SIMBAD references

We describe the reduction of data taken with the PACS instrument on board the Herschel Space Observatory in the Science Demonstration Phase of the Herschel-ATLAS (H-ATLAS) survey, specifically data obtained for a 4x4 deg² region using Herschel's fast-scan (60arcsec/s) parallel mode. We describe in detail a pipeline for data reduction using customized procedures within hipe from data retrieval to the production of science-quality images. We found that the standard procedure for removing cosmic ray glitches also removed parts of bright sources and so implemented an effective two-stage process to minimize these problems. The pronounced 1/f noise is removed from the timelines using 3.4- and 2.5-arcmin boxcar high-pass filters at 100 and 160µm. Empirical measurements of the point spread function (PSF) are used to determine the encircled energy fraction as a function of aperture size. For the 100- and 160-µm bands, the effective PSFs are ∼9 and ∼13arcsec (FWHM), and the 90-per cent encircled energy radii are 13 and 18arcsec. Astrometric accuracy is good to ≲2arcsec. The noise in the final maps is correlated between neighbouring pixels and rather higher than advertised prior to launch. For a pair of cross-scans, the 5σ point-source sensitivities are 125-165mJy for 9-13 arcsec radius apertures at 100µm and 150-240mJy for 13-18 arcsec radius apertures at 160µm.