Science prospects for SPHiNX - a small satellite GRB polarimetry mission

TL;DR

The SPHiNX mission aims to measure gamma-ray burst polarization using a small satellite, providing new insights into GRB emission mechanisms with significantly improved accuracy over existing missions.

Contribution

This paper presents the design and scientific prospects of the SPHiNX satellite, a novel small-satellite mission for high-energy GRB polarimetry, enhancing measurement precision and model discrimination.

Findings

Approximately 200 GRBs observed over two years.

About 50 GRBs will have polarization fraction measured with ≤10% error.

The mission significantly improves polarization measurement accuracy compared to current missions.

Abstract

Gamma-ray bursts (GRBs) are exceptionally bright electromagnetic events occurring daily on the sky. The prompt emission is dominated by X-/$\gamma$-rays. Since their discovery over 50 years ago, GRBs are primarily studied through spectral and temporal measurements. The properties of the emission jets and underlying processes are not well understood. A promising way forward is the development of missions capable of characterising the linear polarisation of the high-energy emission. For this reason, the SPHiNX mission has been developed for a small-satellite platform. The polarisation properties of incident high-energy radiation (50-600 keV) are determined by reconstructing Compton scattering interactions in a segmented array of plastic and Gd$_3$Al$_2$Ga$_3$O$_{12}$(Ce) (GAGG(Ce)) scintillators. During a two-year mission, $\sim$200 GRBs will be observed, with $\sim$50 yielding measurements where the polarisation fraction is determined with a relative error $\leq$10%. This is a significant improvement compared to contemporary missions. This performance, combined with the ability to reconstruct GRB localisation and spectral properties, will allow discrimination between leading classes of emission models.