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Gamma-Ray Detector (GMOD)

GMOD will be used to detect astrophysical gamma-ray bursts and other short-lived events that produce gamma-rays, such as solar flares. It is a gamma-ray detector which operates on the principle of scintillation. A crystal (Cerium Bromide) produces a pulse of optical light when hit by a gamma-ray.

This light signal is detected by an array of sensors called Silicon Photomultipliers or SiPMs. The sensors used in GMOD were originally developed by Irish company SensL (now onsemi).  The Silicon Photomultiplier is revolutionising in-situ and remote sensing of gamma-rays in space by removing the need for conventional photomultiplier tubes that are typically very bulky, fragile and require high voltages to operate.The SiPMs convert the light created by the gamma-ray into an electrical signal. A specially designed integrated circuit called SIPHRA digitises these signals so they can be processed by onboard computers and transmitted back to UCD.

Gamma-ray detectors like GMOD have been in development by Profs. Lorraine Hanlon and Sheila McBreen of the UCD Space Science group in the School of Physics for more than a decade.

GMOD has undergone extensive testing. It has been vibrated several times on its own and as part of EIRSAT-1 to demonstrate that it can withstand the intense vibrations during the rocket launch. A thermal vacuum chamber was used to simulate the environment in Low Earth Orbit. GMOD was tested by being repeatedly heated and cooled in a vacuum. Silicon photomultipliers like those used in GMOD were irradiated by high-energy protons to measure how they will perform after several years in Low Earth Orbit.

GMOD (shown by the red box) in the final flight configuration in the CubeSat.

What are gamma-rays?

Gamma-rays are a form of electromagnetic radiation. Since they cannot penetrate Earth’s atmosphere, satellite-based experiments are needed to detect them.  

Why are gamma-rays important in astrophysics?

Gamma-ray bursts are short, powerful blasts of gamma-ray radiation, which originate in deep space. Some are caused by an exploding star (a type of supernova), while others may be due to a pair of neutron stars (or a black hole and a neutron star) colliding. Gamma-ray bursts are often created by events in the early universe. There's a lot about the early universe that we don't yet understand, and gamma-ray bursts are one of the best tools for investigating it.

The multi-messenger revolution

August 2017, with the event called ‘GW170817’, marked the beginning of the multi-messenger revolution in astrophysics. The nearly simultaneous detection of a gravitational wave signal from a pair of merging Neutron Stars detected by the Advanced LIGO/Virgo experiment, and of a short gamma-ray burst by the NASA Fermi and ESA’s INTEGRAL satellites, proved that some of the shorter GRBs are due to such mergers. 

Keeping the gamma-ray sky under surveillance

During future observing runs by gravitational wave detectors, it is important that we also have gamma-ray eyes on the full sky so we don’t miss any of these rare and short-lived events. Joint observations improve our understanding of such exotic astrophysical objects and provide new insights into fundamental physics. 

GMOD will detect about 10 gamma-ray bursts (GRBS)  every year. Aswell as discovering GRBs, GMOD will provide important data on the behaviour in space of the novel technologies it uses, paving the way for other CubeSats and larger space missions.

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