X-ray Observations of Recurrent Nova U Scorpii 2010 with Suzaku
Abstract
We report the result of an eclipse-induced X-ray spectroscopy in the outburst of the recurrent nova U Scorpii 2010 using the Suzaku observatory. Nova explosions occur in an accreting binary system composed of a white dwarf and a late-type dwarf or giant companion. When the amount of accreted material reaches a critical mass, a thermonuclear runaway due to hydrogen fusion occurs on the white dwarf surface. Most novae are found once from an object, while only some sources are known to show such outbursts recurrently, thus are called recurrent novae. Recurrent novae provide important clues to unveil the nature of an explosion, as they allow multiple visits for us in both outburst and quiescent states.
U Scorpii is an eclipsing binary system causing novae. The tenth eruption in history was discovered on 2010 January 28.4385 UT (Schaefer et al. 2010). Three target-of-opportunity observations were conducted 9, 12, and 15 days after the outburst with the Suzaku X-ray observatory, yielding high signal-to-noise ratio light curves and spectra using the X-ray Imaging Spectrometer. In the light curves, shallow dips were found due to the coincidence with an optical eclipse. We thus constructed time-sliced spectra to compare fluxes between the different orbital phases, and fitted the spectra with simple models. As a result, the flux in the 0.2--1.0 keV band during the eclipse is about 90% of that in the period immediately before and after the eclipse. This strongly suggests that the emitting region of the soft X-rays is enough large comparable with the binary system. In addition, a spectral shape changed in the period of eclipse, where the energies of dominant emission features appear shifted toward higher energies in the soft band spectra during an eclipse. We present the results and discuss their implications for understanding the nature of nova explosions.- Publication:
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AAS/High Energy Astrophysics Division #12
- Pub Date:
- September 2011
- Bibcode:
- 2011HEAD...12.0303T