Hinode EIS: updated in-flight radiometric calibration

Abstract

We present an update to the in-flight radiometric calibration of the Hinode EUV Imaging Spectrometer (EIS), revising and extending our previous studies. We analyze full-spectral EIS observations of quiet Sun and active regions from 2007 until 2022. Using CHIANTI version 10, we adjust the EIS relative effective areas for a selection of dates with emission measure analyses of off-limb quiet Sun. We find generally good agreement (within typically +/- 15%) between measured and expected line intensities. We then consider selected intensity ratios for all the dates and apply an automatic fitting method to adjust the relative effective areas. To constrain the absolute values from 2010 and later we force agreement between EIS and Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) 193 A observations. The resulting calibration, with an uncertainty of about +/- 20%, is then validated in various ways, including flare line ratios from Fe XXIV and Fe XVII, emission measure analyses of cool active region loops, and several density-dependent line ratios.