Cosmological Signatures In Intensity And Break Energy Correlations

We examine the association between the peak of the vF(v) spectrum of gamma ray bursts, E-p, and the burst's energy fluence. Because bursts near the detector threshold are not usually able to provide reliable spectral parameters, we analyze the results for the brightest bursts in which we can better understand the selection effects relevant to E-p and burst strength, We find that there is a strong correlation between total fluence and E-p. We discuss these results in terms of both cosmological and intrinsic effects. In particular, we show that for realistic distributions of the burst parameters, cosmological expansion alone cannot account for the correlation between E-p and total fluence; the observed correlation is likely a result of an intrinsic relation between the burst rest-frame peak energy and the total radiated energy, as expected in an internal shock model.