Creating a Spectrum File Using the HESSI GUI

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===Spectral Units & Pulse Pileup, Decimation and XY Offset===  
===Spectral Units & Pulse Pileup, Decimation and XY Offset===  
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Next we must select the units we want our spectra in. In most cases we want to check the count flux option this will display our data in units of counts*cm<sup>-2</sup>sec<sup>-1</sup>keV<sup>-1</sup>. The result will also be corrected for detector dead time and decimation effects.
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In this same section of the GUI there is 'Change Flags' button on the right. Selecting this will display a menu of options for various properties that can be displayed when the spectrum file is created in the HESSI GUI main window. These can be chosen by the user according to their preferences. They are explained in [http://hesperia.gsfc.nasa.gov/ssw/hessi/doc/guides/obs_summ_plots.htm RHESSI Quicklook Light Curves] document.
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The last panel of the GUI allows to user to toggle between three options when creating the spectrum file. In order they are:
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*The Pileup Correction - This can be toggled on or off. With the current analysis setup this is no longer used. In cases were the count rate is not high it is not necessary. In cases where pileup does occur it is accounted for during spectral analysis using OSPEX by the [[Pileup mod - Pseudo function for correcting pileup|pileup_mod]] component. Make sure this is not selected
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*The Decimation Correction - This should be selected in almost every case. The decimation correction is then implemented when creating the count flux spectra, accounting for the loss of photons below the upper threshold energies
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*The XY Offset from the sun center can be chosen in two ways. In most cases it can be read automatically from the flare catalog. If this dose not have sufficient accuracy for your analysis the 'Get XY Offset from flare catalog' option can be unchecked and the position entered manually in the X and Y boxes below this in arcseconds from the Sun center
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Once these selections are done select 'Accept' at the bottom. we are back at the 'Spectra' GUI.
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===Creating a RHESSI Spectra and Writing an Output File===
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Revision as of 16:16, 7 August 2009

Contents

Creating A Spectrum File with the HESSI GUI

Introduction

Under Construction. See Ospex - The Basics for an older version of the HESSI GUI Documentation. If you have already created a spectrum file go to OSPEX Documentation for a simple tutorial on fitting an interval.

Creating a Count Rate Spectrum File

Start the HESSI GUI at the sswidl command line by typing:

     hessi 

The HESSI GUI start screen will appear. Select the 'File' drop down menu. The GUI should now appear as below.

The Hessi GUI start screen with File drop down menu

From the file drop down menu choose the 'Select Observation Time Interval...' option. The 'Observation Time Interval Selection' GUI will pop up.

Pop up GUI to set time over which to create the spectrum file

We can set the start and end times we would like to use by simply entering times in this widget or selecting 'Start' and entering times in the popup menu, then doing this again for the end time. Once we have selected our times we can plot the observing summary for the flare. In this example we have selected the flare on 21Apr2002 starting at 00:20:00 and continuing until 01:40:00. We can plot the observing summary in the main window by selecting the 'Plot Observing Summary Data' button. The observing summary should appear as below:

The observing Summary for the 21Apr2002 flare

This is the standard time history for the flare of interest on 21 April 2002. Note that it is the summed counting rate of all the front and rear detector segments in counts s-1 detector-1. The detailed markings in this plot are described in detail in Kim Tolbert's write up on RHESSI Quicklook Light Curves. The various changes in count rate with time in the different energy ranges are described in Brian Dennis' write up on Artifacts in RHESSI Light Curves. This count rate plot gives us very important information on the impulsive phase of the flare of interest. We see, for example, that RHESSI came out of nighttime at about 00:33 UT as indicated by the vertical blue dashed line but more accurately, by the rapid increase in the 3 - 6 and 6 - 12 keV count rates. This indicates that a flare was already going on at this time. Images show that it was at a different location than the flare of interest that began at about 00:39 UT. (Note that right clicking on the plot gives you the time at the cursor.) The horizontal purple line at the top of the plot labeled A0 indicates that all attenuators were out of the detector fields of view at this time. The counting rate at all energies up to 25 keV rose very rapidly until at about 00:48 UT the thin attenuators moved into the detector fields of view (as indicated by the purple line dropping to the A1 level); the rates below 25 keV dropped precipitously at this time. Thereafter, every 4 minutes, the thin attenuators were removed for 1-minute intervals to test the low energy rate from the flare. At about 01:30 UT, the thick attenuators were added to the thin attenuators in the detector fields of view (the A3 state as indicated on the purple line) and the rates up to 50 keV dropped precipitously. Finally, at abut 01:33 UT, RHESSI went into night and the rates again fell to their non-solar background levels. Note that the rates up to 300 keV continued to climb as RHESSI entered the South Atlantic Anomaly (SAA) as indicated by the orange line marked with an "S" at the top of the plot. No data is recorded during passages through the most intense parts of the SAA to preserve space in the on-board memory.

Once we have identified the flare for which we would like to create a spectrum file select the Set Obs Time and Close button at the lower left corner of the Observation Time Interval Selection GUI. To create the spectrum files access to the RHESSI data is necessary. In order to access the data, make sure you are online, then from the IDL command line type the following:

IDL>search_network, /enable

When trying to create your spectrum file IDL will now try to automatically download all necessary data from an available RHESSI archive. The files are copied to a local directory specified by the user during setup of X-ray package in ssw.

To begin creating a spectrum file under the File drop down menu select Retrieve/Process Data ->, from the menu that appears to the side of this select Spectrum.... The following GUI should appear:

Spectra GUI for creating RHESSI Spectrum files.

Using this GUI we can set the the parameters for our spectrum file.

The time set in the the Observation Time Interval GUI is already transferred to the Spectra GUI. We are allowed to specify a different time or select a Spectrum Time Interval directly below, which is different (though contained by the observation time interval).

Setting Energy Bins

Next we must choose the energy bins for our spectrum. In the Spectra GUI there are two options associated with selecting energy bins. We can select energy bins based on binning codes. Selecting a binning code automatically defines the energy bins used to create the spectrum file by a predetermined schema. The show binning codes button displays a listing of all available schema. The Define Bins Manually... button allows the user to set energy bins to any scheme they choose. The following GUI appears when the button is selected:

The Select Energy Intervals GUI allows the user to specify energy bins for creating a RHESSI spectrum file.

There are several options for available for selecting energy bins. The top two panels allow the user to edit a list of intervals by doing things such as deleting a current interval or adding a new interval to a preexisting list, defining the intervals graphically, or reading them from a text file. In most cases the easiest way to define intervals is using the bottom panel, Define Intervals Manually.

For instance a set of energy bins from 3keV to 300keV with different size bins for different energy ranges can be defined as follows:

Setting Time Bins

Next we will set the time bins for the spectrum file. The simplest way to do this is to select the 'Define Bins Manually...' button in the Time Bins section of the Spectra GUI. The GUI that appears is similar to 'Select Energy Intervals' GUI, analogously titled 'Select Time Intervals'. The start and end times shown in the bottom third of the GUI below 'Define Intervals Manually below' should be the same as the Observation Times you set earlier. In most cases we want our time bins to be equal for the entire length of time for which we will create our spectra so we simply need to select the duration of our time bins. Select 'Divide this time range into intervals of length D'. Now next to the D(s) below this we can enter the time of each bin. RHESSI has a spin rotation of approximately 4s. In most cases we will want to create our spectra with bins of this size for the following reasons:

Once we have entered 4.0 next to D(s) select the 'Replace List' button to right. The drop down list at the top of the GUI should now show a series of 4sec time intervals starting at the beginning of the Observation Time Interval and ending at the end time. Select the 'Accept' button at the bottom left of the GUI. The time bins are set and we are back at the 'Spectra' GUI.

Selecting Detectors

When selecting which detectors we will use to create a spectrum file there are a list of things to consider, some having to do with the detector performance, some with the actual event we are looking at, and some with how we are planning to analyze it. Things we should consider are as follows:

To select our detectors select the 'Change' button in the 'Collimators and Detector Front/Rear Segments Selected' section of the GUI. A list of all collimators with a check box for the front and rear segment of each will appear. In this case we would like to create a spectrum file for the front segment of detector four. First choose the 'Disable All' button on the upper right of the GUI. All check boxes should be cleared. Simply select the check box for 4F at this point. Note the 'Sum Detectors' button on the right of GUI. When multiple detectors are selected this will allow the display of the spectra created to be viewed as the sum of all selected detectors. Now select the 'Accept' button. We have selected our detectors are back at the main 'Spectra' GUI.

Spectral Units & Pulse Pileup, Decimation and XY Offset

Next we must select the units we want our spectra in. In most cases we want to check the count flux option this will display our data in units of counts*cm-2sec-1keV-1. The result will also be corrected for detector dead time and decimation effects. In this same section of the GUI there is 'Change Flags' button on the right. Selecting this will display a menu of options for various properties that can be displayed when the spectrum file is created in the HESSI GUI main window. These can be chosen by the user according to their preferences. They are explained in RHESSI Quicklook Light Curves document.

The last panel of the GUI allows to user to toggle between three options when creating the spectrum file. In order they are:

Once these selections are done select 'Accept' at the bottom. we are back at the 'Spectra' GUI.

Creating a RHESSI Spectra and Writing an Output File

[STILL UNDER CONSTRUCTION]

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