Repeating Emission Episodes in Gamma-Ray Bursts: Millilensing or Jet Precession?

Abstract

Abstract Recently, some gamma-ray bursts (GRBs) whose light curves consist of repeating emission episodes with similar temporal profiles have attracted extensive attention. They are proposed to be candidates of millilensing events, although smoking gun evidence is lacking, since there are no redshift measurements and no angular offset detections for any of these candidates. Here we show that without invoking gravitational lensing, the repeating light-curve properties of these GRBs could also be interpreted under the jet precession model, as long as the detectable period in every precession circle is less than the precession period, and the precession period is close to the jet emission duration. By fitting the gamma-ray light curves of these GRBs, we suggest that the jet precession angle for these bursts should be relatively small (e.g., θ p < 5.°3), and the jet structure for these bursts are more likely Gaussian. The results suggest us to be careful when identifying millilensing GRBs. Multiband afterglow data and especially angular offset detections are essential to provide comprehensive justification for this identification.