TITLE: GCN CIRCULAR NUMBER: 35655 SUBJECT: GRB 240129A: Fermi GBM Observation DATE: 24/01/31 15:28:04 GMT FROM: Vidushi Sharma at NASA GSFC/UMBC vidushi.sharma@nasa.gov

S. Dalessi (UAH), V Sharma (NASA-GSFC/UMBC) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 15:09:22.53 UT on 29 January 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240129A (trigger 728233767/240129632), which was also detected by Swift/BAT-GUANO (DeLaunay et al. 2024, GCN 35653).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 108.02, Dec = 34.60 (J2000 degrees, equivalent to J2000 07h 12m, 34d 36'), with a statistical uncertainty of 3.18 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error [Connaughton et al. 2015, ApJS, 216, 32]).

The angle from the Fermi LAT boresight is 114 degrees.

The GBM light curve of a single emission episode with a duration (T90) of about 28 s (50-300 keV). The time-averaged spectrum from T0+6.1 to T0+21.5 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.24 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 74 +/- 6 keV.

The event fluence (10-1000 keV) in this time interval is (4.6 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.38 s in the 10-1000 keV band is 4.9 +/- 0.3 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/35655. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...