Kavli Affiliate: Zhuo Li
| First 5 Authors: Yan-Qiu Zhang, Hao-Xiang Lin, Shao-Lin Xiong, Zhuo Li, Ming-Yu Ge
| Summary:
Gamma-ray bursts (GRBs) are believed to launch relativistic jets, which
generate prompt emission by their internal processes and drive external shocks
into surrounding medium, accounting for the long-lasting afterglow emission.
However, how the jet powers the external shock is an open question. The
unprecedented observations of the keV-MeV emission with GECAM and the TeV
emission with LHAASO of so far the brightest burst, GRB 221009A, offer a great
opportunity to study the prompt-to-afterglow transition and the early dynamical
evolution of the external shock. In this letter, we find that the cumulative
light curve of keV-MeV emission could well fit the rising stage of the TeV
light curve of GRB 221009A, with a time delay of $4.45^{+0.26}_{-0.26}$,s for
TeV emission. Moreover, both the rapid increase in the initial stage and the
excess from about T+260,s to 270,s in the TeV light curve could be
interpreted by inverse Compton (IC) scatterings of the inner-coming photons by
the energetic electrons in external shock. Our results not only reveal a close
relation between the keV-MeV and TeV emission, but also indicate a continuous,
rather than impulsive, energy injection to the external shock. Assuming an
energy injection rate proportional to the keV-MeV flux, we build a continuous
energy injection model which well fits the TeV light curve of GRB 221009A, and
provides an estimate of the Lorentz factor of the jet.
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