Abstract
4GREAT is an extension of the German Receiver for Astronomy at Terahertz frequencies (GREAT) operated aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). The spectrometer comprises four different detector bands and their associated subsystems for simultaneous and fully independent science operation. All detector beams are co-aligned on the sky. The frequency bands of 4GREAT cover 491-635, 890-1090, 1240-1525 and 2490-2590 GHz, respectively. This paper presents the design and characterization of the instrument, and its in-flight performance. 4GREAT saw first light in June 2018, and has been offered to the interested SOFIA communities starting with observing cycle 6.
Highlights
SINCE the completion of the Herschel satellite mission [1], the spectrometer GREAT1 [2] on board the Stratospheric Observatory for Infrared Astronomy (SOFIA) airborne observatory [3] is the only instrument that routinely allows performing high-resolution spectroscopy of astronomical signals at far-infrared wavelengths
We will show that making use of the improved performance of today’s dichroic filters, up to 4 frequency bands can be arranged into a single cryostat for simultaneous science operation with co-aligned pixels on the sky
1) SIS Mixers for 4G-1 and 4G-2 The SIS mixers for 4G-1 and 4G-2 are units originally developed for HIFI, the heterodyne instrument [11] onboard the Herschel Space Observatory
Summary
SINCE the completion of the Herschel satellite mission [1], the spectrometer GREAT1 [2] on board the SOFIA airborne observatory [3] is the only instrument that routinely allows performing high-resolution spectroscopy of astronomical signals at far-infrared wavelengths. In its early configuration GREAT operated, in parallel, two single-pixel LHe/LN2 cooled cryostats hosting heterodyne detectors in the 1.5 and 1.9 THz frequency bands. ▪ to allow for the integration of the GREAT single-pixel units operating in the 1.2-1.5 THz and 2.49-2.52 THz frequency bands [4],. To exemplify the new science opportunities: absorption line spectroscopy towards FIR background continuum sources will allow in-depth studies of the galactic interstellar medium with hydrides (many of which have their ground-state transition in the lower 4GREAT bands, see Table 1) – this will be a unique addition to what has commenced so successfully with HIFI/Herschel [8], but operating up to 5 frequency bands simultaneously.
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