Chandra observation of U Scorpii

ATel #2451; M. Orio (Istituto Nazionale di Astrofisica, Padova, Italy and University of Wisconsin, USA), Thomas Nelson (NASA-Goddard and University of Maryland Baltimore County, USA), Juan Luna (Center for Astrophysics, USA), Bradley Schaefer (University of Louisiana Baton Rouge, USA), Kim Page, Andy Beardmore and Julian Osborne (University of Leicester, UK)
on 19 Feb 2010; 19:55 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Marina Orio (orio@astro.wisc.edu)

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U Scorpii was observed with the Chandra HRC-S detector and the LETG grating for 23,240 seconds on 2010 February 14 (JD 2455241.98572917 until JD 2455242.27677083) and it was detected with 0.228+-0.015 and 0.241+-0.015 counts/second in the +1 and -1 order respectively. The observation was done outside of the eclipse measured by one of us (B.S.; The beginning of the observation was 2.0472 days after the eclipse). The observed X-ray spectrum is consistent with a component due to a hot white dwarf atmosphere contributing to about 70\% of the flux, and superimposed emission lines contributing to the remaining ~30\% of the flux. The prominent emission lines are all due to nitrogen, especially N VII Lyman alpha and the N VI He-like triplet. The white dwarf atmosphere seems to have a very low C/N ratio and preliminary fits give a temperature 510,000+-80,000 K with N(H)-2x10(^21) cm^(-2). We are unable to constrain the temperature better due to remaining uncertainties in the abundances. The absorption features of the white dwarf atmosphere are blue-shifted by almost 2000 km/s. The observed (absorbed) flux is 2.72x10(-11) erg/cm^2/s, while the absorbed flux in the continuum is 1.82x10(-11) erg/cm^2/s for our best fit atmospheric model.