Broad band turbulent spectra in gamma-ray burst light curves

TL;DR

This paper introduces a new chirp detection method for analyzing gamma-ray burst light curves, revealing turbulent spectra up to 1 kHz and outperforming traditional Fourier analysis in sensitivity.

Contribution

The paper presents an efficient chirp search technique that surpasses Fourier analysis in detecting transient signals in GRB light curves, enabling better turbulence characterization.

Findings

Turbulent spectra extend up to 1 kHz in GRB light curves.

Chirp detection method is ten times more sensitive than Fourier analysis.

Spectral slopes indicate turbulence in GRB emission mechanisms.

Abstract

Broad band power density spectra offer a window to understanding turbulent behavior in the emission mechanism and, at the highest frequencies, in the putative inner engines powering long GRBs. We describe a chirp search method which steps aside Fourier analysis for signal detection in the Poisson noise-dominated 2 kHz sampled BeppoSAX light curves. An efficient numerical implementation is described in $O(Nn\log n)$ operations, where $N$ is the number of chirp templates and $n$ is the length of the light curve time series, suited for embarrassingly parallel processing. For detection of individual chirps of duration $\tau=1$ s, the method is one order of magnitude more sensitive in SNR than Fourier analysis. The Fourier-chirp spectra of GRB 010408 and GRB 970816 show a continuation of the spectral slope up to 1 kHz of turbulence identified in low frequency Fourier analysis. The same continuation is observed in an ensemble averaged spectrum of 40 bright long GRBs. An outlook on a similar analysis of upcoming gravitational wave data is included.