2020ApJ...892L...6P

We report the discovery of an eclipsing binary millisecond pulsar in the globular cluster M92 (NGC 6341) with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). PSR J1717+4308A, or M92A, has a pulse frequency of 316.5 Hz (3.16 ms) and a dispersion measure of 35.45 pc cm^–3. The pulsar is a member of a binary system with an orbital period of 0.20 days around a low-mass companion that has a median mass of ∼0.18 M_☉. From observations so far, at least two eclipsing events have been observed in each orbit. The longer one lasted for ∼5000 s in the orbital phase range 0.1-0.5. The other lasted for ∼500 s and occurred between 1000 and 2000 s before or after the longer eclipsing event. The lengths of these two eclipsing events also change. These properties suggest that J1717+4308A is a "red-back" system with a low-mass main-sequence or sub-giant companion. Timing observations of the pulsar and further searches of the data for additional pulsars are ongoing.