L-Band Wide Precursor Observations

Abstract of observing proposal submitted in October 2003

This proposal requests time to carry out a pilot study for the GALFA Continuum Transit Survey (GALFACTS). It is submitted on behalf of the GALFA Continuum science sub consortium. The scientific motivation for GALFACTS focuses heavily on exploiting polarimetric observations and measurements of Faraday Rotation to probe the magneto-ionic medium in the disk and halo of the Galaxy. This proposal will test the observing plan for GALFACTS. The observations and the data will be used to assess the success of the observing strategy, measure the effects of instrumental systematics on the scientific results and to develop processing and analysis algorithms. The region chosen for observations contains polarized signals from both a background point source and the distributed Faraday Screen, and will provide not only a rigorous test of these aspects of GALFACTS, but also a scientific investigation of filamentary structures in the Faraday screen.

Proposal ID: Taylor031001171601

Postscript file with the cover sheets of the observing proposal
Postscript file with the body of the observing proposal

Observations were carried out for 11 nights between August an September 2004. Below is a preliminary Stokes U image from the L-band wide observations of the test region. The Effelsberg Mid-latitude survey image of polarized intensity in the same area is shown below the Arecibo image. The Arecibo L-band wide data was constructed using the same observing technique of fast meridian scans that will be used for GALFACTS. Polarization calibration of the electronic gain have applied, but the final correction for the Meuler Matrix of the feed has not been made. Therefore there is an arbitrary rotation of the polarization position angle difference between the Effelsberg and Arecibo images. However, the polarization features in the Effelsberg image are seen in the L-band wide data with higher angular resolution, showing, for instance the structure of the dark lanes surrounding the strong source near the center of the image. The diffuse polarized emission is well represented, and is largely free from Stokes I leakage polarization artifacts, since there is no corresponding highly structured Stokes I counterpart to the emission.

Arecibo Stokes I L-band wide image (top) and corresponding Effelsberg image (gray scale at bottom). The L-band wide image was constructed from 256 spectral channels covering a 100 MHz bandwidth centered at 1170 MHz. Artifacts associated with the san pattern are seen in the Stokes I image. These are residuals of the "basket weaving" algorithm. Only preliminary basket weaving has been applied to correct each day for a single constant offset. More refined basketweaving software is under development.

 

last updated January 3, 2005

GALFACTS Home