This page contains information on 3rd and 4th year projects that I am offering for the 2009/10 academic year. It largely re-iterates the information which you have in the project descriptions, but also goes into some more detail.

MOTIVATION - GAMMA-RAY BURSTS (THIS IS RELEVANT FOR BOTH PROJECTS)

Gamma-ray bursts (GRBs) are the brightest known objects in the universe, releasing as much energy in a few seconds as the sun does in its entire 10 Gyr lifetime. They were first discovered in the 1960s, by US and Russian satellites designed to search for illegal nuclear tests, but which instead located GRBs. GRBs remained largely mysterious until 1997 when they were pinpointed at longer wavelengths (X-ray, optical and radio) by their so-called afterglows. These afterglows provide precise celestial positions for the bursts, and enable us to study their properties in much more detail than was previously. It is breakthroughs since this time which have allowed us to demonstrate that:

• Gamma-ray bursts have total energy releases of >10^47 J if released isotropically, a significant fraction of a solar rest mass!
• GRBs are created in compact regions, and almost certainly involve ultra-relativistic material.
• At least the majority of gamma-ray bursts originate in the core collapse of massive stars, in an unusal kind of supernova, which is sometimes called a hypernova.
• GRBs originate in distant galaxies, with our very recent discovery of the most distant GRB (z~8), being the most distant object ever discovered.

These properteries point to a wide range of uses for GRBs, both in understanding questions in fundamental physics and in contempory cosmology. The two projects being offered address each of these issues. One will aim to provide a better understanding of the progenitors of GRBs via studies of supernova in their afterglows. The second will aim to understand how GRBs are related to star formation throughout the universe.

MPHYS PROJECT - GAMMA-RAY BURSTS AND STAR FORMATION

The determination of the star formation history of the universe is one of the prime goals in contemporary cosmology, and can be addressed from a variety of angles. Most approaches rely on “counting” galaxies of varying star formation rate in differing redshift bins, and computing the total star formation rate per unit volume (or equivalently per unit cosmic time). These surveys inevitably extrapolate to faint galaxies below the survey limits, and suffer from other significant biases. One prime example of this comes from observations in different wavelength regimes. Observations in the sub-mm waveband suggest that the majority of star formation at high redshift occurs in an obscured mode (i.e. in very dusty regions), while observations in the optical do not concur, and can probe only relatively unobscured star formation. In principle the extreme luminosity of gamma-ray bursts neatly side-steps this issue. They are so bright that detection is not commonly problematic, the gamma-rays they emit can stream freely through dusty environments, and they select galaxies independently of the luminosity of the galaxy itself.

However, GRBs are not without biases of their own, and calibrating their use as star formation rate probes is vital in their understanding. The purpose of this project will be to investigate how well gamma-ray bursts trace large scale star formation, and can be approached from a variety of angles. This may involve both the analysis of various existing GRB observations, for example studies of the properties of GRB host galaxies and their large scale environments. It will also be important to compare these to the results from other ongoing surveys, such as the Hubble Ultra Deep field. The ultimate aim is to build a model for the fraction of star formation as traced by gamma-ray bursts as a function of redshift (potentially including more complex selection functions).

To undertake this project you will need to use the CSC computer system and common astronomical software packages. Experience of programming would be an advantage.

References:

 

Madau, P. et al. 1996 MNRAS 283 1388

Jakobsson, P. et al. 2006 Astronomy and Astrophysics 447 897

Smail, I. et al. 1997, Astrophysical Journal (ApJ) 490 5

Fruchter, A. et al. 2006 Nature 441 464

BSC PROJECT - GAMMA-RAY BURST SUPERNOVAE

Gamma-ray bursts (GRBs) are by far the most luminous explosions known in the Universe. In a few seconds they release as much energy as the sun does in its entire 10 billion year lifetime. After the initial burst of gamma-rays the bursts are followed by longer lasting afterglow emission, which can be studied in detail at X-ray and optical wavelengths. Over the past few years it has become apparent that some gamma-ray bursts are related to the core collapse of massive stars in a special type of supernova. These supernovae are identified by their contribution to the afterglow light curve at intermediate times of a few days to weeks.

In this project you will analyse data on several gamma-ray burst afterglows in order to search for supernova signatures and characterize the properties of the underlying supernova explosions. This will involve data taken at a wide range of observatories, and you will become familiar with standard astronomical data processing software. Additionally you will need to perform some modelling of the supernova and gamma-ray burst properties in order to fully interpret your data.

References:

 

Hjorth, J. et al. 2003 Nature 423 847

Pian et al. 2006 Nature 442 1011

Kochanek, C. et al. 2008 ApJ 684 1336