  Swift-detected GRB 080307 showed an unusual smooth rise in its X-ray
light-curve around 100 seconds after the burst, at the start of which the
emission briefly softened. This `hump' has a longer duration than is normal for
a flare at early times and does not demonstrate a typical flare profile. Using
a two component power-law-to-exponential model, the rising emission can be
modelled as the onset of the afterglow, something which is very rarely seen in
Swift-X-ray light-curves. We cannot, however, rule out that the hump is a
particularly slow early-time flare, or that it is caused by upscattered reverse
shock electrons.
