Hardness as a spectral peak estimator for gamma-ray bursts

Simple hardness ratios are found to be a good estimator for the spectral peak energy in gamma-ray bursts (GRBs). Specifically, a high correlation strength is found between the ν F ν peak in the spectrum of Burst and Transient Source Experiment (BATSE) GRBs, E p,obs and the hardness of GRBs, , as defined by the fluences in channels 3 and 4, divided by the combined fluences in channels 1 and 2 of the BATSE Large Area Detectors (LADs). The correlation is independent of the type of the burst, whether long-duration GRB (LGRB) or short-duration (SGRB) and remains almost linear over the wide range of the BATSE energy window (20–2000 KeV). Based on Bayes theorem and Markov Chain Monte Carlo techniques, we also present multivariate analyses of the observational data while accounting for data truncation and sample incompleteness. Prediction intervals for the proposed relation are derived. Results and further simulations are used to compute E p,obs estimates for nearly the entire BATSE catalogue: 2130 GRBs. Based on these estimates, we also obtain for the first time the asymptotic E p,obs distribution of GRBs detectable by BATSE. The observed E p,obs distribution is well fit by the sum of two Gaussians, possibly representing the E p,obs distribution of BATSE LGRBs and SGRBs peaking at 140 and 520 KeV, respectively. These results may be useful for investigating the cosmological utility of the spectral peak energy in GRBs intrinsic luminosity estimates.