2FGL J1653.6-0159: A New Low in Evaporating Pulsar Binary Periods

Understand

We have identified an optical binary with orbital period P_b=4488s as the probable counterpart of the Fermi source 2FGL J1653.6-0159.

• Although pulsations have not yet been detected, the source properties are consistent with an evaporating millisecond pulsar binary; this P_b=75min is the record low for a spin-powered system.
• The heated side of the companion shows coherent radial velocity variations, with amplitude K=666.9+/-7.5 km/s for a large mass function of f(M)=1.60+/-0.05 M_sun.
• This heating suggests a pulsar luminosity ~3x10^34 erg/s.