TITLE:   GCN CIRCULAR
NUMBER:  43835
SUBJECT: GRB 260223A: Fermi GBM Observation
DATE:    26/02/25 17:16:57 GMT
FROM:    Peter Veres at University of Alabama in Huntsville <veresp@gmail.com>

P. Veres (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 04:11:09.81 UT on 23 February 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260223A (trigger 793512674/260223174),
which was also detected by 
DDOTI (Becerra et al. 2026, GCN 43811),
COLIBRI (de Ugarte Postigo  et al. 2026, GCNs 43812, 43814 & 43820),
SVOM/GRM  (Wang et al. 2026, GCN 43815),
SVOM/VT  (Li et al. 2026, GCN 43816) and
Glowbug  (Woolf et al. 2026, GCN 43824).

The Fermi GBM on-ground location (GCN 43808) is consistent with the DDOTI position.

The angle from the Fermi LAT boresight is 33 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 39 s (50-300 keV). The time-averaged spectrum
from T0-9.2 to T0+51.2 s is best fit by
a Band function with Epeak = 70 +/- 6 keV,
alpha = -0.76 +/- 0.09, and beta = -1.91 +/- 0.02.

The event fluence (10-1000 keV) in this time interval is
(2.16 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+18 s in the 10-1000 keV band is 10.4 +/- 0.3 ph/s/cm^2.

The spectral 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/"