The observed spectrum of a supernova remnant (SNR) is a superposition of many
``local'' spectra emitted by regions of SNRs that are under different physical
conditions. The question remains as to whether the broadening of the
high-energy end of the observed nonthermal spectrum of SNRs, like in G347.3-0.5
and SN 1006, can be an artifact of observations or it is a consequence of the
microphysics involved in the acceleration process. In this note we study the
influence of parameters variations (inside the volume and over the surface of
SNR) on the shape of the high-energy end of the synchrotron (and also inverse
Compton) spectrum. We consider three possibilities for these parameter
variations: i) gradients downstream of the shock with constant maximum energy
of the accelerated electrons and the potential variation in time of the
injection efficiency, ii) then we add the possibility of the maximum energy
depending on time, and finally iii) the possible obliquity dependences of
maximum energy and injection efficiency. It is shown that gradients of density
and magnetic field strength downstream of the shock are ineffective in
modifying the shape of the synchrotron spectrum, even if an SNR evolves in the
nonuniform interstellar medium and/or the injection efficiency varies in time.
The time dependence of the maximum energy of the electrons accelerated by the
shock is also not able to make the observed spectrum much broader. The only
possibility of producing considerable broadening in the spectrum is the
variation in the maximum energy of electrons over the surface of SNR. In such a
case, the obliquity dependence of the injection efficiency also affects the
shape of the spectrum, but its role is less significant.Comment: 6 pages, 4 figures, A&A accepte