The Origin of CAL 83 X-Ray Off-States

The close binary supersoft Xray source CAL 83 is a most promising candidate ofSN Ia progenitors. Our XMMNewton and Chandra observations show a massive whitedwarf, exhibit large amplitude shortterm variations of the Xray flux, andestablish definitively its recurrent nature. We propose now to conduct acampaign with EPIC and OM on XMMNewton to substantiate the correlation betweenXray and optical variations on a short, medium, and longterm basis. Thiscampaign will trace the physical relation between the accretion disk and thewhite dwarf, and will discriminate between several models explaining the originof CAL 83 offstates. XMMNewton data will offer unique and timely insights intoaccretion and unstable nuclear burning during the last evolution stages of SN Ia progenitors. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]