Recent 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 March 9 and March 16 2020 ( 935 d to 942 d after the merger ) , a total of 8 photons are measured at the source position , corresponding to a significance of \approx 5 \sigma .
Radio monitoring with the Australian Telescope Compact Array ( ATCA ) shows instead that the source has faded below our detection threshold ( < 33 \mu Jy , 3 \sigma ) .
By assuming a constant spectral index of \beta =0.585 , we derive an unabsorbed X-ray flux of \approx 1.4 \times 10 ^ { -15 } erg cm ^ { -2 } s ^ { -1 } , 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 dataset 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 .