Spectral lag, the time difference between the arrival of high-energy and low-energy photons, is a common feature in gamma-ray bursts (GRBs). Norris et al. reported a correlation between the spectral ...lag and the isotropic peak luminosity of GRBs based on a limited sample. More recently, a number of authors have provided further support for this correlation using arbitrary energy bands of various instruments. In this paper, we report on a systematic extraction of spectral lags based on the largest Swift sample to date of 31 GRBs with measured redshifts. We extracted the spectral lags for all combinations of the standard Swift hard X-ray energy bands: 15-25 keV, 25-50 keV, 50-100 keV, and 100-200 keV and plotted the time dilation corrected lag as a function of isotropic peak luminosity. The mean value of the correlation coefficient for various channel combinations is -0.68 with a chance probability of {approx}0.7 x 10{sup -3}. In addition, the mean value of the power-law index is 1.4 +- 0.3. Hence, our study lends support to the existence of a lag-luminosity correlation, albeit with large scatter.
ABSTRACT Spectral lag, which is defined as the difference in time of arrival of high- and low-energy photons, is a common feature in gamma-ray bursts (GRBs). Previous investigations have shown a ...correlation between this lag and the isotropic peak luminosity for long duration bursts. However, most of the previous investigations used lags extracted in the observer frame only. In this work (based on a sample of 43Swift long GRBs with known redshifts), we present an analysis of the lag-luminosity relation in the GRB source frame. Our analysis indicates a higher degree of correlation -0.82 ± 0.05 (chance probability of 5.5 × 10-5) between the spectral lag and the isotropic peak luminosity,L iso, with a best-fitting power-law index of -1.2 ± 0.2, such thatL isolag-1.2. In addition, there is an anticorrelation between the source-frame spectral lag and the source-frame peak energy of the burst spectrum,E pk(1 +z ). PUBLICATION ABSTRACT
We have investigated the time variations in the light curves from a sample of long and short Fermi/GBM gamma-ray bursts (GRBs) using an impartial wavelet analysis. The results indicate that in the ...source frame, the variability time-scales for long bursts differ from that for short bursts, variabilities of the order of a few milliseconds are not uncommon and an intriguing relationship exists between the minimum variability time and the burst duration.
ABSTRACT
We present a direct link between the minimum variability time‐scales extracted through a wavelet decomposition and the rise times of the shortest pulses extracted via fits of 34 Fermi ...Gamma‐ray Burst Monitor (GBM) Gamma‐Ray Burst (GRB) light curves comprised of 379 pulses. Pulses used in this study were fitted with lognormal functions, whereas the wavelet technique used employs a multiresolution analysis that does not rely on identifying distinct pulses. By applying a corrective filter to published data fitted with pulses, we demonstrate agreement between these two independent techniques and offer a method for distinguishing signal from noise.
Spectral lag, which is defined as the difference in time of arrival of high- and low-energy photons, is a common feature in gamma-ray bursts (GRBs). Previous investigations have shown a correlation ...between this lag and the isotropic peak luminosity for long duration bursts. However, most of the previous investigations used lags extracted in the observer frame only. In this work (based on a sample of 43 Swift long GRBs with known redshifts), we present an analysis of the lag-luminosity relation in the GRB source frame. Our analysis indicates a higher degree of correlation −0.82 ± 0.05 (chance probability of ∼5.5 × 10−5) between the spectral lag and the isotropic peak luminosity, L
iso, with a best-fitting power-law index of −1.2 ± 0.2, such that L
iso ∝ lag−1.2. In addition, there is an anticorrelation between the source-frame spectral lag and the source-frame peak energy of the burst spectrum, E
pk(1 + z).
Curvature effects in gamma-ray bursts (GRBs) have long been a source of considerable interest. In a collimated relativistic GRB jet, photons that are off-axis relative to the observer arrive at later ...times than on-axis photons and are also expected to be spectrally softer. In this work, we invoke a relatively simple kinematic two-shell collision model for a uniform jet profile and compare its predictions to GRB prompt-emission data for observations that have been attributed to curvature effects such as the peak-flux-peak-frequency relation, i.e., the relation between the nuF sub(nu) flux and the spectral peak, E sub(pk) in the decay phase of a GRB pulse, and spectral lags. In addition, we explore the behavior of pulse widths with energy. We present the case of the single-pulse Fermi GRB 110920 as a test for the predictions of the model against observations.
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
Recenzirano
Odprti dostop
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
The dilogarithm function for complex argument Maximon, Leonard C
Proceedings of the Royal Society. A, Mathematical, physical, and engineering sciences,
11/2003, Letnik:
459, Številka:
2039
Journal Article
Recenzirano
This paper summarizes the basic properties of the Euler dilogarithm function, often referred to as the Spence function. These include integral representations, series expansions, linear and quadratic ...transformations, functional relations, numerical values for special arguments and relations to the hypergeometric and generalized hypergeometric function. The basic properties of the two functions closely related to the dilogarithm (the inverse tangent integral and Clausen's integral) are also included. A brief summary of the defining equations and properties for the frequently used generalizations of the dilogarithm (polylogarithm, Nielsen's generalized polylogarithm, Jonquière's function, Lerch's function) is also given. A résumé of the earliest articles that consider the integral defining this function, from the late seventeenth century to the early nineteenth century, is presented. Critical references to details concerning these functions and their applications in physics and mathematics are listed.
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.
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