Yonetoku Relation Research Articles

Redshift-dependent lag—luminosity relation in 565 BATSE gamma-ray bursts

Abstract We compared redshifts zY measured from the Yonetoku relation and zlag from the lag–luminosity relation for 565 BATSE gamma-ray bursts (GRBs) and were surprised to find that the correlation between these two redshifts is very low. Assuming that the luminosity is a function of both zY and the intrinsic spectral lag τlag, we found a new redshift-dependent lag–luminosity relation L= 7.5 × 1050 erg s−1 (1 +z)2.53τ−0.282lag with the correlation coefficient of 0.77 and the chance probability of 7.9 × 10−75. Although the spectral lag is computed from two channels of the Burst and Transient Source Experiment (BATSE), our new lag–luminosity relation suggests that a future lag–luminosity relation defined in the Swift data should also depend on the redshift.

Unstable GRB Photospheres and e ± Annihilation Lines

We propose an emission mechanism of prompt gamma-ray bursts (GRBs) that can reproduce the observed nonthermal spectra with high radiative efficiencies, >50%. Internal dissipation below a photosphere can create a radiation-dominated thermal fireball. If e± pairs outnumber protons, radiative acceleration of e± pairs drives the two-stream instabilities between pairs and protons, leading to "proton sedimentation" in the accelerating pair frame. Pairs are continuously shock heated by proton clumps, scattering the thermal photons into a broken-power-law shape, with a nonthermal energy that is comparable to the proton kinetic energy, consistent with observations. Pair photospheres become unstable around the radius of the progenitor star where strong thermalization occurs, if parameters satisfy the observed spectral (Yonetoku) relation. Pair annihilation lines are predicted above continua, which could be verified by GLAST.

Possible observational evidence for the -2 angular distribution of the opening half-angle of gamma-ray burst jets

We propose a method to estimate the jet opening half-angle of gamma-ray bursts (GRBs) using the spectral peak energy (Ep)-peak luminosity relation (the so-called Yonetoku relation) as well as the Ep-collimation-corrected gamma-ray energy relation (the so-called Ghirlanda relation). For bursts with known jet break times and redshifts, we have compared the derived jet opening half-angle with that measured and found that the differences are within a factor of 2. We apply the method to 689 long GRBs. We have found that the distribution function of the derived jet opening half-angle obeys f(θj) ∝θ−2.2±0.2j, although a lognormal fit is also possible. θ−2 distribution is compatible with the structured jet model. From the distribution function we have found that the beaming correction for the rate of GRBs is ∼340, which means ∼10−5 yr−1 galaxy−1 or only one in 102 Type Ib/c supernovae. We have also found the evolution of the distribution function as a function of the redshift.