A. Eskandarian

SPECTRAL LAGS AND THE LAG-LUMINOSITY RELATION: AN INVESTIGATION WITH SWIFT BAT GAMMA-RAY BURSTS

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.

Minimum variability time-scales of long and short GRBs

ABSTRACT We have investigated the variability of a sample of long and short Fermi/GBM Gammaray bursts (GRBs) using a fast wavelet technique to determine the smallest timescales. The results indicate different variability time scales for long and short burstsin the source frame and that variabilities on the order of a few milliseconds are notuncommon. The data also indicate an intriguing relation between the variability scaleand the burst duration.Key words: Gamma-ray bursts 1 INTRODUCTIONThe prompt emission from Gamma-ray Bursts (GRBs)shows very complicated time profiles that hitherto elude asatisfactory explanation. Fenimore & Ramirez-Ruiz (2000)reported a correlation between variability of GRBs and thepeak isotropic luminosity. The existence of the variability-luminosity correlation suggests that the prompt emissionlight curve is embedded with temporal information relatedto the microphysics of GRBs. Several models have been pro-posed to explain the observed temporal variability of GRBlightcurves. Leading models such as the internal shock model(reference) and the photospheric model (reference) link therapid variability directly to the activity of the central en-gine. Others invoke relativistic outflow mechanisms to sug-gest that local turbulence amplified through Lorentz boost-ing leads to causally disconnected regions which in turnact as independent centers for the observed prompt emis-sion. In more recent models, both Morsony et al. (2010)and Zhang & Yan (2011) argue that the temporal variabil-ity may show two different scales depending on the physicalmechanisms generating the prompt emission.In order to further our understanding of the promptemission phase of GRBs and to explicitly test some of thekey ingredients in the various models it is clearly importantto extract the variability for both short and long gamma-ray bursts in a robust and unbiased manner. It is also clear

Probing Curvature Effects in the Fermi GRB 110920

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 νF{sub ν} 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 minimum variability time‐scale and its relation to pulse profiles of Fermi GRBs

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.

The Hurst exponent of Fermi gamma-ray bursts

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 (GBM) aboard the Fermi satellite. This exponent is a scaling parameter that provides a measure of long-range behavior 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.

A new frequency–luminosity relation for long gamma-ray bursts?

We have studied power density spectra (PDS) of 206 long Gamma-Ray Bursts (GRBs). We fitted the PDS with a simple power-law and extracted the exponent of the powerlaw (�) and the noise-crossing threshold frequency (fth). We find that the distribution

SENSITIVITY OF THE FERMI DETECTORS TO GAMMA-RAY BURSTS FROM EVAPORATING PRIMORDIAL BLACK HOLES (PBHS)

Primordial Black Holes (PBHs), which may have been created in the early Universe, are predicted to be detectable by their Hawking radiation. The Fermi Gamma-ray Space Telescope observatory offers increased sensitivity to the gamma-ray bursts produced by PBHs with an initial mass of

Spectral Lags of Gamma‐Ray Bursts from Primordial Black Hole (PBH) Evaporations

\sim 5\times 10^{14}

A new frequency-luminosity relation for long gamma-ray bursts?: Frequency-luminosity relation

g expiring today. PBHs are candidate progenitors of unidentified Gamma-Ray Bursts (GRBs) that lack X-ray afterglow. We propose spectral lag, which is the temporal delay between the high and low energy pulses, as an efficient method to identify PBH evaporation events with the Fermi Large Area Telescope (LAT).

THE EINSTEIN–PODOLSKY–ROSEN PROPOSITION ON QUANTUM THEORY AND ITS IMPLICATIONS FOR INTUITIVE CLASSICAL LOGIC

Primordial Black Holes (PBHs), which may have been created in the early Universe, are predicted to be detectable by their Hawking radiation. PBHs with an initial mass of ∼5×1014 g should be expiring today with a burst of high energy particles. Evaporating PBHs in the solar neighborhood are candidate Gamma‐Ray Bursts (GRBs) progenitors. We propose spectral lag, which is the temporal delay between the high energy photon pulse and the low energy photon pulse, as a possible method to detect PBH evaporation events with the Fermi Gamma‐ray Space Telescope Observatory.