[vsnet-grb-info 20595] Chandra observations of GW170817 reveal a fading afterglow
GCN Circulars
gcncirc at capella2.gsfc.nasa.gov
Tue May 8 13:00:47 JST 2018
TITLE: GCN CIRCULAR
NUMBER: 22693
SUBJECT: Chandra observations of GW170817 reveal a fading afterglow
DATE: 18/05/08 03:59:58 GMT
FROM: Eleonora Troja at GSFC <eleonora.troja at nasa.gov>
E. Troja (UMD/GSFC), L. Piro (IAPS/INAF), G. Ryan (UMD) report on
behalf of a larger collaboration:
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 at 260 days after the merger.
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.
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