Detecting the orbital period decay of HMCnc: G.W. emission vs magnetic stresses

HMCnc is a system hosting two white dwarfs and has the shortest known orbital period (321s). The Xray monitoring of this unique source over the last 16 years, made it possible to assess that the modulation is steadly decreasing at about 1ms/yr. Two competing scenarios have been suggested: the direct impact model, involving matter accretion, and the unipolar inductor, which considers the WDs as components of an electric circuit. In the former the orbital decay is expected to be ruled by GW emission only with a second period derivative of <1E7s/yr^2, while in the latter magnetic stresses produce a larger component. The additional pointing will allow us to achieve a sensitivity of 8E8 s/yr^2, providing the way of undertanding the nature of HMCnc. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]