TITLE: GCN CIRCULAR NUMBER: 44554 SUBJECT: GRB 260511B: Fermi GBM Detection DATE: 26/05/11 15:37:39 GMT FROM: oliver.roberts@universityofgalway.ie O.J. Roberts (Uni. Of Galway, Ireland) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 11:00:31.70 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511B (trigger 800190036 / 260511459), which was also detected by SVOM /ECLAIRs and MXT (Godet et al. 2026, GCN 44543), with an optical counterpart initially detected by C-GFT (Wu et al. 2026, GCN 44547). The GBM localization is consistent with the SVOM position. The angle from the Fermi LAT boresight is 100 degrees. The GBM light curve consists of a two bright emission episodes with a duration (T90) of about 41 s (50-300 keV). The time-averaged spectrum from T0-0.5 to T0+47.6 s is best fit by a Band function, with Epeak = 209 +/- 16 keV, alpha = -1.01 +/- 0.04, and beta = -2.14 +/- 0.08. The event fluence (10-1000 keV) in this time interval is (2.62 +/- 0.04) E-05 erg/cm^2. The 1-s peak photon flux measured starting from T0+33.5 s in the 10-1000 keV band is 18.3 +/- 0.4 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/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44554. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...