Optimal Source Tracking and Beaming of LISA

We revisit the directionally optimal data streams of LISA first introduced in Nayak etal. It was shown that by using appropriate choice of Time delay interferometric (TDI) combinations, a monochromatic fixed source in the barycentric frame can be optimally tracked in the LISA frame. In this work, we study the beaming properties of these optimal streams. We show that all the three streams V+, Vx and Vo with maximum, minimum and zero directional SNR respectively are highly beamed. We study in detail the frequency dependence of the beaming.