The JCMT Transient Survey: Six-Year Summary of 450/850\,$\mu$m Protostellar Variability and Calibration Pipeline Version 2.0

TL;DR

This paper presents a six-year summary of the JCMT Transient Survey, highlighting improvements in calibration pipeline techniques that enhance detection of protostellar variability at submillimeter wavelengths.

Contribution

Introduction of Pipeline v2 with enhanced image alignment and flux calibration, enabling more robust detection of variable protostars across multiple wavelengths.

Findings

50% increase in detected robust variables over six years

Calibration accuracy improved to 1% at Longs and <5% at Shorts

Detected variables show variability consistent with dust heating from accretion changes

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 \ShortS and \LongS 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 \LongS and \ShortNS, where v1 only allowed investigation of the \LongS data. Pipeline v2 achieves better than $0.5^{\prime\prime}$ relative image alignment, less than a tenth of the submillimeter beam widths. The v2 relative flux calibration is found to be 1\% at \LongS and $<5$\% at \ShortNS. 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 increases by 50\,\%, and at \ShortS we identify four robust variables, all of which are also robust at \LongNS. 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.