A thousand days after the merger: continued X-ray emission from GW170817

Eleanora Troja, Hendrik Van Eerten, Bing Zhang, Geoffrey Scott Ryan, L. Piro, R. Ricci, Brendan O'Connor, M. H. Wieringa, S. B. Cenko, T. Sakamoto

Research output: Contribution to journalArticlepeer-review

75 Citations (SciVal)


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 about 5 sigma. Radio monitoring with the Australian Telescope Compact Array (ATCA) shows instead that the source has faded below our detection threshold (<33 uJy, 3 sigma). By assuming a constant spectral index beta=0.585, we derive an unabsorbed X-ray flux of approximately 1.4E-15 erg/cm^2/s, 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.
Original languageEnglish
Pages (from-to)5643-5651
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 12 Oct 2020


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