087259

We propose joint observations with Chandra and XMM-Newton of the super Chandrasekhar mass white dwarf merger product Cas J005311. A first pilot XMM-Newton observation revealed an astonishingly high X-ray luminosity of Cas J005311 and its remarkable nebula which is strongly enriched in Neand Mg. The proposed ACIS-I observations will map the nebula and probe chemical gradients across it comma as necessary to unravel the evolutionary history of the merger. We will search for X-ray pulsations to test magnetic fields and rotation of Cas J005311. Jointly comma Chandra and XMM-Newton will reveal the physical mechanisms powering the X-rays from the central star and the nebula.