Abstract
Abstract
We employ the formalism developed in [1] and [2] to
study the prospect of detecting an anisotropic Stochastic Gravitational Wave Background (SGWB)
with the Laser Interferometer Space Antenna (LISA) alone, and combined with the proposed
space-based interferometer Taiji. Previous analyses have been performed in the frequency domain
only. Here, we study the detectability of the individual coefficients of the expansion of the SGWB
in spherical harmonics, by taking into account the specific motion of the satellites. This
requires the use of time-dependent response functions, which we include in our analysis to obtain
an optimal estimate of the anisotropic signal. We focus on two applications. Firstly, the
reconstruction of the anisotropic galactic signal without assuming any prior knowledge of its
spatial distribution. We find that both LISA and LISA with Taiji cannot put tight constraints on
the harmonic coefficients for realistic models of the galactic SGWB. We then focus on the
discrimination between a galactic signal of known morphology but unknown overall amplitude and an
isotropic extragalactic SGWB component of astrophysical origin. In this case, we find that the two
surveys can confirm, at a confidence level ≳ 3σ, the existence of both the galactic
and extragalactic background if both have amplitudes as predicted in standard models. We also find
that, in the LISA-only case, the analysis in the frequency domain (under the assumption of a time
average of data taken homogeneously across the year) provides a nearly identical determination of
the two amplitudes as compared to the optimal analysis.
Cited by
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