The Edge of a Gamma Ray Burst Afterglow

We discuss the formation of spectral features in the decelerating ejecta of gamma-ray bursts, including the possible effect of inhomogeneities. These should lead to blueshifted and broadened absorption edges and resonant features, especially from H and He. An external neutral ISM could produce detectable H and He, as well as Fe X-ray absorption edges and lines. Hypernova scenarios may be diagnosed by Fe K-$\alpha$ and H Ly-$\alpha$ emission lines.Comment: M.N.R.A.S., accepted July 16 1998; submitted June 4 1998; latex, 11 page

Gamma-ray bursts as X-ray depth-gauges of the Universe

We discuss the X-ray flux of gamma-ray burst afterglows at redshifts in the range 3-30, including the effects of the intergalactic He II absorption. We point out that strong X-ray lines may form locally in burst afterglows starting minutes after the trigger. This can provide distinctive X-ray distance indicators out to the redshifts where the first generation of massive stars form.Comment: ApJ(Lett) in press 5/31/03; subm. 5/7/0

Delayed Gev Emission from Cosmological Gamma-Ray Bursts : Impact of a Relativistic Wind on External Matter

Sudden collapse of a compact object, or coalescence of a compact binary, can generate an unsteady relativistic wind that lasts for a few seconds. The wind is likely to carry a high magnetic field; and its Lorentz factor depends on the extent to which it is 'loaded' with baryons. If the Lorentz factor is $\sim 100$, internal dissipation and shocks in this wind produce a non-thermal gamma-ray burst, detectable in the range 0.1\MeV \siml E_\gamma \siml 0.1-1\GeV out to cosmological distances. The cooled wind ejecta would subsequently be decelerated by the external medium. The resultant blast wave and reverse shock can then give rise to a second burst component, mainly detectable in the GeV range, with a time delay relative to the MeV burst ranging from minutes to hours.Comment: 5 pages, plain Te

Gamma-Ray Bursts: Multiwaveband Spectral Predictions for Blast Wave Models

In almost any scenario for 'cosmological' gamma-ray bursts (and in many models where they originate in our own Galaxy), the initial energy density is so large that the resulting relativistic plasma expands with $v\sim c$ producing a blast wave ahead of it and a reverse shock moving into the ejecta, as it ploughs into the external medium. We evaluate the radiation expected from these shocks,for both cosmological and galactic bursts, for various assumptions about the strength of the magnetic field and the particle acceleration mechanisms in the shocks. The spectra are evaluated over the whole range from the IR to $>$ GeV, and are compared with the variety of spectral behavior reported by BATSE, and with the X-ray and optical constraints. For bursts of duration \simg 1\s acceptable $\gamma$-ray spectra and $L_x/L_\gamma$ ratios are readily obtained for 'cosmological' models. Blast waves in galactic models can produce bursts of similar gamma-ray fluence and duration, but they violate the X-ray paucity constraint, except for the shorter bursts (\siml 1\s). We discuss the prospects for using O/UV and X-ray observations to discriminate among alternative models.Comment: 7 pages with one figure (figure in uuencoded compressed postscript file),te

Collapsar Jets, Bubbles and Fe Lines

In the collapsar scenario, gamma ray bursts are caused by relativistic jets expelled along the rotation axis of a collapsing stellar core. We discuss how the structure and time-dependence of such jets depends on the stellar envelope and central engine properties, assuming a steady jet injection. It takes a few seconds for the jet to bore its way through the stellar core; most of the energy output during that period goes into a cocoon of relativistic plasma surrounding the jet. This material subsequently forms a bubble of magnetized plasma that takes several hours to expand, subrelativistically, through the envelope of a high-mass supergiant. Jet break-through and a conventional burst would be expected not only in He stars but possibly also in blue supergiants. Shock waves and magnetic dissipation in the escaping bubble can contribute a non thermal UV/X-ray afterglow, and also excite Fe line emission from thermal gas, in addition to the standard jet deceleration power-law afterglow.Comment: Ap.J. Letters, accepted 6/20/01, first subm 4/24/01; aaspp4, 9 pages, no figures; minor revision

Internal Migration and Regional Population Dynamics in Europe: United Kingdom Case Study

This case study examines recent population change patterns and internal migration activity in the United Kingdom. A wealth of knowledge about population dynamics in Britain is revealed. The spatial patterns of population change and net migration are intricate mosaics of gains and losses. Gains and losses in population were principally determined by net internal migration. The decade long population change patterns and one year long migration patterns were in close agreement. This was surprising in view of temporal instability in population change and migration patterns. The dominant spatial pattern was one of deconcentration from the cores of city regions to hinterlands for both the largest metropolises and also their subsidiary partner cities. There were also signs of loss in population and migrants in declining resource regions(former mining areas, fishing ports) and gains in new resource frontiers - particularly in northeast Scotland reflecting the vigorous development of onshore facilities for the offshore oil and gas fields of the North Sea. The pattern of overall population and migrant redistribution was predominantly that of the middle labour force/family ages reinforced at much lower mobility levels but with sharper patterns of redistribution by the pre-retirement and retirement ages. People in the young adult ages in contrast redistributed to different destinations, showing a unique shift to the dense neighbourhoods of big cities. With respect to the urban system, there was significant redistribution both downward and outward. Downward redistribution meant shifts from large metropolitan cities to medium and small sized freestanding cities. Outward redistribution meant shifts to the outer commuting rings around cities, often deep into the countryside, This was not a return to the rural idyll, merely the expansion of the daily urban systems to cover most of lowland Britain. Strong preferences for low density living were revealed by shifts towards districts in Rural Areas and by net flows to low density wards and sectors. Similar strong shifts out of areas of above average into below average unemployment were detected, though both relationships with density and unemployment were either not present or weak for young adults. Some ambiguity was revealed in the fortunes of Inner London areas. Migration data from the 1991 Census showed intense outward movement. Downward population shifts were on a lesser scale because of the compensating effects of higher than average natural increase and high immigration. However, a re-analysis of 1991 population by ONS led to a substantial upward revision of London borough populations, and so places doubt on the size of outward shift of population through internal migration

A New Classification Of UK Local Authorities Using 2001 Census Key Statistics

The 2001 Census has been successfully administered and the Census Organisations are currently engaged in processing the returns. A very large and rich dataset will be produced for the 58,789,194 people of the UK. The Census Area Statistics, for example, delivers 190 tables containing about 6 thousand unique counts relating to the characteristics of the UK population, for output areas and all higher geographies. This paper represents the first results of a project that aims to develop, in collaboration with the Office for National Statistics, a set of general purpose classifications at different geographic scales, including households, neighbourhoods, wards, local authorities and to link the classifications at different levels together. The paper reports on the methods used and results of a classification of the UK’s 434 Local Authorities, using the Key Statistics released in February 2003. This initial classification and description of methods will feed into the ONS/GROS/NISRA project to classify Local Authorities for the whole UK. Further data or digital versions of the classification system are available on request

Creating the National Classification of Census Output Areas: Data, Methods and Results

The purpose of this paper is to describe and explain the processes and decisions that were involved in the creation of the National Area Classification of 2001 Census Output Areas (OAs). The project was carried out on behalf of the Office for National Statistics (ONS) by Daniel Vickers of the School of Geography, University of Leeds as part of his PhD. thesis. The paper describes the creation of the classification: selection of the variables, assembly of the classification database, the methods of standardisation and the clustering procedures, some discussion of alternative methodologies that were considered for use. The processes used for creating the clusters, their naming and description are outlined. The classification is mapped and visualised in a number of different ways. The OA Classification fits into the ONS suite of area classifications complementing published classifications at Local Authority, Health Authority and Ward levels. The classification is freely available, and can be downloaded from the ONS Neighbourhood Statistics website at www.statistics.gov.uk