Observations 2024-04-06 17:30-19:30 UTC

The same setup as in earlier observations was used. This time we had KAIRA, NenuFAR, LWA1, LWA-SV, LWA-NA, LWA-OVRO (unfortunately no useful data this time), DE602,603,604,605,609, FR606, SE607, PL610, PL612, IE613, LV614. DE601 was out of order, and the other DE stations used an incorrect pointing (position of Jupiter one month earlier), but still show signals.

I selected about four seconds (starting 18:20:45 UTC) of data with good Jupiter signals in most stations for the initial analysis. Data were channelised from LOFAR/NenuFAR subbands by a factor of $5^3=125$ and from the 19.6-MHz LWA bands by a factor of $2^8 * 7^2 = 12544$, which produces a final channel width of 1562.5Hz. A simple FFT was used instead of a PFB, even though the latter is also implemented. In this process the data were shifted towards the centre of the Earth as reference by applying an integer sample shift in the time domain and a fractional shift and fringe stopping (post-F) as phase correction after the channelisation. The software for this is not well tested, and all results should be interpreted with care.

For the plots below I uses a polarisation combination that should be close to the dominant circular sense. This is $X+{\rm i}Y$ for NenuFAR and the LWA and $X-{\rm i}Y$ for LOFAR and KAIRA. I only plot a limited part of the band.

The positions of the LOFAR stations can be found at https://www.astron.nl/lofartools/lofarmap.html. Unfortunately KAIRA is not included there, but you can easily find it on google maps at https://maps.app.goo.gl/9DmXfwPr4h3JS6Xm6.

We start with the shortest baseline NenuFAR-FR606. FR606 actually sits within the NenuFAR array (click to show in full size):

The panels show the amplitudes for (top) NenuFAR and FR606 on a logarithmic scale, the phases of the correlation between them and finally a measure for the correlation coefficient (bottom). This is calculated as the phasing efficiency (0 to 1) when integrating the complex visibility over each pixel. The numbers in parentheses on the top right show how many bins in time and frequency are in each pixel.

What do we see? The FR606 data are affected by strong RFI, probably leaking in from lower frequencies. This shows that NenuFAR is much more RFI-robust. In the NenuFAR amplitudes on top, we see the structure of Jupiter's emission modulated by interplanetary scintillation (e.g. dark lanes towards the right).

The phases are very stable, as expected, with the exception of RFI-affected parts. There are about two phase turns per MHz, which corresponds to a residual delay of about $2.2\,\mu\rm sec$. The cause of this is not entirely clear.

The phasing efficiency approaches 0.9 at the strongest parts, which means that the signal strength is well above the SEFD of the baseline.

This is a very long baseline. Here is the full range:

Unfortunately the bright patches at KAIRA coincide with dark patches at NenuFAR, so the baseline does not have much sensitivity. Nevertheless can we see consistent phases, even though at a low SNR, when zooming in:

At this zoom level (only two samples per pixel!) the correlation coefficient is not meaningful anymore, but the fact that we still see phases means that the signal must be very strong.

In the full range we can again see how the modulation differs between the stations:

Fringes can be seen nicely in the zoom in:

The correlation is stronger on this slightly shorter baseline:

In the zoom in we can see how the phases jump at the minima of the modulation:

Here is a long baseline towards the north-east, first full range, then a zoom in:

This baseline shows the power of interferometry. Even though the PL610 data are badly affected by RFI, the correlations still show nice signals:

The zoom in shows another interesting effect: The phases of the narrow pulses (diagonal lines) are clearly different from the phases of the more diffuse emission. This means they must come from a different position on the planet. This can be seen best on the leftmost burst between about 2.3 and 2.4 sec.

Here we see similar effects as on the baseline to PL610: