Gamma-Ray Burst Polarimetry with the COMCUBE-S CubeSat Swarm

TL;DR

This study evaluates COMCUBE-S, a swarm of 16U CubeSats equipped with Compton polarimeters and BGO spectrometers, to measure GRB prompt-emission polarization, spectra, and timing. Using MEGAlib/Cosima-based simulations, it integrates a detailed instrument mass model, a radiation/background environment in LEO, and a synthetic GRB population calibrated to Fermi-GBM data, to predict detection rates and polarimetric sensitivity across swarm configurations. The results indicate a high GRB detection rate (~2 per day) and strong polarimetric capability, with equatorial swarms of ~27–36 sats at ~500 km achieving the key goal of detecting $\ge 60$ GRBs with $MDP \le 30\%$ within ~2 years, thereby enabling discrimination among GRB prompt-emission models. The mission would also contribute to multi-messenger astronomy and broad time-domain transient science beyond GRBs.

Abstract

COMCUBE-S (Compton Telescope CubeSat Swarm) is a proposed mission aimed at understanding the radiation mechanisms of ultra-relativistic jets from Gamma-Ray Bursts (GRBs). It consists of a swarm of 16U CubeSats carrying a state-of-the-art Compton polarimeter and a BGO spectrometer to perform timing, spectroscopic and polarimetric measurements of the prompt emission from GRBs. The mission is currently in a feasibility study phase (Phase A) with the European Space Agency to prepare an in-orbit demonstration. Here, we present the simulation work used to optimise the design and operational concept of the microsatellite constellation, as well as estimate the mission performance in terms of GRB detection rate and polarimetry. We used the MEGAlib software to simulate the response function of the gamma-ray instruments, together with a detailed model for the background particle and radiation fluxes in low-Earth orbit. We also developed a synthetic GRB population model to best estimate the detection rate. These simulations show that COMCUBE-S will detect about 2 GRBs per day, which is significantly higher than that of all past and current GRB missions. Furthermore, simulated performance for linear polarisation measurements shows that COMCUBE-S will be able to uniquely distinguish between competing models of the GRB prompt emission, thereby shedding new light on some of the most fundamental aspects of GRB physics.

Figures (6)

• Figure S1: Representation of the concept of operations of the COMCUBE-S CubeSat swarm.
• Figure S2: COMCUBE-S payload and CubeSat model developed for numerical simulations of the instrument response function with the MEGAlib software.
• Figure S3: Simulated background count rates of the Compton Telescope Unit of a COMCUBE-S satellite for (left) single-interaction events and (right) double-interaction events against geographic position. The satellite is at an altitude of 500 km. The high fluxes of particles trapped inside the inner Van Allen radiation belt in the Earth's polar regions and the South Atlantic Anomaly are not represented in these maps (see Section \ref{['sec:nonoperation']}).
• Figure S4: Simulated regions of non-observation for COMCUBE-S satellites at 500 km altitude due to excessive fluxes of trapped protons (left) and electrons (right). Based on NASA's AP8min and AE8max trapped particle models (see text).
• Figure S5: Number of GRBs detected per year as a function of peak flux for different GRB populations. The blue histogram shows the total population of GRBs in the Universe that would be detected by an ideal instrument. The red histogram shows the distribution of GRBs in the Fermi-GBM catalogue corrected for the field of view and duty cycle of the GBM instrument ($\Omega_{\rm GBM}f_{\rm GBM}=0.59$; see text). The other four histograms show the synthetic GRBs detected by COMCUBE-S, assuming between one and four satellites involved in the trigger scheme (see Section \ref{['sec:results']}). Results for COMCUBE-S were obtained assuming a constellation of 27 satellites in an equatorial orbit at an altitude of 500 km. The vertical hatched lines show the completeness limits of the Fermi-GBM and synthetic catalogues with respect to the simulated GRB total population.