An Iranian rocket (Safir 2 r/b)
Conditions were not perfect (somewhat hazy), but the rocket booster was well visible and I captured it on two images (see below). It showed a clear very slow amplitude brightness variation (amplitude >20 seconds), going between mag. +3 and near-invisibility for the naked eye (> +4). Around the brightness peak it gives a short bright glint. Both my photographs captured such a glint.
(update) Based on the two pictures, and assuming I didn't miss a glint in between them, the glint period is 33.25 seconds, with glints at:
7 Mar 2009 04:26:12.60 UTC
7 Mar 2009 04:26:45.85 UTC
Below the two pictures (as usual, Canon EOS 450D @ 800 ISO + EF 50/2.5 Macro @ F2.8), and the brightness profiles for these trails.