092075

The extraordinary symbiotic binary RT Cru which hosts a massive ( and amp amp amp gt 1.25 solar masses) white dwarf (WD) and thus is a serious candidate to be a SNIa progenitor is currently in a new optical/hard X-ray bright state the previous one was detected in 2012 in optical photometry and with Swift/BAT. At that time the accretion rate onto the WD increased but did not reach the value where the accretion disk boundary layer transitions to the optically thick regime. We propose to observe RTvirgulCru with XMM and NuSTAR during the current maximum --an event that is unlikely to repeat within the next ten years -- in order to fully characterize the 0.3-80 keV spectrum during the maximum allowing us to measure the shock temperature and thus the WD mass and the accretion rate through the boundary layer. [truncated! Please see actual data for full text]