Feasibility of Observing Gamma-ray Polarization from Cygnus X-1 Using a CubeSat

Instruments flown on CubeSats are small. Meaningful applications of CubeSats in astronomical observations rely on the choice of a particular subject that is feasible for CubeSats. Here we report the result of a feasibility study for observing gamma-ray polarization from Cygnus X-1 using a small Compton polarimeter on board a 3U CubeSat. Silicon detectors and cerium bromide scintillators were employed in the instrument models that we discussed in this study. Through Monte Carlo simulations with Geant4-based MEGAlib package, we found that, with a 10-Ms on-axis, zenith-direction observation in a low inclination, low altitude earth orbit radiation background environment, the minimum detectable polarization degree can be down to about 10\% in 160 - 250 keV, 20\% in 250 - 400 keV, and 65\% in 400 - 2000 keV. A 3U CubeSat dedicated to observing Cygnus X-1 can therefore yield useful information on the polarization state of gamma-ray emissions from the brightest persistent X-ray black-hole binary in the sky.