Globular Clusters GMRT Pulsar Search (GCGPS). I. Survey Description, Discovery and Timing of the First Pulsar in NGC6093 (M80)

Abstract This paper describes the new Globular Clusters GMRT Pulsar Search survey. This survey aims to find millisecond pulsars (MSPs) in the globular clusters (GCs) of the Milky Way using the upgraded Giant Metrewave Radio Telescope (uGMRT). Using the uGMRT’s Band-4 (550–750 MHz) and Band-3 (300–500 MHz) receivers, this survey will eventually cover the GCs accessible to the uGMRT sky, avoiding GCs visible to the Five-hundred-meter Aperture Spherical Radio Telescope (i.e., −53° < δ < ​​​​​​−17°), and targeting GCs that have not been targeted with the sensitivity of this survey. In this paper, we present the discovery and follow-up study of the first pulsar from this survey, J1617–2258A, a 4.32 ms binary MSP, the first to be discovered in the GC NGC 6093. We localized this MSP with arcsecond precision from imaging and obtained the unique timing solution from more than one year of timing observations with the uGMRT Band-4 (550–750 MHz) receivers. This revealed an unusual binary MSP, with a ∼19 hr, highly eccentric (e ∼ 0.54) orbit having a low-mass companion. This orbital eccentricity allowed the measurement of the rate of advance of the periastron for this system, which led to the derivation of its total mass, 1.67 ± 0.06 M ⊙; this together with the system’s mass function implies, for the pulsar and the companion, M p < 1.60 M ⊙ and M c > 0.072 M ⊙. The system is most likely a perturbed MSP–helium white dwarf system seen at a low orbital inclination.