This object was actually discovered the day before it entered in the
Earth's atmosphere. Although this kind of impact events occur quite frequently,
this case was unprecedented in that, for the first time, the impact was
predicted in advance.
See the report "Asteroid 2008 TC3 Strikes Earth:
Predictions and Observations Agree" for details.
Some images of this asteroid, taken from La Sagra Observatory about one hour before
the impact, are available here
and at the Mallorca Planetarium.