Chandra observation of Cepheus A: The diffuse emission of HH 168 resolved

TL;DR

This study uses Chandra X-ray observations to analyze the diffuse X-ray emission in HH 168, revealing internal shocks as the source rather than the bow shock, providing new insights into stellar outflow emissions.

Contribution

First detailed Chandra analysis showing diffuse X-ray emission in HH 168 is caused by internal shocks, challenging previous models focusing on bow shocks.

Findings

Diffuse X-ray emission is from plasma at 0.55 keV.

X-ray emission is on two scales with embedded regions.

Internal shocks excite the X-ray emission, not bow shocks.

Abstract

X-ray emission from massive stellar outflows has been detected in several cases. We present a Chandra observation of HH 168 and show that the soft X-ray emission from a plasma of 0.55 keV within HH 168 is diffuse. The X-ray emission is observed on two different scales: Three individual, yet extended, regions are embedded within a complex of low X-ray surface brightness. Compared to the bow shock the emission is displaced against the outflow direction. We show that there is no significant contribution from young stellar objects (YSOs) and discuss several shock scenarios that can produce the observed signatures. We establish that the X-ray emission of HH 168 is excited by internal shocks in contrast to simple models, which expect the bow shock to be the most X-ray luminous.