TITLE: GCN CIRCULAR NUMBER: 43346 SUBJECT: GRB 260105B: Fermi GBM Detection DATE: 26/01/07 00:08:46 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 23:21:36.55 UT on 05 January 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260105B (trigger 789348101/260105973). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 259.71, Dec = 1.74 (J2000 degrees, equivalent to J2000 17h 18m, +1d 44'), with a statistical uncertainty of 2.03 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 68 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 11 s (50-300 keV). The time-averaged spectrum from T0-1.9 to T0+12.5 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.96 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 232 +/- 2 keV. The event fluence (10-1000 keV) in this time interval is (8 +/- 0.4)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.4 s in the 10-1000 keV band is 156 +/- 2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 178 +/- 2 keV, alpha = -0.83 +/- 0.01 and beta = -2.19 +/- 0.03. 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/43346. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...