The Simons Observatory: Dark Characterization of the Large Aperture Telescope

TL;DR

This paper characterizes the noise performance of the Simons Observatory's Large Aperture Telescope in a dark configuration, demonstrating low noise levels and minimal impact from the scan strategy, without atmospheric interference.

Contribution

It provides the first detailed noise characterization of the SO LAT in a dark state, validating the noise model and scan strategy effectiveness.

Findings

Noise below the specified upper limit

Noise properties match the simple noise model

Scan strategy minimally affects noise levels

Abstract

The Simons Observatory (SO) is a cosmic microwave background experiment composed of three 0.42 m Small Aperture Telescopes (SATs) and one 6 m Large Aperture Telescope (LAT) in the Atacama Desert of Chile. The Large Aperture Telescope Receiver (LATR) was integrated into the LAT in August 2023; however, because mirrors were not yet installed, the LATR optical chain was capped at the 4K stage. In this dark configuration we are able to characterize many elements of the instrument without contributions from atmospheric noise. Here we show this noise is below the required upper limit and its features are well described with a simple noise model. Maps produced using this noise model have properties that are in good agreement with the white noise levels of our dark data. Additionally, we show that our nominal scan strategy has a minimal effect on the noise when compared to the noise when the telescope is stationary