Variation of the intensity (in Jy beam^-1) with frequency (in GHz) for four pixels in the Sgr B2(N) (open circles) and Sgr B2(M) (filled circles) regions. The vertical lines correspond to the error in the determination of the continuum level as computed by STATCONT (see Sect. 3.1). The intensity is extracted for each continuum map created at different frequencies (see Sect. 3.1). The numbers in parenthesis next to the name of the sources refer to the number of the sources as listed in Tables 1 and 2 (see also Sect. 3.2). The spectral index (α, defined as I ∝ ν^α) is indicated for each source. The intensity of source Sgr B2(M) AM15 is manually shifted by +0.3 Jy beam^-1.