Enabling Early Transient Discovery in LSST via Difference Imaging with DECam

TL;DR

This work presents SLIDE, a pipeline that enables early transient discovery for LSST by performing LSST-like image subtraction using archival DECam templates. Applied to Rubin DP1 data in the ECDFS and EDFS fields, SLIDE recovers all known transients not faded at observation time and uncovers 29 new candidates, including many likely nuclear events and several with limited DP1 detections due to template contamination. The authors detail the field selection, transient detection, and host-property analysis workflow, demonstrating robust photometry and host associations via FrankenBlast and Pröst. The study shows SLIDE’s potential to support rapid transient science during LSST's early years and for slowly evolving phenomena, with broad applicability to precursor searches, LRNe, and SLSNe in large-scale time-domain surveys.

Abstract

We present SLIDE, a pipeline that enables transient discovery in data from the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), using archival images from the Dark Energy Camera (DECam) as templates for difference imaging. We apply this pipeline to the recently released Data Preview 1 (DP1; the first public release of Rubin commissioning data) and search for transients in the resulting difference images. The image subtraction, photometry extraction, and transient detection are all performed on the Rubin Science Platform. We demonstrate that SLIDE effectively extracts clean photometry by circumventing poor or missing LSST templates. We identified 29 previously unreported transients, 12 of which would not have been detected based on the DP1 DiaObject catalog. SLIDE will be especially useful for transient analysis in the early years of LSST, when template coverage will be largely incomplete or when templates may be contaminated by transients present at the time of acquisition. We present multiband light curves for a sample of known transients, along with new transient candidates identified through our search. Finally, we discuss the prospects of applying this pipeline during the main LSST survey. Our pipeline is broadly applicable and will support studies of all transients with slowly evolving phases.

Figures (4)

• Figure 1: Upper: Image subtraction using DECam templates for visit 2024120200090, detector 8 taken on 2 December 2024 in the $r$ band. The image is oriented with North at the top and East to the left. AT 2024ahzi is visible on the image and marked by the red circle. The left and middle panels show the LSST image and the coadded DECam image, respectively, while the right panel shows the difference image. The displayed cutouts are 400$\times$400 pixels in size, centered on the transient position. The white patches are bad pixels and are masked out prior to subtraction. PSF photometry is performed at the location of AT 2024ahzi on the difference image (center), and the results are annotated on the panel. Lower: Image subtraction for visit 2024111700344, detector 2, taken on 17 November 2024 in the $r$ band. AT 2024ahzi is not visible on the difference image, and an upper limit is derived.
• Figure 2: Light curves and host properties of transients previously reported to TNS. Note that plotted errors represent statistical uncertainty. Host properties include redshift ($z$), stellar mass [$\log(M_{\star}/M_{\odot})$], stellar metallicity [$\log(Z/Z_{\odot})$], star formation rate (SFR; [$M_{\odot},\rm yr^{-1}$]), and mass-weighted stellar population age (Age; [Gyr]).
• Figure 3: Continuation of Figure \ref{['fig:candidates']} for the remaining transients.
• Figure 4: Multiband light curves of a subset of the transient candidates identified by our pipeline. More information about these transients can be found in Table \ref{['tab:ecdfs_transients']} and \ref{['tab:edfs_transients']}.