Evidence for a strong 19.5 Hz flux oscillation in Swift BAT and Fermi GBM gamma-ray data from GRB 211211A

Abstract

The gamma-ray burst (GRB) GRB~211211A is believed to have occurred due to the merger of two neutron stars or a neutron star and a black hole, despite its duration of more than a minute. Subsequent analysis has revealed numerous interesting properties including the possible presence of a $\sim 22$~Hz quasiperiodic oscillation (QPO) during precursor emission. Here we perform timing analysis of Fermi and Swift gamma-ray data on GRB~211211A and, although we do not find a strong QPO during the precursor, we do find an extremely significant 19.5~Hz flux oscillation, which has higher fractional amplitude at higher energies, in a $\sim 0.2$~second segment beginning $\sim 1.6$~seconds after the start of the burst. After presenting our analysis we discuss possible mechanisms for the oscillation.

16 pages, 7 figures, 2 tables

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• Premerger phenomena in neutron-star binary coalescences
• Evidence for a brief appearance of gamma-ray periodicity after a compact star merger
• A search for periodic activity in multi-peaked long gamma-ray bursts
• Searching for quasi-periodicities in short transients: the curious case of GRB 230307A
• A 4.5-s Quasiperiodic Spectral Oscillation in GRB 230307A: Evidence for Free Precession of a Post-Merger Magnetar?
• Nonlinear coupling between magnetar QPOs