Statistical Study of the Swift X-ray Flash and X-ray Rich Gamma-Ray Bursts

Abstract

We build a comprehensive sample to statistically describe the properties of X-ray flashes (XRFs) and X-ray riches (XRRs) from the latest third Swift Burst Alert Telescope (BAT3) catalog of Gamma-ray bursts (GRBs). We obtain 81 XRFs, 540 XRRs, and 394 classical GRBs (C-GRBs). We statistically explore the different properties of the $\gamma$-ray prompt emission, the X-ray emission, the X-ray lightcurve type, the association with supernovae (SNe), and the host galaxy properties for these sources. We confirm that most XRFs/XRRs are long GRBs with low values of peak energy $E^{obs}_{peak}$ and they are low-luminosity GRBs. XRFs, XRRs, and C-GRBs follow the same $E_{X,iso}$-$E_{\gamma,iso}$-$E_{peak,z}$ correlations. Compared to the classical GRBs, XRFs are favorable to have the association with SN explosions. We do not find any significant differences of redshift distribution and host galaxy properties among XRFs, XRRs, and C-GRBs. We also discuss some observational biases and selection effects that may affect on our statistical results. The GRB detectors with wide energy range and low energy threshold are expected for the XRF/XRR research in the future.