Chandra observations of the planetary nebula IC 4593
Abstract
The ACIS-S camera on board the Chandra X-ray Observatory has been used to discover a hot bubble in the planetary nebula (PN) IC4593, the most distant PN detected by Chandra so far. The data are used to study the distribution of the X-ray-emitting gas in IC 4593 and to estimate its physical properties. The hot bubble has a radius of ~2 and is found to be confined inside the optically-bright innermost cavity of IC 4593. The X-ray emission is mostly consistent with that of an optically-thin plasma with temperature kT≈0.15 keV (or TX≈1.7×106 K), electron density ne≈15 cm-3, and intrinsic X-ray luminosity in the 0.3-1.5 keV energy range LX=3.4×1030 erg s-1. A careful analysis of the distribution of hard (E>0.8 keV) photons in IC 4593 suggests the presence of X-ray emission from a point source likely associated with its central star (CSPN). If this were the case, its estimated X-ray luminosity would be LX,CSPN=7×1029 erg s-1, fulfilling the log(LX,CSPN/Lbol)≈-7 relation for self-shocking winds in hot stars. The X-ray detection of the CSPN helps explain the presence of high-ionisation species detected in the UV spectra as predicted by stellar atmosphere models.