AR SCO: THE FIRST WHITE DWARF PULSAR

A RECENT DETECTION OF PULSATIONS WITH THE 1.97 MIN PERIOD MODULATED BY THE BINARY PERIOD OF 3.56 HR IN THE RADIO-IR-OPTICAL-UV SYNCHROTRON EMISSION FROM THE WHITE DWARF (WD) - M-STAR BINARY AR SCO WAS THE FIRST DISCOVERY OF A WD PULSAR POWERED BY WD SPINDOWN. ALTHOUGH IT IS CLEAR THAT THE DETECTED EMISSION IS PRODUCED BY RELATIVISTIC PARTICLES THE ACCELERATION MECHANISM AND THE SITES OF EMISSION REMAIN UNCERTAIN. TO DISTINGUISH BETWEEN DIFFERENT MODELS FOR THE WD-PULSAR - M-STAR BINARY X-RAY OBSERVATIONS ARE PARTICULARLY USEFUL ESPECIALLY AT ENERGIES ABOVE 10 KEV. WE PROPOSE A NUSTAR OBSERVATION SUPPLEMENTED BY A SHORT XMM-NEWTON OBSERVATION TO INVESTIGATE THE X-RAY SPECTRUM AND PULSATIONS OF AR SCO AND INFER A REALISTIC MODEL OF THIS UNIQUE OBJECT.