ROTATION MEASURE SYNTHESIS OF GALACTIC POLARIZED EMISSION WITH THE DRAO 26-m TELESCOPE

Abstract

Radio polarimetry at decimetre wavelengths is the principal source of information on the Galactic magnetic field. The diffuse polarized emission is strongly influenced by Faraday rotation in the magneto-ionic medium and rotation measure is the prime quantity of interest, implying that all Stokes parameters must be measured over wide frequency bands with many frequency channels. The DRAO 26-m Telescope has been equipped with a wideband feed, a polarization transducer to deliver both hands of circular polarization, and a receiver, all operating from 1277 to 1762 MHz. Half-power beamwidth is between 40 and 30 arcminutes. A digital FPGA spectrometer, based on commercially available components, produces all Stokes parameters in 2048 frequency channels over a 485-MHz bandwidth. Signals are digitized to 8 bits and a Fast Fourier Transform is applied to each data stream. Stokes parameters are then generated in each frequency channel. This instrument is in use at DRAO for a Northern sky polarization survey. Observations consist of scans up and down the Meridian at a drive rate of ∼0.9 • per minute to give complete coverage of the sky between declinations −30 • and 90 • . This paper presents a complete description of the receiver and data acquisition system. Only a small fraction of the frequency band of operation is allocated for radio astronomy, and about 20% of the data are lost to interference. The first 8% of data from the survey are used for a proof-of-concept study, which has led to the first application of Rotation Measure Synthesis to the diffuse Galactic emission obtained with a single-antenna telescope. We find rotation measure values for the diffuse emission as high as ∼ ±100 rad m −2 , much higher than recorded in earlier work.

Magnetic Fields in the Milky Way

“…Data acquisition for the southern-sky survey spanning 287−870 MHz with the Parkes telescope is completed and data processing in progress, while the STAPS survey described above will function as the high-band (1300 − 1800 MHz) southern-sky survey for GMIMS. For the high-band survey in the north (1277 − 1740 MHz), performed with the DRAO 26-m single dish [104], observations have finished and data reduction is nearing completion, with first sci-ence results discussed in [81]. Options for observing the remaining GMIMS surveys are being considered.…”

Recognizing magnetic structures by present and future radio telescopes with Faraday rotation measure synthesis

“…-DRAO 26 m single dish (Penticton, Canada), for which a northern sky polarization survey (GMIMS) is ongoing in the frequency range 1277−1762 MHz (Wolleben et al 2010b). -Parkes 64 m single dish (Australia), where a southern sky survey (S-PASS) has been performed in the frequency range 2180−2420 MHz (Carretti 2010).…”

“…Data from ATCA/ASKAP and LOFAR are hard to combine because they cover different parts of the sky. The Global Magneto-Ionic Medium Survey (GMIMS) planned with several single-dish telescopes (Wolleben et al 2010b) will provide a similarly wide frequency coverage as WSRT or GMRT, but with lower angular resolution.…”

Through thick or thin: multiple components of the magneto-ionic medium towards the nearby H ii region Sharpless 2–27 revealed by Faraday tomography

“…This survey will ultimately measure diffuse polarized emission across the entire sky from 300 MHz to 1.8 GHz using single-dish telescopes, giving excellent sensitivity to a wide range of Faraday structures. Results from the GMIMS high-band North (GMIMS-HBN, Wolleben et al 2010a), taken with the DRAO 26 m telescope, have been used directly to investigate the magnetoionic properties of a nearby H i shell (Wolleben et al 2010b), the North Polar Spur (Sun et al 2015), and the Fan Region (Hill et al 2017), and they are incorporated into other work analysing all-sky emission (e.g. Dickey et al 2019;Zheng et al 2017).…”