Daily Image
29-08-2025
Fringe fitting for LOFAR long baselines
| Submitter: | Jacksen Narvaez (supervisors: Tammo Jan Dijkema, Mattia Mancini) |
| Description: | For very long baselines, such as LOFAR with international stations, the phase of visibilities varies rapidly, making it difficult to capture variations in both frequency and time. Fringe fitting corrects these phase residuals by approximating the expected rate of change, which allows visibilities to be coherently combined over longer intervals and improves the signal-to-noise ratio. This technique is widely used in VLBI (CASA, AIPS) but is not yet implemented in the LOFAR software framework (e.g., DP3). We developed a stand-alone fringe fitting pipeline (Python/C++) and tested it on EVN and LOFAR Data. In the image, we observe the radio source ILTJ131028.61+322045.7. Left: original data; Right: after antenna-based fringe-fitting calibration. Fringe-fitting reveals a central point-like source with flux increased by over an order of magnitude with respect to the background. The stand-alone experimental code will be available at https://github.com/JackNarvaez/FringeFitting We have already explored improvements such as modeling dispersive delays and refining the fit via least-squares minimisation. In the future, the stand-alone pipeline can be incorporated into DP3. This work was part of the ASTRON Summer Student Programme. |
| Copyright: | CC-BY 4.0 Jacksen Narvaez |
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