Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Submillimeter Polarimetry with PolKa, a reflection-type modulator for
  the APEX telescope   Imaging polarimetry is an important tool for the study of cosmic magnetic
fields. In our Galaxy, polarization levels of a few up to $\sim$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 $\sim0\fdg2$ in
diameter. %Here we present the results from the commissioning of PolKa, a
polarimeter for 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 towards a point
source is at the level of $\sim0.1$\%, increasing to a few percent at the
$-10$db 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.

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The categories of this paper are: nucl-th
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The categories of this paper are: eess
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The categories of this paper are: nucl-ex
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The categories of this paper are: funct-an
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The categories of this paper are: supr-con
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The categories of this paper are: hep-ph
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The categories of this paper are: q-fin
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: atom-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas
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The categories of this paper are: cmp-lg
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The categories of this paper are: nlin