The flux of quiescent state of Crab Nebular in a time interval of 360 days over a ten-year observation was obtained utilizing Fermi data. The fluxes of point sources in ROI (region of interest) are written in file *results.fits generated by Fermi tool gtlike .

The detail of analysis thread can be found here. However, there were problems not reported in the instruction.

1. Environmental variables

The source model XML file was generated by user donated Python script make3FGLxml.py. Before this process, the event data was selected, the counts map was generated, and the newest version of diffuse models was downloaded from Fermi website.

Because of some unknown glitches, the following steps are required to run make3FGLxml.py successfully:

after compiling Fermi environment by doing

$ fermiinit

$ which python

the path of Python compiler (I’m not sure how to call it) is set to ~/Documents/Fermi/ScienceTools-v10r0p5-fssc-20150518-x86_64-unknown-linux-gnu-libc2.19-10/x86_64-unknown-linux-gnu-libc2.19-10/bin/python

set a link for this path to the path of /usr/bin/python by doing:

$ ln ./python /usr/bin/python

By doing those processes, python script for generating source model XML file is ready to go.

2. Script input parameters

When running gtlike, a bizarre problem occurred: buffer overflow detected, and the process was terminated. We spent a lot of time debugging, and it turns out that the solution is to simplify the input parameters of running python script. I suggest running make3FGLxml.py in the path of point source file gll_psc_v16.fit. In this case, cut the absolute path of point source file to simplify the input parameters.

$ python make3FGLxml.py gll_psc_v16.fit …

3. Another Environmental variables problem

The last step of spectral fitting processes is to use HEASOFT tool farith to subtract model source counts map from observed counts map. The HEASOFT environment is required

$ heainit

Setting heainit environment when finishing all Fermi analysis processes, which includes gtselect, gtmktime, gtbin, gtltcube, gtexpcube2, gtlike, gtmodel, is recommended.