RHESSI Spectroscopy - OSPEX User Guide
From RHESSI Wiki
Contents |
Introduction
This is a general introduction to the Object-oriented version of the SPectrum EXecutive (OSPEX). It covers the steps necessary to fit RHESSI count-rate spectra, starting with the creation of the spectrum and the Spectrometer Response Matrix (SRM) fits files and going through the processes of defining the background spectrum, the time intervals, and the fit functions to be used. The OSPEX - OBJECT SPECTRAL EXECUTIVE GUIDE contains additional information on using OSPEX.
Links to documentation for fitting RHESSI Data
Creating a spectrum file with the HESSI GUI
Starting with the level zero RHESSI data this document goes through the steps necessary to create a spectrum file using the HESSI GUI. Command Line instructions are also included. The documentation is for creating a spectrum and spectrometer response matrix (SRM) file for a single detector, but is easily expandable to creating files for multiple detectors.
An SSW routine to create separate detector spectrum files
An ssw routine that creates a RHESSI spectrum and SRM for the front segment of each detector given a time interval or flare number. Each file is created with native energy bins for the detector and 4 second time binning. Examples of calling the routine from the command line are given in the file header.
Users Guide for the OSPEX GUI
Using a spectrum file and SRM file this document goes through the steps necessary for using the OSPEX GUI to fit a RHESSI spectrum, including defining background, time intervals, a fit model and doing a fit.
Vth - Variable Thermal
The variable thermal fit model component uses a single emission measure and temperature along with a measure of the relative abundance of the Fe-Ni line complex to fit the thermal emission of the RHESSI spectrum for a user defined time interval.
Bpow - Broken Power law
The broken power law fit model component uses a break energy, the spectral index above and below the break energy, and a normalization dependent on the count rate to fit the non-thermal component of the RHESSI spectrum for a user defined time interval. This is the simplest model available for the non-thermal emission during a flare.
Thick Target
The thick target fit model component uses a double power law in electron space to model the non-thermal portion of the RHESSI spectrum. The model of the non-thermal photon spectrum is calculated from the bremsstralung interaction of energetic electrons, determined by the electron distribution function, with thick target plasma. The electron distribution is modeled with a total integrated electron flux, a low energy and high energy cutoff, a break energy, and the indicies of the electron distribution above and below the break energy.
DRM Mod
The drm_mod function adjusts the gain offset and resolution of a fit model to account for small differences in those quantities from the RHESSI calibration measurements. drm_mod uses the Fe-Ni line complex to adjust the resolution and gain offset. Note that drm_mod should only be used with single detector spectrum files.
Pileup Mod
The pileup_mod function adjusts the model to fit pulse pileup effects. This means the values of the parameters for other fit function components are not distorted due to pileup effects. The pileup component is count rate dependent. It's effect is small at low count rates and increases with higher count rate. Note that pileup_mod should only be used with single detector spectrum files.
Fitting Multiple Intervals
Fitting Multiple Intervals describes the methods available through the OSPEX GUI to loop through and fit multiple time intervals defined by the user.
View Fit Results
View Fit Results describes the GUI for viewing the parameters from doing fits of multiple intervals as a function of time or interval number. It also contains an explanation of calculating the non-thermal energy flux from thick target parameters.
Fitting a New Detector
Fitting a new detector contains instructions on editing an OSPEX script created after doing fits for a single detector in order to use the same time intervals, background selections, and final fit parameters as initial parameters when fitting a different detector.
Contact Andy Gopie with any questions, corrections, or suggestions