Gamma Ray Burst spectroscopy

In the following section we explain how to derive spectra of short bursts, such as GRB, from SPI data. We assume that readers have some knowledge about SPI data analysis with the ISDC spi_science_analysis script. Please follow the cookbook example in previous sections if it is not your case. Furthermore, the user is asked to follow the points 1 to 4 from the previous section on GRB imaging. Once this is achieved, you have an observation group in the current directory and you can continue with the following steps.

1. The burst position at which you want to extract a spectrum must now be specified. This is done by providing a ``source_cat.fits'' file containing the GRB position. You can either use an existing file, or create a new one using the spi_science_analysis to run the catalogue extraction step (the spi_science_analysis main GUI is shown in Fig. ).

   Select ``catalogue extraction'' and un-select all other tasks, click on "catalog" to enter the catalogue task parameters. Click ``Ok'' to close the ``catalogue'' window, and on ``Run'' in the main frame to execute spi_science_analysis. The ``source_cat.fits'' catalogue produced contains irrelevant data. It will probably include a number of catalogue sources that may be detected on longer observation, and certainly not the GRB position from which we want to extract a spectrum. The catalogue file should include a single row with the GRB identification and position. Edit this file with``f'' and enter the correct identification and position, deleting extra rows if any, and save the result.

   Alternatively, the position from the SPI image analysis can be used (see Sect.  for how to transform a ``source_res.fits'' into a ``source_cat.fits''), although in most cases a more accurate position should be available, e.g. from IBIS.

   If you use an existing ``source_cat.fits'' file make sure with fv that it contains the correct identification and position of the GRB and that the ISDCLEVL keyword of this file is ``CAT_I''.

2. As in the previous GRB imaging analysis case, two alternatives can be used to specify the parameters of your analysis. The simplest one is to use the spi_science_analysis GUI.
   1. Run spi_science_analysis and specify parameters through the GUI, as displayed in Fig. .

      Figure: Main GUI window of the spi_science_analysis script

      

   2. Check the ``List of detectors'' (use 0-18 in most cases) and the ``Coordinate System'' in that window, un-select ``catalogue extraction'', enter the name of your file (source_cat.fits) in the ``spiros Input Catalog'' entry field and click on ``Energy_definition'' to open the GUI window (see Fig. ).

      Figure: Energy boundaries GUI

      

   3. Select your energy binnning (in this case we use 6 bins ranging from 20 to 200 keV, logarithmically spaced as the bin number is negative), click ``Ok''. This will close this window.

   4. Click on ``Background options'' and un-select the flat-field default options as shown in Fig. , then click ``Ok'' to close this window.

   5. Back in the parent window click the ``spiros'' button to open the GUI window shown in Fig. .

      Figure: spiros GUI main window

      

   6. Make sure the ``SPECTRA'' mode is specified, do not introduce any selection parameters, and specify the ``Background method'' and the ``Optimization statistic'' (see more details on the different options for those parameters in Sect. )

   7. Close all sub-windows by clicking twice ``Ok'', then using the ``Save As'' button, you can save the parameters you have just entered into a file. Enter the name ``grb_analysis.par'' and store it in the current directory.

   8. Once the parameters are ``saved'', click on ``Quit'' to quite the process. We do not want to run the analysis yet. This procedure is just a convenient way to enter parameters for the analyses.

   Again, as indicated in Sect. , the user can alternatively specify the parameter set by editing the spi_science_analysis.par file located in your $PFILES directory.

3. Now, the ``grb_analysis.par'' file located in the current directory contains the main parameters you want to use in your burst analysis and will be used by the script.

4. Run ``spi_grb_analysis''. Without any command line argument you get the following help text.

   Figure: Outputs of spi_grb_analysis when invoked without any input parameters

   

   Since we know the input parameters from the first point above, we can then launch the spi_grb_analysis script. Make sure the ``grb_start'' - ``sec_to_avoid_before_grb'' is not before the pointing start, and that ``grb_stop'' + ``sec_to_avoid_after_grb'' is not after the pointing end, as there is no corresponding checks in the spi_grb_analysis script.

   In our example:

   spi_grb_analysis 2003-05-01T03:10:10.000 2003-05-01T03:10:30.000 UTC 10 10.

   Again, if you want to keep your output before running the script a second time, we suggest you to save them by copying the entire directory (e.g., cd ..; cp -r grb030501 grb030501_spectra; cd grb030501) before continuing.

5. After a successful run of ``spi_grb_analysis" (step 7) you obtain a spectrum of the burst, called spectrum_''your GRB ID''.fits, containing a link to the appropriate RMF response. You can directly enter XSPEC to display and fit your resulting spectrum (see Sect. for more information).

6. ``spi_grb_analysis'' is calling a number of executables and ``spi_science_analysis'' several times. Since ``spi_science_analysis'' produces its own log file, the log file situation after running ``spi_grb_analysis'' is somewhat complicated. The resulting ``/spi_grb_analysis.log'' is the high level log file, containing logs from the executables called directly by "spi_grb_analysis". In addition, you can find three log files ``spi_pointing.log'', ``spi_binning.log'', and ``spi_spiros.log''. The first contains the outputs of spi_obs_point, the second includes the logs from the binning to background steps, and the third contains the results from spiros.

7. After a successful execution of ``spi_grb_analysis'', it is also possible to run spiros again with the ``spi_science_analysis'' script. Launch ``spi_science_analysis'', make sure you select only the spiros step (if you select any other step, the burst background produced by ``spi_grb_analysis'' will be deleted and you will have to start it all again), change the required spiros parameters (making a LIKEH analysis rather than a one for example), and run the show again.