First successful interferometry

The data set L202279 was observed on 2014-01-24 in the time range 20:00-21:25 UTC using the stations CS002-007, DE601,602,603,604,605,FR606,SE607,UK608.

First diagnostic plots were made from the online correlations provided by the ILT. These have a low resolution of 1 sec and 1 subband (200 kHz), which is not sufficient for a proper analysis, but it can be used as a first-look and to find good time ranges for high-resolution correlations.

We have such plots for single stations and selected baselines. In these we see that there are indeed regions in time and frequency with emission from both hemispheres.

For the first real calibration tests, we concentrate on one second of data near 20:16:10.5 UTC, which is at 971 sec offset from the beginning.

Here are 100 sec around that time (only one baseline as overview, reduced frequency range):

The vertical green dashed lines indicate time with jumps in the integer-sample delay, white areas are missing data.

(Most plots here are displayed with reduced resolution. Click on them (maybe twice) for full size.)

Here are 10 sec around that time:

For the analysis we only use 1 sec with further reduced frequency range. Here we have a good overlap of signals from both hemispheres:

We correlate only the stations CS002,DE601,602,604,605,FR606,SE607,UK608, but not the other core stations (only short baselines) or DE603 (missing data).

: The calibration process will be described in detail at a later time. For the moment I just want to present some results. We use all these stations for an eigenvalue decomposition, but later exclude CS002,DE604,UK608 from the interferometry, because their parameters are inconsistent with the rest. This is most probably due to bad station calibration, which causes polarisation leakage of the order 1.

The eigenvalue decomposition is also used as basis for labelling good signals from either hemisphere:

Assuming that the northern and southern emission consist of only one unresolved component each, which may have a frequency-dependent position (as expected for electrons moving along a single field line for each hemisphere), we can first fit the mean S-N offset together with a linear drift with frequency. The following plot shows fits of such parameters for the 1-sec time and frequency range just shown:

The left panel is for the group delay, which is given by the position plus frequency-derivative multiplied with mean frequency, which is not constrained very accurately. The middle panel is the position from the phases. This is much more precise, but it took some effort to solve for the lobe ambiguities, or in other words understand which peak in the dirty map is the real peak. The right panel is the difference of the two, corresponding to the frequency-derivative multiplied with the mean frequency. The straight lines are results from a few individual baselines, the dark spot is a fit to all good baselines. The dotted circles are expectations as explained below.