================================================================================= "Nearly aligned magnetic fields and wandering emission regions in accreting millisecond pulsars" Dr. Stratos Boutloukos University of Maryland ================================================================================= When: Monday, 21st of December of 2009 at 14:00 pm Where: 2nd Floor Seminar Room ================================================================================= Abstract: Twelve accretion-powered millisecond pulsars are now known. I show that many properties of their X-ray oscillations can be understood if the X-ray emitting regions of most are near their spin axes but wander. This is to be expected if their magnetic poles are close to their spin axes, so that accreting gas is channeled there. As the accretion rate and structure of the inner disk vary, gas will be channeled to different locations on the stellar surface, causing the X-ray emitting regions to move with respect to the magnetic field. This model can explain the small amplitudes and nearly sinusoidal waveforms of most of these pulsars and the large, rapid phase variations of several. It may also explain why accretion-powered millisecond pulsars are difficult to detect, why all found so far are transients, and why the oscillations of a few are intermittent. =================================================================================