PSR J1922+37: a 1.9 s Pulsar Discovered in the Direction of the Old Open Cluster NGC 6791

Abstract

More than 300 pulsars have been discovered in Galactic globular clusters; however, none have been found in open clusters. Here we present results from a 20 hr survey of seven open clusters with the Five-hundred-meter Aperture Spherical radio Telescope. Our first discovery is a 1.9 s pulsar (J1922+37) found in the direction of the old open cluster NGC 6791. The measured dispersion measure (DM) implies a distance of 4.79 and 8.92 kpc based on the NE2001 and YMW16 electron density models, respectively. Given the large uncertainty of DM distance estimates, it is plausible that PSR J1922+37 is indeed a member of NGC 6791, for which the distance is 4.19 ± 0.02 kpc based on Gaia Data Release 3. If confirmed, PSR J1922+37 will be the first pulsar found in a Galactic open cluster. We outline future observations that can confirm this pulsar–open cluster association and discuss the importance of this pulsar for calibrating the characteristic ages of the pulsar population.