The Simons Observatory: Development of a Pipeline to Detect Rapid Transients in Time-Ordered Data

Abstract: We introduce a method for detecting astrophysical transients evolving on timescales of milliseconds to minutes using cosmic microwave background (CMB) survey telescopes. While previous transient searches in CMB data operate in map space, our pipeline directly processes the raw time-ordered data, enabling sensitivity to fast, dynamic signals. We integrate our detection approach into the Simons Observatory time-domain pipeline and assess the performance on simulated observations with injected stellar flare-like light curves. For events flaring with a timescale of 0.5 s, the pipeline detects $\gtrsim90$% of events at flux densities of 800, 1150, 1650, and 4250 mJy when measured in the 93, 145, 225, and 280 GHz bands respectively. For longer $\ge5$ second flares, the 90% detection thresholds are reduced by a factor of four. We are able to determine the position of detected events in each observing band, with a positional uncertainty at the detection threshold comparable to the telescope resolution at that band. These results demonstrate the readiness of this pipeline for incorporation into upcoming Simons Observatory data analyses.