The GRB 071112C: A Case Study of Different Mechanisms in X-ray and Optical Temporal Evolution

We present the study on GRB 071112C X-ray and optical light curves. In these two wavelength ranges, we have found different temporal properties. The R-band light curve showed an initial rise followed by a single power-law decay, while the X-ray light curve was described by a single power-law decay plus a flare-like feature. Our analysis shows that the observed temporal evolution cannot be described by the external shock model in which the X-ray and optical emission are produced by the same emission mechanism. No significant color changes in multi-band light curves and a reasonable value of the initial Lorentz factor ({\Gamma}0 = 275 \pm 20) in a uniform ISM support the afterglow onset scenario as the correct interpretation for the early R-band rise. The result suggests the optical flux is dominated by afterglow. Our further investigations show that the X-ray flux could be created by an additional feature related to energy injection and X-ray afterglow. Different theoretical interpretations indicate the additional feature in X-ray can be explained by either late internal dissipation or local inverse-Compton scattering in the external shock.

💡 Research Summary

The paper presents a detailed comparative study of the X‑ray and optical (R‑band) afterglow of GRB 071112C, using Swift/XRT data together with ground‑based optical observations from several facilities. The authors find that the two wavelength regimes exhibit markedly different temporal behaviours, indicating that a single external‑shock model cannot simultaneously account for both light curves.

In the optical band the light curve shows an early rise lasting roughly 100 s, reaching a peak at about 300 s after the trigger, and then decaying as a single power law with a decay index α_opt ≈ 1.0. No significant colour evolution is detected across the V, R, and I bands during the rise, implying that the emitting electrons share a common distribution and that the surrounding medium is homogeneous. By applying the standard afterglow‑onset formalism (Γ₀ ≈ 2