GCN Circular 46098
Subject
GRB 261029A: Fermi GBM Observation
Event
Date
2026-10-29T17:16:12Z (2 days ago)
From
Lorenzo Scotton at UAH <lscottongcn@outlook.com>
Via
Web form
L. Scotton (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 01:27:03.81 UT on 29 October 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 261029A (trigger 814930028/261029060), which was also detected by SVOM (Goto et al. 2026, GCN 46072), Fermi-LAT (Longo et al. 2026, GCN 46085), EP-FXT (Kan et al. 2026, GCN 46086), SVOM/C-GFT (Shi et al. 2026, GCN 46088), AstroSat CZTI (Salunke et al. 2026, GCN 46089), CALET Gamma-Ray Burst Monitor (Marrocchesi et al. 2026, GCN 46095), SVOM/GRM (Yu et al. 2026, GCN 46096).
An optical counterpart is identified by GOTO (ONeill et al. 2026, GCN 46073), TRT (He et al. 2026, GCN 46078), KAIT (Wang et al. 2026, GCN 46079), MDM/MIRAGE (De et al. 2026, GCN 46080), NOT imaging and (Cotter et al. 2026, GCN 46081), LCO (Yin et al. 2026, GCN 46082), SVOM/COLIBRÍ (FM-GFT) (Álvarez et al. 2026, GCN 46083), LCO (Yin et al. 2026, GCN 46084), the PKU 60cm (Kang et al. 2026, GCN 46090), SVOM/VT (Ma et al. 2026, GCN 46092), MDM/MIRAGE (De et al. 2026, GCN 46093).
The redshift of the source is measured to be z = 3.27, NOT imaging and (Cotter et al. 2026, GCN 46081).
The Fermi GBM real-time localization (GCN 46071) is consistent with the SVOM position.
The angle from the Fermi LAT boresight is 69 degrees.
The GBM light curve consists of two emission episodes with a duration (T90) of about 43.8 s (50-300 keV). The time-averaged spectrum from T0-5.9 to T0+86.9 s is best fit by a Band function with Epeak = 621 +/- 7 keV, alpha = -0.85 +/- 0.01, and beta = -2.23 +/- 0.02.
The event fluence (10-1000 keV) in this time interval is (1.100 +/- 0.009)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+39.2 s in the 10-1000 keV band is 34.6 +/- 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/"