A Principal Component Analysis of the 3B Gamma-Ray Burst Data

We have carried out a principal component analysis for 625 gamma-ray bursts in the BATSE 3B catalog for which nonzero values exist for the nine measured variables. This shows that only two out of the three basic quantities of duration, peak flux, and fluence are independent, even if this relation is strongly affected by instrumental effects, and these two account for 91.6% of the total information content. The next most important variable is the fluence in the fourth energy channel (at energies above 320 keV). This has a larger variance and is less correlated with the fluences in the remaining three channels than the latter correlate among themselves. Thus a separate consideration of the fourth channel and an increased attention paid to the related hardness ratio H43 appear useful for future studies. The analysis gives the weights for the individual measurements needed to define a single duration, peak flux, and fluence. It also shows that, in logarithmic variables, the hardness ratio H32 is significantly correlated with peak flux, while H43 is significantly anticorrelated with peak flux. The principal component analysis provides a potentially useful tool for estimating the improvement in information content to be achieved by considering alternative variables or for performing various corrections on available measurements.