Polarization Surveys with the

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Polarization Surveys with the DRAO 26-m Telescope
at 1.4 GHz
Maik Wolleben, T. Landecker, O. Davison Dominion
Radio Astrophysical Observatory W. Reich, R.
Wielebinski Max-Planck-Institut für
Radioastronomie
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Outline
1) - The DRAO 26-m Polarization Survey
(finished) - Brief Representation of Data 2) -
The DRAO/MPI Rotation Measure Survey (ongoing)
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Specifications
First observing period Nov 2002 May
2003, coverage 17 Second observing period
Jun 2004 Mar 2005, coverage 42
TELESCOPE PARAMETER diameter 25.6m polar
mounting resolution 37 arcmin aperture
efficiency 55 hard limits -34 to 90
deg system temperature 125 K
SURVEY PARAMETER frequency 1410
MHz bandwidth 12 MHz observing mode drift
scanning pixel-size 15 arcmin integration
time 60 s / pixel
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Calibration
Observing Calibration Strategy
about 1000 pointings congruent with the
Leiden/Dwingeloo1 polarization survey ?
provides zero-levels in Stokes U and Q (absolute
levels) ? used for the gain calibration of
the receiving system (Müller matrix) ground
radiation profiles ? required to extrapolate
absolute zero-levels below 0 declination compari
son with Effelsberg Medium Latitude Survey ?
refines the (relative) temperature scale
- includes correction for main-beam instrumental
polarization - residual side lobe polarization
visible along the Galactic plane (l 0 - 60) -
systematic errors due to scanning effects (system
temperature variations)
1 A survey of linear polarization at 1415 MHz
Spoelstra, T. A. Th., AAS, 1972
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The l140 Region
B-star
S 203
dist 100 - 400 pc
dist 3.8 kpc
O-star
S 185
dist 1.2 kpc
dist 210 pc
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Data Availability
data available within the next two months!
then, interpolated data can be downloaded as
J2000
Galactic
fits format - interpolated U, Q - coverage mask
(to retrieve original coverage) - anything else
(if requested)
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Future The DRAO/MPI Rotation Measure Survey
What's next? Digital Polarimetry!
frequency range 1300 MHz 1800 MHz channels
about 1,000 10,000 fully Nyquist sampled
between declination -30 and 90 scans along the
Meridian (not drift scanning) rms per 500 MHz
band 0.3 mK observing time 1.5 years
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Future The DRAO/MPI Rotation Measure Survey
Example 2
ne 0.04 cm-3 B 3 µG d 0...4 kpc RM
0.81neBd
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Future The DRAO/MPI Rotation Measure Survey
the observed polarization angle will probably not
depend linearly on ?2 ? observed RM depends on
frequency!
Stokes I data cube
Stokes U Q data cubes
RM-survey products
Rotation Measure Synthesis
RM-cube (pol. int. vs. Faraday depth)
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Summary
1) DRAO 26-m Polarization Survey
http//mpifr-bonn.mpg.de/div/konti/26msurvey
http//www.drao.nrc.ca/26msurvey
(data will be released soon)
2) DRAO/MPI Rotation Measure Survey
- receiving system currently under development -
survey start scheduled for May 2006 - total
observing time required 1.5 years