OSPEX Users Guide

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Contents

Using OSPEX to Analyze a RHESSI Spectrum

Starting the OSPEX GUI and Loading a Spectrum File

To start the OSPEX GUI at the sswidl command line type:

o = ospex()

This command sets up an OSPEX object named o, and starts the OSPEX GUI. The following screen appears when the GUI starts:

The OSPEX GUI Start Screen

Select the file button in the upper left corner, and choose the Select Input button in the drop down menu that appears. From here we can select the spectrum file for the flare we would like to analyze. The path to file can either be entered manually or the file can be selected using the Browse button. Once the spectrum file is selected the accompanying SRM file will be found automatically as long as files are saved in the same directory with the original names. For the 21Apr2002 flare the Select Input GUI looks like the following once the spectrum file for detector four is selected:

The Spectrum File Selection GUI

Note that the GUI allows you to display the spectrum file in various ways. To compare it to the spectrum created in the HESSI GUI we can plot the time profile. For the spectrum file for the 21Apr2002 event using only the front segment of detector 4 (4F), we see:

The RHESSI lightcurve for the 21Apr2002 flare

This should be same as the time profile we created with the HESSI GUI. The countflux data is displayed in the default energy bands. The Select Input GUI also allows you to display an energy profile of data, as well as a spectrogram of the data should these be preferable ways of viewing the spectrum file. For a more in depth discussion of ways to display the data go here.

Selecting Background

Before we can fit any time intervals during the flare we need to select background. Below the simplest method of selecting background will be described. For a more in depth discussion of background selection go here.

Lets look at a simple method for choosing background. First choose the Select Background button under File in the main OSPEX GUI. The Select Background GUI should appear. For our simple case we will leave it at the default settings, because of this we will be using the same background for all energy bands and times.

First we want to display the time profile for the spectrum. The easiest way to do this is to select the plot v. time option in the GUI. Now select change. Using the default settings this takes us to the GUI for defining a background interval graphically. We can simply use the mouse to define a interval. RHESSI begins taking data for approximately five minutes in nighttime before it’s orbit starts and for five minutes after its orbit. This data is non-solar and we can use it to define the non-solar background levels. Simply right click at the beginning of a nighttime interval and left click at the end. Choose the Adjust to data boundaries button then accept and close. You’ve now chosen your background. Select the Plot Spectrum button in the main Select Background GUI and you will see an energy profile of your selected background. The top panel below shows what you should expect to see after picking your background interval, the lower panel, the spectrum of the background chosen.


The Background Interval (upper panel) and Spectrum (lower panel)

Fit Options - Selecting Time Intervals and Doing Fits

We can now start to fit time intervals during the flare. To start choose the Select Fit Options and Do Fit… choice from the File Drop down menu. This brings up the Fit Options GUI. Once again we’ll go through a simple set of options for setting up and fitting time intervals during the flare. A more advanced discussion of these settings can be found here. For our simple case we start by defining our time intervals. To do this select the Change Fit Intervals button on the upper right of the GUI. This brings up the GUI that allows us to select time intervals graphically.


The pop up GUI for selecting time intervals graphically

All we need to do is left click on the main OSPEX window at the point at were we would like to define the start of our time period and left click at the end. Usually you will want to select a large time interval at this step. Once this is done double click in the highlighted interval. A popup menu will appear with various options for breaking up this large interval into smaller intervals. It should appear as below.

The selected time interval(red) along with the menu used to break it into smaller intervals

Usually at this point the easiest option is to break up the interval into sub-intervals of equal length. The length of each interval in seconds is set in the Select Time Intervals for Analysis widget. In this case 20 seconds was selected. Once this is done we simply select the Adjust to Data Boundaries option then Accept and Close. We have defined our time intervals for analysis.

Spectral Fitting

Now we are ready to begin fitting. The first step is to select an interval. We do this by picking an interval from the list that appears in the top right hand panel of the ‘Fit Options’ GUI (see below). After selecting an interval from the list we have created, select the plot spectrum button in the lower panel of the GUI. A plot of the count flux v. energy will appear in the main OSPEX GUI.

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