A Global Photoionization Response to Prompt Emission and Outliers: Different Origin of Long Gamma-ray Bursts?

By using the line ratio C IV lambda 1549/C II lambda 1335 as a tracer of the ionization ratio of the interstellar medium (ISM) illuminated by a long gamma-ray burst (LGRB), we identify a global photoionization response of the ionization ratio to the photon luminosity of the prompt emission assessed by either L-iso/E-peak or L-iso/E-peak(2). The ionization ratio increases with both L-iso/E-peak and L-iso/E-peak(2) for a majority of the LGRBs in our sample, although there are a few outliers. The identified dependence of C IV/C II on L-iso/E-peak(2) suggests that the scatter of the widely accepted Amati relation is related to the ionization ratio in the ISM. The outliers tend to have relatively high C IV/C II values as well as relatively high C IV lambda 1549/Si IV lambda 1403 ratios, which suggests an existence of Wolf-Rayet stars in the environment of these LGRBs. We finally argue that the outliers and the LGRBs following the identified C IV/C II-L-iso/E-peak (L-iso E-peak(2)) correlation might come from different progenitors with different local environments.