Can the Cosmological Dilation Explain the Skewness in the Gamma-Ray Burst Duration Distribution?

Cosmological Time Dilation in Durations of Swift Long Gamma-Ray Bursts

Cosmological time dilation is a fundamental phenomenon in an expanding universe, which stresses that both the duration and wavelength of the emitted light from a distant object at the redshift $z$ will be dilated by a factor of $1+z$ at the observer. By using a sample of 139 \emph{Swift} long GRBs with known redshift ($z\leq8.2$), we measure the observed duration ($T_{90}$) in the observed energy range between $140/(1+z)$ keV and $350/(1+z)$ keV, corresponding to a fixed energy range of 140-350 keV in the rest frame. We obtain a significant correlation between the duration and the factor $1+z$…

Investigating signatures of cosmological time dilation in duration measures of prompt gamma-ray burst light curves

We study the evolution with redshift of three measures of gamma-ray burst (GRB) duration ($T_{\rm 90}$, $T_{\rm 50}$ and $T_{\rm R45}$) in a fixed rest frame energy band for a sample of 232 Swift/BAT detected GRBs. Binning the data in redshift we demonstrate a trend of increasing duration with increasing redshift that can be modelled with a power-law for all three measures. Comparing redshift defined subsets of rest-frame duration reveals that the observed distributions of these durations are broadly consistent with cosmological time dilation. To ascertain if this is an instrumental effect, a …

Search for Cosmological time dilation from Gamma-Ray Bursts -- A 2021 status update

We carry out a search for signatures of cosmological time dilation in the light curves of Gamma Ray Bursts (GRBs), detected by the Neil Gehrels Swift Observatory. For this purpose, we calculate two different durations ($T_{50}$ and $T_{90}$) for a sample of 247 GRBs in the fixed rest frame energy interval of 140-350 keV, similar to Zhang et al. We then carry out a power law-based regression analysis between the durations and redshifts. This search is done using both the unbinned as well as the binned data, where both the weighted mean and the geometric mean was used. For each analysis, we also…

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

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 as a function of redshift as one would expect from the cosmological expansion of a Friedman-Lemaitre-Robertson-Walker Universe. In fact, the duration of individual puls…

How does the shape of gamma-ray bursts' pulses affect the duration distribution?

Gamma-ray bursts (GRBs) come in two types, short and long. The distribution of logarithmic durations of long GRBs is asymmetric rather than Gaussian. Such an asymmetry, when modelled with a mixture of Gaussian distributions, requires an introduction of an additional component, often associated with another class of GRBs. However, when modelled with inherently asymmetric distributions, there is no need for such a component. The cosmological dilation was already ruled out as a source of the asymmetry, hence its origin resides in the progenitors. GRB light curves (LCs) are usually well described …

暗能量巡天超新星项目：慢速超新星在红移$z \sim 1$处展现宇宙学时间膨胀效应

The Dark Energy Survey Supernova Program: Slow supernovae show cosmological time dilation out to $z \sim 1$

本研究利用暗能量巡天的1504颗Ia型超新星光变曲线，通过两种方法验证宇宙学时间膨胀效应，测得幂指数b接近1，为迄今最精确的相关测量，有力支持了宇宙膨胀理论。