TITLE:   GCN CIRCULAR
NUMBER:  40218
SUBJECT: EP250421a: Upper limits from Fermi-GBM Observations
DATE:    25/04/23 14:26:25 GMT
FROM:    mariaedvige.ravasio@ru.nl

M. E. Ravasio (Radboud Univ.), E. Burns (LSU), C. Malacaria (INAF-OAR) and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team:

Fermi-GBM had full spatial coverage of the transient EP250421a detected by EP-WXT (Zhao et al., GCN 40198). There was no Fermi-GBM onboard trigger around the EP starting time T0=2025-04-21T16:16:28 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. A candidate was found at T0+380 s, but its location is not consistent with the EP transient. 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