TITLE: GCN CIRCULAR NUMBER: 43489 SUBJECT: GRB 260120B: Fermi GBM Observation DATE: 26/01/21 16:21:32 GMT FROM: Matt Godwin <msg0028@uah.edu> Matt Godwin (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 18:00:26.05 UT on 20 January 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260120B (trigger 790624831/260120750), which was also detected by Swift BAT (Ferro et al. 2026, GCN 43479), Swift XRT (Goad et al. 2026, GCN 43484), and SVOM/C-GFT (Wu et al. 2026, GCN 43483). The Fermi GBM real-time localization (GCN 43477) is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 10 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 7 s (50-300 keV). The time-averaged spectrum from T0-1.1 to T0+9.9 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.19 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 214 +/- 4 keV. The event fluence (10-1000 keV) in this time interval is (3.1 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.38 s in the 10-1000 keV band is 5.8 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 152 +/- 2 keV, alpha = 0.36 +/- 0.02 and beta = -2.26 +/- 0.05. 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/" View this GCN Circular online at https://gcn.nasa.gov/circulars/43489. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...