Frequently Asked Questions
This page provides answers to common questions about Sherpa functionality; feel free to submit a new one via the CXC Helpdesk.
Warnings and General Behavior
- What is the difference between the 'load', 'read', and 'unpack' Sherpa commands?
- What do the Sherpa 'get' commands do?
- How do Sherpa 'load' commands handle ASCII files?
- How can I modify a single plot in a display containing multiple plots?
- How can I plot a model-fitted spectrum in photon flux units (photons s-1 cm-2 keV-1)?
- How can I plot an unfolded source spectrum in flux units, independent of a model spectrum?
- How can I set the axis scaling of plots to linear or logarithmic?
- How can I change the size of axis labels in a plot?
- How can I plot the ungrouped fitted source model on my grouped data?
- How can I plot my data in units of Counts versus Energy(keV)?
- How can I create multiple plots in the same window?
- How can I include multiple datasets in the same plot?
- How can I define my own fit statistic in Sherpa?
- How can I specify which measurement errors to use in fitting a PHA data set?
- How does Sherpa apply the BACKSCAL value recorded in the header of a spectrum file?
- How does Sherpa calculate errors on PHA data values given as a rate rather than counts?
- How does Sherpa handle Level=3 PHA spectra downloaded from the Chandra Source Catalog?
- How can I simulate a PHA data set in Sherpa, with/without added Poisson noise?
- How can I group net counts?
- Why is there data being plotted or fit outside the energy range I noticed?
- How do I change an XSPEC xset variable?
- How do I change the AtomDB version used by XSPEC Apec models?
- What is the function of a Sherpa model's "cache" attribute?
- How can I log the command output from my Sherpa fitting session?
- How can I suppress the screen output from Sherpa commands?