Analyzing Fermi GBM Data

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To view or analyze the Fermi GBM data using our tools, you need to have the following installed on your computer:

The primary analysis package for GBM solar data is OSPEX, our object-oriented interface for X-ray spectral analysis of solar data. Click here for a full explanation of OSPEX.  Click here to see what's new in OSPEX.

Current status of OSPEX

To view or analyze Fermi data in OSPEX, the first step is to retrieve the data files.  You can do that through the OSPEX widget interface, or manually.  Once you have retrieved and set the spectrum file (and DRM file if you will be fitting the data) in OSPEX, you can proceed in OSPEX as you would with any other data type (see OSPEX document for details).

Either the CSPEC (128 energy channels, 4.096 / 1.024 s time resolution) or CTIME (8 energy channels, 0.256 / .064 s time resolution) data files (daily or trigger files) can be used as input to OSPEX.  The CSPEC detector response files are used for both CSPEC and CTIME data file input -  the OSPEX software groups the CSPEC DRM energy bins to the CTIME energy bins.  The CTIME capability was added 26 January, 2012.

I.  Using the OSPEX GUI to find and set input files.

Summary of steps:

  1. Start OSPEX by typing  o = ospex() in sswidl
  2. Click File / Select Input
  3. Click Browse / On remote sites
  4. Select Time Interval or Flare Number
  5. Select CSPEC or CTIME option
  6. Click Search
  7. Click Accept and Close
  8. Continue in OSPEX as usual.

Elaboration of those steps:

The Spectrum File Browse button has two options.  You can either navigate to a file on your local computer or you can browse on remote sites.  If you select the option to browse on remote sites, a new widget pops up that lets you set a search time interval (either manually, or by selecting from the FERMI GBM or RHESSI solar flare catalogs).  Once your time interval is set, select the CSPEC or CTIME option, and click the Search button.  A list of all of the daily data files (PHA) in your time interval and response files (RSP or RSP2) for the largest flare in the time interval will appear.  The files containing data for the four most sunward detectors will automatically be highlighted, but you can change the selection of file(s) if you prefer.  Clicking Accept and Close will download the highlighted files to your local computer. Or you can click Download Selected Files to download files, remain in this interface, and make another selection to download.  The downloaded files are copied to the current working directory in your IDL session (type pwd to see what it is).  After clicking Accept and Close, the file with the most sunward detector of the selected files will automatically be set as the input spectrum file in OSPEX.  If you want to use a different file that was downloaded, you can click Browse / On this computer to select it. 

When you select an input file, OSPEX automatically searches for and sets the appropriate response file (if it's not in your current directory, it downloads it from the RSP file archive on hesperia).  Response files have been created for the time intervals of the solar flares found in the GBM data.  If you select a time interval that doesn't contain a flare, no response file will be found.  In that case, you can still view the spectrum data (plot the time history or the spectrum) through OSPEX, but you won't be able to analyze the data.  If you would like us to create a response file even though no solar flare was identified, please ask, or  The response files have either a .rsp extension, which means the file contains a single response matrix, or .rsp2, which means the file contains multiple matrices corresponding to different times as the detector slews across the flare region.  OSPEX handles either type of response file, and for multiple matrices, will automatically set the correct matrix for your analysis time interval by  forming a weighted average of the responses in your interval.

II.  Finding and setting input files manually.

  1. Select a time of interest from the online list of solar flares observed by GBM.  Note which detectors are most sunward.
  2. Retrieve the daily CSPEC or CTIME file for your date and selected detector from here
  3. Retrieve the response matrix file for your event from here.  Files are organized in date (yyyymmdd) directories, and the file name includes the detector and start time..  For example, glg_cspec_n5_bn100612_0054_038_v00.rsp2 is the response file for NaI detector 5 starting at 12-Jun-2010 at 00:54 (the 038 is the fraction of day).  The .rsp2 extension means the file contains multiple matrices to cover the changing slew positions.  Single matrix files have a .rsp extension.  Response matrix files have been created for each solar flare identified in the GBM data.
  4. Open OSPEX by typing o=ospex(), click the File / Select Input button to bring up the Select Input widget.  Click the two Browse buttons to select the spectrum (PHA) and response (SRM) files. Proceed as usual with OSPEX.


After selecting a time interval and input file in OSPEX, you way want to view the angles between the various detectors and the Sun. You can do this via the 'Detector Angles' button on the OSPEX GUI, or via the routine gbm_plot_det_cos.  For large flares, you may want to select a less sunward-facing detector in order to avoid pileup issues.


Planned Enhancements to OSPEX

We plan to allow spectral analysis using the higher time resolution, but lower energy resolution, CTIME files.  We will write software to modify the response matrix information in the RSP files (which correspond to the energy bins in the CSPEC files) to adjust the response for the CTIME file's energy edges.   Completed 26 January, 2012.


Last updated 27 January, 2012 by Kim Tolbert