On Detecting Millisecond Pulsars at the Galactic Center

TL;DR

This paper explores optimal radio frequencies and telescope strategies for detecting millisecond pulsars at the Galactic Center, considering different scattering scenarios and suggesting feasible observation plans.

Contribution

It proposes specific search frequencies and telescope integration times tailored to scattering conditions, enhancing prospects for detecting MSPs at the GC.

Findings

Optimal search frequency is ~8 GHz for weak scattering.

Optimal search frequency is ~25 GHz for strong scattering.

Detection feasible with current telescopes in weak scattering, requiring SKA in strong scattering.

Abstract

The lack of detected pulsars at the Galactic Center (GC) region is a long-standing mystery. We argue that the high stellar density in the central parsec around the GC is likely to result in a pulsar population dominated by millisecond pulsars (MSPs), similar to the situation in globular cluster environments. Earlier GC pulsar searches have been largely insensitive to such an MSP population, accounting for the lack of pulsar detections. We estimate the best search frequency for such an MSP population with present and upcoming broad-band radio telescopes for two possible scattering scenarios, the "weak-scattering" case suggested by the recent detection of a magnetar close to the GC, and the "strong-scattering" case, with the scattering screen located close to the GC. The optimal search frequencies are $\approx 8$ GHz (weak-scattering) and $\approx 25$ GHz (strong-scattering), for pulsars with periods 1-20 ms, assuming that GC pulsars have a luminosity distribution similar to that those in the rest of the Milky Way. We find that 10-30 hour integrations with the Very Large Array and the Green Bank Telescope would be sufficient to detect MSPs at the GC distance in the weak-scattering case. However, if the strong-scattering case is indeed applicable to the GC, observations with the full Square Kilometre Array would be needed to detect the putative MSP population.