2026/07/15 by Tom Kimpson, Joseph O'Leary
#astro-ph.HE
The emission mechanism of fast radio bursts (FRBs) remains unknown. Whether the bursts from a repeating FRB arrive at random or in a structured sequence is a key constraint on that mechanism. We apply ε-machine reconstruction, a tool from computational mechanics that infers the minimal model capturing all predictive information in a stochastic process. Applied to the waiting-time sequences of three repeating FRBs (FRB~20121102A and FRB~20201124A from FAST; FRB~20220912A from CHIME), the method yields the statistical complexity Cμ, the minimum number of bits required for optimal prediction. Both FAST sources carry roughly one bit of temporal memory (significant against permutation surrogates, p ≤ 0.01; per-source false-discovery-rate-adjusted p ≤ 0.028), while FRB~20220912A is consistent with memoryless emission. FRB~20201124A's memory spans hours-to-days across four sessions, FRB~20121102A's spans hours-to-weeks across thirty-nine, and neither source shows defensible within-session predictive memory. For FRB~20121102A the ordering of those sessions is itself predictive (session-shuffle p = 0.02), whereas FRB~20201124A's signal reflects the contrast between heterogeneous sessions rather than their order. A simulated windowing test shows that CHIME's short transit observations would suppress comparable structure in the FAST data, leaving FRB~20220912A's null result ambiguous. This first application of ε-machine reconstruction to astrophysical transients yields a model-independent constraint: the bursting of at least two of these repeaters is not memoryless, but is governed by a hidden state that occupies distinct activity-rate regimes varying across observing sessions, behaviour that any viable physical model must reproduce.