TITLE: GCN CIRCULAR NUMBER: 40372 SUBJECT: GRB 250504A: EIRSAT-1 GMOD Detection DATE: 25/05/06 21:03:59 GMT FROM: Padraig McDermott at University College Dublin padraig.mcdermott@ucdconnect.ie
P. McDermott, D. Murphy, C. McKenna, C. de Barra, A. Ulyanov, G. Finneran, G. Corcoran, L. Cotter, A. Empey, J. Fisher, F. Gibson Kiely, J. Thompson, D. McKeown, A. Martin-Carrillo, L. Hanlon, S. McBreen, on behalf of the EIRSAT-1 team:
EIRSAT-1 reports the detection of the long gamma-ray burst GRB 250504A by the Gamma-ray Module (GMOD) instrument, which was also detected by Fermi GBM (GCN [40342](https://gcn.nasa.gov/circulars/40342) and [40346](https://gcn.nasa.gov/circulars/40346)) and Swift-BAT (GCN [40343](https://gcn.nasa.gov/circulars/40343)). The GMOD detection was made starting at 2025-05-04 23:25:56.5 UTC.
The GMOD light curve for GRB 250405A, with 1.2s binning, shows multiple peaks consistent with the detections by Fermi GBM and Swift-BAT.
The spacecraft location at time of detection was 9.886º S, 164.567° E and an altitude of 386 km.
The light curve for this event as measured by GMOD can be found here: https://grb.eirsat1.ie/250504A/250504A_LC_onboard_preliminary.png
EIRSAT-1 is Ireland’s first satellite (Doyle et al. Proceedings of the 4th SSEA, 2022). It is a 2U CubeSat and carries onboard a number of experiments including the Gamma-Ray Module (GMOD), a novel, compact, gamma-ray detector (Murphy et al, Experimental Astronomy, 53, 961–990, 2022). GMOD consists of a 25 mm × 25 mm × 40 mm Cerium Bromide scintillator coupled to SiPMs and is designed to detect gamma-ray bursts in the ~ 60 keV - 1.5 MeV range. EIRSAT-1 was developed in University College Dublin with support from ESA’s Fly Your Satellite! programme and was launched on 1st December 2023.
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