Spitzer Documentation & Tools
IRAC Instrument Handbook

Table of Contents

1       Introduction.

1.1         Document Purpose and Scope.

1.2         Basic Definitions.

1.3         IRAC Essentials.

1.4         Standard Acknowledgments for IRAC Publications.

1.5         How to Contact Us.

2       Instrument Description.

2.1         Overview

2.2         Description of Optics.

2.2.1      Field of View (FOV)

2.2.2      IRAC Image Quality.

2.2.3      Spectral Response.

2.2.4      Distortion.

2.3         Detectors.

2.3.1      Design.

2.3.2      Linearity.

2.4         Electronics.

2.4.1      Hardware.

2.4.2      Fowler Sampling.

2.4.3      Exposure Times and Frame Time.

2.4.4      Subarray Mode.

2.4.5      Calibration Lamps.

2.4.6      Firmware.

2.5         Sensitivity and Saturation

2.5.1      Sensitivity.

2.5.2      Saturation.

3       Operating Modes.

3.1         Readout Modes and Frame Times.

3.2         Map Grid Definition

3.3         Dithering Patterns.

4       Calibration.

4.1         Darks.

4.2         Flat Fields.

4.3         Photometric Calibration

4.4         Color Correction

4.5         Array Location-Dependent Photometric Corrections for Compact Sources with Stellar Spectral Slopes 

4.6         Pixel Phase-Dependent Photometric Correction for Point Sources.

4.7         IRAC Point Spread and Point Response Functions.

4.7.1      Core PRFs.

4.7.2      Extended PSFs.

4.7.3      Point Source Fitting Photometry.

4.8         Calculation of IRAC Zmags.

4.9         Astrometry and Pixel Scales.

4.9.1      Optical Distortion.

4.9.2      Pixel Solid Angles.

4.10       Point Source Photometry

4.11       Extended Source Photometry

4.11.1        Best Practices for Extended Sources.

4.11.2        Extended Source Aperture Correction.

4.11.3        Low Surface Brightness Measurements and the Maximum Scaling Factors.

4.11.4        Caveats & Cautionary Notes.

4.11.5        Faint Surface Brightness Behavior.

4.11.5.1       Binning.

4.11.5.2       Small Scales.

4.11.5.3       Medium Scales.

4.11.5.4       Large Scales.

4.11.5.5       Increasing exposure time.

4.12       Pointing Performance.

4.12.1        Pointing Accuracy.

4.12.2        Jitter and Drift

5       Pipeline Processing.

5.1         Level 1 (BCD) Pipeline.

5.1.1      SANITY DATATYPE (parameter checking)

5.1.2      SANITY CHECK (image contents checking)

5.1.3      TRANHEAD (header processing)

5.1.4      INSBPOSDOM (InSb array sign flipping)

5.1.5      CVTI2R4 (byte type changing)

5.1.6      Wraparound Correction: IRACWRAPDET AND IRACWRAPCORR

5.1.7      IRACNORM (Fowler sampling renormalization)

5.1.8      SNESTIMATOR (initial estimate of uncertainty)

5.1.9      IRACEBWC (limited cable bandwidth correction)

5.1.10        Dark Subtraction I: FFCORR (first frame effect correction) or LABDARKSUB (lab dark subtraction)

5.1.11        MUXBLEEDCORR (electronic  ghosting correction)

5.1.12        DARKDRIFT (readout channel’’ bias offset correction)

5.1.13        FOWLINEARIZE (detector linearization)

5.1.14        BGMODEL (zodiacal background estimation)

5.1.15        Dark Subtraction II: SKYDARKSUB (sky “delta-dark” subtraction)

5.1.16        FLATAP (flatfielding)

5.1.17        IMFLIPROT.

5.1.18        DETECT-RADHIT (cosmic ray detection)

5.1.19        DNTOFLUX (flux calibration)

5.1.20        Pointing Transfer (calculation of pointing information)

5.1.21        PREDICTSAT (HDR saturation processing)

5.1.22        LATIMFLAG (residual image flagging)

5.2         The Artifact-Corrected BCD Pipeline.

5.2.1      Stray Light

5.2.2      Saturation.

5.2.3      Sky Background Estimation.

5.2.4      Column Pulldown.

5.2.5      Banding Correction (Channels 3 and 4)

5.2.6      Muxstripe Correction (Channels 1 and 2)

5.3         Level 2 (Post-BCD) Pipeline.

5.3.1      Pointing Refinement

5.3.2      Superboresight Pointing Refinement

5.3.3      Mosaicking and Coaddition.

6       Data Products.

6.1         File-Naming Conventions.

6.2         IRAC Specific Header Keywords.

7       Data Features and Artifacts.

7.1         Darks, Flats, Missing Data and Bad Pixels.

7.1.1      Bad Pixels.

7.1.2      Flatfield.

7.1.3      Missing Data.

7.2         Electronic Artifacts.

7.2.1      Saturation and Nonlinearity.

7.2.2      Muxbleed (InSb)

7.2.3      Bandwidth Effect (Si:As)

7.2.4      Column  Pull-Down/Pull-Up.

7.2.5      Row Pull-Up.

7.2.6      Full-Array Pull-Up.

7.2.7      Inter-Channel Crosstalk.

7.2.8      Persistent Images.

7.2.8.1         Cryogenic Mission Persistent Images.

7.2.8.2         Warm Mission Persistent Images.

7.3         Optical Artifacts.

7.3.1      Stray Light from Array Covers.

7.3.2      Optical Banding and Internal Scattering.

7.3.3      Optical Ghosts.

7.3.4      Large Stray Light Ring and Splotches.

7.4         Cosmic Rays and Solar Protons.

8       Introduction to Data Analysis.

8.1         Post-BCD Data Processing

8.1.1      Pointing Refinement

8.1.2      Overlap Correction.

8.1.3      Mosaicking of IRAC Data.

8.1.3.1         Creating a Common Fiducial Frame.

8.1.3.2         Outlier Rejection.

8.1.3.3         Mosaicker Output Files.

8.1.3.4         To Drizzle or Not to Drizzle?.

8.1.3.5         Mosaicking Moving Targets.

8.1.4      Source Extraction.

8.1.4.1         Noise Estimation.

8.1.4.2         PRF Estimation.

8.1.4.3         Background Estimation.

8.1.4.4         Source Extraction.

8.1.4.5         Outlier Rejection.

Appendix A.       Pipeline History Log.

Appendix B.        Performing Photometry on IRAC Images.

Appendix C.       Point Source Fitting IRAC Images with a   PRF.

C.1   Use of the Five Times Oversampled PRFs Outside of APEX

C.2   Modifications to the IRAC PRFs for Use with APEX

C.3   Results of Tests with PRF fitting

C.3.1     Test on Calibration Stars.

C.3.2     Subpixel Response in Channels 1 and 2.

C.3.3     The Serpens Test Field.

C.3.4     The GLIMPSE Test Field.

C.3.5     Photometry of Moderately-Resolved Sources.

C.3.6     Positional Accuracy.

C.3.7     A How-To-Guide for IRAC Point Source Photometry with APEX

C.3.8     Pixel Phase.

Appendix D.       IRAC BCD File Header.

Appendix E.        Acronyms.

Appendix F.        Acknowledgments.

Appendix G.       List of Figures.

Appendix H.       List of Tables.

Appendix I.         Version Log.

Bibliography.