A Decline in the X-Ray through Radio Emission from GW170817 Continues to Support an Off-axis Structured Jet
Berger, E.; Chornock, R.; Fong, W.; Nicholl, M.; Eftekhari, T.; Metzger, B. D.; Guidorzi, C.; Margutti, R.; Alexander, K. D.; Blanchard, P. K.; Hajela, A.; MacFadyen, A.; Williams, P. K. G.; Villar, V. A.; Cowperthwaite, P. S.; Giannios, D.; Kathirgamaraju, A.; Sironi, L.; Xie, X.; Zrake, J.
United States, Italy
Abstract
We present new observations of the binary neutron star merger GW170817 at Δt ≈ 220-290 days post-merger, at radio (Karl G. Jansky Very Large Array; VLA), X-ray (Chandra X-ray Observatory), and optical (Hubble Space Telescope; HST) wavelengths. These observations provide the first evidence for a turnover in the X-ray light curve, mirroring a decline in the radio emission at ≳5σ significance. The radio-to-X-ray spectral energy distribution exhibits no evolution into the declining phase. Our full multi-wavelength data set is consistent with the predicted behavior of our previously published models of a successful structured jet expanding into a low-density circumbinary medium, but pure cocoon models with a choked jet cannot be ruled out. If future observations continue to track our predictions, we expect that the radio and X-ray emission will remain detectable until ∼1000 days post-merger.