Three Binary Millisecond Pulsars in NGC 6266

Abstract

We present rotational and astrometric parameters of three millisecond pulsars located near the center of the globular cluster NGC 6266 (M62), resulting from timing observations with the Parkes radio telescope. Their accelerations toward the cluster center yield values of the cluster central density and mass-to-light ratio consistent with those derived from optical data. The three pulsars are in binary systems. One (spin period P=5.24 ms) is in a 3.5 day orbit around a companion of minimum mass 0.2 Msolar. The other two millisecond pulsars (P=3.59 and 3.81 ms) have shorter orbital periods (3.4 and 5.0 hr) and lighter companions (minimum masses of 0.12 and 0.07 Msolar, respectively). The pulsar in the closest system is the fifth member of an emerging class of millisecond pulsars displaying irregular radio eclipses and having a relatively massive companion. This system is a good candidate for optical identification of the companion star. The lack of known isolated pulsars in NGC 6266 is also discussed.