The Simons Observatory (SO) group of instruments are together pursuing a major step forward in the ground-based study of the Cosmic Microwave Background (CMB). With one 6 m large-aperture telescope and three 0.4 m small-aperture telescopes (SATs), SO will strive to recover faint CMB polarization signals at a wide range of angular scales and across six frequency bands inside of atmospheric transmission windows spanning the range 27 GHz to 280 GHz. The first instrument to record celestial light is the first of two mid-frequency SATs, SAT MF-1, with over 3,000 dichroic pixels sensitive to two frequency bands centered at 90 and 150 GHz. This instrument began observing in October 2023, and features a cryogenically-cooled polarization modulator consisting of a spinning half-wave plate, a set of three silicon lenses with metamaterial anti-reflection coating, and a focal plane of seven modules referred to as universal focal-plane modules (UFMs), each containing 1,720 AlMn transition-edge sensor (TES) bolometers coupled to a 100 mK bath. In this proceedings, we report on initial efforts to calibrate the TES bolometer response to electrical and optical signals and preliminary characterization of possible confounding signals like scan-synchronous pickup. We comment on how these elements pertain to the analysis of systematic errors relating to the ultimate goal of the SO SAT program: the further constraint of the tensor-to-scalar ratio, r, and the possibility of primordial gravitational waves generated in the early universe by a period of inflation.
SPIDER is a balloon-borne instrument designed to map the cosmic microwave background at degree-angular scales in the presence of Galactic foregrounds. Spider has mapped a large sky area in the Southern Hemisphere using more than 2000 transition-edge sensors (TESs) during two NASA Long Duration Balloon flights above the Antarctic continent. During its first flight in January 2015, Spider observed in the 95 GHz and 150 GHz frequency bands, setting constraints on the B-mode signature of primordial gravitational waves. Its second flight in the 2022-23 season added new receivers at 280 GHz, each using an array of TESs coupled to the sky through feedhorns formed from stacks of silicon wafers. These receivers are optimized to produce deep maps of polarized Galactic dust emission over a large sky area, providing a unique data set with lasting value to the field. In this work, we describe the instrument’s performance during SPIDER’s second flight.
In this work we describe upgrades to the Spider balloon-borne telescope in preparation for its second flight, currently planned for December 2021. The Spider instrument is optimized to search for a primordial B-mode polarization signature in the cosmic microwave background at degree angular scales. During its first flight in 2015, Spider mapped ~10% of the sky at 95 and 150 GHz. The payload for the second Antarctic flight will incorporate three new 280 GHz receivers alongside three refurbished 95- and 150 GHz receivers from Spider's first flight. In this work we discuss the design and characterization of these new receivers, which employ over 1500 feedhorn-coupled transition-edge sensors. We describe pre-flight laboratory measurements of detector properties, and the optical performance of completed receivers. These receivers will map a wide area of the sky at 280 GHz, providing new information on polarized Galactic dust emission that will help to separate it from the cosmological signal.
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