The Simons Observatory: Commissioning and Early Observations for the Mid-frequency Small Aperture Telescopes

The Simons Observatory (SO) is a next generation cosmic microwave background (CMB) experiment now operating in the Chilean Atacama Desert. The initial SO configuration includes three 0.5-meter Small Aperture Telescopes (SATs) with front-end cryogenic continuously rotating half waveplates. The SATs are observing the larger angular scales of the CMB polarization anisotropy in a search for the B-mode polarization signature that would indicate the presence of inflation-sourced primordial gravitation waves. A measurement of the amplitude of this B-mode signature would be evidence of inflationary expansion in the early universe and constrain the amplitude of the inflaton field. The two mid-frequency SATs, both observing in bands around 90 and 150 GHz with about 12,000 transition edge sensor detectors, completed commissioning in Fall 2024. I will discuss commissioning results from these instruments and analysis from our initial science observations.