SUPERCAL: CROSS-CALIBRATION OF MULTIPLE PHOTOMETRIC SYSTEMS TO IMPROVE COSMOLOGICAL MEASUREMENTS WITH TYPE Ia SUPERNOVAE

Abstract

Current cosmological analyses which use Type Ia supernova (SN Ia) observations combine SN samples to expand the redshift range beyond that of a single sample and increase the overall sample size. The inhomogeneous photometric calibration between different SN samples is one of the largest systematic uncertainties of the cosmological parameter estimation. To place these different samples on a single system, analyses currently use observations of a small sample of very bright flux standards on the HST system. We propose a complementary method, called 'Supercal', in which we use measurements of secondary standards in each system, compare these to measurements of the same stars in the Pan-STARRS1 (PS1) system, and determine offsets for each system relative to PS1, placing all SN observations on a single, consistent photometric system. PS1 has observed 3π of the sky and has a relative calibration of better than 5 mmag (for ∼ 15 < griz < 21 mag), making it an ideal reference system. We use this process to recalibrate optical observations taken by the following SN samples: PS1, SNLS, SDSS, CSP, and CfA1-4. We measure discrepancies on average of 10 mmag, but up to 35 mmag, in various optical passbands. We find that correcting for these differences changes recovered values for the dark energy equation-of-state parameter, w, by on average 2.6%. This change is roughly half the size of current statistical constraints on w. The size of this effect strongly depends on the error in the B − V calibration of the low-z surveys. The Supercal method will allow future analyses to tie past samples to the best calibrated sample.

The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. II. UV, Optical, and Near-infrared Light Curves and Comparison to Kilonova Models

“…Pointspread function (PSF) photometry was performed on the subtracted images using an implementation of DoPhot optimized for difference images (Schechter et al 1993). We performed astrometric and photometric calibration relative to the Pan-STARRS1/ p 3 catalog (PS1/ p 3 ; Chambers et al 2016), with appropriate corrections between magnitude systems (Scolnic et al 2015). The typical calibration error is on the order of »3%.…”

Measuring Dark Energy Properties with Photometrically Classified Pan-STARRS Supernovae. II. Cosmological Parameters

“…Nearly all of these SNe are all included in the JLA analysis, including the CfA1-3 SN samples (Riess et al 1999;Jha et al 2006;Hicken et al 2009aHicken et al , 2009b and CSP SNe from the first data release (Contreras et al 2010;Folatelli et al 2010). 17 We exclude Calan/Tololo SNe (Hamuy et al 1996), as most lie below the PS1 3π survey area and therefore cannot take advantage of the PS1-based photometric calibration system we use in this paper (Supercal; Scolnic et al 2015). We also include the most recent CfA SN compilation (CfA4; Hicken et al 2012) and the second CSP data release (Stritzinger et al 2011), which were not included in the JLA analysis but are used in the Rest et al (2014) and S17 PS1 cosmological analyses.…”

Deep ugrizY imaging and DEEP2/3 spectroscopy: a photometric redshift testbed for LSST and public release of data from the DEEP3 Galaxy Redshift Survey

“…To eliminate false detections, we require that an object has at least three "good" detections (nmag ok≥1) in the six bands. The PS1 photometry has been found to have small zero-point offsets compared to the standard AB system (Scolnic et al 2015); we have shifted the PS1 grizy magnitudes by +20, +33, +24, +28, and +11 mmag (griz offsets from Table 3 of Scolnic et al 2015; y-band offset from private communication from Dan Scolnic), respectively, to match to the AB system.…”