GCN Circular 37697
Subject
Fermi-GBM Sub-Threshold Detection of GRB 241002D
Date
2024-10-03T16:30:22Z (6 months ago)
From
Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov>
Via
Web form
O.J. Roberts (USRA/NASA-MSFC), E. Burns (LSU), A. Goldstein (USRA/NASA-MSFC), J. Wood (NASA-MSFC) report on behalf of the Fermi-GBM Team:
SVOM detected GRB 241002D on 2024-10-02 at 22:08:07.000 UTC (Tan et al., GCN #37693). There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no candidates.
The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, identified an unambiguous transient starting -0.128 s before the SVOM trigger time most significantly on the 1.024 s timescale, with a LogLR = 297. Fermi-GBM did not trigger on-board due to intentional suppression of soft transients. The Fermi-MET of the start time of this transient is 749599691.872 s. Using the standard search protocol, the Targeted Search localized the signal to an RA=24.6 deg., Dec.= 20.3 deg., with an error of 11.4 deg. (90 % confidence level, includes the systematic error), at a SNR of 24.0.
Additionally, the GBM Targeted Search event was found with the highest significance using a "soft" spectrum (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. The duration is about 5s, consistent with the T90 reported previous by Tan et al.
The Targeted Search data release product for this event can be found here: https://zenodo.org/uploads/13886511
[1] Goldstein et al. 2019 arXiv:1903.12597