TITLE:   GCN CIRCULAR
NUMBER:  40984
SUBJECT: GRB 250703A: EIRSAT-1 GMOD Detection
DATE:    25/07/05 22:38:57 GMT
FROM:    Laura Cotter at University College Dublin <laura.cotter@ucdconnect.ie>

L. Cotter,C. McKenna, D. Murphy, C. de Barra, A. Ulyanov, P. McDermott, G. Finneran,  M. Doyle, R. Dunwoody, J. Mangan, G. Corcoran, 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 GRB250703A (Fermi-GBM detection GCN 40909; IPN localization GCN 40976; Kounus Wind GCN 40977) by the Gamma-ray Module (GMOD) instrument. The GMOD detection was made, starting at 2025-07-03 09:07:31.6 UTC.

The GMOD light-curve for GRB250703A with 1.2s binning shows a single bright pulse starting at 09:07:31.6 UTC, also visible on the Fermi light-curve.

The spacecraft location at the time of detection was 47.364º N, 32.160º E, at an altitude of 361.2 km.
The GMOD light curve for this event can be found here:

[https://grb.eirsat1.ie/250703A/250703A_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 at University College Dublin with support from ESA’s Fly Your Satellite! programme and was launched on 1st December 2023.