Results of the summarizing process for the arXiv paper: 2303.13517v1

The Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST) uses three Si:As impurity band conduction (IBC) detector arrays to record the output voltage level of each MIRI detector pixel by sampling-up-the-ramp. While pixel ramps become non-linear in a predictable way for uniform or low-contrast illumination, they become much more complex in areas of high contrast. This phenomenon is known as the Brighter-Fatter Effect (BFE). We provide observational evidence of it in MIRI conventional and high-contrast coronographic imaging, low-resolution spectroscopy, and medium-resolution spectroscopy data. We investigate the physical mechanism that gives rise to this effect on the detector pixel raw voltage integration ramps using public data from the JWST/MIRI commissioning and Cycle 1 phase. We also develop a numerical electrostatic model of the MIRI detectors using a modified version of the public Poisson_CCD code. Our findings show that the physical mechanism behind the MIRI BFE is fundamentally different from that of CCDs and Hawaii-2RG (H2RG) detectors due to most photo-excited electric charges not being stored at pixels but at the input to the MIRI detector unit cell buffer amplifier capacitance. The resulting debiasing-induced BFE alters the electrostatic potential inside the infrared active layer, causing new photo excited electrons generated at a bright pixel to be guided towards neighboring fainter pixels. Observationally, we find that this debiasing induced BFE makes JWST MIRI data yield 10 - 25% larger and 0.5 - 8% brighter point sources and spectral line profiles as a function of output level covered by detector pixels. Additionally, we note that profile shrinking detector depletion regions have implications for developing a pixel ramp non linearity model for point sources observed with MIRI. Our study provides a more detailed understanding of the BFE in MIRI detectors and its impact on science. We also present a new numerical model that can be used to account for this effect when analyzing data from JWST/MIRI commissioning and Cycle 1 phase.

• The Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST) uses three Si:As impurity band conduction (IBC) detector arrays to record the output voltage level of each MIRI detector pixel by sampling-up-the-ramp.
• Pixel ramps become non-linear in a predictable way for uniform or low-contrast illumination, but become much more complex in areas of high contrast, known as the Brighter-Fatter Effect (BFE).
• Observational evidence of BFE is found in MIRI conventional and high-contrast coronographic imaging, low-resolution spectroscopy, and medium-resolution spectroscopy data.
• The physical mechanism behind the MIRI BFE is fundamentally different from that of CCDs and Hawaii-2RG detectors due to most photo-excited electric charges not being stored at pixels but at the input to the MIRI detector unit cell buffer amplifier capacitance.
• The resulting debiasing-induced BFE alters the electrostatic potential inside the infrared active layer, causing new photo excited electrons generated at a bright pixel to be guided towards neighboring fainter pixels.
• Debiasing induced BFE makes JWST MIRI data yield 10 - 25% larger and 0.5 - 8% brighter point sources and spectral line profiles as a function of output level covered by detector pixels.
• Profile shrinking detector depletion regions have implications for developing a pixel ramp non linearity model for point sources observed with MIRI.
• A new numerical model is presented that can be used to account for this effect when analyzing data from JWST/MIRI commissioning and Cycle 1 phase.

The Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST)

The Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST)

Introduction:

The Mid-Infrared Instrument (MIRI) is an instrument aboard the James Webb Space Telescope (JWST), a large, infrared-optimized space observatory that will be launched in 2021. MIRI uses three Si:As impurity band conduction (IBC) detector arrays to record the output voltage level of each MIRI detector pixel by sampling-up-the-ramp. This article discusses a phenomenon known as the Brighter Fatter Effect (BFE), which occurs when pixel ramps become nonlinear in areas of high contrast, and provides observational evidence of it in MIRI data from JWST/MIRI commissioning and Cycle 1 phase. Additionally, this article presents a numerical electrostatic model of the MIRI detectors using a modified version of the public Poisson_CCD code.

What is The Brighter Fatter Effect?

The Brighter Fatter Effect is an effect caused by nonlinearity in pixel ramps when illuminated with uniform or low contrast illumination. It can cause pixels to appear brighter and fatter than they should be due to most photo excited electric charges not being stored at pixels but at the input to the MIRI detector unit cell buffer amplifier capacitance.