Thermal and non-thermal emission from a peculiar long-duration GRB 211211A

Long-duration GRB 211211A that lacks a supernova emission even down to very stringent limits at such a low redshift $z=0.076$ and associate with kilonova emission, suggest that its physical origin is from binary compact stars merger. By re-analyzing its data observed with the GBM on board Fermi mission, we find that both time-integrated and time-resolved spectra can be fitted well by using Band plus blackbody (Band+BB) model in the prompt emission. The bulk Lorentz factors ($\Gamma_{\rm ph}$) of the outflow can be inferred by invoking the observed thermal emission at photosphere radius within a pure fireball model, and find out that the temporal evolution of $\Gamma_{\rm ph}$ seems to be tracking with the light curve. The derived values of $\Gamma_{\rm ph}$ are also consistent with the $\Gamma_{\rm ph}$ - $L_{\gamma, iso}$/$E_{\gamma, iso}$ correlations that had been found in other bursts. Moreover, we also calculate the magnetization factor $\sigma_{0}$ in the central engine and $\sigma_{\rm ph}$ at the photosphere radius within the framework of hybrid jet model, and find that the values of both $1+\sigma_{\rm 0}$ and $1+\sigma_{\rm ph}$ are larger than 1 for different time slices. It suggests that at least the Poynting-flux component is indeed existent in the outflow. If this is the case, one possible physical interpretation of thermal and non-thermal emissions in GRB 211211A is from the contributions of both $\nu\bar{\nu}$ annihilation and the Blandford-Znajek mechanisms in the relativistic jet when a stellar mass black hole reside in the central engine.
Comment: 12 pages, 6 figures, and 4 tables