Three pulsars discovered by FAST in the globular cluster NGC 6517 with a pulsar candidate sifting code based on dispersion measure to signal-to-noise ratio plots

We report the discovery of three new pulsars in the globular cluster (GC) NGC 6517, namely NGC 6517 E, F and G, made with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The spin periods of NGC 6517 E, F and G are 7.60 ms, 24.89 ms and 51.59 ms, respectively. Their dispersion measures are 183.29, 183.713 and 185.3 pc cm(-3), respectively, all slightly larger than those of the previously known pulsars in this cluster. The spin period derivatives are at the level of 1 x 10 - 18 s s(-1), which suggests these are recycled pulsars. In addition to the discovery of these three new pulsars, we updated the timing solutions of the known isolated pulsars, NGC 6517 A, C and D. The solutions are consistent with those from Lynch et al. but with smaller timing residuals. From the timing solution, NGC 6517 A, B (position from Lynch et al.), C, E and F are very close to each other on the sky and only a few arcseconds from the optical core of NGC 6517.With currently published and unpublished discoveries, nine pulsars have been discovered in NGC 651, ranking it 6th for GCs with the most known pulsars. The discoveries take advantage of the high sensitivity of FAST and a new algorithm used to check and filter possible candidate signals.

Automated summary

Researchers have discovered three new pulsars in the globular cluster NGC 6517 using the FAST telescope, with slightly different spin periods and dispersion measures compared to previously known pulsars. They have also updated the timing solutions of known isolated pulsars in the cluster, showing that these new pulsars are close to each other on the sky and near the optical core of NGC 6517. The discoveries were made possible by the high sensitivity of FAST and a new algorithm for identifying candidate signals.