TITLE: GCN CIRCULAR NUMBER: 43573 SUBJECT: GRB 260127B: Fermi GBM Detection DATE: 26/01/30 21:27:55 GMT FROM: atrigg2@lsu.edu A. C. Trigg (NPP ORAU, NASA MSFC) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 20:02:32.57 UT on 27 January 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260127B (trigger 791236957/260127835). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 190.42, Dec = 56.88 (J2000 degrees, equivalent to J2000 12h 41m, +56d 52'), with a statistical uncertainty of 5.21 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 109 degrees. The GBM light curve displays a single short peak with a duration (T90) of about 1 s (50-300 keV). The time-averaged spectrum from T0-0.1 to T0+0.3 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.11 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 710 +/- 30 keV. The event fluence (10-1000 keV) in this time interval is (1.29 +/- 0.09)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.064 s in the 10-1000 keV band is 22 +/- 2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 570 +/- 20 keV, alpha = -0.040 +/- 0.002 and beta = -2 +/- 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/43573. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...