TITLE: GCN CIRCULAR NUMBER: 44266 SUBJECT: GRB 260411B: Fermi GBM Detection DATE: 26/04/11 13:46:30 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07@gmail.com> U. Pathak (IITB) and R. Sonawane (IISER TVM) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 08:04:35.31 UT on 11 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260411B (trigger 797587480/260411337). The Fermi GBM final real-time Localization is reported in GCN 44262. An optical counterpart is also detected by GOTO (O'Neill et al. 2026 GCN 44265). The angle from the Fermi LAT boresight is 60 degrees. The GBM light curve consists of two spikes in a single emission episode, with a duration (T90) of about 33 s (50-300 keV). The time-averaged spectrum from T0-2.9 to T0+29.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.62 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 348 +/- 4 keV. The event fluence (10-1000 keV) in this time interval is (2.31 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+8.3 s in the 10-1000 keV band is 21.8 +/- 0.4 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 293 +/- 3 keV, alpha = -0.54 +/- 0.05 and beta = -2.3 +/- 0.1. 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/44266. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...