A new method of dark-current estimation for diffuse sky measurements with the AKARI infrared camera

We developed a new method for estimating the dark current of near-infrared (NIR) data from the Infra-Red Camera (IRC) aboard the AKARI satellite. The existing method of dark-current estimation is insufficient because the dark current is enhanced by charged particles hitting the detector in the South Atlantic Anomaly (SAA). We could trace this dark-current drift even during astronomical observations by monitoring the dark current in the masked region on the focal plane of IRC. We analyzed approximately 4500 dark frames, and found a relation in the integrated dark charge between the masked region and the exposed one of the detector array. Using this relation, we can estimate the integrated dark charge at each pixel from the average integrated dark charge in the masked region even during astronomical observations. Residuals in our new method were shown to be approximately 1ADU (corresponding to 3 nWm ^-2sr^-1 for the N2 band), even for the SAA-enhanced case, which is better than those in any existing methods by five or more times.