Determine Pointing Offsets

 

This process can now be achieved under computer control (either by the controller or observer).

1. Ask the controller to give control of the telescope to arthur, if it is not already.
2. Stop any current integration.
3. If you wish the controller to run offset scans, he should start the PSRCONTROL program in the usual way for timing, then select OFFSETS from the main menu.
4. If you wish to run the program yourself, log in to ARTHUR as PULSAR (or a pulsar group account) and type OFFSET1. The procedure is now the same for observer or controller.
5. Configure the scan routine from the OFFSET startup menu. In general the default values are recommended and you should only need to select a source).
   • Decide whether to make initial scan in Azimuth or Elevation (this item toggles if you hit return).
   • Select a source. (Hit return to be presented with a list of calibration sources, move the cursor to the source you want and hit RETURN, Press ENTER to continue).
   • For a strong calibrator, you can add extra attenuation (type in an integer number of dBs, press RETURN).
   • Change the parameter file if necessary (default is recommended).
   • Optionally choose a graphics device for a pretty printout.
   • Check initial az and el offsets (these are taken from the PSRACQ parameter file.) Check length of scan, offset rate and errors tolerance. (Default values are recommended).
   • Auto reverse scan can be toggled ON or OFF (Default will scan in both Azimuth and elevation, forward and reverse)
   • ENTER to start scanning, CTRL-Z to chicken out.
6. The program will make two scans along the initial scan axis, measuring signal levels (on both polarisations summed) through the Pulsar timing hardware (filter bank and DDU)
7. A gaussian is fit to the scans and the axis offset is set to the value found.
8. two furthur scans are made and fitted along the other axis.
9. Offset values are given and can be noted down as the program progresses, but more accurate values can be obtained after the scans are finished, by running PLOTOFFSET 1. This process incorporates some spike rejection, and produces a graphics output for posterity.
10. File the offset graph in the Pulsar calibration folder, note the values in the log book and update the default parameter file using MENU