Citation

BibTex format

@article{Gersbach:2026:10.1103/D55K-75P9,
author = {Gersbach, KA and Taylor, SR and Becsy, B and Lemke, AM and Mitridate, A and Pol, N},
doi = {10.1103/D55K-75P9},
journal = {Physical Review D},
title = {Mapping the gravitational-wave background across the spectrum with a next-generation anisotropic per-frequency optimal statistic},
url = {http://dx.doi.org/10.1103/D55K-75P9},
volume = {113},
year = {2026}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - With pulsar timing arrays (PTAs) having observed a gravitational wave background (GWB) at nanohertz frequencies, the focus of the field is shifting toward determining and characterizing its origin. While the primary candidate is a population of GW-emitting supermassive black hole binaries (SMBHBs), many other cosmological processes could produce a GWB with similar spectral properties as have been measured. One key argument to help differentiate an SMBHB GWB from a cosmologically sourced one is its level of anisotropy; a GWB sourced by a finite population will likely exhibit greater anisotropy than a cosmological GWB through finite source effects (“shot noise”) and potentially large-scale structure. Current PTA GWB anisotropy detection methods often use the frequentist PTA optimal statistic for its fast estimation of pulsar pair correlations and relatively low computational overhead compared to spatially correlated Bayesian analyses. However, there are critical limitations with the status quo approach. In this paper, we improve this technique by incorporating three recent advancements: accounting for covariance between pulsar pairwise estimates of correlated GWB power, the per-frequency optimal statistic to dissect the GWB across the spectrum, and constructing null-hypothesis statistical distributions that include cosmic variance. By combining these methods, our new pipeline can localize GWB anisotropies to specific frequencies, through which anisotropy detection prospects—while impacted by cosmic variance—are shown to improve in our simulations from a p value of ~0.2 in a broadband search to ~0.01 in the perfrequency search. Our methods are already incorporated in community-available code and ready to deploy on forthcoming PTA datasets.
AU  - Gersbach,KA
AU  - Taylor,SR
AU  - Becsy,B
AU  - Lemke,AM
AU  - Mitridate,A
AU  - Pol,N
DO  - 10.1103/D55K-75P9
PY  - 2026///
SN  - 2470-0010
TI  - Mapping the gravitational-wave background across the spectrum with a next-generation anisotropic per-frequency optimal statistic
T2  - Physical Review D
UR  - http://dx.doi.org/10.1103/D55K-75P9
VL  - 113
ER  -
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