The relevant quantity in ultra high energy cosmic rays (like OMG!) is the GZK limit (initials of a paper's authors), which is an upper limit on the energy-momentum of an intergalactic proton, set by interactions with charged matter and cosmic microwaves along the way, which transfer an UHEC proton's momentum to particles resulting from the interactions. OMG! is one of several curious possible violations of the GZK speed limit. (GZK does not deal with re-acceleration close to our galaxy via coupling to magnetic fields for instance, nor says anything about a galactic origin for something with cosmic-ray energies; it's all about how very fast protons can be slowed down over cosmological distances).
The highest energies of UHEC protons are probably not caused by "instant" accelerations as in a supernova (which certainly produces high energy protons that fly across the cosmos). Instead, they're more likely drawn up magnetically around the supermassive black holes powering active galactic nuclei (quasars, blazars and so on) and into jets, where they spend possibly weeks or accelerating through a natural counterpart to a particle accelerator which benefits from things like inverse Compton scattering (a hard X-ray from the black hole hits our proton boosting the proton's momentum and lengthening the X-ray's wavelength (i.e., reducing its momentum)).
But because we don't know OMG!'s origin, we can't say if OMG! tests any acceleration limit originating in uncertainty relations. Also, the Caianiello limit is unhealthy for protons (which OMG! likely was) staying protons: that they are composite structures makes them liable to be blown apart by extreme acceleration. Assuming it's a proton and had a blazar origin, OMG! is (really rough back-of-envelope work) likely to have fallen between 7 and 40 orders of magnitude short of the maximum (proper) acceleration. The intuition here is that OMG! is well short of Planck energy (by some 7 orders of magnitude) and super-high acceleration should take a proton from thermal energies to Planck energies. Of course a proton much closer to Planck energy could lose proportionally more along the way than a less-energetic proton, so who knows? There could be a doctoral dissertation waiting to be written on this!
The highest energies of UHEC protons are probably not caused by "instant" accelerations as in a supernova (which certainly produces high energy protons that fly across the cosmos). Instead, they're more likely drawn up magnetically around the supermassive black holes powering active galactic nuclei (quasars, blazars and so on) and into jets, where they spend possibly weeks or accelerating through a natural counterpart to a particle accelerator which benefits from things like inverse Compton scattering (a hard X-ray from the black hole hits our proton boosting the proton's momentum and lengthening the X-ray's wavelength (i.e., reducing its momentum)).
But because we don't know OMG!'s origin, we can't say if OMG! tests any acceleration limit originating in uncertainty relations. Also, the Caianiello limit is unhealthy for protons (which OMG! likely was) staying protons: that they are composite structures makes them liable to be blown apart by extreme acceleration. Assuming it's a proton and had a blazar origin, OMG! is (really rough back-of-envelope work) likely to have fallen between 7 and 40 orders of magnitude short of the maximum (proper) acceleration. The intuition here is that OMG! is well short of Planck energy (by some 7 orders of magnitude) and super-high acceleration should take a proton from thermal energies to Planck energies. Of course a proton much closer to Planck energy could lose proportionally more along the way than a less-energetic proton, so who knows? There could be a doctoral dissertation waiting to be written on this!
Also, sorta disappointingly, OMG! could have had an electric charge greater than +1 (i.e., some ion with more than one proton) and in that case could have originated as close as our own sun <https://en.wikipedia.org/wiki/Solar_energetic_particles> <https://en.wikipedia.org/wiki/HZE_ions>.