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Submillimeter Polarimetry with PolKa, a Reflection-Type Modulator for the APEX Telescope

Wiesemeyer, H. and Hezareh, T. and Kreysa, E. and Weiss, A. and Güsten, R. and Menten, K. M. and Siringo, G. and Schuller, F. and Kovács, A. (2014) Submillimeter Polarimetry with PolKa, a Reflection-Type Modulator for the APEX Telescope. Publications of the Astronomical Society of the Pacific, 126 (945). pp. 1027-1047. ISSN 0004-6280.

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Imaging polarimetry is an important tool for the study of cosmic magnetic fields. In our Galaxy, polarization levels of a few up to ~10% are measured in the submillimeter dust emission from molecular clouds and in the synchrotron emission from supernova remnants. Only few techniques exist to image the distribution of polarization angles as a means of tracing the plane-of-sky projection of the magnetic field orientation. At submillimeter wavelengths, polarization is either measured as the differential total power of polarization-sensitive bolometer elements, or by modulating the polarization of the signal. Bolometer arrays such as LABOCA at the APEX telescope are used to observe the continuum emission from fields as large as ~0º.2 in diameter. Here we present PolKa, a polarimeter for LABOCA with a reflection-type waveplate of at least 90% efficiency. The modulation efficiency depends mainly on the sampling and on the angular velocity of the waveplate. For the data analysis, the concept of generalized synchronous demodulation is introduced. The instrumental polarization toward a point source is at the level of ~0.1%, increasing to a few percent at the -10db contour of the main beam. A method to correct for its effect in observations of extended sources is presented. Our map of the polarized synchrotron emission from the Crab nebula is in agreement with structures observed at radio and optical wavelengths. The linear polarization measured in OMC1 agrees with results from previous studies, while the high sensitivity of LABOCA enables us to also map the polarized emission of the Orion Bar, a prototypical photon-dominated region.

Item Type:Article
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URLURL TypeDescription Paper
Weiss, A.0000-0003-4678-3939
Menten, K. M.0000-0001-6459-0669
Additional Information:© 2014 Astronomical Society of the Pacific. Received 2014 May 27; accepted 2014 September 12; published 2014 November 14. We owe the APEX observatory staff a debt of gratitude. We thank Dr. S. Risse from the Fraunhofer IOF (Jena, Germany) for very fruitful discussions concerning the design of PolKa. The analyzer grids were donated by Manfred Tonutti (RWTH Aachen University, Germany). H.W. acknowledges helpful comments from C. Thum and insightful discussions with D. Muders, S. Heyminck, A. Lobanov and M. Houde. The referee helped to improve the paper further. T. Hezareh’s research was funded by the Alexander von Humboldt foundation. The data reduction software used the GILDAS and CFITSIO libraries ( and heasarc.gsfc.nasa .gov/docs/software/). The opacity coefficients were obtained from the am model (S. Paine, SMA technical memo #152, 2012) via the kalibrate module of the KOSMA software, Department of Physics, Cologne University.
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Alexander von Humboldt FoundationUNSPECIFIED
Issue or Number:945
Record Number:CaltechAUTHORS:20150115-154340387
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Official Citation:Submillimeter Polarimetry with PolKa, a Reflection-Type Modulator for the APEX Telescope H. Wiesemeyer, T. Hezareh, E. Kreysa, A. Weiss, R. Güsten, K. M. Menten, G. Siringo, F. Schuller, and A. Kovacs Publications of the Astronomical Society of the Pacific, Vol. 126, No. 945 (November 2014), pp. 1027-1047 Published by: The University of Chicago Press on behalf of the Astronomical Society of the Pacific Article DOI: 10.1086/679002 Article Stable URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:53801
Deposited By: Ruth Sustaita
Deposited On:16 Jan 2015 16:43
Last Modified:03 Oct 2019 07:52

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