Abstract
The Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) on board the ESA Herschel Space Observatory has two detector setting modes: (a) a nominal mode, which is optimized for observing moderately bright to faint astronomical targets, and (b) a bright-source mode recommended for sources significantly brighter than 500 Jy, within the SPIRE FTS bandwidth of 446.7–1544 GHz (or 194–671 microns in wavelength), which employs a reduced detector responsivity and out-of-phase analog signal amplifier/demodulator. We address in detail the calibration issues unique to the bright-source mode, describe the integration of the bright-mode data processing into the existing pipeline for the nominal mode, and show that the flux calibration accuracy of the bright-source mode is generally within 2 % of that of the nominal mode, and that the bright-source mode is 3 to 4 times less sensitive than the nominal mode.
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Notes
This figure was adapted from [11], based on the document of The SPIRE Analogue Signal Chain and Photometer Detector Data Processing Pipeline, available at http://herschel.esac.esa.int/twiki/pub/Public/SpireCalibrationWeb/Phot_Pipeline_Issue7.pdf
The SPIRE pipeline description document, available at http://herschel.esac.esa.int/twiki/bin/view/Public/SpireCalibrationWeb, will be updated to reflect the PCAL data reduction algorithm described here.
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Acknowledgments
We thank both an anonymous referee and Dr. Locke Spencer for their useful comments that helped improve the overall clarity of the paper. SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC (UK); and NASA (USA). The Herschel spacecraft was designed, built, tested, and launched under a contract to ESA managed by the Herschel/Planck Project team by an industrial consortium under the overall responsibility of the prime contractor Thales Alenia Space (Cannes), and including Astrium (Friedrichshafen) responsible for the payload module and for system testing at spacecraft level, Thales Alenia Space (Turin) responsible for the service module, and Astrium (Toulouse) responsible for the telescope, with in excess of a hundred subcontractors. Support for this work was in part provided by NASA through an award issued by JPL/Caltech.
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Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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Lu, N., Polehampton, E.T., Swinyard, B.M. et al. Herschel SPIRE fourier transform spectrometer: calibration of its bright-source mode. Exp Astron 37, 239–252 (2014). https://doi.org/10.1007/s10686-013-9359-9
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DOI: https://doi.org/10.1007/s10686-013-9359-9