PACS instrument and calibration web pages

Introduction

This page provides up-to-date information about using the PACS instrument: from preparing observations to reducing your data. This page also provides you with the latest calibration accuracies and known PACS calibration issues.

Observing with PACS

• The PACS Observer's Manual: the first thing to read before applying for time with PACS as it tells you how the instrument works: HTML PDF (11 Mb), version 2.3, 8-June-2011

• AOT Release Notes: dedicated release notes per AOT (the astronomer's observing template, i.e. planning your observing time). These contain information about how the standard observing blocks work, transmission functions, sensitivity, etc.

• In-flight scientific capabilities of the PACS instrument: The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory (1.5 Mb), Poglitsch et al., 2010, A&A, 518, L2

• A quick guide to the PACS instrument: PACS fact sheet

Reducing PACS data

• HIPE (Herschel Interactive Processing Environment): The latest User Release HCSS version that you should use for reducing PACS data is HIPE v11.0 It can be downloaded from: http://herschel.esac.esa.int/HIPE_download.shtml. In the CIB (continuous integration build) this version corresponds to Track 11, build 2934.

• Within HIPE you can access all the PACS data reduction and HIPE-user documentation for Track 11. We also include the PACS Data Reduction Guides as PDF files here:
  • PACS spectrometer PDRG for Hipe 11
  • PACS photometer PDRG for Hipe 11

Note that within the standalone pdf version, external links will go nowhere. The PDRG follows the pipeline scripts (see "Cookbooks" below) and also explains what you are doing as you pipeline process.

• The what's new in HIPE 11 page lists the changes in HIPE version 11.0 with respect to the 10.x series, provides a detailed lists of updated functionalities and calibration aspects.

• The Nasa Herschel Science center (NHSC) has also posted some PACS Data Processing Tutorials

• Link to the General HCSS Public Twiki page (with general framework information and updates): http://herschel.esac.esa.int/twiki/bin/view/Public/WebHome

Cookbooks

• Our version of cookbooks are the pipeline scripts, because (i) we recommend you rereduce your data in any case and (ii) these scripts are heavily commented to guide you through the data reduction process. These data reduction scripts are available in HIPE under the menu: Pipeline --> PACS --> Photometer/Spectrometer.
• See also the walkthroughs on the NHSC PACS page.
• The PACS Launch Pads from May 2012 for photometry are provided here for photometry. These are taken from the first chapter of the PDRGs and are a useful quick-start guide to loading your data into HIPE, and then what to know and do before you begin reprocessing your data with one of the pipelines.
• The PACS Launch Pads from Jun 2013 (for Track 11) are provided here for spectroscopy. These are taken from the first chapter of the PDRGs and are a useful quick-start guide to loading your data into HIPE, and then what to know and do before you begin reprocessing your data with one of the pipelines. In addition, we take you through all the things you need to think about before reprocessing your PACS spectroscopy through the pipeline yourself:
  • why we recommend you do re-pipeline your data
  • what you need to pay attention to for different types of astronomical source
  • what the post-pipeline processing tasks are you can, or must, do.

PACS calibration file versions

• When starting HIPE, you will be informed if new calibration files are available. Clicking on 'show details' will show you the release note of the new calibration set, with details about the changes. This is all also explained in the PDRG (chap 2)

• The history of the calibration files that have been released to the community is provided here: PACS Calibration File History

• You can inspect the release notes for the calibration sets installed on your machine from within HIPE. Open the Calibration Sets View from the menu Window -> Show Views -> Workbench.

PACS calibration and performance

Photometer calibration in scan maps

• Point Spread Function: PACS Photometer Point Spread function (10 Mb), version 2.0, 4 April 2012. A detailed document of the in-flight observed PSF. The accompanying tarball can be found here (76 Mb).

• Herschel/PACS modelled point spread functions (3.1 Mb) is a related document presenting Zemax modelled point spread functions for both an `ideal' and an 'as built' Herschel telescope model. Tarballs with corresponding broad-band and monochromatic PSFs for these two cases are at http://pacs.ster.kuleuven.ac.be/pubtool/PSF. These are useful in addition to the observed PSFs but cannot replace them, since the models do not capture all effects found in the observed PSFs.

• Point-source photometry: PACS uses 5 stars as primary calibrators with fluxes ranging from 0.6 to 15 Jy, plus fainter stars and asteroids as secondary calibrators. The absolute flux scale accuracy is dominated by the model uncertainties and amounts to 5% in the 3 filter bands. At the same time, the reproducibility for a given non-variable point source is about 2% for all PACS bands. The flux calibration is described in detail in the technical note "PACS photometer point-source flux calibration (3.1 Mb) (PICC-ME-TN-037), version 1.0, 12 April 2011.

• Point-source photometry in deep PACS maps/surveys: The effect of the high-pass filter data reduction technique on the PACS Photometer PSF, point-source photometry and noise has been investigated in depth in this technical note

• colour correction:
  • PACS Photometer Passbands and Colour Correction Factors for various source SEDs (2.5 Mb), PICC-ME-TN-038, version 1.0, 12 April 2011.
  • The bandwidth of the PACS photometric system, PICC-CR-TN-044 provides supplementary information on colour correction with the PACS photometer.

• Extended emission photometry: Three technical reports which assess the extended emission (or surface brightness) measured from PACS data and compare that to IRAS and Spitzer/MIPS data:
  • Assessment analysis of the extended emission calibration for the PACS red channel, version 1.0, April 2012: latest results on the comparison of extended emission in the PACS red channel (i.e. 160um) with corresponding data from Spitzer/MIPS 160um.
  • Experiments in photometric measurements of extended sources (3.2 Mb), (report SAp-PACS-MS-0718-11, March 18, 2011). This report compares photometry of large extended galaxies (using large apertures) between PACS, IRAS and MIPS.
  • Surface brightness comparison of PACS blue array with IRAS and Spitzer/MIPS images (1 Mb), (report PICC-NHSC-TN-029, v1.01, 12 April 2011). This report summarises pixel-to-pixel comparisons between extended emission as measured between PACS, IRAS and MIPS.
  • We refer to the paper Common-Resolution Convolution Kernels for Space- and Ground-Based Telescopes, G. Aniano et al. (2011) for kernels and associated routines (IDL) to match spatial resolution between several infrared instruments PSFs (PACS, SPIRE, Spitzer/MIPS, Spitzer/IRAC, WISE) as well as GALEX (UV) and other PSF families (gaussian, bi-gaussian, Moffat).

• Point-source observations:
  • We refer to: PACS Photometer: chop/nod point-source & mini-scan map AOT release note: (2 Mb) version 2.0, 12 November 2010. We recommend you use the mini scan-map technique in all science cases related to point-sources, compact sources and also in cases of faint extended emission around point-sources. The chop/nod mode is no longer recommended for use.
  • However, for a technical assessment of the original chop/nod mode sensitivity intended for point-sources, we refer to SAp-PACS-MS-0711-09 (5.5 Mb).

Photometer map-makers

Three fundamentally different map-makers are offered in Hipe 11 with ipipe scripts, starting from level 1 on pairs of obsids :

• highpass filtering branch, where the bolometer timelines are highpass filtered to remove the 1/f noise at the expense of extended emission. It provides optimum sensitivity to point-sources.
• MADmap, a GLS (generalized least square) map-maker, that allows to preserve extended emission at all scale.
• JyScanam, a Java-version of the IDL Scanamorphos map-maker.

Another two public map-makers, also starting from level 1, widely used and both very easy to use are :

• Scanamorphos, an IDL map-maker from Hélène Roussel (IAP) with an advanced and powerful destriper for PACS maps.
• Unimap a light (memory wise) GLS map-maker from Lorenzo Piazzo ('La Sapienza' University of Rome ) under a free Matlab runtime environment, with an advanced pre-processing (drift correction, jump detection) and post-processing stages (bright sources).

PACS spectrometer calibration

• PACS Spectrometer performance and calibration: The PACS Spectrometer Calibration Document v2.4 (16-June-2011) provides details on the calibration accuracy and the necessary information to optimally interpret PACS spectroscopy observations. New issues of this document will be released with new versions of the pipeline and new versions of the calibration tree provided in the Herschel interactive data analysis system. Please note, the above linked document refers to the calibration status and performance of pipeline version v8.0. An update compatible with HIPE v9.0 release will be provided soon.

• Data processing known issues of standard products: Browse quality Level 2 products are provided in the Herschel Science Archive. This summary page describes typical problems and caveats the observer needs to be familiar when looking at these preview products. Aspects of product quality which can be further optimised by interactive processing are also summarised here. The document refers to the version of data processing pipeline currently being used for processing of incoming Herschel data (version number provided therein).

• PACS spectrometer beams, version 3,can be downloaded here: PCalSpectrometer_Beam_v3.tar.gz. These beams are based on measurements of a raster with step size 2.5" around Neptune. These beams are useful to compare the flux seen in the different IFU spaxels with with a point source, or a certain brightness distribution in the sky. Version 3 has the beam effiencies for all IFU spaxels, and has a drastic improvement wrt version 2 since the spacecraft pointing was reconstructed more accurately. This resulted in a non-equidistant sampling of the beam efficiency in the sky. The beam products offered are equidistantly sampled on a grid of 0.5 arcseconds. The central part of the beam is the Gaussian fit to the measured beam efficiencies. This has been verified to be a very good description on the different raster observations we have of the central spaxels for wavelengths longer than 80 micron. Below 80 micron, the actual beam shows the square detector footprint, and the Gaussian approximation in the beam products v3 overpredicts the real beam efficiency by 1.5 to 2 percent. The outer part of the beams contains the interpolated values of the irregularly sampled measurements. Thanks to the improved data reduction quality, version 3 of the spectrometer beams are sharper than version 2, and shows the ghosts (see also the PACS spectrometer calibration document) more clearly, as well as the three-lobe structure of the Herschel telescope PSF. Each beam is normalised to the fitted peak value of the central spaxel. The WCS associated with the beam is in sky coordinates for position angle 0.
• The raw data from which the PACS spectrometer beams above have been derived, is also made available to the users in tables (y, z offset - signal):
  • SpecSpatial_BeamEfficiency_central_spaxel_tables_v1.tar.gz: Raw measurements PACS beams - central spaxel only. This contains a fits file for each wavelenght measured for the CENTRAL SPAXEL only. Raw data of the coarse and fine rasters are combined. The array dimension of the fits file is [3,npoints] where the first column gives the y raster position, the 2nd column the z raster position and the 3rd column the normalised flux measured at this raster position.
  • SpecSpatial_BeamEfficiency_tables_v1.tar.gz: Raw measurements PACS beams - all spaxels, coarse raster measurements only: each fits files corresponds to one wavelength. Each file contains the data for all spaxels of the coarse raster measurement only. Each fits file holds an array of 3x25x25x25 where: (0,25,25,25) : y raster position (1,25,25,25): z raster position (2,25,25,25): flux normalized to the central spaxel. The second and third dimensions are the raster position indexes (y and z) and the last dimension is the module number (=spaxel).

Planned processing and calibration improvements

• The PACS ICC and the HSC calibration scientist teams are currently working on making the following processing and calibration improvements available to the users:
  • Making spectrometer convolution kernels available. These products will be useful to estimate line-ratios in oversampled spectral maps.
  • Improved a-posteriori pointing reconstruction based on guide star positions used for the observation and the gyroscope raw output.
  • Point source flux correction for observations not perfectly centered on the central spaxel.
  • Improved correction for systematics affecting the spectral shape of sources and detectability of unresolved lines.

Interest Groups and Scripts

• PACS Photometry (point source) interest group
• Large maps and point source extraction for PACS and SPIRE
• PACS Spectroscopy
• Spectral maps for PACS, SPIRE and HIFI

Links

• PACS NHSC homepage
• Key information of PACS on the NHSC web site.
• Scanamorphos by H. Roussel can be used to build maps from scan observations made with bolometer arrays, in particular with the PACS and SPIRE photometers.