Transient effects in Herschel/PACS spectroscopy
Abstract
Context. The Ge:Ga detectors used in the PACS spectrograph onboard the Herschel space telescope react to changes of the incident flux with a certain delay. This generates transient effects on the resulting signal which can be important and last for up to an hour. Aims. The paper presents a study of the effects of transients on the detected signal and proposes methods to mitigate them especially in the case of the unchopped mode. Methods. Since transients can arise from a variety of causes, we classified them in three main categories: transients caused by sudden variations of the continuum due to the observational mode used; transients caused by cosmic ray impacts on the detectors; transients caused by a continuous smooth variation of the continuum during a wavelength scan. We propose a method to disentangle these effects and treat them separately. In particular, we show that a linear combination of three exponential functions is needed to fit the response variation of the detectors during a transient. An algorithm to detect, fit, and correct transient effects is presented. Results. The solution proposed to correct the signal for the effects of transients substantially improves the quality of the final reduction with respect to the standard methods used for archival reduction in the cases where transient effects are most pronounced. Conclusions. The programs developed to implement the corrections are offered through two new interactive data reduction pipelines in the latest releases of the Herschel Interactive Processing Environment.
Additional Information
© 2016 ESO. Received: 21 October 2015; Accepted: 18 January 2016; Published online 17 October 2016. 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. HCSS and HIPE are a joint developments by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS and SPIRE consortia. We are grateful to the entire spectroscopy group of PACS for their help and support. In particular, we would like to acknowledge P. Royer and B. Vanderbusche for testing the pipeline and pointing out significant bugs, as well as A. Poglitsch, R. Vavrek, A. Contursi, and J. de Jong for many useful discussions. We thank K. Exter and the anonymous referee for their careful reading of the manuscript and very useful suggestions. We would like to thank B. Ali and R. Paladini for their constant support at the NASA Herschel Science Center. Finally, D.F. is indebted to Prof. I. Perez-Fournon for his support at the IAC in a particularly difficult moment of his scientific carrier.Attached Files
Published - aa27612-15.pdf
Submitted - 1601.07729v1.pdf
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Additional details
- Eprint ID
- 64147
- Resolver ID
- CaltechAUTHORS:20160202-081550227
- NASA
- Created
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2016-02-03Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)