Development micro-satellite TSUBAME for polarimetry of gamma-ray bursts

Gamma-ray bursts (GRBs) are the most drastic and intriguing phenomena in high energy astophysics. The nature of relativistic collimated outflows that might be generated by gravitational collapses of massive stars is still unclear. For this problem hard X-ray polarization is believed to be one of the most promising methods to investigate the physical process just around the central engines by constraining magnetic environment. For this purpose we developed a compact and high sensitive hard X-ray polarimeter aboard a university class micro-satellite "TSUBAME". Unsurprisingly, any micro-satellites have stringent limitations on size, mass, and power consumption restricting the effective area of detectors. However high luminosities of GRBs allow us to measure their polarizations only if we start observations just after the ignitions. TSUBAME overcomes this problem by using compact and high-torque actuators, control moment gyroscopes, that enables high speed attitude control faster than 6 degrees s(-1). Cooperating with a wide field burst monitor on board for real time position determination of GRBs, TSUBAME can start a pointing observation within similar to 15 s after the detection for any GRBs in the half-sky field of view of the burst monitor.