Targeted search for eccentric supermassive binary black holes in OJ 287 and nearby galaxy clusters with PPTA DR3

TL;DR

This study uses Bayesian analysis of pulsar timing data to search for gravitational waves from eccentric supermassive black hole binaries in specific sky regions, setting new constraints on their masses and mass ratios.

Contribution

It introduces an eccentricity-inclusive Bayesian search method applied to PPTA DR3 data, providing novel limits on supermassive binary black hole properties in targeted regions.

Findings

No significant gravitational wave signals detected.

Constraints on total binary mass in OJ 287 are set below 5.25 x 10^{10} solar masses.

Excludes binaries with mass ratios greater than approximately 10^{-2} in selected galaxy clusters.

Abstract

We perform Bayesian targeted searches for continuous gravitational waves from eccentric supermassive binary black holes (SMBBHs) using the Parkes Pulsar Timing Array third data release (PPTA DR3). Six electromagnetically motivated sky directions are analyzed, including the blazar OJ~287 and five nearby galaxy clusters (Virgo, Fornax, Norma, Hercules, and Coma). No significant signals are found. For OJ 287, by explicitly incorporating orbital eccentricity (up to $e_0 = 0.8$) to robustly capture signal power spread across multiple harmonics, we constrain the total binary mass to $M_{\rm tot} < 5.25 \times 10^{10} M_{\odot}$ (95\% credible level). We also place upper limits on the chirp mass of potential SMBBHs residing in galaxy clusters. By combining these limits with independent black hole mass estimates, we place novel constraints on the allowed binary mass ratios for potential hosts such as M87 and NGC~4889. Specifically, our results exclude binaries with mass ratios $q \gtrsim 10^{-2}$ at around 10 nHz for these massive systems, effectively ruling out equal-mass black hole mergers in the sampled parameter space. These findings demonstrate the growing power of pulsar timing arrays to probe SMBBH populations.