CORRELATION BETWEEN HARDNESS RATIO AND DURATION OF FERMI GAMMA-RAY BURSTS

Using the latest gamma-ray bursts (GRB) observed by Fermi-GBM, we perform a statistical analysis of the relation between hardness ratio (HR) and duration (ΔT) of GRBs, and find that HR and ΔT are still anti-correlated. we also find that this correlation strongly depends upon the spectral shape of GRBs and energy bands, and the bursts with the curved spectra in the typical BATSE energy bands show a tighter anti-correlation than those with the power-law spectra in the typical BAT energy bands. This might explain why the HR – ΔT correlation is not evident for Swift-BAT GRB sample as well as other GRB sample detected by instruments with a narrower/softer energy bandpass such as HETE-2.