Chandra observations of nova KT Eridani in outburst

Abstract

ABSTRACT We analyze 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 ≃5 × 1037 erg s−1, it is likely that we observed only up to ≃40 per cent of the surface of the white dwarf, which may have been partially hidden by clumpy ejecta. Our fit with atmospheric models indicates a massive white dwarf in the 1.15–1.25 M⊙ 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 ≃35-s oscillation that was reported earlier was detected in the last observation done on day 159 of the outburst.