A revised radiometric calibration for the Hinode/EIS instrument

Abstract

An assessment of the in-flight radiometric calibration of the Hinode EUV Imaging Spectrometer (EIS) is presented. This is done with the line ratio technique applied to a wide range of observations of the quiet Sun, active regions, and flares from 2006 until 2012. The best diagnostic lines and the relevant atomic data are discussed in detail. Radiances over the quiet Sun are also considered, with comparisons with previous measurements. Some departures in the shapes of the ground calibration responsivities are found at the start of the mission. These shapes do not change significantly over time, with the exception of the shorter wavelengths of the EIS short-wavelength (SW) channel, which shows some degradation. The sensitivity of the SW channel at longer wavelengths does not show significant degradation, while that of the long-wavelength (LW) channel shows a significant degradation with time. By the beginning of 2010 the responsivity of the LW channel was already lower than the values measured on the ground by a factor of two or more. A first-order correction is proposed. With this correction, the main ratios of lines in the two channels become constant to within a relative 20%, and the He ii 256 Å radiances over the quiet Sun also become constant over time. This correction removes long-standing discrepancies for a number of lines and ions, in particular those involving the strongest Fe x, Fe xiii, Fe xiv, Fe xvii, and Fe xxiv lines, where discrepancies of factors of more than two were found. These results have important implications for various EIS science analyses, in particular for measurements of temperatures, emission measures and elemental abundances.

Signatures of the non-Maxwellianκ-distributions in optically thin line spectra

“…We also note that this sensitivity is comparable to the typical calibration uncertainty of the EUV spectrometers (e.g. Culhane et al 2007;Wang et al 2011;Del Zanna 2013), which makes the diagnostics using these Fe x lines unrealistic at present.…”

“…Liang et al 2009Liang et al , 2010Liang et al , 2012O'Dwyer et al 2012;Del Zanna et al 2010, 2012aDel Zanna 2011a,b;Del Zanna et al 2012b;, 2013Del Zanna et al 2014). These calculations represent significant improvements to previous atomic data, since they include a large number of levels and the associated cascading and resonances.…”

“…1, top) is a distribution of electron energies characterized by a power-law high-energy tail (Owocki & Scudder 1983;Livadiotis & McComas 2009, 2013 f (E, κ)dE = A κ 2 √ π(k B T ) 3/2 E 1/2 dE 1 +…”

“…This may, however, not be true if there are correlations between the particles in the system. These correlations may be induced by any long-range interactions in the emitting plasma (Collier 2004;Livadiotis & McComas 2009, 2010, 2011, 2013, such as wave-particle interactions, shocks, or particle acceleration and associated streaming of fast, weakly collisional particles from the reconnection site. Under such conditions, the distribution function may depart from the Maxwellian one.…”

The multi-thermal emission in solar active regions

“…from all the iron ionisation stages from Fe vii to Fe xvi and above 10 MK from Fe xxiii and Fe xxiv, as presented in detail in Del Zanna 2009a;Del Zanna 2012b, 2008Del Zanna et al 2011b). We have also recently provided an in-flight calibration for EIS (Del Zanna 2013). These spectrometers have great temperature resolution but poor spatial (CDS: 4-5 ; EIS: 3-4 ) and temporal resolution.…”