Correlation between Peak Energy and Peak Luminosity in Short Gamma-Ray Bursts

A correlation between the peak luminosity and the peak energy has been found by Yonetoku et al. as $L_{p}\propto E_{p,i}^{2.0}$ for 11 pre-Swift long gamma-ray bursts. In this study, for a greatly expanded sample of 148 long gamma-ray bursts in the Swift era, we find that the correlation still exists, but most likely with a slightly different power-law index, i.e., $L_{p}\propto E_{p,i} ^{1.7}$. In addition, we have collected 17 short gamma-ray bursts with necessary data. It is found that the correlation of $L_{p}\propto E_{p,i} ^{1.7}$ also exists for this sample of short events. It is argued that the radiation mechanism of both long and short gamma-ray bursts should be similar, i.e., of quasi-thermal origin caused by the photosphere and the dissipation occurring very near the central engine. Some key parameters of the process are constrained. Our results suggest that the radiation process of both long and short bursts may be dominated by thermal emission, rather than the single synchrotron radiation. This might put strong physical constraints on the theoretical models.