TITLE: GCN CIRCULAR NUMBER: 43585 SUBJECT: GRB 260131A/B: Fermi GBM Observation DATE: 26/01/31 23:12:56 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 06:39:30.44 UT on 31 January 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260131A/B (trigger 791534375/260131277). which was also detected by MAXI (H. Sugai et al. 2026, GCN 43580). The Fermi GBM final real-time Localization (GCN 43579) is consistent with the MAXI position. The MAXI burst triggered on the second pulse of 260131A. We note both bursts have similar locations and are likely the same event. The angle from the Fermi LAT boresight using the MAXI location is 112 degrees. The GBM light curve consists of two separated FRED emission episodes with a duration (T90) of about 257 s (50-300 keV). The time-averaged spectrum from T0-2.0 to T0+280.0 s is best fit by a Band function with an Epeak of 148 +/- 39 keV, alpha is -0.90 +/- 0.16 and beta is -1.76 +/- 0.06. The event fluence (10-1000 keV) in this time interval is (2.82 +/- 0.09)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.6 s in the 10-1000 keV band is 8.3 +/- 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/43585. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...