  We present our extensive observational campaign on the Swift-discovered
GRB141121A, al- most ten years after its launch. Our observations covers radio
through X-rays, and extends for more than 30 days after discovery. The prompt
phase of GRB 141121A lasted 1410 s and, at the derived redshift of z = 1.469,
the isotropic energy is E{\gamma},iso = 8.0x10^52 erg. Due to the long prompt
duration, GRB141121A falls into the recently discovered class of UL-GRBs.
Peculiar features of this burst are a flat early-time optical light curve and a
radio-to-X-ray rebrightening around 3 days after the burst. The latter is
followed by a steep optical-to-X-ray decay and a much shallower radio fading.
We analyze GRB 141121A in the context of the standard forward-reverse shock
(FS,RS) scenario and we disentangle the FS and RS contributions. Finally, we
comment on the puzzling early-time (t ~3 d) behavior of GRB 141121A, and
suggest that its interpretation may require a two-component jet model. Overall,
our analysis confirms that the class of UL-GRBs represents our best opportunity
to firmly establish the prominent emission mechanisms in action during powerful
GRB explosions, and future missions (like SVOM, XTiDE, or ISS-Lobster) will
provide many more of such objects.
