TITLE: GCN CIRCULAR NUMBER: 41273 SUBJECT: EP250806a: Upper limit from Fermi-GBM Observations DATE: 25/08/07 20:05:54 GMT FROM: mariaedvige.ravasio@ru.nl

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 transient EP250806a detected by EP-WXT (Yang et al., GCN 41246). There was no Fermi-GBM onboard trigger around the refined EP starting time T0=2025-08-06T09:17:30 UTC (Liang et al., GCN 41256).

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 transient, both temporally and spatially, is identified, as confirmed also by visual inspection of the data.

Assuming a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7), and a duration of 8.192 s, we derive a flux upper limit of 3.7e-08 erg/cm2/s in the energy band 10-1000 keV.

[1] Goldstein et al. 2019 arXiv:1903.12597

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