{
  "bibcode": "2021GCN.31127....1L",
  "body": "T. Laskar (Radboud University), R. Margutti (UC Berkeley), K. D. Alexander\n(Northwestern), E. Berger (Harvard), and R. Chornock (UC Berkeley) report:\n\n\"We observed GRB 210905A (Sonbas et al., GCN 30765) with Chandra/ACIS,\nstarting on 2021 November 24 at 13:08:25 UT (80.7 days after the GRB\ntrigger), for a total exposure of 20 ks. We detect a point source at the\nposition of the Swift/XRT afterglow with a 0.5-8 keV (observed) count rate\nof ~ 3.1e-4 counts/s. Using spectral parameters from fitting the Swift/XRT\nPC-mode spectrum at a redshift of z=6.318 (Tanvir et al., GCN 30771), we\nfind a preliminary unabsorbed flux of ~ 5.4e-15 erg/(s cm^2) in the 0.3-10\nkeV band (observer frame).\n\nThis measurement confirms a potential break in the Swift/XRT observations\nat ~ 30 days after the trigger. The post-break decline rate is consistent\nwith -2. Interpreting this break as a jet break, assuming EKiso ~\nEgamma,iso, and using the isotropic-equivalent gamma-ray energy from\nKonus-Wind (Frederiks et al., GCN 30780), the inferred opening angle is ~ 9\ndeg * (E/1.1e54 erg) / (n/ (1particle/cm^3))] ^(-3/8) for a uniform density\nenvironment, leading to a beaming-corrected energy of ~ 1.3e52 erg. Further\nanalysis is underway.\n\nWe thank Harvey Tananbaum and Pat Slane for approving our DDT request and\nthe entire CXC staff for arranging and executing the observations.\"",
  "circularId": 31127,
  "createdOn": 1637859336000,
  "email": "tanmoylaskar@gmail.com",
  "subject": "Chandra observations of GRB 210905A",
  "submitter": "Tanmoy Laskar at U of Bath  <tanmoylaskar@gmail.com>",
  "eventId": "GRB 210905A"
}