GW170817: Continued X-ray emission detected with Chandra at 940 days post-merger
ATel #13565; 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
on 18 Mar 2020; 18:12 UT
Credential Certification: Eleonora Troja (eleonora@umd.edu)
Subjects: X-ray, Gamma-Ray Burst, Gravitational Waves, Neutron Star
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 sigma at an average count rate of (8+/-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, 1919), yet still consistent with this model within the uncertainties (see link). 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.
Updated X-ray light curve and structured jet model
