Upper limits on column density of a broad H I Lyα. Top panel: model of the (narrow) H I Lyα blend used in the upper limit determination. Bottom panel: normalized residual spectrum after model removal. Red and blue curves show the broad (b_HI = 200 km s⁻¹) line profiles at limiting column densities as indicated. Purple vertical lines mark the expected centroid wavelength of the broad line, as based on the X-ray prediction.