Calibration and Performance of the AKARI Far-Infrared Surveyor (FIS) -- Slow-Scan Observation Mode for Point Sources

TL;DR

This paper details the calibration and characterization of the AKARI FIS Slow-Scan mode, demonstrating improved sensitivity and providing detailed PSF and flux calibration results for far-infrared point source observations.

Contribution

It introduces the calibration process and performance assessment of the AKARI FIS Slow-Scan mode, enhancing far-infrared imaging capabilities for point sources.

Findings

Sensitivity is 10-100 times better than All-Sky Survey.

PSF FWHMs are ~30'' and ~40'' for shorter and longer wavelengths.

Photometric accuracy is better than ±15% in most bands.

Abstract

We present the characterization and calibration of the Slow-Scan observation mode of the Far-Infrared Surveyor (FIS) onboard the AKARI satellite. The FIS, one of the two focal-plane instruments on AKARI, has four photometric bands between 50--180 um with two types of Ge:Ga array detectors. In addition to the All-Sky Survey, FIS has also taken detailed far-infrared images of selected targets by using the Slow-Scan mode. The sensitivity of the Slow-Scan mode is one to two orders of magnitude better than that of the All-Sky Survey, because the exposure time on a targeted source is much longer. The point spread functions (PSFs) were obtained by observing several bright point-like objects such as asteroids, stars, and galaxies. The derived full widths at the half maximum (FWHMs) are ~30'' for the two shorter wavelength bands and ~40'' for the two longer wavelength bands, being consistent with those expected by the optical simulation, although a certain amount of excess is seen in the tails of the PSFs. The flux calibration has been performed by the observations of well-established photometric calibration standards (asteroids and stars) in a wide range of fluxes. After establishing the method of aperture photometry, the photometric accuracy for point-sources is better than +-15% in all of the bands expect for the longest wavelength.