{
  "bibcode": "2018GCN.23137....1H",
  "body": "Daryl Haggard, Melania Nynka, and J. J. Ruan (McGill/MSI) report:\n\nWe analyze new Chandra X-ray observations of neutron star merger \nGW170817 at 358.6 days post-merger, which now reveals fading at a t^-1.6 \nrate.\n\nChandra obtained a 67.16 ks observation of GW170817 (ObsID: 21371, PI: \nTroja) on 10 August 2018, at 358.6 days post-merger. GW170817 is still \nclearly detected, and we measure a 0.5-8 keV count rate of 4.9 \n(+0.9/-0.9) cts/s. We extract and fit the X-ray spectrum assuming an \nabsorbed power-law spectral model, with fixed NH = 7.5e20 cm^-2. We \nmeasure an absorbed flux of f(0.3-8 keV) = 6.3 (+3.8/-2.1) x10^-15 \nerg/s/cm^2 (90% c.l.) and photon index of Gamma = 1.6 (+1.3/-0.9), which \ncorresponds to an unabsorbed luminosity of L(0.3-10 keV) = 1.7 \n(+1.1/-0.5) x10^39 erg/s assuming a luminosity distance of 42.5 Mpc.\n\nThe previous Chandra observation at 260.0 days showed an absorbed flux \nof f(0.3-8 keV) = 1.09 (+0.24/-0.20) x10^-14 erg/s/cm^2 (Nynka et al. \n2018). A power-law fit of this previous 260.0 day flux to the new 358.6 \nday flux reveals fading at a t^-1.6 rate. This is steeper than the \nt^-1.3 fading observed between 159.7 and 260.0 days post-merger, and \nthus the X-ray afterglow light curve is now fading more rapidly.",
  "circularId": 23137,
  "createdOn": 1534125160000,
  "email": "daryl.haggard@mcgill.ca",
  "subject": "Chandra X-ray observations of GW170817 at 1 year post-merger: increasingly rapid fading",
  "submitter": "Daryl Haggard at McGill U  <daryl.haggard@mcgill.ca>"
}