The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory

TL;DR

PACS on the Herschel Space Observatory is a versatile far-infrared instrument employing photoconductor and bolometer arrays for imaging and spectroscopy, with performance close to pre-launch expectations.

Contribution

This paper details the design, observing modes, calibration, data analysis, and in-orbit performance assessment of the PACS instrument.

Findings

PACS is fully operational with performance near pre-launch predictions.

The instrument successfully performs integral-field spectroscopy and imaging photometry.

In-orbit tests confirm the instrument's capabilities meet scientific requirements.

Abstract

The Photodetector Array Camera and Spectrometer (PACS) is one of the three science instruments on ESA's far infrared and submillimetre observatory. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16x25 pixels, each, and two filled silicon bolometer arrays with 16x32 and 32x64 pixels, respectively, to perform integral-field spectroscopy and imaging photometry in the 60-210\mu\ m wavelength regime. In photometry mode, it simultaneously images two bands, 60-85\mu\ m or 85-125\mu\m and 125-210\mu\ m, over a field of view of ~1.75'x3.5', with close to Nyquist beam sampling in each band. In spectroscopy mode, it images a field of 47"x47", resolved into 5x5 pixels, with an instantaneous spectral coverage of ~1500km/s and a spectral resolution of ~175km/s. We summarise the design of the instrument, describe observing modes, calibration, and data analysis methods, and present our current assessment of the in-orbit performance of the instrument based on the Performance Verification tests. PACS is fully operational, and the achieved performance is close to or better than the pre-launch predictions.