Properties of the Intergalactic Magnetic Field Constrained by Gamma-ray Observations of Gamma-Ray Bursts

The magnetic field in intergalactic space gives important information about magnetogenesis in the early universe. The properties of this field can be probed by searching for radiation of secondary e$^+$e$^-$ pairs created by TeV photons, that produce GeV range radiation by Compton-scattering cosmic microwave background (CMB) photons. The arrival times of the GeV "echo" photons depend strongly on the magnetic field strength and coherence length. A Monte Carlo code that accurately treats pair creation is developed to simulate the spectrum and time-dependence of the echo radiation. The extrapolation of the spectrum of powerful gamma-ray bursts (GRBs) like GRB 130427A to TeV energies is used to demonstrate how the IGMF can be constrained if it falls in the $10^{-21}$ - $10^{-17}$ G range for 1 Mpc coherence length.Comment: 8 pages, 6 figure

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.Comment: 7th Huntsville Gamma-Ray Burst Symposium, GRB 2013: paper 15 in eConf Proceedings C130414

Possible optical counterparts of ULXs in NGC 1672

In this study, we use archival data from HST, Chandra, XMM-Newton, and Swift-XRT, to probe the nature of 9 (X1-X9) candidate ULXs in NGC 1672. Our study focuses on using the precise source positions obtained via improved astrometry based on {\it Chandra} and HST observations to search for and identify optical counterparts for these ULXs.Unique optical counterparts are identified for X2 an{d X6; two potential counterparts were determined for X1, X5 and X7 within the respective error radii while no optical counterparts were found for the remaining four sources. Based on spectral energy distributions (SEDs), X-ray and optical temporal analyses, some evidences about the nature of X1 and X2 were obtained.Comment: To appear in Astronomische Nachrichten / Astronomical Notes (AN). arXiv admin note: substantial text overlap with arXiv:2207.0630

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 $\Gamma$'s, the variability timescale exhibits a shallow (plateau) region. For large $\Gamma$'s, the variability timescale declines steeply as a function of $\Gamma$ ($\delta T\propto\Gamma^{-4.05\pm0.64}$). Evidence is also presented for an intriguing correlation between the peak times, t$_p$, of the afterglow emission and the prompt emission variability timescale.Comment: Accepted for publication in Ap

Screening High-z GRBs with BAT Prompt Emission Properties

Detecting high-z GRBs is important for constraining the GRB formation rate, and tracing the history of re-ionization and metallicity of the universe. Based on the current sample of GRBs detected by Swift with known redshifts, we investigated the relationship between red-shift, and spectral and temporal characteristics, using the BAT event-by-event data. We found red-shift trends for the peak-flux-normalized temporal width T90, the light curve variance, the peak flux, and the photon index in simple power-law fit to the BAT event data. We have constructed criteria for screening GRBs with high red-shifts. This will enable us to provide a much faster alert to the GRB community of possible high-z bursts.Comment: 4 pages, 4 figures, to be published in the proceedings of ''Gamma Ray Bursts 2007'', Santa Fe, New Mexico, November 5-