Probability distributions of the spectral index of pulsar B’s radio emission, calculated assuming a single power-law between 685 and 1400 MHz (light grey shade) and 685 and 3100 MHz (dark grey shade), from multi-frequency profiles corresponding to roughly the same orbital phase and separated in time by roughly 30 days. The joint probability distribution is shown with a solid black line, and the corresponding median spectral index and 68% confidence interval, with solid and dashed vertical lines, respectively.