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GCN Circular 27411

GW170817: Continued X-ray emission detected with Chandra at 940 days post-merger
2020-03-18T17:59:10Z (4 years ago)
Eleonora Troja at NASA/GSFC/UMD <>
E. Troja (UMD/NASA/GSFC), L. Piro (INAF/IAPS), G. Ryan (UMD), H. van Eerten
(Bath U.), B. Zhang (UNLV) ob behalf of a larger collaboration

The Chandra X-ray Observatory re-observed the field of GW170817 between
March 9th and March 15th, 2020,and performed four short exposures
observations (ObsIDs: 21323, 23183, 23184, 23185)
for a total of 96 ks, as part of its on-going monitoring program. At the
afterglow position, an X-ray source is detected with significance >4.5
at an average count rate of (8+/-0.4)e-05 cts/s in the 0.5-8.0 keV energy
band. By using an absorbed power-law model with absorption column fixed at
the Galactic value of 7.5E20 cm^-2 and a photon index Gamma=1.585, as
derived from our broadband analysis, we estimate an unabsorbed X-ray flux
of (1.1 +/- 0.6)E-15 erg/cm2/s in the 0.3-10 keV energy band. The quoted
error is at the 68% confidence level.
This new measurement is higher than earlier predictions of a structured
jet, based on a full year of data (Troja E., et al., 2019, MNRAS, 489,
yet still consistent with this model within the uncertainties.

Additional components of emission, such as continued energy injection from
a long-lived neutron star (Piro L., et al., 2019, MNRAS, 483, 1912) or
afterglow from the sub-relativistic ejecta (Kathirgamaraju A., Giannios D.,
Beniamini P., 2019, MNRAS, 487, 3914), cannot be excluded at this time.

Further analysis is on-going.
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