GRB 221009A: NICER follow-up observations

W. Iwakiri*, G. K. Jaisawal, G. Younes, Z. Wadiasingh , S. Guillot, K. C. Gendreau, Z. Arzoumanian, E. C. Ferrara, T. Mihara, D. R. Pasham, J. M. Miller, A. Sanna, C. Malacaria

*Corresponding author for this work

Research output: Other contributionNet publication - Internet publicationResearch


We report on initial NICER observations of the exceptionally bright GRB 221009A, at a redshift of 0.1505 (GCN #32648, #32686) and observed from radio to TeV energies (GCNs #32632, #32635, #32636, #32641, #32658, #32661, #32668, #32677, and ATels #15653, #15655, #15656, #15660, #15661).
NICER observed GRB 221009A intermittently from 2022 Oct 9 17:11 to Oct 11 00:12 UT, or 14.7 ksec to 126 ksec after the Fermi/GBM trigger time (GCN #32636). During this period, NICER made 12 observations with exposure times ranging from 40 to 400 sec each. The initial count rate registered with NICER is 1400 counts/s which declined to about 38 counts/s at the time of the last observation reported here. From a preliminary analysis, we find that the decline follows a power law with an index of -1.6. The 1-10 keV spectrum of each observation is well reproduced by an absorbed power-law model with a spectral index of about 2.0. We used the tbabs model with wilms abundance in XSPEC (Wilms, Allen & McCray 2000) for an assumed Galactic absorption of 5.4 x 1021 cm-2 (Willingale et al. 2013; GCN #32651). The average column density of these observations with the ztbabs model is 1.1 x 1022 cm-2 at a redshift of 0.151 (GCN #32648). The absorbed (unabsorbed) flux in the 0.3 - 10 keV band declined from 6.1 x 10-9 (1.3 x 10-8) to 1.8 x 10-10 (3.3 x 10-10) erg/sec/cm2.

NICER initially received notification of the GRB through OHMAN (On-orbit Hookup of MAXI and NICER) at 14:10:57 UT on Oct 9, but poor visibility delayed a prompt follow-up. OHMAN is software on an International Space Station laptop computer that provides a new automated triggering capability, monitoring live MAXI data and communicating new transient alerts to NICER for follow-up within minutes, visibility permitting. NICER is continuing to monitor GRB 221009A. Detailed temporal and spectral analysis is ongoing. The NICER schedule can be found at

NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA.
Original languageEnglish
Publication date11 Oct 2022
Publication statusPublished - 11 Oct 2022
SeriesThe Astronomer's telegram
NumberATel #15664


  • X-ray
  • Gamma-Ray Burst
  • Transient analysis


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