The milestone of GW 170817-GRB 170817A-AT 2017gfo 1 has shown that gravitational wave (GW) is produced during the merger of neutron star-neutron star/black hole and that in electromagnetic (EM) wave a gamma-ray burst (GRB) and a kilonovae (KN) are generated in sequence after the merger. Observationally, however, EM property during a merger is still unclear. Here we report a peculiar precursor in a KN-associated long GRB 211211A. The duration of the precursor is ∼ 0.2 s, and the waiting time between the precursor and the main emission (ME) of the burst is ∼ 1 s, which is about the same as the time interval between GW 170817 and GRB 170817A. Quasi-Periodic Oscillations (QPO) with frequency ∼22 Hz (at > 5σ significance) are found throughout the precursor, the first detection of periodic signals from any bona fide GRBs. This indicates most likely that a magnetar participated in the merger, and the precursor might be produced due to a catastrophic flare accompanying with torsional or crustal oscillations of the magnetar. The strong seed magnetic field of ∼ 10 14−15 G at the surface of the magnetar may also account for the prolonged duration of GRB 211211A. However, it is a challenge to reconcile the rather short lifetime of a magnetar
The brightest gamma-ray burst, GRB 221009A, has spurred numerous theoretical investigations, with particular attention paid to the origins of ultrahigh-energy TeV photons during the prompt phase. However, analyzing the mechanism of radiation of photons in the ∼MeV range has been difficult because the high flux causes pileup and saturation effects in most GRB detectors. In this Letter, we present systematic modeling of the time-resolved spectra of the GRB using unsaturated data obtained from the Fermi Gamma-ray Burst Monitor (precursor) and SATech-01/GECAM-C (main emission and flare). Our approach incorporates the synchrotron radiation model, which assumes an expanding emission region with relativistic speed and a global magnetic field that decays with radius, and successfully fits such a model to the observational data. Our results indicate that the spectra of the burst are fully in accordance with a synchrotron origin from relativistic electrons accelerated at a large emission radius. The lack of thermal emission in the prompt emission spectra supports a Poynting flux–dominated jet composition.
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