Abstract
The Educational Irish Research Satellite 1 (EIRSAT-1) is a 2U CubeSat being developed under ESA’s Fly Your Satellite! programme. The project has many aspects, which are primarily educational, but also include space qualification of new detector technologies for gamma-ray astronomy and the detection of gamma-ray bursts (GRBs). The Gamma-ray Module (GMOD), the main mission payload, is a small gamma-ray spectrometer comprising a 25 mm × 25 mm × 40 mm cerium bromide scintillator coupled to an array of 16 silicon photomultipliers. The readout is provided by IDE3380 (SIPHRA), a low-power and radiation tolerant readout ASIC. GMOD will detect gamma-rays and measure their energies in a range from tens of keV to a few MeV. Monte Carlo simulations were performed using the Medium Energy Gamma-ray Astronomy Library to evaluate GMOD’s capability for the detection of GRBs in low Earth orbit. The simulations used a detailed mass model of the full spacecraft derived from a very high-fidelity 3D CAD model. The sky-average effective area of GMOD on board EIRSAT-1 was found to be 10 cm2 at 120 keV. The instrument is expected to detect between 11 and 14 GRBs, at a significance greater than 10σ (and up to 32 at 5σ), during a nominal one-year mission. The shape of the scintillator in GMOD results in omni-directional sensitivity which allows for a nearly all-sky field of view.
Highlights
Gamma-ray bursts (GRBs) are intense flashes of gamma radiation which originate from distant galaxies and typically last from a fraction of a second to several minutes [1]
The full EIRSAT-1 spacecraft has been included in the mass model as it is important to characterise the capabilities of the Gamma-ray Module (GMOD) detector in the environment in which it will operate
The high-fidelity model of EIRSAT-1 was simplified to the point that it contained only solids which could be represented using these supported Medium Energy Gamma-ray Astronomy Library (MEGAlib) volumes. While this has the effect of removing finer details from the model, the overall mass distribution is not significantly changed and provides equivalent effective shielding. This simplification process was performed manually using AutoCAD, as it was significantly easier to place the volumes in a 3D environment and ensure that they correctly represented the EIRSAT-1 geometry using the AutoCAD interface than using the MEGAlib text-based volume description format
Summary
Gamma-ray bursts (GRBs) are intense flashes of gamma radiation which originate from distant galaxies and typically last from a fraction of a second to several minutes [1]. Current and planned near-future large scale missions, including SVOM [23], a Chinese-French mission due for launch in 2022, will not provide the full-sky coverage required for efficient detection of electromagnetic counterparts to GW events [24] This potential gap has led to a search for alternative solutions, such as a fleet of small satellites with gamma-ray detecting technology. The detector would require a compact low-power readout system, such as the SIPHRA ASIC, to fit in a CubeSat and the EIRSAT-1 Gamma-ray Module (GMOD) was envisaged as a demonstrator to combine all the necessary components in a CubeSat payload Such a payload is seen as a significant advance over legacy instrumentation which typically relied on classical photomultiplier tube scintillator detection and discrete control and readout electronics. The final detector design has been environmentally qualified [50]
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