GRB 221009A: Fermi GBM detection of an extraordinarily bright GRB

"At 2022-10-09 13:16:59.000 UT on 9 October 2022, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 221009A (trigger 687014224 / 221009553). This event, if it is a GRB, it is the brightest among the GBM detected GRBs. If it is not a GRB then it is a rare transient event. Follow-up across all wavelengths is encouraged. The on-ground calculated location, using the GBM trigger data, is RA = 290.4, DEC = 22.3 (J2000 degrees, equivalent to 19 h 22 m, 22 d 15 '), with a statistical uncertainty of 1 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ). This location is consistent with the Swift J1913.1+1946 localization (Dichiara et al. GCN 32632) though it precedes the Swift trigger by an hour. The angle from the Fermi LAT boresight at the GBM trigger time is 76 degrees. The GBM light curve consists of an initial ~10 s long pulse, followed by an extraordinarily bright episode at ~180 s after the trigger time, lasting at least 100 seconds. The analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"