EIRSAT-1, the student-built satellite from University College Dublin that was launched into space last December, has detected two gamma-ray bursts on 21 August.

The miniature cube satellite, or cubesat, was designed, built, and tested at UCD under guidance of the European Space Agency (ESA) Education division ‘Fly Your Satellite’ programme, and is Ireland's first-ever satellite.

One of the payloads on board the satellite is the gamma-ray detector – the Gamma-ray Module (GMOD). It has been the first experiment in-orbit to net a major success for the mission. The module was designed to detect bursts of high energy radiation emitted from the biggest, most destructive events in the universe such as the formation of a black hole from a collapsar (death of a massive star) or the merging of neutron stars.

The Irish cubesat detected both its first and its second gamma-ray bursts within about 80 minutes of each other. Different spacecraft also reported these gamma-ray bursts, confirming the detections and validating the full GMOD instrument performance in-orbit – a great moment for the UCD team and the ESA programme, which hails EIRSAT-1 as a flagship project.

Post-doctoral researcher in UCD Space Science Group and EIRSAT-1 Systems Engineer and GMOD Lead, Dr David Murphy said: “It was incredibly exciting to downlink the data from GMOD and discover such clear unambiguous detections of these two gamma-ray bursts. Having spent so many years designing, building and testing the GMOD instrument as well as calibrating it and figuring out how to operate it in-orbit, these detections are an amazing validation of all the hard work put in by the team. It's astonishing to think that this satellite that we hand-built in our lab is now in space detecting photons that have travelled across the universe for billions of years to reach it. It's a real boost for us as we're beginning work on bigger and better space missions.”

ESA congratulated the team on the “groundbreaking gamma-ray burst detections” on X, posting: “EIRSAT-1 is making waves in the scientific community, congratulations to the team and everyone involved!”

Gamma-ray bursts only last seconds or minutes but they are incredibly intense and can cross vast intergalactic distances to be picked up by GMOD. As EIRSAT-1 orbits earth from pole to pole, GMOD’s design and calibration enables fully optimised instrument performance when operational, as well as the ability to switch off to avoid overloading the on-board computer in high radiation regions around the poles, giving it the best chance of detecting the elusive gamma-ray bursts.

EIRSAT-1 Science Lead and gamma-ray expert, Professor Sheila McBreen said: “The detection of these bursts is a major milestone for the EIRSAT-1 mission and the GMOD instrument. GMOD was designed, built and integrated in UCD, all the code to run it was developed in UCD, and it is now working in-orbit and has detected events caused by end points of stars. We hope these events are the first of many detected by GMOD on EIRSAT-1 and future instruments we are already developing in the Space Science Group.”

Optical light produced in the aftermath and environment of a gamma-ray burst can be used to measure its distance. To further examine the detected events, gamma-ray burst and pulsar expert at UCD, Dr Antonio Martin Carrillo and his collaborators used an eight-metre telescope at the European Southern Observatory (ESO) in Chile. They found that one of the gamma-ray bursts detected by GMOD is roughly 3 billion light years away and likely the result of two neutron stars merging.

He said: “After the detection of a new gamma-ray burst, as part of an international collaboration with a large ESO programme, my international colleagues and I search for its optical counterpart to find its distance. This is a fundamental step to understand the true energy power of these events. With the aid of other space and ground-based telescopes, we were able to pinpoint the sky coordinates of one of EIRSAT-1’s gamma-ray bursts. I coordinated a series of observations with the eight metre VLT telescopes at Cerro Paranal (Chile) to gather the necessary data to constrain its distance. Its relative proximity and the properties of the optical counterpart seems to suggest that it was produced by the merger of two compact objects, likely neutron stars.”


Technical Information

Below are the three general coordinates network (GCN) notices with the technical information on the two GMOD detections and the optical redshift confirmation.

TITLE: GCN CIRCULAR
NUMBER: 37231
SUBJECT: GRB240821B: First GRB Detected by EIRSAT-1 GMOD
DATE: 24/08/22 17:57:02 GMT
FROM: David Murphy

D. Murphy, C. McKenna, C. de Barra, A. Ulyanov, P. McDermott, M. Doyle, R. Dunwoody, J. Mangan, G. Finneran, 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 GRB240821B by the Gamma-ray Module (GMOD) instrument, which was also detected by Fermi GBM (GCN [37224](https://gcn.nasa.gov/circulars/37224)). The detection was made at 24-08-21 17:17:35.6 UTC.

The GMOD light curve for GRB240821B with 1.2s binning shows a burst with multiple pulses. The spacecraft location at time of detection was 38.677 N, 65.093 E and an altitude of 481.9 km.

The GMOD light curve for this event can be found here:
https://grb.eirsat1.ie/20240821B/20240821B_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.

View this GCN Circular online at https://gcn.nasa.gov/circulars/37231.

TITLE: GCN CIRCULAR
NUMBER: 37232
SUBJECT: GRB240821A: EIRSAT-1 GMOD Detection
DATE: 24/08/22 18:00:10 GMT
FROM: David Murphy

D. Murphy, C. McKenna, C. de Barra, A. Ulyanov, P. McDermott, M. Doyle, R. Dunwoody, J. Mangan, G. Finneran, 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 short gamma-ray burst GRB240821A which was also detected by Fermi GBM (GCN [37219](https://gcn.nasa.gov/circulars/37219)) and SVOM (GCN [37220](https://gcn.nasa.gov/circulars/37220), GCN [37226](https://gcn.nasa.gov/circulars/37226)). The detection was made at 24-08-21 18:36:03.2 UTC.

The GMOD light curve for GRB240821A, with 1.2s binning shows a single peak. The spacecraft location at time of detection was 21.884 S, 54.418 E and an altitude of 490.5 km.

The light curve for this event as measured by GMOD can be found here:
https://grb.eirsat1.ie/20240821A/20240821A_LC_onboard_preliminary.png
TITLE: GCN CIRCULAR
NUMBER: 37731
SUBJECT: GRB 240821A: Host galaxy redshift from VLT/X-shooter
DATE: 24/10/07 15:42:50 GMT
FROM: Benjamin Schneider at MIT

B. Schneider (MIT), A. Rossi (INAF-OAS), M. Ferro (INAF-OAB), H. Fausey (GWU), A. L. Thakur (INAF-IAPS), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud Univ.), N. R. Tanvir (U. Leicester), A. J. Levan (Radboud Univ. and Warwick Univ.), J. T. Palmerio (CEA), A. Saccardi (GEPI/Obs. de Paris), S. D. Vergani (GEPI/Obs. de Paris) report on behalf of the Stargate collaboration:

We observed the location of the SVOM and Fermi short GRB 240821A (Cangemi et al., GCN 37220; He et al., GCN 37226; Murphy et al., GCN 37232; Dalessi & Meegan, GCN 37239, Quirola-Vasquez et al., GCN 37319) with the X-shooter spectrograph mounted on the ESO VLT UT3 (Melipal) as a follow-up to our previous VLT/X-shooter observation (Saccardi et al., GCN 37369). The observation consisted of two consecutive observations of 4x1200 s each, with mid-times at 03:53:33 UT and 05:18:58 UT on 2024 October 1 (~40.4 days after the trigger). The seeing delivered is significantly better than for our previous observation reported in GCN 37369.

In addition to the emission line at 8120 AA mentioned by Saccardi et al. (GCN 37369), which is clearly detected also in the new spectra, two fainter features are also visible. This allows solving the conundrum from the previous observation, as the three lines nicely match [O II] 3729, H alpha, and [N II] 6584, all at a common redshift z = 0.238.

We acknowledge the expert support from the ESO observing staff at Paranal, in particular Jonathan Smoker and Cedric Ledoux.