TITLE: GCN CIRCULAR NUMBER: 39622 SUBJECT: GRB 250306A: EIRSAT-1 GMOD detection DATE: 25/03/08 19:48:12 GMT FROM: Cuán de Barra at UCD cuan.debarra@ucdconnect.ie

C. de Barra, D. Murphy, C. McKenna, A. Ulyanov, P. McDermott, G. Finneran, M. Doyle, R. Dunwoody, J. Mangan, 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 GRB250306A by the Gamma-ray Module (GMOD) instrument, which was also detected by Swift BAT (GCN 39606), AstroSat CZTI (GCN 39611), and NuSTAR (GCN 39616)

The GMOD detection was made starting at 2025-03-06 16:30:05.7 UTC.

The GMOD light-curve for GRB250306A with 1.2s binning shows two distinct pulses consistent with the observation seen by Swift-BAT.

The spacecraft location at the time of detection was 37.285 S, 98.479 E, at an altitude of 439.15 km.

The GMOD light curve for this event can be found here:

https://grb.eirsat1.ie/250306A/250306A_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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