Chandra co-added X-ray spectra from GRB 170817A in a 93.4 ks exposure at 15.6 days (left) and a 98.8 ks exposure at 109.2 days post-burst (right). Spectral data and residuals are shown in black and the best-fit spectral models are in red. The neutral hydrogen absorption column is fixed to N_H = ﹩7.5\times {10}^{20}﹩ cm⁻² (see Section 2). These spectra at 15.6 and 109.2 days each consist of two exposures that were jointly fit. In the joint fit for each epoch, the spectral index Γ was tied between the exposures and the power-law normalization was left free.