Pulsar Binning

In this mode the integration time in any one cycle, normally 10 seconds, is divided into an integral number of pulsar periods. Each pulsar period is further divided into N equal time intervals called bins. The integration in the correlator is done separately for each bin, such that at the end of the cycle, N quantities are produced, each of which represents the integrated value at a particular pulsar phase. At the beginning of each cycle, the time at which the integration begins is adjusted according to a prediction of the pulsar timing at the current epoch.

With our standard pulsar binning mode, there is a lower limit of 2048$\mu$s on the bin time. Generally, $no.bins \times no.channels < 4096$ on any baseline and polarisation. However, there is a non-standard binning mode which allows bin times down to around 250$\mu$s, but with a maximum of 8 bins (as $no.bins \times no.freq. \times no.pol. < 8$). In an example case, with a period of 33.4ms the limit is 16 bins. This requires a new configuration. If you believe you will need new configurations or any non-standard configuration, you should get in touch with Warwick Wilson (Warwick.Wilson@csiro.au) at least a month before your observations and preferably before the proposal is submitted.

Pulsar binning mode is enabled if:

• mode=PSR in the ATCASCHED file,
• the correlator is configured with a suitable configuration file,
• a special file, source.polyco, containing a timing prediction for the pulsar at the epoch of observations, is present in the area /home/corr/cor/pulsar on CACCC.

Setting mode=PSR causes the software to look for the ephemeris file for that source -- thus, for calibration sources, set mode=STANDARD. A default period of 0.2 seconds, or the last value of a mode=PSR scan, will be used for the calibration sources.

Below are some examples of the configurations currently available.

PSR8_128_2

Similar to FULL_128_2 but with 8 bins in each frequency. 2 Frequencies, both 128MHz bandwidth, 4 polarisations per frequency, 32 channels and 8 bins.

PSR8_4_1024-128

Similar to FULL_4_1024-128 but with 8 bins in the second frequency. 2 Frequencies. 1st frequency has: 4MHz bandwidth, 2 polarisations, 1024 channels for each polarisation and no binning. The 2nd frequency has: 128MHz bandwidth, 4 polarisations, 32 channels and 8 bins.

PSR16_128_1

Similar to FULL_128_1 but with 16 bins. 1 Frequency, 128MHz bandwidth, 4 polarisation, 32 channels and 16 bins.

The /home/corr/cor/pulsar area on CACCC must contain a file source.polyco, where source is the source name given in the schedule file. If this file is not present or is invalid, an error message will appear on the CACOR screen. This file can be created by the program polyco, from the Pulsar group, available on the workstations at ATNF Headquarters.

As yet, the Compact Array visibility viewing program, VIS, can display only one bin at a time. This is because the data for only one bin is sent from CACOR to VIS. The choice of which bin data is sent to VIS is made using the SPD task , normally used for displaying the output from the correlator.

In SPD, return to the top level of the menu and choose:

• 2 - Time Variables
• 1 - Setup Variables
• 4 - Default setup
• then, in the ensuing question and answer session, accept the defaults and enter the bin number of choice.

Note that it takes a few cycles for the new bin to appear on VIS (but the time of the change is correctly represented).