Abstract
We report the Suzaku detection of the earliest X-ray eclipse seen in the recurrent nova U Scorpii 2010. A target-of-opportunity observation 15 days after the outburst found a 27+/-5% dimming in the 0.2-1.0 keV energy band at the predicted center of an eclipse. In comparison with the X-ray eclipse depths seen at two later epochs by XMM-Newton, the source region shrank by about 10-20% between days 15 and 35 after the outburst. The X-ray eclipses appear to be deeper than or similar to contemporaneous optical eclipses, suggesting the X-ray and optical source region extents are comparable on day 15. We raise the possibility of the energy dependency in the photon escape regions, and that this would be a result of the supersoft X-ray opacity being higher than the Thomson scattering optical opacity at the photosphere due to bound-free transitions in abundant metals that are not fully ionized. Assuming a spherically symmetric explosion model, we constrain the mass-loss rate as a function of time. For a ratio of actual to Thomson opacity of 10-100 in supersoft X-rays, we find a total ejecta mass of about 10^{-7}-10^{-6} M_{\odot}.
Highlights
A nova explosion occurs in an accreting binary system comprising a white dwarf and a red dwarf companion
In this Letter, we investigate the development of the supersoft source (SSS) region for the eclipsing recurrent nova U Scorpii 2010
Through comparison with a 30%–50% dimming in X-ray eclipses at two subsequent epochs observed by XMM-Newton (Ness et al 2012), we find that the X-ray source shrank with time
Summary
A nova explosion occurs in an accreting binary system comprising a white dwarf and a red dwarf companion. While all novae are thought to be binaries, and some fraction will inevitably be eclipsing, the utilization of eclipses during an explosion as a powerful and direct probe of the emitting geometry has not yet been fully realized Observing such a phenomenon is difficult for most novae because they spend many thousands of years between outbursts and are observed only once, with no prior information on the nature of the progenitor. Through comparison with a 30%–50% dimming in X-ray eclipses at two subsequent epochs observed by XMM-Newton (Ness et al 2012), we find that the X-ray source shrank with time. A 30%–50% dimming in X-rays during expected times of eclipse were found by XMM-Newton on days 23 and 35 (Ness et al 2012), suggesting that the size of the X-ray source was comparable to the optical and orbital sizes. The X-ray light curve on day 23 exhibited oscillations, which Ness et al (2012) interpreted in terms of a reforming accretion disk
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