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Astron. Astrophys. 338, 781-794 (1998)

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Appendix A: spectral fit models with a thawed photon index

In Sect. 4.4we froze the photon index to 1.7 to reduce the number of free parameters; this was required by the low statistics of the continuum data points in most of the spectra. However, many authors often fit hard X-ray data with transmission models whose photon index is left free. To allow for a fair comparison of our data with these studies, here we report the results obtained by fitting such transmission models to our data (Table A1). The only exceptions are NGC1386 and NGC 4941, whose NH and [FORMULA] turn out to be completely indetermined once [FORMULA] is thawed.

It is worth noting that most of the sources are characterized by a very flat photon index ([FORMULA]); this result supports our interpretation that the sources are Compton thick, dominated by a cold reflection component. The only exceptions are NGC3081, that we indeed identified as Compton thin, and NGC5643, that is thought to be Compton thick, warm scattering dominated.


[TABLE]

Table A1. Spectral fit by using a transmission model where [FORMULA] is a free parameter
Notes:
a) frozen parameter;
b) rest frame.


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© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998
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