{
  "bibcode": "2022GCN.32694....1I",
  "body": "W. Iwakiri (Chuo U.), G. K. Jaisawal (DTU Space), G. Younes\n(NASA/GSFC/GWU), Z. Wadiasingh (UMCP, NASA/GSFC), S. Guillot (IRAP/CNRS),\nK. C. Gendreau (NASA/GSFC), Z. Arzoumanian (NASA/GSFC), E. C. Ferrara\n(UMCP, NASA/GSFC), T. Mihara (RIKEN), D. Pasham (MIT), J. M. Miller (Univ.\nof Michigan), A. Sanna (Univ. of Cagliari), C. Malacaria (ISSI), C. B.\nMarkwardt (NASA/GSFC)\n\nWe report on initial NICER observations of the exceptionally bright GRB\n221009A, at a redshift of 0.1505 (GCN #32648, #32686) and observed from\nradio to TeV energies (GCNs #32632, #32635, #32636, #32641, #32658, #32661,\n#32668, #32677, and ATels #15653, #15655, #15656, #15660, #15661). NICER\nobserved GRB 221009A intermittently from 2022 Oct 9 17:11 to Oct 11 00:12\nUT, or 14.7 ksec to 126 ksec after the Fermi/GBM trigger time (GCN #32636).\nDuring this period, NICER made 12 observations with exposure times ranging\nfrom 40 to 400 sec each. The initial count rate registered with NICER is\n1400 counts/s which declined to about 38 counts/s at the time of the last\nobservation reported here. From a preliminary analysis, we find that the\ndecline follows a power law with an index of -1.6. The 1-10 keV spectrum of\neach observation is well reproduced by an absorbed power-law model with a\nspectral index of about 2.0. We used the tbabs model with wilms abundance\nin XSPEC (Wilms, Allen & McCray 2000) for an assumed Galactic absorption of\n5.4 x 10^21 cm^-2 (Willingale et al. 2013; GCN #32651). The average column\ndensity of these observations with the ztbabs model is 1.1 x 10^22 cm^-2 at\na redshift of 0.151 (GCN #32648). The absorbed (unabsorbed) flux in the 0.3\n- 10 keV band declined from 6.1 x 10^-9 (1.3 x 10^-8) to 1.8 x 10^-10 (3.3\nx 10^-10) erg/sec/cm^2.\n\nNICER initially received notification of the GRB through OHMAN (On-orbit\nHookup of MAXI and NICER) at 14:10:57 UT on Oct 9, but poor visibility\ndelayed a prompt follow-up.  OHMAN is software on an International Space\nStation laptop computer that provides a new automated triggering\ncapability, monitoring live MAXI data and communicating new transient\nalerts to NICER for follow-up within minutes, visibility permitting. NICER\nis continuing to monitor GRB 221009A.  Detailed temporal and spectral\nanalysis is ongoing.\n\nThe NICER schedule can be found at\nhttps://heasarc.gsfc.nasa.gov/docs/nicer/schedule/nicer_sts_current.html.\n\nNICER is a 0.2-12 keV X-ray telescope operating on the International Space\nStation. The NICER mission and portions of the NICER science team\nactivities are funded by NASA.",
  "circularId": 32694,
  "createdOn": 1665513714000,
  "email": "gyounes@email.gwu.edu",
  "subject": "GRB 221009A: NICER follow-up observations",
  "submitter": "George A. Younes at George Washington U  <gyounes@email.gwu.edu>",
  "eventId": "GRB 221009A"
}