TITLE: GCN CIRCULAR NUMBER: 44430 SUBJECT: GRB 260429A: Fermi GBM Detection DATE: 26/04/30 07:10:23 GMT FROM: Lorenzo Scotton at UAH <lscottongcn@outlook.com> L. Scotton (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:24:02.02 UT on 29 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260429A (trigger 799197847/260429975). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 283.92, Dec = 18.10 (J2000 degrees, equivalent to J2000 18h 55m, +18d 6'), with a statistical uncertainty of 2.61 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 76 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 0.16 s (50-300 keV). The time-averaged spectrum from T0-0.1 to T0+0.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 900 +/- 20 keV. The event fluence (10-1000 keV) in this time interval is (2.41 +/- 0.07)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.0 s in the 10-1000 keV band is 69 +/- 2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 600 +/- 20 keV, alpha = -0.92 +/- 0.03 and beta = -2 +/- 0.09. 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/44430. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...