期刊
ASTROPHYSICAL JOURNAL LETTERS
卷 862, 期 2, 页码 -出版社
IOP Publishing Ltd
DOI: 10.3847/2041-8213/aad32d
关键词
galaxies: individual (NGC 4993); gamma-ray burst: individual (GRB 170817A); gravitational waves; stars: neutron; X-rays: binaries
资金
- Chandra Award by the Chandra X-ray Observatory Center [GO7-18033X]
- National Aeronautics Space Administration (NASA) [NAS8-03060]
- Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery grant
- Fonds de recherche du Quebec-Nature et Technologies (FRQNT) Nouveaux Chercheurs grant
- McGill Trottier Chair in Astrophysics and Cosmology
- Canadian Institute for Advanced Research (CIFAR)
- UKSA
The multi-wavelength electromagnetic afterglow from the binary neutron star merger GW170817/GRB 170817A has displayed long-term power-law brightening, and has presented challenges to post-merger models of the non-thermal emission. The most recent radio observations up to 200 days post-merger suggest that the afterglow has finally peaked and may now be fading, but fading has not been confirmed in the X-rays. We present new, deep Chandra observations of GW170817/GRB 170817A at 260 days post-merger that reveal an X-ray flux of F0.3-8keV = 1.1x10(-14) 14 erg s(-1) cm(-2), and confirm that the X-ray light curve is now also fading. Through rigorous comparisons with previous Chandra observations of GW170817/GRB 170817A, X-ray fading is detected between 160 and 260 days post-merger at a 4.4 sigma significance on the basis of the X-ray data alone. We further constrain the X-ray photon index to steepen by <0.5 at 3.1 sigma significance during this period, which disfavors the passing of the synchrotron cooling frequency through the X-ray band as the cause of the observed fading. These observations remain consistent with optically thin synchrotron afterglow emission. If this afterglow emission arises from a quasi-spherical mildly relativistic outflow, the X- ray fading suggests that the outflow is now decelerating. Alternatively, if this afterglow arises from a successful off-axis structured jet, the X-ray fading suggests that emission from the jet core has already entered the line of sight.
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