The Hurst exponent of Fermi gamma-ray bursts MacLachlan, G. A.; Shenoy, A.; Sonbas, E. ...
Monthly notices of the Royal Astronomical Society,
12/2013, Letnik:
436, Številka:
4
Journal Article
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Using a wavelet decomposition technique, we have extracted the Hurst exponent for a sample of 46 long and 22 short gamma-ray bursts (GRBs) detected by the Gamma-ray Burst Monitor aboard the Fermi ...satellite. This exponent is a scaling parameter that provides a measure of long-range behaviour in a time series. The mean Hurst exponent for the short GRBs is significantly smaller than that for the long GRBs. The separation may serve as an unbiased criterion for distinguishing short and long GRBs. PUBLICATION ABSTRACT
In an exclusive measurement of the reaction gammad-->K(+)K(-)pn, a narrow peak that can be attributed to an exotic baryon with strangeness S=+1 is seen in the K(+)n invariant mass spectrum. The peak ...is at 1.542+/-0.005 GeV/c(2) with a measured width of 0.021 GeV/c(2) FWHM, which is largely determined by experimental mass resolution. The statistical significance of the peak is (5.2+/-0.6)sigma. The mass and width of the observed peak are consistent with recent reports of a narrow S=+1 baryon by other experimental groups.
From a sample of gamma-ray bursts (GRBs) detected by the Fermi and Swift missions, we have extracted the minimum variability timescales for temporal structures in the light curves associated with the ...prompt emission and X-ray flares. A comparison of this variability timescale with pulse parameters such as rise times, determined via pulse-fitting procedures, and spectral lags, extracted via the cross-correlation function, indicates a tight correlation between these temporal features for both the X-ray flares and the prompt emission. These correlations suggest a common origin for the production of X-ray flares and the prompt emission in GRBs.
The neutron elastic magnetic form factor was extracted from quasielastic electron scattering on deuterium over the range Q2=1.0-4.8 GeV2 with the CLAS detector at Jefferson Lab. High precision was ...achieved with a ratio technique and a simultaneous in situ calibration of the neutron detection efficiency. Neutrons were detected with electromagnetic calorimeters and time-of-flight scintillators at two beam energies. The dipole parametrization gives a good description of the data.
The longitudinal target-spin asymmetry AUL for the exclusive electroproduction of high-energy photons was measured for the first time in ep-->e;'pgamma. The data have been accumulated at JLab with ...the CLAS spectrometer using 5.7 GeV electrons and a longitudinally polarized NH3 target. A significant azimuthal angular dependence was observed, resulting from the interference of the deeply virtual Compton scattering and Bethe-Heitler processes. The amplitude of the sinvarphi moment is 0.252+/-0.042stat+/-0.020sys. Theoretical calculations are in good agreement with the magnitude and the kinematic dependence of the target-spin asymmetry, which is sensitive to the generalized parton distributions H and H.
We have studied power density spectra (PDS) of 206 long gamma-ray bursts. We fitted the PDS with a simple power law and extracted the exponent of the power law (α) and the noise-crossing threshold ...frequency (f
th). We find that the distribution of the extracted α peaks around −1.4 and that of f
th around 1 Hz. In addition, based on a subset of 58 bursts with known redshifts, we show that the redshift-corrected threshold frequency is positively correlated with the isotropic peak luminosity. The correlation coefficient is 0.57 ± 0.03.
We report measurements of the beam spin asymmetry in deeply virtual Compton scattering (DVCS) at an electron beam energy of 4.8 GeV using the CLAS detector at the Thomas Jefferson National ...Accelerator Facility. The DVCS beam spin asymmetry has been measured in a wide range of kinematics, 1.0<Q{sup 2}<2.8 (GeV/c){sup 2}, 0.12<x{sub B}<0.48, and 0.1<-t<0.8 (GeV/c){sup 2}, using the reaction e-vector p{yields}e{sup '}pX. The number of H(e,e{sup '}{gamma}p) and H(e,e{sup '}{pi}{sup 0}p) events are separated in each (Q{sup 2},x{sub B},t) bin by a fit to the line shape of the H(e,e{sup '}p)X M{sub x}{sup 2} distribution. The validity of the method was studied in detail using experimental and simulated data. It was shown that with the achieved missing mass squared resolution and the available statistics, the separation of DVCS-Bethe-Heitler and {pi}{sup 0} events can reliably be done with less than 5% uncertainty. Also, the Q{sup 2} and t dependences of the sin{phi} moments of the asymmetry are extracted and compared with theoretical calculations.
Differential cross sections for the reaction gamma p --> eta' p have been measured with the CLAS spectrometer and a tagged photon beam with energies from 1.527 to 2.227 GeV. The results reported here ...possess much greater accuracy than previous measurements. Analyses of these data suggest for the first time the coupling of the eta'N channel to both the S11(1535) and P11(1710) resonances, known to couple strongly to the etaN channel in photoproduction on the proton, and the importance of J = 3/2 resonances in the process.
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