The upGREAT Heterodyne Arrays for the SOFIA Telescope
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Christophe Risacher
MPIfR Bonn
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We present the upGREAT heterodyne arrays for astronomy, used with the SOFIA airborne observatory. The upGREAT array receivers will operate at two different frequency ranges, the low frequency array (LFA) covering the 1.9-2.5 THz band with 14 pixels, and the high frequency array (HFA) covering the 4.745 THz line of atomic oxygen [O I] with 7 pixels. The frontend operates superconducting Hot Electron Bolometers (HEB) waveguide mixers. The local oscillators are based on commercial synthesizer driven solid-state multiplier chains for the LFA and a QCL for the HFA. Both receivers are cooled using closed cycle pulse tube refrigerators, reaching temperatures below 4 K. The upGREAT LFA receiver, with its 14 channels, was successfully commissioned in May and December 2015. We will present details on the instrument design and performance and the main results of the commissioning flights. At 1.9 THz the array performed nominally on sky, with state of the art performance for 12 out of 14 pixels, reaching about 600-800 K DSB uncorrected receiver noise temperature at 0.5 GHz IF with an IF noise bandwidth of ~3.5 GHz. The stability was excellent and allowed efficient large scale mapping, demonstrating already that a factor of at least 10 was gained in time efficiency compared to the previous single pixel receiver at 1.9 THz.

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