Polarization Profiles of Globular Cluster Pulsars from FAST I. 25 Profiles from Previously Known Pulsars

Abstract

Pulsar polarization profiles are critical for understanding their magnetospheric structures and radiation mechanisms. We present polarization profile measurements for 25 pulsars in globular clusters (GCs) from the observation of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The diversity of polarization profiles shows complex magnetic structure and emission pattern of pulsars. Among these, the polarization profiles of 15 pulsars were firstly measured. M53A present a 57\% linear polarization ratio, being highest among these 25 GC pulsars. M15H present a 42\% circular polarization ratio, which is the highest among these 25 pulsars. The average ratios of circular and absolute circular polarization of these GC pulsars are -1\% and 10\% respectively, lower than normal pulsars measured with Parkes (\citealt{Oswald2023}), which are 5\% and 32\%, respectively. The Rotation Measure (RM) values of each pulsar were measured, giving the range of pulsar(s) from M3, M5, M15, M71, M53, NGC6517, NGC6539, NGC6760 being 8(1) to 16(1) rad $m^{-2}$, -1(2) to -4(6) rad $m^{-2}$, -70(2) to -76(1) rad $m^{-2}$, -480(14) rad $m^{-2}$ (M71A only), -2(1) rad $m^{-2}$ (M53A only), 187(1) to 212(2) rad $m^{-2}$, 109(1) rad $m^{-2}$ (NGC6539A only), and 102(1) to 129(4) rad $m^{-2}$. The GCs closer to the Galactic plane (GP) tend to have larger RM. This is consistent with previous study (\citealt{Hutschenreuter2022}).