A 1.9 s Pulsar Discovered in the Direction of the Old Open Cluster NGC 6791

Liu, Xiaojin

The binary pulsar system has provided unique opportunities to test theories of gravity in strong gravitational fields, while pulsar-black hole binaries will further improve our ability to test these theories and are hailed as the holy grail of pulsar astronomy. The number of such systems is, however, expected to be small, and their whereabouts are more uncertain. Aiming to search for pulsar-black hole binaries, we conducted a survey of 7 old open clusters along the Galactic plane. In this talk, I will present our search strategy and report initial results, including the discovery of a 1.9-second pulsar toward the old open cluster NGC 6791. The relationship between the pulsar and the cluster, along with its potential implications, will be discussed.