Gamma-Ray Burst Polarimeter - GAP - aboard the Small Solar Power Sail Demonstrator IKAROS

TL;DR

The paper introduces the Gamma-Ray Burst Polarimeter (GAP) aboard the IKAROS solar sail spacecraft, highlighting its design, calibration, and role in observing gamma-ray polarization of GRBs during the spacecraft's cruise phase.

Contribution

This work presents the first gamma-ray polarization instrument on a solar sail spacecraft and details its ground and onboard calibration procedures.

Findings

GAP successfully observed gamma-ray polarization of GRBs.

The detector demonstrated effective onboard calibration.

GAP's design enables it to serve as part of the interplanetary network.

Abstract

The small solar power sail demonstrator "IKAROS" is a Japanese engineering verification spacecraft launched by H-IIA rocket on May 21, 2010 at JAXA Tanegashima Space Center. IKAROS has a huge sail with 20 m in diameter which is made of thin polyimide membrane. This sail converts the solar radiation-pressure into the propulsion force of IKAROS and accelerates the spacecraft. The Gamma-Ray Burst Polarimeter (GAP) aboard IKAROS is the first polarimeter to observe the gamma-ray polarization of Gamma-Ray Bursts (GRBs) during the IKAROS cruising phase. GAP is a tinny detector of 3.8 kg in weight and 17 cm in size with an energy range between 50-300 keV. The GAP detector also plays a role of the interplanetary network (IPN) to determine the GRB direction. The detection principle of gamma-ray polarization is the anisotropy of the Compton scattering. GAP works as the GRB polarimeter with the full coincidence mode between the central plastic and the surrounding CsI detectors. GAP is the first instrument, devoted for the observation of gamma-ray polarization in the astronomical history. In this paper, we present the GAP detector and its ground and onboard calibrations.