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TITLE:   GCN CIRCULAR
NUMBER:  30865
SUBJECT: GRB 210923A: Fermi GBM Final Real-time Localization
DATE:    21/09/23 11:57:13 GMT
FROM:    Fermi GBM Team at MSFC/Fermi-GBM  <do_not_reply@GIOC.nsstc.nasa.gov>

The Fermi GBM team reports the detection of a likely SHORT GRB

At 11:49:36 UT on 23 Sep 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210923A (trigger 654090581.820056 / 210923493).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 90.0, Dec = -6.5 (J2000 degrees, equivalent to J2000 06h 00m, -6d 30'), with a statistical uncertainty of 10.9 degrees.

The angle from the Fermi LAT boresight is 47.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210923493/quicklook/glg_skymap_all_bn210923493.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210923493/quicklook/glg_healpix_all_bn210923493.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210923493/quicklook/glg_lc_medres34_bn210923493.gif

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TITLE:   GCN CIRCULAR
NUMBER:  30873
SUBJECT: Retraction of Fermi GBM GRB 210923A: the trigger is not a GRB
DATE:    21/09/23 22:03:59 GMT
FROM:    Joe Mangan at UCD  <joseph.mangan@ucdconnect.ie>

J.Mangan (UCD), S.Lesage (UAH) report on behalf of the Fermi Gamma-ray
Burst Monitor Team:

The Fermi Gamma-ray Burst Monitor (GBM) trigger 654090581/210923493 at
11:49:36.820 UT
on 23 September 2021, tentatively classified as a GRB (GCN 30865), is in
fact not due
to a GRB. This trigger is likely due to a terrestrial electron beam (TEB).