A joint MeerKAT and Parkes view of Omega Centauri: New TRAPUM Searches and Pulsar Timing

TL;DR

This study uses MeerKAT and Parkes telescopes to discover and analyze millisecond pulsars in Omega Centauri, revealing new pulsars, updated orbital parameters, and insights into the cluster's gravitational potential and evolutionary history.

Contribution

The paper presents the discovery of a new isolated MSP, updates to binary pulsar parameters, and constraints on the cluster's gravitational potential, advancing understanding of MSP populations in Omega Centauri.

Findings

Discovered a new isolated MSP, PSR J1326-4728S.

Updated orbital parameters for multiple binary pulsars.

Placed an upper limit of <10^5 M_sun on an intermediate-mass black hole.

Abstract

Millisecond pulsars (MSPs) are powerful probes of globular clusters (GCs), tracing stellar evolution, cluster dynamics, and the local gravitational potential. We investigate the MSP population in GC Omega Centauri. We perform Fourier-domain acceleration and jerk searches on MeerKAT observations, and carry out pulsar timing using MeerKAT and Parkes Murriyang data spanning 2021-2025. We fold Fermi LAT and NICER photons using updated radio ephemerides to search for high-energy pulsations. We discover a new isolated MSP, PSR J1326-4728S (hereafter S), with a spin period of 4.538 ms and a dispersion measure of 96.24 cm$^3$pc. We update the orbital parameters of all known binary systems, with those of I, N, and Q differing significantly from previous estimates, and obtain new timing solutions for G, H, and K. Pulsars B, G, H, K, and L exhibit black widow-like properties, I, N and Q are found in wider binaries, with N and Q having >0.2 M$_\odot$ companions, and N showing a significant orbital eccentricity (e=0.093). Significant spin period derivatives are measured for eight pulsars and interpreted as arising from the cluster gravitational potential. No pulsed high-energy emission is detected from individual pulsars. The inferred line-of-sight accelerations are consistent with a King-model gravitational potential. While our measurements are insensitive to an intermediate-mass black hole with mass 10$^3$-10$^4$ M$_\odot$, they place an upper limit of <10$^5$ M$_\odot$ at 90% confidence. The high fraction of isolated MSPs and black widows systems, and possibly the eccentricity of N, are difficult to reconcile with MSP population predictions based solely on encounter rates. Instead, these properties likely reflect the complex evolutionary history of Omega Centauri, with part of its MSP population having formed in denser environments than the one observed today.