A Characterization of JWST MIRI Detector Persistence and Implications for High-Contrast Imaging

TL;DR

This paper characterizes the flux deficit persistence in JWST MIRI detectors, quantifies its decay over hours, and discusses its implications for high-contrast imaging and exoplanet detection.

Contribution

It provides the first detailed measurement of flux deficit persistence in MIRI detectors and models its decay, informing strategies to mitigate false positives in exoplanet imaging.

Findings

Persistence level immediately after saturation is 1.69%.

Persistence decays to one-tenth in about 5.16 hours.

Persistence can cause false positives and PSF degradation in high-contrast imaging.

Abstract

The JWST MIRI detector exhibits a flux deficit persistence, but its timescales and impacts remain largely uncharacterized, particularly at the longest imaging wavelengths. In this study, we analyze full-field MIRI imager observations at 21 $\mu$m (F2100W) to quantify detector persistence following a saturation event by a bright (K = 5.65 mag) nearby (8.12 $\pm$ 0.04 pc) mid M-dwarf star, IRAS 21500+5903. Unlike typical persistence that appears as excess flux, this effect presents as a flux deficit in pixels previously illuminated by the saturating or near saturating source. We measure persistence at two post-saturation epochs: shortly after saturation (11.6 minutes) and an hour later (1.39 hours). Immediately after the saturation event, we detect a persistence level of $1.69 \pm 0.10$%. By fitting a Bayesian exponential decay model to the two epochs, we estimate that persistence decreases to one-tenth of its initial value after $5.16^{+1.49}_{-0.94}$ hours. We examine the implications of persistence for MIRI high-contrast imaging using the imager (not coronagraphy). Specifically, we discuss how MIRI detector persistence can produce false-positive exoplanet signals in direct imaging surveys, as well as degrade PSF subtraction, particularly at small inner working angles. We also outline mitigation strategies to avoid these impacts in future observations.