Extremely energetic Fermi Gamma-Ray Bursts obey spectral energy correlations

The extremely energetic Fermi GRBs 080916C, with its Eiso of ~ 10^{55} erg in 1 keV - 10 GeV and intense GeV emission, and 090323 give us a unique opportunity to test the reliability and extension of spectral energy correlations. Based on Konus/WIND and Fermi spectral measurements, we find that both events are fully consistent with the updated (95 events as of April 2009) Ep,i - Eiso correlation, thus further confirming and extending it and pointing against a possible flattening or increased dispersion at very high energies. This also suggests that the physics behind the emission of peculiarly bright and hard GRBs is the same as for softer and weaker ones. In addition, we find that the normalization of the correlation obtained by considering these two GRBs and the other long ones for which Ep,i was measured with high accuracy by the Fermi/GBM are fully consistent with those obtained by other instruments (e.g., BeppoSAX, Swift, Konus-WIND), thus indicating that the correlation is not affected significantly by detectors limited thresholds and energy bands. Prompted by the extension of the spectrum of GRB 080916C up to several GeVs without any excess or cut-off, we also investigated if the evaluation of Eiso in the commonly adopted 1 keV - 10 MeV energy band may bias the Ep,i - Eiso correlation contributing to its scatter. By computing Eiso from 1 keV to 10 GeV, the slope of the correlation becomes slightly flatter, while its dispersion does not change significantly. Finally, we find that GRB 080916C is also consistent with most of the other spectral energy correlations derived from it, with the possible exception of the Ep,i - Eiso - tb correlation.Comment: 9 pages, 5 figures, final revised version accepted for pubblication in Astronomy & Astrophysics (main Journal

The GRB Variability/Peak Luminosity Correlation: new results

We report test results of the correlation between time variability and peak luminosity of Gamma-Ray Bursts (GRBs), using a larger sample (32) of GRBs with known redshift than that available to Reichart et al. (2001), and using as variability measure that introduced by these authors. The results are puzzling. Assuming an isotropic-equivalent peak luminosity, as done by Reichart et al. (2001), a correlation is still found, but it is less relevant, and inconsistent with a power law as previously reported. Assuming as peak luminosity that corrected for GRB beaming for a subset of 16 GRBs with known beaming angle, the correlation becomes little less significant.Comment: 11 pages, 10 figures, MNRAS, accepte

A search for pulsations in short gamma-ray bursts to constrain their progenitors

We searched for periodic and quasiperiodic signal in the prompt emission of a sample of 44 bright short gamma-ray bursts detected with Fermi/GBM, Swift/BAT, and CGRO/BATSE. The aim was to look for the observational signature of quasiperiodic jet precession which is expected from black hole-neutron star mergers, but not from double neutron star systems. Thus, this kind of search holds the key to identify the progenitor systems of short GRBs and, in the wait for gravitational wave detection, represents the only direct way to constrain the progenitors. We tailored our search to the nature of the expected signal by properly stretching the observed light curves by an increasing factor with time, after calibrating the technique on synthetic curves. In none of the GRBs of our sample we found evidence for periodic or quasiperiodic signals. In particular, for the 7 unambiguously short GRBs with best S/N we obtained significant upper limits to the amplitude of the possible oscillations. This result suggests that BH-NS systems do not dominate the population of short GRB progenitors as described by the kinematic model of Stone, Loeb, & Berger (2013).Comment: 7 pages, 5 figures, accepted to ApJ, added reference

Average power density spectrum of long GRBs detected with BeppoSAX/GRBM and with Fermi/GBM

From past experiments the average power density spectrum (PDS) of GRBs with unknown redshift was found to be modelled from 0.01 to 1 Hz with a power-law, f^(-alpha), with alpha broadly consistent with 5/3. Recent analyses of the Swift/BAT catalogue showed analogous results in the 15-150 keV band. We carried out the same analysis on the bright GRBs detected by BeppoSAX/GRBM and Fermi/GBM. The BeppoSAX/GRBM data, in the energy range 40-700 keV and with 7.8 and 0.5-ms time resolutions, allowed us to explore for the first time the average PDS at very high frequencies (up to 1 kHz) and reveal a break around 1-2 Hz, previously found in CGRO/BATSE data. The Fermi/GBM data, in the energy band 8-1000 keV, allowed us to explore for the first time the average PDS within a broad energy range. Our results confirm and extend the energy dependence of the PDS slope, according to which harder photons have shallower PDS.Comment: 13 pages, 9 figures, accepted to MNRA

Intermittency and scaling laws for wall bounded turbulence

Well defined scaling laws clearly appear in wall bounded turbulence, even very close to the wall, where a distinct violation of the refined Kolmogorov similarity hypothesis (RKSH) occurs together with the simultaneous persistence of scaling laws. A new form of RKSH for the wall region is here proposed in terms of the structure functions of order two which, in physical terms, confirms the prevailing role of the momentum transfer towards the wall in the near wall dynamics.Comment: 10 pages, 5 figure

A common stochastic process rules gamma-ray burst prompt emission and X-ray flares

Prompt gamma-ray and early X-ray afterglow emission in gamma-ray bursts (GRBs) are characterized by a bursty behavior and are often interspersed with long quiescent times. There is compelling evidence that X-ray flares are linked to prompt gamma-rays. However, the physical mechanism that leads to the complex temporal distribution of gamma-ray pulses and X-ray flares is not understood. Here we show that the waiting time distribution (WTD) of pulses and flares exhibits a power-law tail extending over 4 decades with index ~2 and can be the manifestation of a common time-dependent Poisson process. This result is robust and is obtained on different catalogs. Surprisingly, GRBs with many (>=8) gamma-ray pulses are very unlikely to be accompanied by X-ray flares after the end of the prompt emission (3.1 sigma Gaussian confidence). These results are consistent with a simple interpretation: an hyperaccreting disk breaks up into one or a few groups of fragments, each of which is independently accreted with the same probability per unit time. Prompt gamma-rays and late X-ray flares are nothing but different fragments being accreted at the beginning and at the end, respectively, following the very same stochastic process and likely the same mechanism.Comment: 11 pages, 7 figures, accepted by Ap

On the origin of the difference between time and space

We suggest that the difference between time and space is due to spontaneous symmetry breaking. In a theory with spinors the signature of the metric is related to the signature of the Lorentz-group. We discuss a higher symmetry that contains pseudo-orthogonal groups with arbitrary signature as subgroups. The fundamental asymmetry between time and space arises then as a property of the ground state rather than being put into the formulation of the theory a priori. We show how the complex structure of quantum field theory as well as gravitational field equations arise from spinor gravity - a fundamental spinor theory without a metric.Comment: 4 page