Troja, E.E.Trojavan Eerten, H.H.van EertenZhang, B.B.ZhangRyan, G.G.RyanPIRO, LuigiLuigiPIRORICCI, ROBERTOROBERTORICCIO'Connor, B.B.O'ConnorWieringa, M. H.M. H.WieringaCenko, S. B.S. B.CenkoSakamoto, T.T.Sakamoto2025-02-142025-02-1420200035-8711http://hdl.handle.net/20.500.12386/35949Recent observations with the Chandra X-ray telescope continue to detect X-ray emission from the transient GW170817. In a total exposure of 96.6 ks, performed between 2020 March 9 and 16 (935-942 d after the merger), a total of 8 photons are measured at the source position, corresponding to a significance of ≍5σ. Radio monitoring with the Australian Telescope Compact Array (ATCA) shows instead that the source has faded below our detection threshold (<33-= $\mu$ Jy, 3σ). By assuming a constant spectral index of β = 0.585, we derive an unabsorbed X-ray flux of ≍1.4 × 10<SUP>-15</SUP>-=erg-=cm<SUP>-2</SUP>-=s<SUP>-1</SUP>, higher than earlier predictions, yet still consistent with a simple structured jet model. We discuss possible scenarios that could account for prolonged emission in X-rays. The current data set appears consistent both with energy injection by a long-lived central engine and with the onset of a kilonova afterglow, arising from the interaction of the sub-relativistic merger ejecta with the surrounding medium. Long-term monitoring of this source will be essential to test these different models....STAMPAenArticle10.1093/mnras/staa2626https://academic.oup.com/mnras/article/498/4/5643/5918334FIS/05 - ASTRONOMIA E ASTROFISICA