Correlation between peak energy and Fourier power density spectrum slope in gamma-ray bursts

Abstract

Context. The origin of the gamma-ray burst (GRB) prompt emission still defies explanation, in spite of recent progress made, for example, on the occasional presence of a thermal component in the spectrum along with the ubiquitous non-thermal component that is modelled with a Band function. The combination of finite duration and aperiodic modulations make GRBs hard to characterise temporally. Although correlations between GRB luminosity and spectral hardness on one side and time variability on the other side have long been known, the loose and often arbitrary definition of the latter makes the interpretation uncertain. Aims. We characterise the temporal variability in an objective way and search for a connection with rest-frame spectral properties for a number of well-observed GRBs. Methods. We studied the individual power density spectra (PDS) of 123 long GRBs with measured redshift, rest-frame peak energy E p,i of the time-averaged ν F ν spectrum, and well-constrained PDS slope α detected with Swift, Fermi and past spacecraft. The PDS were modelled with a power law either with or without a break adopting a Bayesian Markov chain Monte Carlo technique. Results. We find a highly significant E p,i -α anti-correlation. The null hypothesis probability is ∼10 −9 . Conclusions. In the framework of the internal shock synchrotron model, the E p,i -α anti-correlation can hardly be reconciled with the predicted E p,i ∝ Γ −2 , unless either variable microphysical parameters of the shocks or continual electron acceleration are assumed. Alternatively, in the context of models based on magnetic reconnection, the PDS slope and E p,i are linked to the ejecta magnetisation at the dissipation site, so that more magnetised outflows would produce more variable GRB light curves at short timescales ( 1 s), shallower PDS, and higher values of E p,i .

Clustering of gamma-ray burst types in the Fermi GBM catalogue: indications of photosphere and synchrotron emissions during the prompt phase

“…It is clear that the synchrotron bursts have more variable light curves. This is shown by the short ∆tmin as well as the small value of the smoothness parameter S. This result is consistent with the finding in Dichiara et al (2016) who found that high E pk bursts tend to be more variable on shorter time scales. In more detail, they found a strong correlation between the slope of the power density spectrum (PDS) of the light curve and the E pk values.…”

Individual power density spectra ofSwiftgamma-ray bursts

“…source rest-frame) peak energy E p,i , and the isotropic-equivalent radiated energy, E iso , involved in the eponymous correlation (Amati et al 2002); iii) we search for occasional features emerging from the PDS continuum, such as coherent pulsations or QPOs, which, if any, would be completely washed out by averaging the PDS of many different GRBs. In a companion paper (Dichiara et al 2016, hereafter D16) we focus on the E p,i -PDS correlation and its theoretical implications for a large number of GRBs with known redshift detected by several past and present spacecraft.…”

Variability of magnetically-dominated jets from accreting black holes

“…Furthermore, several correlations between the variability properties and GRB energetics have been detected. The peak energy is anti-correlated with the PDS index (Dichiara et al 2016). The general idea behind the correlations this kind invokes the jet Lorentz factor, Γ, being the main driver responsible relations between both peak energy an luminosity, and GRB duration and its luminosity (Dainotti & Del Vecchio 2017).…”