A Comprehensive Power Spectral Density Analysis of Astronomical Time Series. II. The Swift/BAT Long GammaRay Bursts
Abstract
We have investigated the prompt light curves of long gammaray bursts (GRBs) from the Swift/BAT catalog. We aimed to characterize their power spectral densities (PSDs), search for quasiperiodic oscillations (QPOs), and conduct novel analyses directly in the time domain. We analyzed the PSDs using LombScargle periodograms, and searched for QPOs using wavelet scalograms. We also attempted to classify the GRBs using the Hurst exponent, H, and the ${ \mathcal A }\mbox{}{ \mathcal T }$ plane. The PSDs fall into three categories: power law (PL; P(f) ∝ 1/f^{β}) with index β ∈ (0, 2), PL with a nonnegligible Poisson noise level (PLC) with β ∈ (1, 3), and a smoothly broken PL (with Poisson noise level) yielding highfrequency index β_{2} ∈ (2, 6). The latter yields break timescales of the order of 1100 s. The PL and PLC models are broadly consistent with fully developed turbulence, β = 5/3. For an overwhelming majority of GRBs (93%), H > 0.5, implying ubiquity of the longterm memory. We find no convincing substructure in the ${ \mathcal A }\mbox{}{ \mathcal T }$ plane. Finally, we report on 34 new QPOs, with one or more constant leading periods, as well as several chirping signals. The presence of breaks and QPOs suggests the existence of characteristic timescales that in at least some GRBs might be related to the dynamical properties of plasma trajectories in the accretion disks powering the relativistic jets.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 2021
 DOI:
 10.3847/15384357/abe5b1
 arXiv:
 arXiv:2102.05330
 Bibcode:
 2021ApJ...911...20T
 Keywords:

 Gammaray bursts;
 Astrostatistics;
 Astronomy data analysis;
 Light curves;
 629;
 1882;
 1858;
 918;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Physics  Space Physics
 EPrint:
 22 pages, 9 figures, 2 tables (one online only ancillary file)