  Searches for dijet resonances with sub-TeV masses using the ATLAS detector at
the Large Hadron Collider can be statistically limited by the bandwidth
available to inclusive single-jet triggers, whose data-collection rates at low
transverse momentum are much lower than the rate from Standard Model multijet
production. This Letter describes a new search for dijet resonances where this
limitation is overcome by recording only the event information calculated by
the jet trigger algorithms, thereby allowing much higher event rates with
reduced storage needs. The search targets low-mass dijet resonances in the
range 450-1800 GeV. The analyzed dataset has an integrated luminosity of up to
29.3 fb$^{-1}$ and was recorded at a center-of-mass energy of 13 TeV. No
excesses are found; limits are set on Gaussian-shaped contributions to the
dijet mass distribution from new particles and on a model of dark-matter
particles with axial-vector couplings to quarks.
