Wide-Band X-Ray and Gamma-Ray Camera, Inspire, Onboard the 65 Kg Small Satellite GRAPHIUM

Waseda University and Science Tokyo are developing the 65 kg small satellite GRAPHIUM, which is planned for launch in FY2026. Its main detector, named INSPIRE, is a box-shaped hybrid Compton camera that supports both pinhole mode (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$30-200 \text{keV}$</tex>) and Compton mode (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$200 \text{keV}-3$</tex> MeV). Simulations show that its sensitivity is comparable to that of COMPTEL. INSPIRE also possesses a wide field of view and is capable of simultaneously monitoring approximately onequarter of the sky. This feature enables the detection of transient phenomena such as gamma-ray bursts, whose locations cannot be predicted in advance. Should GRAPHIUM observe transient events originating from kilonovae due to neutron star mergers, it may provide vital insights into the currently unknown origins of heavy-element synthesis, including that of Au and Pt. In addition, we aim to observe steady sources such as active galactic nuclei (AGNs). In this study, we constructed an engineering model (EM). This EM partially replicates the actual INSPIRE, integrating real detectors in selected sections, with the remaining parts replaced by massequivalent dummy components. Using the EM, we performed imaging tests with various radiation sources, along with environmental and vibration tests. By conducting imaging tests with multiple radiation sources, we demonstrated that the angular resolution measure (ARM) cut, a simple and effective technique developed for Compton camera imaging, enables the successful extraction of spectra from multiple gamma-ray sources within a single field of view. Furthermore, we assumed the Falcon 9, recognized for its stringent vibration environment, for vibration testing and conducted a qualification test to evaluate the effects of launch conditions. The results confirmed that the detector's performance was unaffected by the test.