MIRI Bright Source Limits

Bright source limits of JWST's Mid-Infrared Instrument (MIRI) are predicted by a saturation model that uses measurements obtained during ground testing.

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The performance of MIRI has been measured directly at both the component and system level using the fully assembled MIRI flight model in a flight-like radiative environment with a well characterized radiometric source (Glasse et al. 2015).  Results of these JWST throughput measurements have been integrated into a sensitivity model, which includes the following components: (1) background, (2) photon conversion efficiency (PCD), (3) encircled energy, and (4) detector performance  (Pontoppidan 2016).

Users should ultimately use the Exposure Time Calculator (ETC) for all bright limit calculations.


Tables 1 and 2, and Figure 1 show bright source limits for point sources assuming a five group integration. The values shown represent the fluxes at which the detector reaches 70% of the pixels' full-well capacity, which is the saturation limit in the ETC.

The values in the table and plots below were obtained from ETC 1.2.


Table 1.MIRI imager bright source limits (for Ngroups = 5)

Table 2.MIRI imager subarray bright source limits (for Ngroups = 5)

Figure 1. MIRI bright source limits for point sources (for Ngroups = 5)

MIRI imager bright source limits for point sources for all modes, assuming FULL frame.

1  Bold italics font style is used to indicate parameters, parameter values, and/or special requirements that are set in the APT GUI.


Glasse, A. et al. 2015, PASP, 127, 686
The Mid-Infrared Instrument for the James Webb Space Telescope, IX: Predicted Sensitivity

Pontoppidan, K. 2016, Proc of SPIE, 9910, 16
Pandeia: a multi-mission exposure time calculator for JWST and WFIRST 



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