Correlation plots of the HXR photon spectral index γ observed by RHESSI and the electron spectral index δ obtained from STEREO/SEPT, plotted for all events (left) and only the events with distinct anisotropy of the in situ electron flux (right). In the case of events with broken power-laws, we use here the spectral index below the break, δ₁. For three events, we consider either δ₁ (red), or δ₂ (blue). The dotted lines indicate linear fits to the data. The dashed lines indicate the relationships between γ and δ expected for thick and thin-target bremsstrahlung, respectively. The fit parameters are indicated, as well as the linear correlation coefficients C.