Kavli Affiliate: Zhuo Li
| First 5 Authors: Zhen Zhang, Haoxiang Lin, Zhuo Li, Shao-Lin Xiong, Yan-Qiu Zhang
| Summary:
Ultra-relativistic jets are believed to play important role in producing
prompt emission and afterglow of gamma-ray burst (GRB), but the nature of the
jet is poorly known owing to the lack of decisive features observed in the
prompt emission. The discovery of emission line evolving from about 37 MeV to 6
MeV in the brightest-of-all-time GRB 221009A provides an unprecedented
opportunity to probe GRB-jet physics. The time evolution of the central energy
of the line with power-law index $-1$ is naturally explained by high-latitude
curvature effect. Under the assumption that the line emission is generated in
the prompt emission by $e^pm$ pair production, cooling and annihilation in the
jet, we can strictly constrain jet physics with observed line-emission
properties. We find that the radius of the emission region is $rgtrsim10^{16}$
cm. The narrow line width of $sim10%$ requires that the line emission occurs
within 10% of the dynamical time, which further implies short timescales of
pair cooling to non-relativistic state and pair annihilation, and a slightly
clumpy emission region. If the jet’s Lorentz factor is $Gammagtrsim400$, the
fast cooling requirement needs an energy density of magnetic field in the jet
much larger than that of prompt gamma-rays, i.e., a magnetically dominated jet.
The temporal behavior of line flux suggests some angle dependence of line
emission. We also discuss the difficulties of other scenarios for the observed
emission line.
| Search Query: ArXiv Query: search_query=au:”Zhuo Li”&id_list=&start=0&max_results=3