The born-again planetary nebula A78: an X-ray twin of A30

TL;DR

This paper reports the discovery of X-ray emission from the born-again planetary nebula A78, revealing similarities with A30, and provides detailed spectral analysis of the central star and diffuse emission using advanced modeling techniques.

Contribution

First X-ray spectral analysis of A78's CSPN using NLTE expanding atmosphere models, and comparison with A30 to understand born-again planetary nebulae.

Findings

X-ray emission detected from both CSPN and diffuse nebula in A78.

Diffuse emission characterized by a plasma temperature of approximately 1 million Kelvin.

X-ray luminosities estimated for the CSPN and diffuse components.

Abstract

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 a NLTE code for expanding atmospheres which 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 temperature $kT$=0.088 keV ($T\approx$1.0$\times$10${^6}$ K). We estimate X-ray luminosities in the 0.2--2.0 keV energy band of $L_{\mathrm{X,CSPN}}$=(1.2$\pm$0.3)$\times$10$^{31}$ erg~s$^{-1}$ and $L_{\mathrm{X,DIFF}}$=(9.2$\pm$2.3)$\times$10$^{30}$ erg~s$^{-1}$ for the CSPN and diffuse components, respectively.