arXiv subjects

G. A. MacLachlan

Publications and source records attributed to G. A. MacLachlan.

7 recordsLinked to original sources

arXiv2015

Gamma-Ray Bursts: Temporal Scales and the Bulk Lorentz Factor

For a sample of Swift and Fermi GRBs, we show that the minimum variability timescale and the spectral lag of the prompt emission is related to the bulk Lorentz factor in a complex manner: For small $Γ$'s, the variability timescale exhibits a shallow (plateau) region. For large $Γ$'s, the variability timescale declines steeply as a function of $Γ$ ($δT\proptoΓ^{-4.05\pm0.64}$). Evidence is also presented for an intriguing correlation between the peak times, t$_p$, of the afterglow emission and the prompt emission variability timescale.

astro-ph.HE↗

arXiv2013

X - Ray Flares and Their Connection With Prompt Emission in GRBs

We use a wavelet technique to investigate the time variations in the light curves from a sample of GRBs detected by Fermi and Swift. We focus primarily on the behavior of the flaring region of Swift-XRT light curves in order to explore connections between variability time scales and pulse parameters (such as rise and decay times, widths, strengths, and separation distributions) and spectral lags. Tight correlations between some of these temporal features suggest a common origin for the production of X-ray flares and the prompt emission.

astro-ph.HE↗

arXiv2013

A New Correlation Between GRB X-Ray Flares And The Prompt Emission

From a sample of GRBs detected by the $Fermi$ and $Swift$ missions, we have extracted the minimum variability time scales for temporal structures in the light curves associated with the prompt emission and X-ray flares. A comparison of this variability time scale with pulse parameters such as rise times,determined via pulse-fitting procedures, and spectral lags, extracted via the cross-correlation function (CCF), indicate a tight correlation between these temporal features for both the X-ray flares and the prompt emission. These correlations suggests a common origin for the production of X-ray flares and the prompt emission in GRBs.

astro-ph.HE↗

arXiv2013

Minimum Variability Time Scales of Long and Short GRBs

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, that variabilities on the order of a few milliseconds are not uncommon, and that an intriguing relationship exists between the minimum variability time and the burst duration.

astro-ph.HE↗

arXiv2012

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 GBM GRB light curves comprised of 379 pulses. Pulses used in this study were fitted with log-normal 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.

astro-ph.HE↗

arXiv2011

The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles

In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam-monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cerenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed.

nucl-ex↗

arXiv2005

Strangeness contribution to the vector and axial form factors of the nucleon

The strangeness contribution to the vector and axial form factors of the nucleon is presented for momentum transfers in the range $0.45<Q^2<1.0$ GeV$^2$. The results are obtained via a combined analysis of forward-scattering parity-violating elastic $\vec{e}p$ asymmetry data from the $G^0$ and HAPPEx experiments at Jefferson Lab, and elastic $νp$ and $\barν p$ scattering data from Experiment 734 at Brookhaven National Laboratory. The parity-violating asymmetries measured in elastic $\vec{e}p$ scattering at forward angles establish a relationship between the strange vector form factors $G_E^s$ and $G_M^s$, with little sensitivity to the strange axial form factor $G_A^s$. On the other hand, elastic neutrino scattering at low $Q^2$ is dominated by the axial form factor, with still some significant sensitivity to the vector form factors as well. The combination of the two data sets allows the simultaneous extraction of $G_E^s$, $G_M^s$, and $G_A^s$ over a significant range of $Q^2$ for the very first time.

hep-ex↗