Photometric and Thermal Cross-calibration of Solar EUV Instruments

Abstract

We present an assessment of the accuracy of the calibration measurements and atomic physics models that go into calculating the SDO/AIA response as a function of wavelength and temperature. The wavelength response is tested by convolving SDO/EVE and {\it Hinode}/EIS spectral data with the AIA effective area functions and comparing the predictions with AIA observations. For most channels, the AIA intensities summed over the disk agree with the corresponding measurements derived from the current Version (V2) of the EVE data to within the estimated 25% calibration error. This agreement indicates that the AIA effective areas are generally stable in time. The AIA 304 \AA\ channel, however, does show degradation by a factor of almost 3 from May 2010 through September 2011, when the throughput apparently reached a minimum. We also find some inconsistencies in the 335 \AA\ passband, possibly due to higher-order contamination of the EVE data. The intensities in the AIA 193 \AA\ channel agree to within the uncertainties with the corresponding measurements from EIS full CCD observations. Analysis of high-resolution X-ray spectra of the solar-like corona of Procyon, and of EVE spectra, allows us to investigate the accuracy and completeness of the CHIANTI database in the AIA shorter wavelength passbands. We find that in the 94 \AA\ channel, the spectral model significantly underestimates the plasma emission owing to a multitude of missing lines. We derive an empirical correction for the AIA temperature responses by performing differential emission measure (DEM) inversion on a broad set of EVE spectra and adjusting the AIA response functions so that the count rates predicted by the full-disk DEMs match the observations.