Discovery and Timing Follow-Up of Two FAST-Discovered Pulsars from the FAST CRAFTS Survey

TL;DR

This paper reports the discovery and detailed timing analysis of two pulsars found by FAST, highlighting their properties, challenges in electron density modeling, and implications for future pulsar surveys.

Contribution

First timing solutions and polarization measurements for two pulsars discovered by FAST, revealing insights into their nature and the limitations of current electron density models.

Findings

PSR J0535-0231 is likely a disrupted recycled pulsar.

Existing electron density models underestimate the DM for PSR J0535-0231.

Future FAST discoveries can improve Galactic electron density models.

Abstract

We present the results of Green Bank Telescope (GBT) observations of two pulsars discovered with the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) during the 19-beam Commensal Radio Astronomy FasT Survey (CRAFTS). We highlight the first timing solutions, pulse profiles, flux densities, and polarization measurements at 820 MHz for PSR J0535-0231, with a spin period of 415 ms, and PSR J1816-0518, with a spin period of 1.93 s, from a year-long follow-up campaign. PSR J0535-0231 appears to be partially recycled, but isolated, and likely belongs to the class of disrupted recycled pulsars (DRPs). We find that the two widely used electron density models, NE2001 and YMW16, both fall short of accurately modeling the line-of-sight to PSR J0535-0231, as the maximum dispersion measure (DM) predicted by both models is lower than the pulsar's DM of 117.6 pc cm$^{-3}$. Finally, we place both pulsar discoveries in the context of other FAST pulsars discovered in the CRAFTS survey and of the currently known pulsar population, in general, and discuss ways in which future FAST discoveries of faint, distant pulsars might facilitate the development of improved versions of the aforementioned electron density models in certain regions of our Galaxy.