GCN Circular 41815
Subject
EP250911a: Upper limit from Fermi-GBM Observations
Event
Date
2025-09-12T14:23:51Z (9 days ago)
From
mariaedvige.ravasio@ru.nl
Via
Web form
M. E. Ravasio and P.G. Jonker (Radboud Univ.) on behalf of the Einstein Probe Team
and
E. Burns (LSU) on behalf of the Fermi-GBM Team, report:
Fermi-GBM had full spatial coverage of the transients EP250911a (Liang et al., GCN 41788 and GCN 41809) detected by EP-WXT, and found to be at z=3.84 (Malesani et al., GCN 41811). There was no Fermi-GBM onboard trigger around the refined EP trigger time T0=2025-09-11T08:57:55 (UTC).
The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [T0-50; T0+500] s, seeking signals between 64 ms and 32.768 s in duration. No signal consistent with the EP transients, both temporally and spatially, is identified, as confirmed also by visual inspection of the data.
Assuming a “normal” spectral template (Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3), whose alpha value is consistent with the power law index reported by EP (Liang et al., GCN 41809), and a timescale of 8.192 s, we derive a flux upper limit of 5.3e-08 erg/cm2/s in the energy band 10-1000 keV.
[1] Goldstein et al. 2019 arXiv:1903.12597