Chandra observations of GW170817 reveal a fading afterglow
ATel #11619; E. Troja (UMD/GSFC), L. PIro (INAF/IAPS), G. Ryan (UMD)
on 8 May 2018; 04:16 UT
Credential Certification: Eleonora Troja (eleonora.troja@nasa.gov)
Subjects: X-ray, Gamma-Ray Burst, Gravitational Waves
The Chandra X-ray Observatory re-observed the field of GW170817 starting on May 3rd, 2018 as part of its on-going monitoring program (PI: Wilkes). Observations were split into two exposures of 50.7 ks and 46 ks, respectively.
The X-ray afterglow is significantly detected at an average level of (8.5 +/- 1.4)E-04 cts/s, well below the value (14.8 +/- 1.1)E-04 cts/s
measured at ~160 d after the merger (Troja & Piro, GCN Circ. 22374; Troja et al. 2018). The spectrum is well described by an absorbed power-law model with photon index 1.5 +/- 0.2, consistent with the value of 1.575 derived at earlier times from the broadband spectrum.
By using this value we derive an unabsorbed X-ray flux of (1.4 +/- 0.2)E-14 erg/cm2/s (0.3-10 keV) at 260 days after the merger. The quoted errors are at the 68% confidence level.
A comparison with the afterglow models derived in Troja et al. (2018) is shown at this link:
https://www.astro.umd.edu/~gsryan/GW170817/xray.png
This new X-ray observation supports earlier claims (D'Avanzo et al. 2018; Dobie et al. 2018) that the afterglow entered its post-peak decay phase. However, no clear distinction between the competing models is possible.
Further observations are critical to probe the structure of the relativistic outflow.
Updated X-ray Afterglow Light Curve for GW170817
