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I am extracting gamma ray spectrum from Fermi-LAT data. My spectrum is a lot higher than the ones on previous studies of the same object. What could cause a spectrum to go too high?

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    $\begingroup$ There are many possibilities: Did the fit work well enough? Is the spectral model the same? Is the object variable? Is only the normalisation higher or is also the index different? Same energy range? To give a useful answer seeing the count map, mode map, residuals as well as fit results would be helpful. $\endgroup$ – samcarter Jul 19 at 18:43
  • $\begingroup$ Which calibration version was used? Which time range was analysed? $\endgroup$ – samcarter Jul 19 at 18:50
  • $\begingroup$ How long were the gamma rays detected? Longer time, more counts, higher peaks. $\endgroup$ – jmh Jul 20 at 1:06
  • $\begingroup$ @jmh Usually spectra in gamma-ray astronomy are normalised for instrument response and observation time $\endgroup$ – samcarter Jul 20 at 19:26
  • $\begingroup$ ok. he didn'd mention that so i didn't know it it was raw data or processed in some way. Thanks for pointing that out. $\endgroup$ – jmh Jul 20 at 21:37