Expectations for the first supermassive black-hole binary resolved by PTAs. I. Model efficacy
Phys. Rev. D 114, 023034 – Published 20 July, 2026
DOI: https://doi.org/10.1103/vncm-5j2n
Abstract
One of the most promising targets for pulsar timing arrays (PTAs) is identifying an individual supermassive black hole binary (SMBHB) out of the population of binaries theorized to produce a gravitational wave background (GWB). In this work, we emulate an evolving PTA dataset, complete with an increasing number of pulsars and timing baselines, into which we inject a single binary on top of a Gaussian GWB signal. We vary the binary’s source parameters, including sky position and frequency, and create ten noise realizations for each source/PTA combination to synthesize an ensemble of simulated datasets with which we assess current Bayesian binary search techniques. We develop a novel, cross-correlation based model tuned for individual SMBHBs and compare its binary detection and characterization capabilities to two waveform-based template models. This spike pixel (SP) technique is designed to identify the frequency-specific anisotropy induced by an individual SMBHB. We find that a template-based search, including the full gravitational wave signal structure (i.e., both the Earth and pulsar effects of an incident GW) returns the highest Bayes factors (BF) and has the most robust parameter estimations. SP attains a realization-median at source strengths . Interestingly, despite being a deterministic model, the Earth-term template struggles to identify and characterize low-frequency binaries (i.e., at 5 nHz). These binaries require higher source strengths () to reach the same BF threshold. This is likely due to neglected confusion effects between the pulsar and Earth terms. By contrast, the SP shows promise for parameter estimation despite treating a binary’s GW signal as excess directional GW power without phase modeling. Sky location and frequency parameter constraints returned by the SP are only surpassed by the Earth-term template model at . Milestones for a first detection using the full-signal GW model are included in a following paper, Petrov et al. [Expectations for the first supermassive black-hole binary resolved by PTAs. II. Milestones for binary characterization, Phys Rev. D 114, 023033 (2026).].
