On The Lack of Time Dilation Signatures in Gamma-ray Burst Light Curves

Abstract

We examine the effects of time dilation on the temporal profiles of gamma-ray burst (GRB) pulses. By using prescriptions for the shape and evolution of prompt gamma-ray spectra, we can generate a simulated population of single pulsed GRBs at a variety of redshifts and observe how their light curves would appear to a gamma-ray detector here on Earth. We find that the observer frame duration of individual pulses does not increase with redshift as 1 = z that one would expect from the cosmological expansion. This time dilation is masked by an opposite and often stronger effect which is that with increasing redshift and decreasing signal-to-noise ratio only the brightest portion of the light curve can be detected. The results of our simulation are consistent with the fact that the simple time dilation of GRB light curves has not materialized in either the Swift or Fermi detected GRBs with known redshift. We show that the measured durations and associated E iso estimates for GRBs detected near the instrument's detection threshold should be considered lower limits to the true values. Furthermore, we conclude that attempts at distinguishing between long and short GRBs, at even moderate redshifts, cannot be done based on a burst's temporal properties alone.

Expanding Space, Quasars and St. Augustine’s Fireworks

“…However, a recent study of over 800 quasar light curves found no evidence of the expected effects of time dilation [2]. This is a very surprising result with no explanation within the conventional cosmological framework (note that some studies report the lack of time dilation signatures also in gamma-ray burst light curves [29,30]. See however [31,32]).…”

A framework for the next generation of stationary cosmological models

“…However, no such time dilation was found in the light curves of quasars [97,98] or in duration measures of GRBs [99,100], casting doubts on a key prediction of Lemaitre cosmologies, namely, the generality of the phenomenon.…”

Has the density of sources of gamma-ray burts been constant over the last ten billion years ?

“…It has been claimed that, as predicted by Lemaitre cosmologies [31,32,33], the light curves of Type Ia supernovae are dilated by (1 + z) [34,35,36] and that, as a consequence, theories in which photons dissipate their energy during travel are excluded [34,35]. However, no such time dilation was detected in GRB [37] or quasar [38,39] light curves, casting doubts on the generality of the phenomenon.…”