A single exponential pulse bound flags 139 of 4415 selected Fermi GBM entries under reported duration errors

We derive a duration bound for a pulse with exponential rise and decay. T90/T50 cannot exceed log(10)/log(2). We test 4415 selected Fermi GBM entries in a query frozen on 2026-11-09. Of these, 139 exceed the bound by more than five times a covariance-safe bound on the reported statistical error. Error inflation and time-bin margins reduce but do not remove the flags. The strongest case is the known GRB 160625B, whose emission sequence has independent Konus-Wind support. The next case, GRB 110825A, has independent bright-peak detection but no independent late-tail confirmation in the sources checked here. A source FITS audit matches the catalog durations. A single smooth lognormal pulse can exceed the bound. Some two-pulse signals can fall below it. Thus, the result is a test of a limited pulse family and a tool for follow-up. It is not a discovery of a new source or proof of separate emission episodes. Code, proof, aggregate results, source hashes, and retrieval steps are included. External data and record-level outputs remain outside the baseline package.

astronomy · Fermi GBM · gamma-ray bursts · duration ratio · pulse model · quantile bound · extended emission · model limitation