Limits on anisotropy in the nanohertz stochastic gravitational-wave background
Taylor, S. R. · Mingarelli, C. M. F. · Gair, J. R. · Sesana, A. · Theureau, G. · Babak, S. · Bassa, C. G. · Brem, P. · Burgay, M. · Caballero, R. N. · Champion, D. J. · Cognard, I. · Desvignes, G. · Guillemot, L. · Hessels, J. W. T. · Janssen, G. H. · Karuppusamy, R. · Kramer, M. · Lassus, A. · Lazarus, P. · Lentati, L. · Liu, K. · Osłowski, S. · Perrodin, D. · Petiteau, A. · Possenti, A. · Purver, M. B. · Rosado, P. A. · Sanidas, S. A. · Smits, R. · Stappers, B. · Tiburzi, C. · van Haasteren, R. · Vecchio, A. · Verbiest, J. P. W.
Original · EN
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.
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