Spectral index map for the H II region W49. Top panel: spectral index fitting result of the peak of the continuum source G43.171+0.007 (denoted with a cross in the panel). Middle panel: averaged image of spw-1440 and spw-1820, the white contours represent the area of the source extracted by BLOBCAT, and the cross denotes the peak of the source G43.171+0.007 in the catalog. The circles indicate the H II regions from Anderson et al. (2014) matched with the continuum sources in the THOR catalog. Bottom panel: the spectral index map produced by fitting the flux of the six SPWs pixel by pixel. The synthesized beams of the averaged image and the spectral index map are shown in the bottom left corner of each panel.