We have discovered a new eccentric binary millisecond pulsar in the globular cluster NGC 6652. We searched for pulsars in this and one other cluster, NGC 6388, following the detections of these clusters in gamma-rays by the LAT, as the discovery of gamma-ray emission from many MSPs and the prevalence of MSPs in globular clusters points to cluster MSPs as a likely source of the detected GeV emission. No MSPs were known in either cluster prior to our searches. We observed NGC 6388 and NGC 6652 at 2 GHz with the Green Bank Ultimate Pulsar Processing Instrument (GUPPI) pulsar backend at the Green Bank Telescope in coherent dedispersion mode.
The MSP found in NGC 6652 was detected in each of the six observations, and the period and period derivative were used to perform an initial fit to the binary orbit. We find that the orbital period is ~9.2 days, and an initial measurement of the eccentricity yields a value in the range 0.4-0.9. This high eccentricity points to the MSP having had a colorful past -- MSP orbits are circularized during the accretion and spin-up phase, and therefore a more recent event such as, for example, a companion exchange, must have occurred for eccentricity to be introduced into the system.