A tiny fraction of observed gamma-ray bursts (GRBs) may be lensed. The time delays induced by the gravitational lensing are milliseconds to seconds if the point lenses are intermediate-mass black holes. The prompt emission of the lensed GRBs, in principle, should have repeated pulses with identical light curves and spectra but different fluxes and slightly offset positions. In this work, we search for such candidates within the GRBs detected by Fermi/GBM, Swift/Burst Alert Telescope, and HXMT/HE and report the identification of an attractive event GRB 200716C that consists of two pulses. Both the autocorrelation analysis and the Bayesian inference of the prompt emission light curve are in favor of the gravitational-lensing scenario. Moreover, the spectral properties of the two pulses are rather similar and follow the so-called Amati relation of short GRBs rather than long-duration bursts. The measured flux ratios between the two pulses are nearly constant in all channels, as expected from gravitational lensing. We therefore suggest that the long-duration burst GRB 200716C was a short event being lensed. The redshifted mass of the lens was estimated to be 4.25 − 1.36 + 2.46 × 10 5 M ⊙ (90% credibility). If correct, this could point toward the existence of an intermediate-mass black hole along the line of sight of GRB 200716C.
In this paper, we model the dynamics and radiation physics of the rarity event GRB 221009A afterglow in detail. By introducing a top-hat jet that propagates in an environment dominated by stellar winds, we explain the publicly available observations of afterglow associated with GRB 221009A over the first week. It is predicted that GRB 221009A emits a luminous very high energy afterglow based on the synchrotron self-Compton (SSC) process in our model. We show the broadband spectral energy distribution (SED) analysis results of GRB 221009A and find that the SSC radiation component of GRB 221009A is very bright in the 0.1–10 TeV band. The integrated SED shows that the SSC emission in the TeV band has detection sensitivity significantly higher than that of LHASSO, MAGIC, and CTA. However, since the release of further observations, deviations from the standard wind environment model have gradually shown up in data. For example, the late-time multiband afterglow cannot be consistently explained under the standard wind environment scenario. It may be necessary to consider modeling with a structured jet with complex geometry or a partial revision of the standard model. Furthermore, we find that the inclusion of GeV observations could break the degeneracy between model parameters, highlighting the significance of high-energy observations in determining accurate parameters for GRB afterglows.
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