RHESSI Spectroscopy - OSPEX User Guide

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==Introduction==
==Introduction==
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This is a general introduction to X-ray spectroscopy from RHESSI front-segment data using 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 [http://hesperia.gsfc.nasa.gov/ssw/packages/spex/doc/ospex_explanation.htm OSPEX - OBJECT SPECTRAL EXECUTIVE GUIDE] contains additional information on using OSPEX. Note that similar techniques can also be used for rear-segment data but the detailed analysis of gamma-ray spectra is not covered here.  
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This is a general introduction to X-ray spectroscopy from RHESSI [http://adsabs.harvard.edu/abs/2002SoPh..210...33S front-segment] data using 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 [http://hesperia.gsfc.nasa.gov/ssw/packages/spex/doc/ospex_explanation.htm OSPEX - OBJECT SPECTRAL EXECUTIVE GUIDE] contains additional information on using OSPEX. Note that similar techniques can also be used for rear-segment data but the detailed analysis of gamma-ray spectra is not covered here.  
Much work has already been done by fitting spectra to data from multiple detectors simultaneously. Detectors are chosen for inclusion in the analysis based on their energy coverage and the energy range of interest. Detector #2, for example is generally not usable below ~20 keV, detector #7 below ~10 keV, and detector #8 is occasionally contaminated by pickup from the spacecraft transmitter during passes over a ground stations. This type of analysis is generally adequate above ~20 keV and provides for the greatest sensitivity, but it does not allow various differences between detectors to be taken into account. It should not be used where the highest spectral accuracy is desired or where it is important to estimate uncertainties on the fitted spectral parameters that depend on the systematic differences between detectors.
Much work has already been done by fitting spectra to data from multiple detectors simultaneously. Detectors are chosen for inclusion in the analysis based on their energy coverage and the energy range of interest. Detector #2, for example is generally not usable below ~20 keV, detector #7 below ~10 keV, and detector #8 is occasionally contaminated by pickup from the spacecraft transmitter during passes over a ground stations. This type of analysis is generally adequate above ~20 keV and provides for the greatest sensitivity, but it does not allow various differences between detectors to be taken into account. It should not be used where the highest spectral accuracy is desired or where it is important to estimate uncertainties on the fitted spectral parameters that depend on the systematic differences between detectors.
-
The general spectral analysis philosophy adopted here is to analyze the count-rate spectra for each of the nine RHESSI front segments independently. Only in this way can the different characteristics of the different detectors be fully accounted for. Currently, the following detector characteristics can only be taken into account by analyzing the data from each detector separately:
+
The general spectral analysis philosophy adopted here is to analyze the count-rate spectra for each of the nine RHESSI front segments independently. Only in this way can the different characteristics of the nine detectors be fully accounted for. Currently, the following detector characteristics can only be taken into account by analyzing the data from each detector separately:
# native 1/3 keV energy bins that have different energy edges for each detector,  
# native 1/3 keV energy bins that have different energy edges for each detector,  
# conversion factors from the detector pulse amplitude to energy loss in keV,  
# conversion factors from the detector pulse amplitude to energy loss in keV,  
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# FWHM resolution, and
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# FWHM energy resolution,
# relative central-to-total attenuation of each attenuator, and
# relative central-to-total attenuation of each attenuator, and
# pulse pile-up.
# pulse pile-up.
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==Links to documentation for fitting RHESSI Data==
==Links to documentation for fitting RHESSI Data==
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===[[HESSI GUI Users Guide|Creating a Spectrum File using the HESSI GUI]]===
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===[[Creating a Spectrum File Using the HESSI GUI]]===
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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.  
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This document goes through the steps necessary to create a spectrum file using either the HESSI GUI or the IDL Command Line. The documentation is for creating a spectrum file and a spectrometer response matrix (SRM) file for a single detector, but is easily expandable to creating files for multiple detectors. There is also [http://beauty.nascom.nasa.gov/~zarro/php/ssw_print.php?file=$SSW/hessi/idl/spectra/hsi_spectrum_sep_det_files.pro an ssw routine] which can be used to create single detector spectrum files. Each file is created with native 1/3 keV energy bins for the detector and 4 second time binning. It covers the whole daytime part of the orbit containing the flare plus the available before and after nighttime data for use in background estimation. Examples of calling the routine from the command line are given in the file header.
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*[http://beauty.nascom.nasa.gov/~zarro/php/ssw_print.php?file=$SSW/hessi/idl/spectra/hsi_spectrum_sep_det_files.pro An SSW routine to create separate detector spectrum files]
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===[[OSPEX GUI Users Guide|User Guide for OSPEX]]===
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**An ssw routine that creates a RHESSI spectrum and SRM file 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.
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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. This section also includes information on individual [[Fit function components]], [[Fitting multiple intervals]], [[View fit results|Viewing Fit Results]], and [[Fitting a new detector|using the final fit results from one detector to fit another]].  
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===[[OSPEX GUI Users Guide|OSPEX GUI User Guide]]===
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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.  
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*[[Vth - Variable Thermal|Vth - Variable Thermal]]
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**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.
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*[[Bpow - Broken Power Law|Bpow - Broken Power law]]
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**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. 
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*[[Thick2 - Thick Target Bremsstrahlung Version 2| Thick Target]]
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**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.
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*[[Drm mod - Pseudo function for fine tuning RHESSI DRM parameters| DRM Mod]]
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**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.
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*[[Pileup mod - Pseudo function for correcting pileup|Pileup Mod]]
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**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.
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===[[Fitting multiple intervals|Fitting Multiple Intervals]]===
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Fitting Multiple Intervals describes the methods available through the OSPEX GUI to loop through and fit multiple time intervals defined by the user.
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===[[View fit results|Viewing Fit Results]]===
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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. 
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===[[Fitting a new detector|Using final fit results from one detector as starting parameters for another]]===
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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.
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Latest revision as of 19:27, 9 June 2010

Contents

Introduction

This is a general introduction to X-ray spectroscopy from RHESSI front-segment data using 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. Note that similar techniques can also be used for rear-segment data but the detailed analysis of gamma-ray spectra is not covered here.

Much work has already been done by fitting spectra to data from multiple detectors simultaneously. Detectors are chosen for inclusion in the analysis based on their energy coverage and the energy range of interest. Detector #2, for example is generally not usable below ~20 keV, detector #7 below ~10 keV, and detector #8 is occasionally contaminated by pickup from the spacecraft transmitter during passes over a ground stations. This type of analysis is generally adequate above ~20 keV and provides for the greatest sensitivity, but it does not allow various differences between detectors to be taken into account. It should not be used where the highest spectral accuracy is desired or where it is important to estimate uncertainties on the fitted spectral parameters that depend on the systematic differences between detectors.

The general spectral analysis philosophy adopted here is to analyze the count-rate spectra for each of the nine RHESSI front segments independently. Only in this way can the different characteristics of the nine detectors be fully accounted for. Currently, the following detector characteristics can only be taken into account by analyzing the data from each detector separately:

  1. native 1/3 keV energy bins that have different energy edges for each detector,
  2. conversion factors from the detector pulse amplitude to energy loss in keV,
  3. FWHM energy resolution,
  4. relative central-to-total attenuation of each attenuator, and
  5. pulse pile-up.

A further advantage of analyzing spectra from each detector separately is that each spectrum so obtained is an independent estimate of the true solar spectrum. Thus, the scatter of the values obtained for any one of the various spectral fit parameters gives perhaps the best indication of the uncertainties in that parameter. This is superior to the uncertainties derived from the least-squares fitting routine used in OSPEX since it includes any systematic uncertainties in the response of each detector in addition to the statistical uncertainties considered in OSPEX.

Links to documentation for fitting RHESSI Data

Creating a Spectrum File Using the HESSI GUI

This document goes through the steps necessary to create a spectrum file using either the HESSI GUI or the IDL Command Line. The documentation is for creating a spectrum file and a spectrometer response matrix (SRM) file for a single detector, but is easily expandable to creating files for multiple detectors. There is also an ssw routine which can be used to create single detector spectrum files. Each file is created with native 1/3 keV energy bins for the detector and 4 second time binning. It covers the whole daytime part of the orbit containing the flare plus the available before and after nighttime data for use in background estimation. Examples of calling the routine from the command line are given in the file header.

User Guide for OSPEX

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. This section also includes information on individual Fit function components, Fitting multiple intervals, Viewing Fit Results, and using the final fit results from one detector to fit another.


Contact Andy Gopie with any questions, corrections, or suggestions

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