TITAN DR1: An Improved, Validated, and Systematically-Controlled Recalibration of ATLAS Photometry toward Type Ia Supernova Cosmology

Elijah G. Marlin; Yukei S. Murakami; Dillon Brout; Jack W. Tweddle; Brodie Popovic; Ken W. Smith; Stephen J. Smartt; Daniel M. Scolnic; David Jones; Erik R. Peterson; Adam G. Riess; Maria Vincenzi; Nora F. Sherman; Maria Acevedo; Jasper Milstein; Mitchell Dixon; Armin Rest

arXiv · 2512.21903

TITAN DR1: An Improved, Validated, and Systematically-Controlled Recalibration of ATLAS Photometry toward Type Ia Supernova Cosmology

Elijah G. Marlin·Yukei S. Murakami·Dillon Brout·Jack W. Tweddle·Brodie Popovic·Ken W. Smith·Stephen J. Smartt·Daniel M. Scolnic·David Jones·Erik R. Peterson·Adam G. Riess·Maria Vincenzi·Nora F. Sherman·Maria Acevedo·Jasper Milstein·Mitchell Dixon·Armin Rest

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Abstract

ATLAS (Asteroid Terrestrial Last Alert System) is a time-domain survey using four telescopes, covering the entire sky. It has observed over 10,000 spectroscopically confirmed Type Ia supernovae (SNe~Ia), with thousands of cosmology-grade light curves (to be released as TITAN DR1). To prepare this massive, low-redshift dataset for cosmology, we evaluate and cross-calibrate ATLAS forced photometry using tertiary stars from the DES (Dark Energy Survey) Y6 release. The 5000 deg$^2$ DES footprint overlaps regions both in and out of the PS1 (Pan-STARRS DR1) footprint, allowing tests of the primary calibrator for the ATLAS Refcat2 catalog. Initial offsets are at the $\sim$40 mmag scale. To improve this we determine $\Delta$ zeropoint offsets for two cases: (1) pixel-to-pixel offsets within individual CCDs (reduced from $\sim$8 to $\sim$4 mmag RMS) and (2) chip-to-chip offsets across the 9 CCDs and filters (reduced from $\sim$17 to $\sim$3 mmag RMS). We also identify the largest systematic uncertainty as a transmission-function color dependence, requiring shifts in the assumed ATLAS filters at the $\sim$30 mmag level if uncorrected. We validate our calibration using (a) CALSPEC standards, (b) an independent tertiary catalog, and (c) distance moduli of cross-matched SNe~Ia, all showing improved consistency. Overall, we estimate combined calibration-related systematics at the $\sim$5--10 mmag level, supporting competitive cosmological constraints with the TITAN SN~Ia dataset.

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Elijah G. Marlin, Yukei S. Murakami, Dillon Brout, Jack W. Tweddle, Brodie Popovic, Ken W. Smith, Stephen J. Smartt, Daniel M. Scolnic, David Jones, Erik R. Peterson, Adam G. Riess, Maria Vincenzi, Nora F. Sherman, Maria Acevedo, Jasper Milstein, Mitchell Dixon, Armin Rest. 2025-12-26. TITAN DR1: An Improved, Validated, and Systematically-Controlled Recalibration of ATLAS Photometry toward Type Ia Supernova Cosmology. https://arxiv.org/abs/2512.21903

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