A search for thermal X-ray signatures in Gamma-Ray Bursts I: Swift bursts with optical supernovae

The X-ray spectra of Gamma-Ray Bursts can generally be described by an absorbed power law. The landmark discovery of thermal X-ray emission in addition to the power law in the unusual GRB 060218, followed by a similar discovery in GRB 100316D, showed that during the first thousand seconds after trigger the soft X-ray spectra can be complex. Both the origin and prevalence of such spectral components still evade understanding, particularly after the discovery of thermal X-ray emission in the classical GRB 090618. Possibly most importantly, these three objects are all associated with optical supernovae, begging the question of whether the thermal X-ray components could be a result of the GRB-SN connection, possibly in the shock breakout. We therefore performed a search for blackbody components in the early Swift X-ray spectra of 11 GRBs that have or may have associated optical supernovae, accurately recovering the thermal components reported in the literature for GRBs 060218, 090618 and 100316D. We present the discovery of a cooling blackbody in GRB 101219B/SN2010ma, and in four further GRB-SNe we find an improvement in the fit with a blackbody which we deem possible blackbody candidates due to case-specific caveats. All the possible new blackbody components we report lie at the high end of the luminosity and radius distribution. GRB 101219B appears to bridge the gap between the low-luminosity and the classical GRB-SNe with thermal emission, and following the blackbody evolution we derive an expansion velocity for this source of order 0.4c. We discuss potential origins for the thermal X-ray emission in our sample, including a cocoon model which we find can accommodate the more extreme physical parameters implied by many of our model fits.Comment: 16 pages, 6 figures, accepted for MNRA

Interferometric weak value deflections: quantum and classical treatments

We derive the weak value deflection given in a paper by Dixon et al. (Phys. Rev. Lett. 102, 173601 (2009)) both quantum mechanically and classically. This paper is meant to cover some of the mathematical details omitted in that paper owing to space constraints

All Optical Waveguiding in a Coherent Atomic Rubidium Vapor

We demonstrate an all optical waveguide imprinted by a low power Laguerre Gaussian control laser beam using a coherent Raman process in warm atomic rubidium vapor. We show that the signal beam propagates with a small spot size over several diffraction lengths. We also show that the coupling efficiency of the signal beam into the waveguide varies linearly with the signal power

The extinction properties of long GRB host galaxies from H and He I recombination lines

In this paper we show how a self-consistent treatment of hydrogen and helium emission line fluxes of the hosts of long gamma-ray bursts can result in improved understanding of the dust properties in these galaxies. In particular, we find that even with modest signal to noise spectroscopy we can differentiate different values for R_V, the ratio of total to selective extinction. The inclusion of Paschen and Brackett lines, even at low signal to noise, greatly increase the accuracy of the derived reddening. This method is often associated with strong systematic errors, caused by the need for multiple instruments to cover the wide wavelength range, the requirement to separate stellar hydrogen absorption from the nebular emission, and because of the dependancy of the predicted line fluxes on the electron temperature. We show how these three systematic errors can be negated, by using suitable instrumentation (in particular X-shooter on the Very Large Telescope) and wide wavelength coverage. We demonstrate this method using an extensive optical and near-infrared spectroscopic campaign of the host galaxy of gamma-ray burst 060218 (SN 2006aj), obtained with FORS1, UVES and ISAAC on the VLT, covering a broad wavelength range with both high and low spectral resolution. We contrast our findings of this source with X-shooter data of a star forming region in the host of GRB 100316D, and show the improvement over existing published fluxes of long GRB hosts.Comment: 10 pages, 7 figures; accepted for publication in MNRA

VCBART: Bayesian trees for varying coefficients

Many studies have reported associations between later-life cognition and socioeconomic position in childhood, young adulthood, and mid-life. However, the vast majority of these studies are unable to quantify how these associations vary over time and with respect to several demographic factors. Varying coefficient (VC) models, which treat the covariate effects in a linear model as nonparametric functions of additional effect modifiers, offer an appealing way to overcome these limitations. Unfortunately, state-of-the-art VC modeling methods require computationally prohibitive parameter tuning or make restrictive assumptions about the functional form of the covariate effects. In response, we propose VCBART, which estimates the covariate effects in a VC model using Bayesian Additive Regression Trees. With simple default hyperparameter settings, VCBART outperforms existing methods in terms of covariate effect estimation and prediction. Using VCBART, we predict the cognitive trajectories of 4,167 subjects from the Health and Retirement Study using multiple measures of socioeconomic position and physical health. We find that socioeconomic position in childhood and young adulthood have small effects that do not vary with age. In contrast, the effects of measures of mid-life physical health tend to vary with respect to age, race, and marital status. An R package implementing VC-BART is available at https://github.com/skdeshpande91/VCBAR

Swift captures the spectrally evolving prompt emission of GRB 070616

The origins of Gamma-ray Burst prompt emission are currently not well understood and in this context long, well-observed events are particularly important to study. We present the case of GRB 070616, analysing the exceptionally long-duration multipeaked prompt emission, and later afterglow, captured by all the instruments on-board Swift and by Suzaku WAM. The high energy light curve remained generally flat for several hundred seconds before going into a steep decline. Spectral evolution from hard to soft is clearly taking place throughout the prompt emission, beginning at 285 s after the trigger and extending to 1200 s. We track the movement of the spectral peak energy, whilst observing a softening of the low energy spectral slope. The steep decline in flux may be caused by a combination of this strong spectral evolution and the curvature effect. We investigate origins for the spectral evolution, ruling out a superposition of two power laws and considering instead an additional component dominant during the late prompt emission. We also discuss origins for the early optical emission and the physics of the afterglow. The case of GRB 070616 clearly demonstrates that both broadband coverage and good time resolution are crucial to pin down the origins of the complex prompt emission in GRBs.Comment: 13 pages, 11 figures (2 in colour), MNRAS accepte

Robust photometric redshift determinations of gamma-ray burst afterglows at z > 2

Theory suggests that about 10% of Swift-detected gamma-ray bursts (GRBs) will originate at redshifts greater than 5 yet a number of high redshift candidates may be left unconfirmed due to the lack of measured redshifts. Here we introduce our code, GRBz, a method of simultaneous multi-parameter fitting of GRB afterglow optical and near infrared, spectral energy distributions. It allows for early determinations of the photometric redshift, spectral index and host extinction to be made. We assume that GRB afterglow spectra are well represented by a power-law decay and model the effects of absorption due to the Lyman forest and host extinction. We use a genetic algorithm-based routine to simultaneously fit the parameters of interest, and a Monte Carlo error analysis. We use GRBs of previously determined spectroscopic redshifts to prove our method, while also introducing new near infrared data of GRB 990510 which further constrains the value of the host extinction. Our method is effective in estimating the photometric redshift of GRBs, relatively unbiased by assumptions of the afterglow spectral index or the host galaxy extinction. Monte Carlo error analysis is required as the method of error estimate based on the optimum population of the genetic algorithm underestimates errors significantly.Comment: Accepted to A&A: 8 pages, 5 figure

Gas and dust properties in the afterglow spectra of GRB 050730

We present early WHT ISIS optical spectroscopy of the afterglow of gamma-ray burst GRB 050730. The spectrum shows a DLA system with the highest measured hydrogen column to date: N(HI) = 22.1 +/- 0.1 at the third-highest GRB redshift z = 3.968. Our analysis of the Swift XRT X-ray observations of the early afterglow show X-ray flares accompanied by decreasing X-ray absorption. From both the optical and the X-ray spectra we constrain the dust and gas properties of the host galaxy. We find the host to be a low metallicity galaxy, with low dust content. Much of the X-ray absorbing gas is situated close to the GRB, whilst the HI absorption causing the DLA is most likely located further out.Comment: 5 pages, 2 figures. Accepted for A&A Letter