicinity of $\zeta$ Oph. After a careful analysis of its spectral characteristics we conclude that this emission has a thermal nature with a plasma temperature of $T \approx 2 \times10^{6}$ K. The cometary shape of this emission seems to be in line with recent predictions of radiation-hydrodynamic models of runaway stars. The case of BD+43$^{\circ}$3654 is puzzling as non-thermal emission has been reported in a previous work for this source.