{
  "bibcode": "2020GCN.29019....1H",
  "body": "A. Hajela, R. Margutti, K. D. Alexander (Northwestern U.), T. Laskar (U. of\nBath), D. Giannios (Purdue U.), V. A. Villar (Columbia U.) report:\n\n\nWe observed GW170817 with the Chandra X-ray Observatory (CXO) at t =1209\ndays (~3.3 years) after the binary neutron star merger. Here we report the\npreliminary results from the analysis of the first epoch of data acquired\nso far, for a total exposure time of 29.7  ks (out of a total of ~100 ks to\nbe completed over the next few days) corresponding to ObsID 22677 (PI\nMargutti; program 21510449).\n\nNo X-ray emission is detected at the location of GW170817 and we infer a\n3-sigma 0.5-8 keV count-rate upper limit of 1.0e-4 cts/s. Assuming a simple\npower-law spectral model with a photon index Gamma =1.57 and no intrinsic\nabsorption NHint = 0 cm-2 (as found from previous CXO observations of\nGW170817, e.g., Hajela et al. 2019), the corresponding 3-sigma absorbed\nflux limit is Fx<1.6e-15 erg/cm2/s (0.3-10 keV), which is Lx< 3.5e+38 erg/s\nat the distance of 40.7 Mpc (Cantiello et al., 2018).  The Galactic neutral\nhydrogen column density in the direction of GW170817 is NH,gal = 7.8e+20\ncm-2  (Kalberla et al., 2005).  As a comparison, the off-axis jet models\nthat best fit the earlier multi-band evolution of the afterglow predict a\nluminosity of  Lx~1.5e+38 erg/s (0.3-10 keV) at the present epoch, which is\nbelow the sensitivity of current CXO observations.  Further Chandra\nobservations planned in the next few days will probe deeper fluxes.\n\nWe thank the entire Chandra team for scheduling and executing these\nobservations.",
  "circularId": 29019,
  "createdOn": 1607553517000,
  "email": "AprajitaHajela2015@u.northwestern.edu",
  "subject": "Chandra observations of GW170817 at ~3.3 years since merger (Observation 1 of 4)",
  "submitter": "Aprajita Hajela at Northwestern U  <AprajitaHajela2015@u.northwestern.edu>"
}