ICTS

A recently discovered class of pulsars, called transitional millisecond pulsars (tMSPs), are systems that switch between a low-mass X-ray binary (LMXB) and a radio millisecond pulsar (RMSP) state, establishing a firm evolutionary link between the two source classes. tMSPs provide a great avenue to study the low-level accretion processes that spin-up pulsars to millisecond periods. Previously, we have timed the tMSP J1023+0038, in the RMSP state. In this state the orbital variations and radio eclipses complicated the timing model. Recently, using a dedicated XMM-Newton campaign we have found a way to model the changing orbital parameters and, for the first time, have been able to precisely measure the spin period derivative of a tMSP in the accreting state. Moreover, using this timing solution and our new estimate of orbital period derivative, we are systematically searching the Fermi data to understand the origin of excess gamma-ray emission when tMSPs switch from RMSP to LMXB state. In my talk, I will present our techniques and results from both X-ray and gamma-ray timing campaigns.