We present the XMM-Newton discovery of X-ray emission from the planetary nebula (PN) A78, the second born-again PN detected in X-rays apart from A30. These two PNe share similar spectral and morphological characteristics: they harbor diffuse soft X-ray emission associated with the interaction between the H-poor ejecta and the current fast stellar wind and a point-like source at the position of the central star (CSPN). We present the spectral analysis of the CSPN, using for the first time an NLTE code for expanding atmospheres that takes line blanketing into account for the UV and optical spectra. The wind abundances are used for the X-ray spectral analysis of the CSPN and the diffuse emission. The X-ray emission from the CSPN in A78 can be modeled by a single C VI emission line, while the X-ray emission from its diffuse component is better described by an optically thin plasma emission model with a temperature of kT = 0.088?keV (T ≈?1.0?×?106 K). We estimate X-ray luminosities in the 0.2-2.0?keV energy band of L X, CSPN = (1.2 ± 0.3)?×?1031 erg s–1 and L X, DIFF = (9.2 ± 2.3)?×?1030 erg s–1 for the CSPN and diffuse components, respectively.
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