Complete Archive Processing

Code was written to batch process all 1350 filterbank archive files - totalling about 1800 hours of observations over a period of ~3.5 years.

Results are curated to eliminate the more obvious cases of RFI - but this still left about 370 examples of dispersed pulses ranging from about DM=40 to 70.

Plotting Dispersed Transients vs MJD

As well as individual plots for each transient it is useful to plot an overall result.

Aggregate results built from the dispersed transient database were plotted in the terms of DM vs Epoch (MJD).

Around the mid-point of the 3.5 years of observation both the frequency of observation and the antenna configuration was altered.  The observation frequency was changed from 436 MHz to 427.5 MHz (ironically to avoid rising levels of RFI) and the antenna array was changed from a single circularly-polarised Yagi to an array of four CP Yagis.

The plot is shown below with comments following.

A number of significant features can be seen in the plot above.

1. The change of observation frequency from 436 MHz to 427.5 MHz near MJD 58310 results in a negative shift in measured DM of about 10.  If these were cosmic transients then the measured DM would remain the same.

2. The 'Crab Pular GP' transients are likely just members of the above population distribution which - just by coincidence - have the DM of the Crab Pulsar.

3. There is no discernible correlation between the transient DMs and the change of antenna configuration.

4. The vertical light-blue rectangles show MJDs where observations occurred when the city airport (Sydney) was under curfew (radar dormant?).   These seem to coincide with 'quiet periods' where the number of transients detected is low.

These results seem to indicate that the low-DM dispersed transients are not cosmic in origin - but are produced by terrestrial RFI events.

Rogues Gallery of Dispersed Pulses Near the Crab Pulsar Dispersion Measure 

A 'rogues gallery' of the dispersed pulses with DMs right on the Crab Pulsar's DM (56.7) - about 44 of them - which could easily be mistaken for Giant Pulses - has been loaded up to the cloud - 'Pseudo Crab Transients'.

Be sure to view using 'Large Grid' to see low resolution previews.

Rogues Gallery of Pulses with Dispersion Measures Below The Crab Pulsar Dispersion Measure

An additional 'rogues gallery' of pulses with DMs from about 40 to below the Crab Pulsar DM (56.7).  There are about 350 of these. These can be seen in 'Other Low DM Transients'.

Be sure to view using 'Large Grid' to see low resolution previews.

Further searches were done for higher-DM dispersed transients the results of which can be seen in High-DM Dispersed Transients.