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A broadband flux scale for low frequency radio telescopes

Submitter: George Heald
Description: Much of the ongoing LOFAR commissioning effort is focused on producing good-looking images. However, looks are not everything! A very important aspect of the images produced by the system is that they are tied to a well understood flux scale. In this way, the sources detected by LOFAR can be meaningfully compared with data from other radio telescopes.

With that in mind, and in preparation for generating output (images and catalogs) from MSSS, we have recently made an effort to produce a consistent and clearly defined flux scale that LOFAR can use. A key factor is that this flux scale has to be intrinsically broadband, so that the entire (huge!) bandwidth of the telescope is properly, and consistently, calibrated.

The results are presented in this recently accepted paper. A short list of well-known compact and bright northern calibrator sources were selected, and literature flux measurements were collected and placed on a common scale. Next, simple spectral models were fitted to the data points. The resulting models (as shown in today's image) are the basis of the flux scale that underlies MSSS. The vertical red-dashed lines show the range of frequencies that LOFAR covers. Future work will address the conversion of this relative spectral scale to an absolute measure of flux density.
Copyright: Scaife & Heald 2012, MNRAS, in press
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