GRB 190530A: From Precursor, Prompt Emission to Afterglow all Originated from Synchrotron Radiation

Abstract The GRB 190530A was jointly observed by the High Energy X-ray Telescope of the Hard X-ray Modulation Telescope ($Insight$-HXMT/HE) and the Ground-Based Wide-Angle Camera network (GWAC-N) with the extremely large field of view. After triggered by $Insight$-HXMT/HE and $Fermi$/GBM, we observed the optical emission of GRB 190530A, using the 30 cm telescope of GWAC (GWAC-F30) to search and locate its position. Subsequent observation of the late afterglow of GRB 190530A was made with the 2.16 m telescope at Xinglong Observatory. In this paper, we make a detailed exploration of the origin of GRB 190530A. In the prompt emission, a ``double-tracking'' pattern is presented both for the low-energy spectral index $\alpha$ and the peak energy $E_p$ in the Band function with $Insight$-HXMT/HE and $Fermi$/GBM data; the results of GRB 190530A are consistent with the \emph{Amati} and \emph{Yonetoku} correlations; the spectral lag ($\tau$) Vs. energy ($E$) can be estimated with $\tau = -3.0\pm0.06 + (0.17\pm0.03){\rm log}E$. The synchrotron radiation can account for the origin of GRB 190530A prompt emission behaviors. The $\alpha$ and $E_p$ of the precursor are essentially the same as that of the main prompt emission, implying that they have the same origin. For the afterglow, it can be described with the external forward shock model in ISM circumstellar medium. In summary, from precursor, prompt emission to afterglow of GRB 190530A all originated from synchrotron radiation.