The DESI Transients Survey: Legacy Classifications and Methodology

TL;DR

This paper details the first systematic spectroscopic classification of extragalactic transients using DESI, demonstrating its capability to classify faint transients and its potential as a pathfinder for future large-scale surveys like LSST.

Contribution

It introduces a novel methodology for transient classification with DESI, including archival data analysis and a dedicated transient program, expanding the transient catalog and demonstrating DESI's capabilities.

Findings

Classified over 250 transients, mostly previously unclassified.

Demonstrated DESI's ability to classify faint transients down to r~22.5 mag.

Showcased DESI as an effective tool for transient discovery and classification.

Abstract

We present the first systematic spectroscopic observations of extragalactic transients from the Dark Energy Spectroscopic Instrument (DESI), as part of the DESI Transients Survey program. With 5,000 fibers and an ${\sim} 8$ deg$^2$ field of view, we exploit DESI as a machine for the discovery and classification of transients. We present transient classifications from archival DESI data in Data Releases 1 and 2, relying on a combination of a secondary target program and serendipitous observations. We also present observations from the first 6 months of the DESI spare fiber program dedicated to transients. The program is run in coordination with a dedicated DECam time-domain survey, serving as a pathfinder for what we will be able to achieve in conjunction with the Rubin Observatory Legacy Survey of Space and Time (LSST). We classify over 250 transients, of which the majority were previously unclassified. The sample comprises thermonuclear and core-collapse supernovae and tidal disruption events (TDEs), including a TDE observed before its discovery in imaging. We demonstrate DESI's ability to classify a population of faint transients down to $r\sim 22.5$ mag during main survey operations, with negligible impacts on DESI's main observations.