Beyond T90: Using the Bp–P0 Plane to Diagnose Anomalous GRB Central Engines

The traditional short/long classification of gamma-ray bursts (GRBs), based primarily on T90, is increasingly insufficient for interpreting anomalous events that combine long-duration prompt emission with merger-like signatures, extended central-engine activity, kilonova-like components, atypical host environments, or the absence of an accompanying supernova. Recentwork on magnetar-powered GRBs has introduced an empirical Bp–P0 relation for short GRBs with internal X-ray plateaus, showing that short and long GRBs may share a similar scaling slope while occupying different magnetic-field normalizations. This paper proposes the Bp–P0 plane as an additional central-engine diagnostic for anomalous GRBs. Using GRB 211211Aand GRB 250702B as motivating cases, and GRB 241025A as a methodological reminder of model non-specificity, we argue that ambiguous GRBs should be evaluated not only by duration and environmental diagnostics, but also by the inferred or expected location of their engine in magnetar parameter space whenever plateau or late-injection observables permit such a test.