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Author

P. J. Brown

Bio: P. J. Brown is an academic researcher. The author has contributed to research in topics: Gamma-ray burst. The author has an hindex of 1, co-authored 3 publications receiving 4 citations.

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Journal ArticleDOI
TL;DR: In this article, the observed properties of the optical and X-ray afterglows of short and long-duration {gamma}-ray bursts (GRBs) were compared.
Abstract: We present a comparative study of the observed properties of the optical and X-ray afterglows of short- and long-duration {gamma}-ray bursts (GRBs). Using a large sample of 37 short and 421 long GRBs, we find a strong correlation between the afterglow brightness measured after 11 hr and the observed fluence of the prompt emission. Both the optical (R band) and X-ray flux densities (F{sub R} and F{sub X} ) scale with the {gamma}-ray fluence, F {sub {gamma}}. For bursts with a known redshift, a tight correlation exists between the afterglow flux densities at 11 hr (rest frame) and the total isotropic {gamma}-ray energy, E {sub {gamma}}{sub ,ISO}: F {sub R,X} {proportional_to} E {sub {gamma}}{sub ,ISO} {sup {alpha}}, with {alpha} {approx_equal} 1. The constant of proportionality is nearly identical for long and short bursts, when E {sub {gamma}}{sub ,ISO} is obtained from the Swift data. Additionally, we find that for short busts with F {sub {gamma}} {approx}> 10{sup -7} erg cm{sup -2}, optical afterglows are nearly always detected by reasonably deep early observations. Finally, we show that the ratio F{sub R} /F{sub X} has very similar values for short and long bursts. These results are difficult to explain in the frameworkmore » of the standard scenario, since they require that either (1) the number density of the surrounding medium of short bursts is typically comparable to, or even larger than the number density of long bursts; (2) short bursts explode into a density profile, n(r) {proportional_to} r {sup -2}; or (3) the prompt {gamma}-ray fluence depends on the density of the external medium. We therefore find it likely that either basic assumptions on the properties of the circumburst environment of short GRBs or else the standard models of GRB emission must be re-examined. We believe that the most likely solution is that the ambient density surrounding typical short bursts is higher than has generally been expected: a typical value of {approx}1 cm{sup -3} is indicated. We discuss recent modifications to the standard binary merger model for short bursts which may be able to explain the implied density.« less

183 citations

Journal ArticleDOI
TL;DR: Two separate analyses using the half-complete IceCube detector produced no evidence for neutrinos from pγ interactions in the prompt phase of the gamma-ray burst fireball.
Abstract: IceCube has become the first neutrino telescope with a sensitivity below the TeV neutrino flux predicted from gamma-ray bursts if gamma-ray bursts are responsible for the observed cosmic-ray flux above 10(18) eV. Two separate analyses using the half-complete IceCube detector, one a dedicated search for neutrinos from p gamma interactions in the prompt phase of the gamma-ray burst fireball and the other a generic search for any neutrino emission from these sources over a wide range of energies and emission times, produced no evidence for neutrino emission, excluding prevailing models at 90% confidence.

148 citations

Journal ArticleDOI
TL;DR: In this paper, afterglow light curves were computed using a single-zone approximation for the shocked region or a detailed multizone method that more accurately accounts for the compression of the material.
Abstract: Context. GRB 080503, detected by Swift, belongs to the class of bursts whose prompt phase consists of an initial short spike followed by a longer soft tail. It did not show any transition to a regular afterglow at the end of the prompt emission but exhibited a surprising rebrightening after one day. Aims. We aim to explain this rebrightening with two different scenarios – refreshed shocks or a density clump in the circumburst medium – and two models for the origin of the afterglow, the standard one where it comes from the forward shock, and an alternative one where it results from a long-lived reverse shock. Methods. We computed afterglow light curves either using a single-zone approximation for the shocked region or a detailed multizone method that more accurately accounts for the compression of the material. Results. We find that in several of the considered cases the detailed model must be used to obtain a reliable description of the shock dynamics. The density clump scenario is not favored. We confirm previous results that the presence of the clump has little effect on the forward shock emission, except if the microphysics parameters evolve when the shock enters the clump. Moreover, we find that the rebrightening from the reverse shock is also too weak when it is calculated with the multi-zone method. On the other hand, in the refreshed-shock scenario both the forward and reverse shock models provide satisfactory fits of the data under some additional conditions on the distribution of the Lorentz factor in the ejecta and the beaming angle of the relativistic outflow.

10 citations

Dissertation
01 Jan 2009
TL;DR: In this article, a multivariate data analysis technique, Principal Component Analysis (PCA), is applied to the data in order to determine parameters such as seasonal and diurnal changes which affect the variation of these signals.
Abstract: Very Low Frequency (VLF) radio waves propagate within the Earth-ionosphere waveguide with very little attenuation. Modifications of the waveguide geometry affect the propagation conditions, and hence, the amplitude and phase of VLF signals. Changes in the ionosphere, such as the presence of the D-region during the day, or the precipitation of energetic particles, are the main causes of this modification. Using narrowband receivers monitoring remote VLF transmitters, the amplitude and phase of these signals are recorded. A multivariate data analysis technique, Principal Component Analysis (PCA), is applied to the data in order to determine parameters such as seasonal and diurnal changes which affect the variation of these signals. Data was then analysed for effects from extragalactic gamma ray bursts, terrestrial gamma ray flashes and solar flares. Only X-rays from solar flares were shown to have an appreciable affect on ionospheric propagation.

1 citations