092028

PSR J1653-0158 is exceptional with the shortest orbital period of any pulsarbinary the largest neutron star mass function and an unusual H-free companionbeing evaporated by pulsar irradiation. Its optical light curve shows aremarkable hard-spectrum veiling flux likely synchrotron emission from anIntraBinary Shock (IBS) and the PL X-ray spectrum indicates IBS domination inthis band as well. Measurement of this IBS components light curve and spectrumin the critical UV-X-ray band is the key to modeling the system. Since J1653 isan exemplar of short period binary evolution and is a major contributor towardsNS mass limits constraining the dense matter equation of state a sensitive XMM-Newton observation of this source offers an important probe of compact object physics. [truncated! Please see actual data for full text]