{
  "bibcode": "2020GCN.29055....1H",
  "body": "A. Hajela, R. Margutti, K. D. Alexander, W. Fong (Northwestern U.), E.\nBerger (Harvard), T. Laskar (Bath), T. Eftekhari (Harvard), D. Giannios\n(Purdue U.), P. K. Blanchard, R. Chornock, D. L. Coppejans (Northwestern\nU.),  V. A. Villar (Columbia U.),  P. Cowperthwaite (Carnegie), L. Sironi\n(Columbia), B. Margalit (Berkeley) report:\n\nWe report on the complete Chandra data set of observations of GW170817\nacquired at t=1209-1213 days since merger (IDs 22677, 24887, 24888, and\n24889; PI Margutti; program 21510449) for a total exposure time of ~91 ks.\nPreliminary results from a subset of these observations have been reported\nby Hajela et al., GCN 29041, GCN 29019; Troja et al., GCN 29038.\n\nWe confirm the presence of significant X-ray emission from GW170817\n(significance of detection > 5 sigma, Gaussian equivalent) from the merged\nobservations, with a source count rate of (0.9 +/- 0.3) e-4 cps (0.5-8\nkeV). From a joint spectral fit with a simple power-law spectral model\nusing a photon index Gamma ~ 1.6, no intrinsic absorption NHint = 0 cm-2\n(as found in e.g. Hajela et al. 2019), and Galactic neutral hydrogen column\ndensity NH,gal = 7.8e+20 cm-2 (Kalberla et al., 2005), we estimate an\nunabsorbed flux of 3.46(+1.06 -1.31) e-15 erg/cm2/s (0.3-10 keV, 1-sigma\nuncertainties), corresponding to a luminosity of 6.9 (+2.1 -2.6) e+38 erg/s\nat the distance of 40.7 Mpc (Cantiello et al., 2018). The observed emission\nis a factor of ~2 brighter than the first X-ray non-detection of GW170817\nat ~2 days after merger.\n\nAs previously reported in Hajela et al., GCN 29041, the inferred flux is in\nexcess to the extrapolation of the off-axis jet model that best fits the\nbroad-band afterglow observations at t<580 days (e. g., Hajela et al. 2019)\nand might represent the emergence of a new component of emission. An\nupdated plot of the X-ray evolution of GW170817 can be found here:\nhttps://sites.google.com/u.northwestern.edu/synchrotron-emission-from-gw17/home\n\n\nWe thank the entire Chandra team for scheduling and executing these\nobservations.\n\nWe thank the entire Chandra team for scheduling and executing these\nobservations.",
  "circularId": 29055,
  "createdOn": 1608125310000,
  "email": "AprajitaHajela2015@u.northwestern.edu",
  "subject": "Chandra observations of GW170817 at ~3.3 years since merger (Full report)",
  "submitter": "Aprajita Hajela at Northwestern U  <AprajitaHajela2015@u.northwestern.edu>"
}