Geography, Demography, and Economic Growth in Africa

macroeconomics, Geography, Demography, Economic Growth, Africa

Properties of Gamma-Ray Burst Time Profiles Using Pulse Decomposition Analysis

The time profiles of many gamma-ray bursts consist of distinct pulses, which offers the possibility of characterizing the temporal structure of these bursts using a relatively small set of pulse shape parameters. This pulse decomposition analysis has previously been performed on a small sample of bright long bursts using binned data from BATSE, which comes in several data types, and on a sample of short bursts using the BATSE Time-Tagged Event (TTE) data type. We have developed an interactive pulse-fitting program using the phenomenological pulse model of Norris, et al. and a maximum-likelihood fitting routine. We have used this program to analyze the Time-to-Spill (TTS) data for all bursts observed by BATSE up through trigger number 2000, in all energy channels for which TTS data is available. We present statistical information on the attributes of pulses comprising these bursts, including relations between pulse characteristics in different energy channels and the evolution of pulse characteristics through the course of a burst. We carry out simulations to determine the biases that our procedures may introduce. We find that pulses tend to have shorter rise times than decay times, and tend to be narrower and peak earlier at higher energies. We also find that pulse brightness, pulse width, and pulse hardness ratios do not evolve monotonically within bursts, but that the ratios of pulse rise times to decay times tend to decrease with time within bursts.Comment: 40 pages, 19 figures. Submitted to Astrophysical Journal. PostScript and PDF with un-bitmapped figures available at http://www.slac.stanford.edu/pubs/slacpubs/8000/slac-pub-8364.html . Accompanying paper astro-ph/0002218 available at http://www.slac.stanford.edu/pubs/slacpubs/8000/slac-pub-8365.htm

On the Evidence for Axion-like Particles from Active Galactic Nuclei

Burrage, Davis, and Shaw recently suggested exploiting the correlations between high and low energy luminosities of astrophysical objects to probe possible mixing between photons and axion-like particles (ALP) in magnetic field regions. They also presented evidence for the existence of ALP's by analyzing the optical/UV and X-ray monochromatic luminosities of AGNs. We extend their work by using the monochromatic luminosities of 320 unobscured Active Galactic Nuclei from the Sloan Digital Sky Survey/Xmm-Newton Quasar Survey (Young et al., 2009), which allows the exploration of 18 different combinations of optical/UV and X-ray monochromatic luminosities. However, we do not find compelling evidence for the existence of ALPs. Moreover, it appears that the signal reported by Burrage et al. is more likely due to X-ray absorption rather than to photon-ALP oscillation.Comment: 16 pages, 12 figures. Updated to reflect the minor changes introduced in the published versio

Discovery of a supernova associated with GRB 031203: SMARTS Optical-Infrared Lightcurves from 0.2 to 92 days

Optical and infrared monitoring of the afterglow site of gamma-ray burst (GRB) 031203 has revealed a brightening source embedded in the host galaxy, which we attribute to the presence of a supernova (SN) related to the GRB ("SN 031203"). We present details of the discovery and evolution of SN 031203 from 0.2 to 92 days after the GRB, derived from SMARTS consortium photometry in I and J bands. A template type Ic lightcurve, constructed from SN 1998bw photometry, is consistent with the peak brightness of SN 031203 although the lightcurves are not identical. Differential astrometry reveals that the SN, and hence the GRB, occurred less than 300 h_71^-1 pc (3-sigma) from the apparent galaxy center. The peak of the supernova is brighter than the optical afterglow suggesting that this source is intermediate between a strong GRB and a supernova.Comment: 11 pages, 3 figures, submitted to ApJ Letter

Expected characteristics of the subclass of Supernova Gamma-ray Bursts (S-GRBs)

The spatial and temporal coincidence between the gamma-ray burst (GRB) 980425 and supernova (SN) 1998bw has prompted speculation that there exists a class of GRBs produced by SNe (``S-GRBs''). Robust arguments for the existence of a relativistic shock have been presented on the basis of radio observations. A physical model based on the radio observations lead us to propose the following characteristics of supernovae GRBs (S-GRBs): 1) prompt radio emission and implied brightness temperature near or below the inverse Compton limit, 2) high expansion velocity of the optical photosphere as derived from lines widths and energy release larger than usual, 3) no long-lived X-ray afterglow, and 4) a single pulse (SP) GRB profile. Radio studies of previous SNe show that only type Ib and Ic potentially satisfy the first condition. Accordingly we have investigated proposed associations of GRBs and SNe finding no convincing evidence (mainly to paucity of data) to confirm any single connection of a SN with a GRB. If there is a more constraining physical basis for the burst time-history of S-GRBs beyond that of the SP requirement, we suggest the 1% of light curves in the BATSE catalogue similar to that of GRB 980425 may constitute the subclass. Future optical follow-up of bursts with similar profiles should confirm if such GRBs originate from some fraction of SN type Ib/Ic.Comment: 11 pages of LaTeX with 1 figure. Submitted to the Astrophysical Journal Letter

Dust and dark Gamma-Ray Bursts: mutual implications

In a cosmological context dust has been always poorly understood. That is true also for the statistic of GRBs so that we started a program to understand its role both in relation to GRBs and in function of z. This paper presents a composite model in this direction. The model considers a rather generic distribution of dust in a spiral galaxy and considers the effect of changing some of the parameters characterizing the dust grains, size in particular. We first simulated 500 GRBs distributed as the host galaxy mass distribution, using as model the Milky Way. If we consider dust with the same properties as that we observe in the Milky Way, we find that due to absorption we miss about 10% of the afterglows assuming we observe the event within about 1 hour or even within 100s. In our second set of simulations we placed GRBs randomly inside giants molecular clouds, considering different kinds of dust inside and outside the host cloud and the effect of dust sublimation caused by the GRB inside the clouds. In this case absorption is mainly due to the host cloud and the physical properties of dust play a strong role. Computations from this model agree with the hypothesis of host galaxies with extinction curve similar to that of the Small Magellanic Cloud, whereas the host cloud could be also characterized by dust with larger grains. To confirm our findings we need a set of homogeneous infrared observations. The use of coming dedicated infrared telescopes, like REM, will provide a wealth of cases of new afterglow observations.Comment: 16 pages, 8 figures, accepted by A&

GRB Energetics and the GRB Hubble Diagram: Promises and Limitations

We present a complete sample of 29 GRBs for which it has been possible to determine temporal breaks (or limits) from their afterglow light curves. We interpret these breaks within the framework of the uniform conical jet model, incorporating realistic estimates of the ambient density and propagating error estimates on the measured quantities. In agreement with our previous analysis of a smaller sample, the derived jet opening angles of those 16 bursts with redshifts result in a narrow clustering of geometrically-corrected gamma-ray energies about E_gamma = 1.33e51 erg; the burst-to-burst variance about this value is a factor of 2.2. Despite this rather small scatter, we demonstrate in a series of GRB Hubble diagrams, that the current sample cannot place meaningful constraints upon the fundamental parameters of the Universe. Indeed for GRBs to ever be useful in cosmographic measurements we argue the necessity of two directions. First, GRB Hubble diagrams should be based upon fundamental physical quantities such as energy, rather than empirically-derived and physically ill-understood distance indicators. Second, a more homogeneous set should be constructed by culling sub-classes from the larger sample. These sub-classes, though now first recognizable by deviant energies, ultimately must be identifiable by properties other than those directly related to energy. We identify a new sub-class of GRBs (``f-GRBs'') which appear both underluminous by factors of at least 10 and exhibit a rapid fading at early times. About 10-20% of observed long-duration bursts appear to be f-GRBs.Comment: Accepted to the Astrophysical Journal (20 May 2003). 19 pages, 3 Postscript figure

Investigation of laser dynamics, modulation and control by means of intra-cavity time varying perturbation

The generation of tunable visible, infrared, and ultraviolet light is examined, along with the control of this light by means of novel mode-locking and modulation techniques. Transient mode-locking of the Nd:YAG laser and generation of short tunable pulses in the visible and the alkali metal inert gas excimer laser systems were investigated. Techniques for frequency conversion of high power and high energy laser radiation are discussed, along with high average power blue and UV laser light sources

Scaling and Duality in Semi-exclusive Processes

We discuss extending scaling and duality studies to semi-exclusive processes. We show that semi-exclusive hard pion photoproduction should exhibit scaling behavior in kinematic regions where the photon and pion both interact directly with the same quark. We show that such kinematic regions exist. We also show that the constancy with changing momentum transfer of the resonance peak/scaling curve ratio, familiar for many resonances in deep inelastic scattering, is also expected in the semi-exclusive case.Comment: 8 pages, 4 figures, submitted to Phys.Rev.