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A soft X-ray halo around SU UMa

Abstract

The dwarf nova SU UMa was observed with the imaging proportional counter (IPC) detector1 on the Einstein X-Ray Observatory on 4 October 1979 at 4 h UT for 3,000 s. An X-ray source was detected at the position of the star. It had a flux of 1.3 × 10−11 erg cm−2 s−1 (0.6 counts per s) in the 0.1–4.5 keV energy range of the IPC, assuming a spectral temperature of 10 keV (ref. 2). In addition, several areas of weaker emission were observed which form a ring that is symmetrically disposed about the position of the dwarf nova. This latter emission is detected only at energies below 0.7 keV. We discuss here the possibility that it arises in material that has been ejected from the star in a nova-like event.

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