부산대학교 도서관

Very long baseline radio interferometry (VLBI) with ground-based observatories is limited by the size of Earth, the geographic distribution of antennas, and the transparency of the atmosphere. In this whitepaper, we present Capella, a tentative design of a space-only VLBI system. Using four small (<500 kg) satellites in two orthogonal polar low-Earth orbit planes, and single-band heterodyne receivers operating at frequencies around 690 GHz, the interferometer is able to achieve angular resolutions of approximately 7 microarcsec. Within a total observing time of three days, a near-complete uv plane coverage can be reached. All key components required for Capella - radio telescope, receiver, sampler, recorder, atomic frequency standard, positioning system, data downlink, and pointing control system - are already available, some of them off-the-shelf; the science payload of each satellite has a mass of about 230 kg and consumes about 550 W of power. The data from the telescopes can be correlated on the ground using dedicated versions of existing Fourier transform (FX) software correlators; in addition to the steps required by VLBI data correlation and calibration in general, dedicated routines will be needed to handle the effects of orbital motion, including relativistic corrections. With the specifications assumed in this whitepaper, Capella will be able to address a range of science cases, including: photon rings around supermassive black holes; the acceleration and collimation zones of plasma jets emitted from the vicinity of supermassive black holes; the chemical composition of accretion flows into active galactic nuclei through observations of molecular absorption lines; mapping supermassive binary black holes; the magnetic activity of stars; and nova eruptions of symbiotic binary stars - and, like any substantially new observing technique, has the potential for unexpected discoveries.
Comment: 19 pages, 3 figures, 1 table. Whitepaper version 1.3. Updates: telescope design, sensitivity, list of authors. Abstract abridged. Living document, will be updated when necessary