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tokens: power-law decline begins roughly when the jet centroid comes into view. The sharpness of the light curve peak and the immediate transition to t − p decline implies that we are in the regime 20 20 If ( θ v − θ j ) ≲ θ j there will be a long-lived phase during which the light curve decays as t −1 . θ v − θ j ≫ θ j . We denote by t 1 as the time that we see the edge of the jet, namely Γ( t 1 ) ≃ 1/( θ v − θ j ), and t 2 as the time that we see the jet axis, Γ( t 2 ) ≃ 1/ θ v . Now, ignoring sideways spreading of the jet we can approximate (e.g., Sari et al. 1998 ) to obtain //. Here we use the approximation that θ j / θ v is much smaller than unity. Observationally, t 1 occurs sometime during the transition from the t 0.8 rise to the peak of the light curve and t 2 occurs when the decay phase approaches t − p . Using the results from our MCMC analysis, we find that Δ t / t ≲ 1/3 (68% confidence or better, depending on the where t 1 and t 2 lie), indicating that θ v ≳ 8 θ j . To verify this simple estimate we produced light curves from a top-hat jet using semi-analytic code. 21 21 The semi-analytic code (Soderberg et al. 2006 ) takes proper account of all relativistic effects such as Lorentz boost and light arrival time from each point in the jet and it includes lateral spreading of the jet. Following corollary comparison of the code results to BOXFit (van Eerten et al. 2012 ), we use lateral spreading of 30% of the local thermal speed. We verify that varying the spread velocity, including taking no spreading at all, does not change the result significantly. We find that light curves that fit the transition seen from the peak to the decline of the light curve have θ v ≃ 6 θ j . Together with the upper limit on the observing angle from the Laser Interferometer Gravitational-Wave Observatory (LIGO)-Virgo Collaboration ( θ v ≲ 28°; Abbott et al. 2017a ), our constraint implies θ j ≲ 5°. If instead we use the estimate of Γ ≃ 4.1 ± 0.5 close to the peak of the light curve from the very long baseline interferometry (VLBI) measurement (Mooley et al. 2018a ), then we get θ j ≲ 3° and θ v ≃ 15°. 5. Summary and Conclusions In this companion Letter to our polarization and high angular resolution imaging studies, we have presented deep VLA, ATCA, MeerKAT, and uGMRT observations (Section 2 ) of GW170817 post-peak of the light curve, i.e., between 180 and 300 days post-merger. Our spectral analysis does not yield any evidence for the cooling break to have entered the radio band, or of any achromatic steepening in the light curve indicating the transition of the outflow into the non-relativistic regime (Section 3.1 ). We find that the light curve decay is consistent with t −2.2 (Section 3.2 ), which is a classic signature of a jet where the slope of the decay is equal to the power-law energy index p of the synchrotron-emitting electrons. We also find that the transition from the power-law rise to decay ( t 0.8 to t −2.2 ) is fairly sharp. The data on the light