  Gamma-ray bursts (GRBs) are intense bursts of high-energy photons (prompt
emissions) caused by relativistic jets. After the emissions, multi-wavelength
afterglows, from radio to very-high-energy (VHE) gamma-ray, last for more than
a few days. In the past three years, the VHE gamma-ray photons from four GRBs
(GRBs 180720B, 190114C, 190829A and 201216C) were detected by ground-based
Imaging Atmospheric Cherenkov Telescopes, such as the Major Atmospheric Gamma
Imaging Cherenkov (MAGIC) telescopes and the High Energy Stereoscopic System
(H.E.S.S.). One of them, GRB 190829A, had some peculiar features of showing
achromatic peaks in X-ray and optical bands at $1.4\times10^3$ s and being
classified as low-luminosity GRBs. Previously, we proposed a two-component jet
model, which has `narrow jet' with a small initial opening half-angle
$\theta_0=0.015$ rad and large bulk Lorentz factor $\Gamma_0=350$, and `wide
jet' with $\theta_0=0.1$ rad and $\Gamma_0=20$. The narrow jet explained the
early X-ray and optical emissions and apparently small isotropic gamma-ray
energy and peak energy in the off-axis viewing case. Furthermore, the late
X-ray and radio (1.3 and 15.5 GHz) afterglows were emitted from the wide jet.
Here, we calculate the VHE gamma-ray flux by the synchrotron self-Compton (SSC)
emission. The multi-wavelength afterglows of GRB 190829A including the VHE
gamma-ray emission are well explained by our two-component jet model. The
afterglow emissions from our two-component jet are also consistent with the
observational results of GRBs 180720B, 190114C and 201216C, when the jets are
viewed on-axis. Furthermore, we discuss the detectability of off-axis orphan
afterglows by the Cherenkov Telescope Array (CTA).
