{
  "bibcode": "2022GCN.32788....1B",
  "body": "Daniel Brethauer (UC Berkeley), Raffaella Margutti (UC Berkeley), Judith\nRacusin (NASA/GSFC), Brian Grefenstette (Caltech), Kate D. Alexander\n(Arizona), Tom Barclay (NASA/GSFC), Edo Berger (Harvard), Eric Burns (LSU),\nBrad Cenko (NASA/GSFC), Yvette Cendes (Harvard), Ryan Chornock (UC\nBerkeley), Tarraneh Eftekhari (Northwestern), Jamie Kennea (PSU), Tanmoy\nLaskar (Utah)\n\n\nA second epoch of NuSTAR observations of GRB221009A was obtained on October\n15, 2022 starting at 05:21:09 UTC (~5.6 days since trigger; Dichiara et\nal., GCN 32632; Veres et al., GCN 32636) with an exposure time of 25 ks\n(PIs Racusin and Margutti).\n\n\nThe 3-79 keV spectrum is well fit by a power law with a photon index of\nGamma = 1.91 +/- 0.02 (1 sigma c.l.), which suggests spectrally softer\nemission than observed during the first NuSTAR epoch (Brethauer et al., GCN\n32695). The inferred NuSTAR power-law index is consistent with the value\ninferred from contemporaneous Swift-XRT observations, which indicate Gamma=\n1.79 +/- 0.11 and a best-fitting intrinsic absorption NHint=(0.46 +/-\n0.10)e22 cm-2 at z=0.151 for an assumed Galactic neutral hydrogen column\ndensity NH_mw=0.563e22 cm-2 (Willingale et al., 2013). The corresponding\nunabsorbed flux is ~4.5e-11 ergs/cm^2/s  (3-79 keV), indicating a factor\n~10 fading with respect to the previous epoch of NuSTAR data (Brethauer et\nal., GCN 32695).\n\n\nAdditional epochs of NuSTAR monitoring are planned on October 20th, and\nNovember 2nd. We thank the entire NuSTAR SOC for promptly implementing\nthese observations.",
  "circularId": 32788,
  "createdOn": 1666063737000,
  "email": "daniel_brethauer@berkeley.edu",
  "subject": "GRB 221009A: Second epoch of NuSTAR data",
  "submitter": "Daniel Brethauer at UC Berkeley  <daniel_brethauer@berkeley.edu>",
  "eventId": "GRB 221009A"
}