TITLE: GCN CIRCULAR NUMBER: 40249 SUBJECT: GRB 250424A: EIRSAT-1 GMOD Detection DATE: 25/04/25 20:36:05 GMT FROM: Caimin McKenna at University College Dublin caimin.mckenna@ucdconnect.ie

C. McKenna, P. McDermott, D. Murphy, 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 250424A by the Gamma-ray Module (GMOD) instrument, which was also detected by Swift-BAT (GCN [40224](https://gcn.nasa.gov/circulars/40224)), Calet/CGBM (Trigger No. 1429512582), AstroSat CZTI (GCN [40231](https://gcn.nasa.gov/circulars/40231)), and Konus-Wind (GCN [40243](https://gcn.nasa.gov/circulars/40243)). The GMOD detection was made starting at 2025-04-24 06:52:12.6 UTC.

The GMOD light curve for GRB 250424A, with 1.2s binning, shows a long, smooth, single pulse, consistent with other observations.

The spacecraft location at time of detection was 23.407 S, 123.088 W and an altitude of 402.9 km.

The light curve for this event as measured by GMOD can be found here: https://grb.eirsat1.ie/250424A/250424A_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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