Doctoral Thesis: Spectral and Temporal Studies of Gamma-Ray Bursts
Wednesday 16 May 2007
to 15:15 at
Luis Borgonovo (Stockholm University, Department of Astronomy)
Gamma-ray bursts (GRBs) are sporadic flashes of light observed primarily in the gamma-ray band. Being the brightest explosions in the Universe since its birth, they are at present also the furthest astronomical sources detected. Since their serendipitous discovery in the late 1960s the study of GRBs has grown into one of the most active fields in astrophysics with ramifications in many other scientific areas.
Despite intense studies many of the basic questions about the nature of GRBs remain unanswered. Long duration bursts are believed to be the result of ultra-relativistic outflows associated with the collapse of very massive stars. The mechanisms responsible for the emission, the geometry of the emitter, and the radiative processes involved are still a matter of research. Common multi-pulse bursts display a spectral evolution as complex as their light curves. However, it is unclear what produces the observed variability. The works presented in this thesis aim to build the necessary base to answer these open questions.
A characterization of the spectral evolution is presented (based on time-resolved spectral analysis) that provides insight into the underlying emission processes and imposes severe constraints on current physical models (Paper I).
We report the results of a multi-variate analysis on a broad range of GRB physical parameters covering temporal and spectral properties. Empirical relations were found that indicate a self-similar property in burst light curves and a luminosity correlation with potential use as a distance indicator (Paper II).
Determining the relevant timescales of any astronomical phenomenon is essential to understand its associated physical processes. Linear methods in time-series analysis are powerful tools for the researcher that can provide insight into the underlying dynamics of the studied systems. For the first time these methods were used on GRB light curves correcting for cosmic time dilation effects which revealed two classes of variability. The possible origin of these classes is discussed (Papers III & IV).