Introducing a New Spitzer Master BLISS Map to Remove the Instrument-Systematic -- Phase-Curve-Parameter Degeneracy, as Demonstrated by a Reanalysis of the 4.5$\mu m$ WASP-43b Phase Curve

TL;DR

This paper introduces a new intrapixel sensitivity map for Spitzer IRAC data at 4.5μm, effectively removing degeneracies in phase curve analysis of WASP-43b and improving the robustness of derived planetary emission properties.

Contribution

The paper presents a novel fixed sensitivity map derived from over 3.7 million exposures, reducing parameter degeneracies and eliminating the need for certain detrending techniques in phase curve analysis.

Findings

The fixed sensitivity map removes the dependence of phase curve results on data binning.

The analysis confirms night side emission of WASP-43b with a temperature of 806 ± 48 K.

Time variability in sensitivity was observed at 3.6μm, but not at 4.5μm.

Abstract

While Spitzer IRAC systematics are generally well understood, each data set can provide its own challenges that continue to teach us about the underlying functional form of these systematics. Multiple groups have analyzed the phase curves of WASP-43b with varying detrending techniques, each obtaining different results. In this work, we take another look at WASP-43b while exploring the degenerate relation between Bilinearly-Interpolated Subpixel Sensitivity (BLISS) mapping, point response function full width at half-maximum (PRF-FWHM) detrending, and phase curve parameters. We find that there is a strong correlation between the detrending parameters in the two models, and best fit phase curve amplitudes vary strongly when the data are temporally binned. To remove this degeneracy, we present a new Gaussian centroided intrapixel sensitivity map (hereafter fixed sensitivity map), generated using 3,712,830 exposures spanning 5 years, for a variety of aperture sizes at 4.5$\mu m$. We find evidence for time variability in the sensitivity at 3.6$\mu m$ and do not generate a visit-independent map for this channel. With the fixed 4.5 $\mu m$ intrapixel sensitivity map, the best fits for WASP-43b no longer vary strongly with bin size and PRF-FWHM detrending is no longer required to remove correlated noise. For data sets that do not fall completely within the sweet spot, temporal binning should not be used in the analysis of Spitzer phase curves. We confirm night side emission for WASP-43b with a disk integrated nightside temperature of 806 $\pm$ 48 K at 4.5$\mu m$. The 4.5$\mu m$ maps are available at \url{github.com/kevin218/POET}