# The JCMT Transient Survey: Data Reduction and Calibration Methods

## TL;DR

This paper details the data reduction, calibration, and analysis techniques used in the JCMT Transient Survey to study brightness variations in protostars, achieving high-precision imaging and identifying sources with potential variability.

## Contribution

It introduces novel data processing and calibration methods for submillimetre observations, enabling precise alignment and flux measurement in a large-scale star formation variability survey.

## Key findings

- Achieved better than 1" spatial alignment between observations
- Attained 2-3% uncertainty in relative peak brightness
- Identified sources with potential brightness variations

## Abstract

Though there has been a significant amount of work investigating the early stages of low-mass star formation in recent years, the evolution of the mass assembly rate onto the central protostar remains largely unconstrained. Examining in depth the variation in this rate is critical to understanding the physics of star formation. Instabilities in the outer and inner circumstellar disk can lead to episodic outbursts. Observing these brightness variations at infrared or submillimetre wavelengths sets constraints on the current accretion models. The JCMT Transient Survey is a three-year project dedicated to studying the continuum variability of deeply embedded protostars in eight nearby star-forming regions at a one month cadence. We use the SCUBA-2 instrument to simultaneously observe these regions at wavelengths of 450 $\mu$m and 850 $\mu$m. In this paper, we present the data reduction techniques, image alignment procedures, and relative flux calibration methods for 850 $\mu$m data. We compare the properties and locations of bright, compact emission sources fitted with Gaussians over time. Doing so, we achieve a spatial alignment of better than 1" between the repeated observations and an uncertainty of 2-3\% in the relative peak brightness of significant, localised emission. This combination of imaging performance is unprecedented in ground-based, single dish submillimetre observations. Finally, we identify a few sources that show possible and confirmed brightness variations. These sources will be closely monitored and presented in further detail in additional studies throughout the duration of the survey.