Chandra observations of nova KT Eridani in outburst

TL;DR

This study analyzes four Chandra X-ray observations of nova KT Eri during its supersoft phase, revealing complex spectral features, evidence of a massive white dwarf, and persistent oscillations, providing insights into nova outburst mechanisms.

Contribution

First detailed X-ray spectral analysis of KT Eri during outburst, identifying white dwarf mass, ejecta properties, and oscillation detection.

Findings

White dwarf mass estimated at 1.15-1.25 M_sun

Spectral features indicate complex ejecta with photoionized and shock components

Detection of 35 s oscillation in late outburst stage

Abstract

We analyse here four observations of nova KT Eri (Nova Eri 2009) done with the Chandra High Resolution Camera Spectrometer (HRC-S) and the Low Energy Transmission Grating (LETG) in 2010, from day 71 until day 159 after the optical maximum, in the luminous supersoft X-ray phase. The spectrum presents many absorption features with a large range of velocity, from a few hundred km s$^{-1}$ to 3100 km s$^{-1}$ in the same observation, and a few prominent emission features, generally redshifted by more than 2000 km s$^{-1}$. Although the uncertainty on the distance and the WD luminosity from the approximate fit do not let us rule out a larger absolute luminosity than our best estimate of $\simeq 5 \times 10^{37}$ erg s$^{-1}$, it is likely that we observed only up to $\simeq$40% of the surface of the white dwarf, which may have been partially hidden by clumpy ejecta. Our fit with atmospheric models indicate a massive white dwarf in the 1.15-1.25 M$_\odot$ range. A thermal spectrum originating in the ejecta appears to be superimposed on the white dwarf spectrum. It is complex, has more than one component and may be due to a mixture of photoionized and shock ionized outflowing material. We confirm that the $\simeq$35 s oscillation that was reported earlier, was detected in the last observation, done on day 159 of the outburst.