The Deeper, Wider, Faster programme's first DECam optical data release

TL;DR

Deeper, Wider, Faster (DWF) presents the first DECam optical data release focused on minute-cadence, deep photometry ($g\sim22.2$) over 112 field-nights and 166 hr. A novel post-run pipeline, dwf-postpipe, generates complete light curves for all detected sources without image subtraction, enabling broad variability studies and synthetic-transient validation against a traditional difference-imaging approach. The release demonstrates high recovery efficiency for $g<22$ transients and highlights differences in sensitivity for host-galaxy–embedded events, while also uncovering uncatalogued variable stars and short-timescale phenomena in CDFS. Data are publicly accessible via AAO Data Central and NOIRLab, offering a valuable resource to complement Rubin-era time-domain surveys and to inform future high-cadence, wide-field instrumentation.

Abstract

The transient and variable optical sky is relatively poorly characterised on fast ($<$1$\,$hr) timescales. With the Dark Energy Camera (DECam), the Deeper, Wider, Faster programme (DWF) probes a unique parameter space with its deep (median of $g\sim22.2$ AB mag), minute-cadence imaging. In this work, we present DWF's first data release which comprises high cadence photometry extracted from $\sim$12000 images and 166 hours of telescope time. We present a novel data processing pipeline, $\texttt{dwf-postpipe}$, developed to identify sources and extract their light curves. The accuracy of the photometry is assessed by cross-matching to public catalogues. In addition, we injected a population of synthetic GRB afterglows into a subset of the DWF DECam imaging to compare the efficiency of our pipeline with a standard difference imaging approach. Both pipelines show performance and reliably recover injected transients with peak magnitudes $g<22$ AB mag with an efficiency of $97.24^{+0.7}_{-1.0}$ percent for \texttt{dwf-postpipe} and $96.14^{+0.9}_{-1.1}$ percent for a difference imaging approach. However, we find that $\texttt{dwf-postpipe}$ is less likely to recover transients appearing in galaxies that are brighter or comparable in brightness to the transient itself. To demonstrate the power of the data in this release, we conduct a search for uncatalogued variable stars in a single night of DWF DECam imaging and find ten pulsating variables, two eclipsing binaries and one ZZ ceti. We also conduct a search for variable phenomena in the Chandra Deep Field South, a Rubin deep drilling field, and identify two flares from likely UV ceti type stars.

Figures (9)

• Figure 1: Approximate timescales and luminosities of known and theorised optical transients. The peak luminosities of Soft-gamma-ray repeater flares, flare stars and X-ray binaries extend lower than the axes shown on the plot for readability. Adapted from Cooke et al., in preparation.
• Figure 2: Sky locations of the DWF fields presented in this data release. A solid black line marks the Galactic plane and the dotted black lines denote $\pm10^{\circ}$ from the plane. The number of nights each field has been observed is indicated by the colourbar on the right. The footprints of the SkyMapper Southern Survey DR4 2024PASA...41...61O and DES 2016MNRAS.460.1270D are shown in blue and orange, respectively.
• Figure 3: Histograms of the median $g$-band limiting magnitudes (left) and median seeing FWHM (right) for the field-nights included in this data release. The $g$-band depth and seeing FWHM are affected by the need for DECam observations to occur up to relatively high airmass ($\sim$1.3--2.0) in order to enable simultaneous observations of each field by telescopes in Chile, Australia and other parts of the world. Dark time is defined as field-night observations that begin and end with a moon below the horizon and grey time is defined as those that begin or end with a moon altitude $>0^{\circ}$. The median values for each distribution are indicated by the vertical dashed lines.
• Figure 4: Schematic diagram of dwf-postpipe used in this data release. This methodology is applied to each of the 112 field-nights shown in Table \ref{['tab:fields']}.
• Figure 5: Top panel: Relative difference between the injected flux, $F_I$ and recovered flux, $F_R$, with injected AB magnitude. These values are calculated from each data point independently from each injected 'fake' source. Bottom panel: Efficiency at which injected fakes with the peak magnitude are recovered as detections using the data processing pipelines photpipe and dwf-postpipe. Both panels show only the fakes that were injected randomly throughout the field, excluding those that were injected onto galaxies.