Skip to main content
Testing. You are viewing the public testing version of GCN. For the production version, go to
Introducing Einstein Probe, Astro Flavored Markdown, and Notices Schema v4.0.0. See news and announcements

GCN Circular 32642

GRB 221009A: Fermi GBM observation
2022-10-10T04:04:41Z (2 years ago)
Stephen Lesage at Fermi-GBM Team <>
S. Lesage (UAH), P. Veres (UAH), O.J. Roberts (USRA),
E. Burns (LSU), and E. Bissaldi (Politecnico and INFN Bari)
report on behalf of the Fermi GBM Team:

"At 13:16:59.99 UT on 09 October 2022, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 221009A (trigger 687014224/221009553) which
was also detected by Swift-BAT (S. Dichiara, et al. 2022, GCN 32632;
J. A. Kennea, et al. 2022, GCN 32635), Fermi-LAT (E. Bissaldi et al. 2022,
GCN 32637), INTEGRAL (SPI-ACS), Konus-Wind, and triangulated by IPN
(D. Svinkin et al. 2022, GCN 32641). The GBM on-ground location (GCN 32636)
consistent with the Swift-BAT and Fermi-LAT locations and the IPN

The angle from the Fermi LAT boresight is 73 degrees.

The GBM light curve consists of two emission episodes, a single isolated
followed by a longer, extremely bright, multi-pulsed emission episode with
a duration (T90) of about 327 s (10-1000 keV).

The time-averaged spectrum for the first emission episode
from T0-0.0 to T0+43.4 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.70 +/- 0.02 and the cutoff energy,
parameterized as Epeak, is 375 +/- 87 keV.
The event fluence (10-1000 keV) in this time interval is
(2.12 +/- 0.05)E-05 erg/cm^2.

Due to the brightness of the second emission episode, the likelihood of
pulse pile-up and other systematic effects are very high and no single
spectral model provides an adequate fit in this preliminary analysis.
The event fluence (10-1000 keV) from T0+175 to T0+1458 s
is on the order of (2.912 +/- 0.001)E-02 erg/cm^2.
The 1.024 sec peak photon flux measured
starting from T0+238.8 s in the 10-1000 keV band
is on the order of 2385 +/- 3 ph/s/cm^2,
making this the most intense and fluent GRB detected by Fermi GBM.

Further analysis is being performed.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:

For Fermi GBM data and info, please visit the official Fermi GBM Support
Looking for U.S. government information and services? Visit