The JCMT Transient Survey: Six-Year Summary of 450/850 μm Protostellar Variability and Calibration Pipeline Version 2.0

Abstract

The JCMT Transient Survey has been monitoring eight Gould Belt low-mass star-forming regions since December 2015 and six somewhat more distant intermediate-mass star-forming regions since February 2020 with SCUBA-2 on the JCMT at 450 µm and 850 µm and with an approximately monthly cadence. We introduce our Pipeline v2 relative calibration procedures for image alignment and flux calibration across epochs, improving on our previous Pipeline v1 by decreasing measurement uncertainties and providing additional robustness. These new techniques work at both 850 µm and 450 µm, where v1 only allowed investigation of the 850 µm data. Pipeline v2 achieves better than 0.5′′ relative image alignment, less than a tenth of the submillimeter beam widths. The v2 relative flux calibration is found to be 1% at 850 µm and < 5% at 450 µm. The improvement in the calibration is demonstrated by comparing the two pipelines over the first four years of the survey and recovering additional robust variables with v2. Using the full six years of the Gould Belt survey the number of robust variables in creases by 50 %, and at 450 µm we identify four robust variables, all of which are also robust at 850 µm. The multi-wavelength light curves for these sources are investigated and found to be consistent with the variability being due to dust heating within the envelope in response to accretion luminosity changes from the central source