2020MNRAS.494.3784T

The Advanced CCD Imaging Spectrometer (ACIS-S) camera on board the Chandra X-ray Observatory has been used to discover a hot bubble in the planetary nebula (PN) IC 4593, 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 arcsec 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 T_X ≃ 1.7 x 10⁶ K), electron density n_e ≃ 15 cm^–3, and intrinsic X-ray luminosity in the 0.3-1.5 keV energy range L_X = 3.4 x 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 was the case, its estimated X-ray luminosity would be L_X, CSPN_ = 7 x 10²⁹ erg s^–1, fulfilling the log(L_X, CSPN_/Lbol_) ≃ -7 relation for self-shocking winds in hot stars. The X-ray detection of the CSPN helps explain the presence of high-ionization species detected in the ultraviolet spectra as predicted by stellar atmosphere models.