The Black Hole Explorer (BHEX) is a next-generation space very long baseline interferometry (VLBI) mission concept that will extend the ground-based millimeter/submillimeter arrays into space. The mission, closely aligned with the science priorities of the Japanese VLBI community, involves an active engagement of this community in the development of the mission, resulting in the formation of the Black Hole Explorer Japan Consortium. Here we present the current Japanese vision for the mission, ranging from scientific objectives to instrumentation. The Consortium anticipates a wide range of scientific investigations, from diverse black hole physics and astrophysics studied through the primary VLBI mode, to the molecular universe explored via a potential single-dish observation mode in the previously unexplored 50-70 GHz band that would make BHEX the highest-sensitivity explorer ever of molecular oxygen. A potential major contribution for the onboard instrument involves supplying essential elements for its high-sensitivity dual-band receiving system, which includes a broadband 300 GHz SIS mixer and a space-certified multi-stage 4.5K cryocooler akin to those used in the Hitomi and XRISM satellites by the Japan Aerospace Exploration Agency. Additionally, the Consortium explores enhancing and supporting BHEX operations through the use of millimeter/submillimeter facilities developed by the National Astronomical Observatory of Japan, coupled with a network of laser communication stations operated by the National Institute of Information and Communication Technology.
We are promoting the Hybrid Installation Project in Nobeyama, Triple-band Oriented (HINOTORI), a project aiming at triple-band simultaneous single-dish and VLBI observation in the 22-, 43- and 86-GHz bands using the Nobeyama 45-m Telescope. The triple-band simultaneous observation becomes possible by developing two perforated plates and mounting them in the Nobeyama 45-m Telescope optics. One is a 22/43-GHz-band perforated plate, which transmits the higher frequency (43-GHz) band and reflects the lower frequency (22-GHz) band, and the other is a 43/86-GHz-band perforated plate, which transmits the 86-GHz band and reflects the 43-GHz band or lower. Both plates are designed to be installed in the large telescope optics with a beam diameter as large as 50 cm and insertion/reflection losses are both 0.22 dB (5%) or less in the design. The receivers used in triple-band simultaneous observation system are the H22 and H40 receivers, which are already installed in the Nobeyama 45-m Telescope, and the TZ receiver, which is a 100-GHz-band receiver including the 86-GHz band and reinstalled in the Nobeyama 45-m Telescope. A system of simultaneous observations in the 22- and 43-GHz bands of the Nobeyama 45-m Telescope with the 22/43- GHz-band perforated plate has been completed and commissioned for scientific observations. Also VLBI fringes between the Nobeyama 45-m telescope with the dual-band observation system and the VERA 20-m telescopes at 22 and 43 GHz was detected successfully.
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