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.

Keywords

• Radio pulsars
• Open star clusters
• Globular star clusters