The lower energy thresholds of large wide-field gamma-ray observatories are
often determined by their capability to deal with the very low-energy cosmic
ray background. In fact, in observatories with areas of tens or hundreds of
thousands of square meters, the number of background events generated by the
superposition of random, very low energy cosmic rays is huge and may exceed by
far the possible signal events. In this article, we argue that a trigger
strategy based on pattern recognition of the shower front can significantly
reject the background, keeping a good efficiency and a good angular accuracy
(few square degrees) for gamma rays with energies as low as tens of GeV. In
this way, alerts can be followed or emitted within time lapses of the order of
the second, enabling wide-field gamma-ray observatories to better contribute to
global multi-messenger networks of astrophysical observatories.Comment: 9 pages, 14 figure