The paucity of observed supermassive black hole binaries (SMBHBs) may imply that the gravitational wave background (GWB) from this population is anisotropic, rendering existing analyses sub-optimal. We present the first constraints on the angular distribution of a nanohertz stochastic GWB from circular, inspiral-driven SMBHBs using the 2015 European Pulsar Timing Array data [Desvignes et al. (in prep.)]. Our analysis of the GWB in the ∼2−90 nHz band shows consistency with isotropy, with the strain amplitude in l>0 spherical harmonic multipoles ≲40% of the monopole value. We expect that these more general techniques will become standard tools to probe the angular distribution of source populations.
@article{arxiv.1506.08817,
title = {Limits on anisotropy in the nanohertz stochastic gravitational-wave background},
author = {S. R. Taylor and C. M. F. Mingarelli and J. R. Gair and A. Sesana and G. Theureau and S. Babak and C. G. Bassa and P. Brem and M. Burgay and R. N. Caballero and D. J. Champion and I. Cognard and G. Desvignes and L. Guillemot and J. W. T. Hessels and G. H. Janssen and R. Karuppusamy and M. Kramer and A. Lassus and P. Lazarus and L. Lentati and K. Liu and S. Osłowski and D. Perrodin and A. Petiteau and A. Possenti and M. B. Purver and P. A. Rosado and S. A. Sanidas and R. Smits and B. Stappers and C. Tiburzi and R. van Haasteren and A. Vecchio and J. P. W. Verbiest},
journal= {arXiv preprint arXiv:1506.08817},
year = {2015}
}
Comments
6 pages, 2 figures, 1 table. Accepted for publication in Physical Review Letters