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Abstract: Using the published WMAP 5-year data, we first show how sensitive the WMAPpower spectra are to the form of the WMAP beam. It is well known that the beamprofile derived from observations of Jupiter is non-Gaussian and indeedextends, in the W band for example, well beyond its 12.-6 FWHM core out to morethan 1 degree in radius. This means that even though the core width correspondsto wavenumber l\approx1800, the form of the beam still significantly affectsthe WMAP results even at l\approx200 which is the scale of the first acousticpeak. The difference between the beam convolved C l and the final C l is\approx70% at the scale of the first peak, rising to \approx400% at the scaleof the second.New estimates of the Q, V and W-band beam profiles are then presented, basedon a stacking analysis of the WMAP5 radio source catalogue and temperaturemaps. The radio sources show a significantly 3-4\sigma broader beam profileon scales of 10-30- than that found by the WMAP team whose beam analysis isbased on measurements of Jupiter. Beyond these scales the beam profiles fromthe radio sources are too noisy to give useful information. Furthermore, wefind tentative evidence for a non-linear relation between WMAP and ATCA-IRAM 95GHz source fluxes. We discuss whether the wide beam profiles could be causedeither by radio source extension or clustering and find that neitherexplanation is likely. We also argue against the possibility that Eddingtonbias is affecting our results. The reasons for the difference between the radiosource and the Jupiter beam profiles are therefore still unclear. If the radiosource profiles were then used to define the WMAP beam, there could be asignificant change in the amplitude and position of even the first acousticpeak. It is therefore important to identify the reasons for the differencesbetween these two beam profile estimates.

Author: U. Sawangwit, T. Shanks Durham University, UK


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