Scanamorphos for the APEX-ArT\'eMiS 350-450 $\mu$m camera : description and user guide

Abstract

Scanamorphos is public software initially developed to post-process scan observations performed with the Herschel photometer arrays. This post-processing mainly consists in subtracting the total low-frequency noise (both its thermal and non-thermal components), masking cosmic ray hits, and projecting the data onto a map. Building upon the results obtained for P-ArT\'eMiS (the prototype of ArT\'eMiS), Herschel and then NIKA2 (a resident camera of the IRAM 30-m telescope operating at 1.25 and 2 mm), it has now been tailored to the ArT\'eMiS camera, an ESO and OSO P.I. instrument installed at the APEX 12-m telescope, demonstrating our initial claim that the software principles were directly transposable to scan observations made with other instruments, including from the ground, provided they entail sufficient redundancy. This document explains how the algorithm was modified to cope with the specificities of ArT\'eMiS observations and with the atmospheric emission at 350 and 450 $\mu$m, far dominating the instrumental drifts that were the only low-frequency noise component in Herschel data. Like in the original software, this was accomplished without assuming any noise model and without applying any Fourier-space filtering, by exploiting the redundancy built in the observations - taking advantage of the fact that each portion of the sky is sampled at multiple times by multiple bolometers. It remains an interactive software in the sense that the user is allowed to optionally visualize and control results at each intermediate step, but the processing is fully automated. It has been grafted onto the ArT\'eMiS pipeline, in charge of the formatting, calibration and projection of the data, that is described elsewhere.