PSRCHIVE user documentation: fluxcal

1.0 Purpose

The fluxcal program uses observations of the reference source and a standard candle in order to determine both the system temperature and the flux density of the reference source. The solutions produced by fluxcal are used by pac to perform absolute flux calibration of pulsar observations. Absolute flux calibration must be preceded by a stage of polarimetric calibration that normalizes the observed flux density by the flux density of the reference source.

2.0 Usage

2.1 Before running fluxcal

The Observations

In order to run fluxcal, you will need sets of Pulsar::Archive files containing observations of the reference source (as described in Appendix A of the pac documentation). A set of flux calibrator observations must include at least one of each of the following:
  1. FluxCalOn - An observation of the reference source made while the antenna is directed at a standard candle. (Pulsar::Archive::get_type must return Signal::FluxCalOn).
  2. FluxCalOff - An observation of the reference source made while the antenna is pointing at least a full beam width away from the standard candle. (Pulsar::Archive::get_type must return Signal::FluxCalOff).
The observations in each set must have the same observing parameters, such as centre frequency and bandwidth, as determined by the Pulsar::Archive::calibrator_match method.

The Standard Candles

The fluxcal program also requires information about the standard candle(s) to be used for absolute flux calibration. This information is parsed from a text file (by default, $PSRHOME/runtime/psrchive/fluxcal.cfg) which includes a row for each flux calibrator. The columns in this file are:
  1. source name
  2. reference frequency (MHz)
  3. reference flux density (Jy)
  4. spectral index
Following each row, any number of aliases for the source name may be specified using the aka keyword. An example input file is: 

#
# Flux calibrator parameters used by fluxcal program
#
# NAME    Frequency   Flux (Jy)   spectral index

0407-658   1400.0       14.4          1.189

3C353      1400.0       57.3          0.76

3C274      1400.0       200.          0.81
aka Virgo
aka B1228+126

3C218      1400.0       43.1          0.91
aka Hydra
aka J0918-1205

2.2 Running fluxcal

Input

There are two modes of operation, as determined by the input method:
  1. From File: In this mode of operation, flux calibrator observation filenames are specified on the command line, fluxcal sorts the files by name and, as they are loaded, breaks the list up into sets. In order for the solutions to be used, the calibrator database text file must later be regenerated using pac.
  2. With Database: In this mode of operation, a calibrator database text file, as produced by pac, is provided using the -d filename command line option; fluxcal sorts the observations by the MJD of each database entry and, as they are loaded, breaks the list up into sets. For each new flux calibration solution successfully written to disk, fluxcal will add a new entry to the database. The updated database text file will be written at the end of operation.
A flux calibrator set is defined by the time elapsed between the end of the last observation in the set and the start of the first observation in the next set. This separation time is 5 minutes by default and can be changed using the -i command line option.

Output

For each set, fluxcal solves for the system temperature and reference flux density, and outputs these values as a function of radio frequency into the FLUXCAL binary table extension of a PSRFITS file. If another file format can be used to store the FluxCalibratorExtension data, this file format can optionally be specified using the -a command line option.

The solution is written to a file with the same name as the first FluxCalOn observation in the set, with the extension replaced by .fluxcal. To change the extension, use the -e command line option.

The solutions produced by fluxcal may be plotted by running pacv filename.fluxcal.

3.0 Algorithms

The solution implemented by fluxcal is described in the appendix.

4.0 Testing and examples

The following simple example shows a successful run. Notice that the output filename need not necessarily be based upon the first file loaded. Rather, it is based on the first FluxCalOn observation: 

> fluxcal w030814_*.cf
Pulsar::Archive::Agent::init 
fluxcal: loading w030814_021414.cf
fluxcal: starting new FluxCalibrator
fluxcal: loading w030814_021709.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w030814_022009.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w030814_022310.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w030814_022610.cf
fluxcal: observation added to FluxCalibrator
fluxcal: creating PSRFITS Archive
fluxcal: unloading w030814_021709.fluxcal
The following example illustrates the automatic division of observations into sets, and includes an error condition that arises when an incomplete set is encountered: 

> fluxcal w031029_*.cf
Pulsar::Archive::Agent::init 
fluxcal: loading w031029_232004.cf
fluxcal: starting new FluxCalibrator
fluxcal: loading w031029_232252.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w031029_232532.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w031029_232816.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w031029_233106.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w031029_234326.cf
fluxcal: gap=10.3min > interval=5.0min
fluxcal: creating PSRFITS Archive
fluxcal: unloading w031029_232252.fluxcal
fluxcal: starting new FluxCalibrator
fluxcal: loading w031029_235143.cf
fluxcal: gap=6.2min > interval=5.0min
fluxcal: creating PSRFITS Archive
fluxcal: error unloading solution
        no FluxCal-On data
fluxcal: starting new FluxCalibrator
fluxcal: creating PSRFITS Archive
fluxcal: error unloading solution
        no FluxCal-On data
In the following example, the square wave form of the pulsed reference source (e.g. linear noise diode) is not detected. 

> fluxcal w040219_*.cf
Pulsar::Archive::Agent::init 
fluxcal: loading w040219_164032.cf
fluxcal: starting new FluxCalibrator
fluxcal: loading w040219_164326.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w040219_164624.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w040219_164927.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w040219_165227.cf
fluxcal: observation added to FluxCalibrator
fluxcal: creating PSRFITS Archive
fluxcal: error unloading solution
        Flux calibrator not detected
In the following example, a new set of flux calibrator observations follows the previous set within the five minute separation interval, but with a different configuration. The change in configuration is noticed, the first solution is written to disk, and a new flux calibrator set is started. 

> fluxcal w040509_*.cf
Pulsar::Archive::Agent::init 
fluxcal: loading w040509_085200.cf
fluxcal: starting new FluxCalibrator
fluxcal: loading w040509_085515.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w040509_085838.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w040509_090157.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w040509_090518.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w040509_091148.cf
fluxcal: failed to add observation
        mismatch between
        w040509_085515.cf and
        w040509_091148.cf
        centre frequency mismatch: 1433.000000 and 3100.000000
        bandwidth mismatch: -256.000000 and -512.000000
fluxcal: creating PSRFITS Archive 
fluxcal: unloading w040509_085515.fluxcal
fluxcal: starting new FluxCalibrator
fluxcal: loading w040509_091501.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w040509_091814.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w040509_092135.cf
fluxcal: observation added to FluxCalibrator
fluxcal: loading w040509_092457.cf
fluxcal: observation added to FluxCalibrator
fluxcal: creating PSRFITS Archive
fluxcal: unloading w040509_091501.fluxcal

5.0 Known bugs and features that require implementation


Last Updated 24/10/2004 by Willem van Straten