New Deep Radio Continuum Imaging Still Indicates a Large Reservoir of Undiscovered Millisecond Pulsars in Terzan 5

TL;DR

This study uses deep, high-resolution radio imaging to reveal a large, previously underestimated population of millisecond pulsars in the globular cluster Terzan 5, emphasizing its importance for future radio astronomy.

Contribution

It provides the deepest radio continuum imaging of Terzan 5 and estimates a significantly larger pulsar population than previous studies, highlighting the potential for discovering more pulsars.

Findings

Detected 38 of 49 known pulsars in the cluster

Estimated a minimum of 250 pulsars in total

Indicated a large reservoir of undiscovered millisecond pulsars

Abstract

We present the deepest and highest-resolution radio continuum imaging of the Galactic globular cluster Terzan 5, one of the most crowded locations in the radio sky. In these new 2$-$4 GHz Karl G. Jansky Very Large Array images, we detect 38 of the 49 confirmed pulsars, including extensive multi-frequency eclipse mapping of the luminous redback Ter5A. Nonetheless, there is still a large amount of diffuse residual flux from pulsars that are fainter than our 2.5 GHz continuum detection limit of $\sim 11\,\mu$Jy. Using a range of approaches including image-based simulations, we model the fluxes of the detected pulsars together with the residual flux. We find a minimum total population of $N\sim250$ detectable pulsars in Terzan 5 and perhaps substantially more, though the luminosity function remains very uncertain. Consideration of the $\gamma$-ray properties of the cluster, though also not unambiguous to interpret, leads to consistent conclusions. These pulsar population estimates are larger than inferred from previous work and highlight Terzan 5 as a keystone target for next-generation radio facilities.