Master thesis - UBC Physics & Astronomy

2 M. Alexandersen : Master thesis
1. Abstract
In this project, I have investigated methods for discovering and mapping
dust clouds in our Galaxy. This has been done using the expanding X-
ray haloes created around the afterglow of some Gamma Ray Bursts
(GRBs). These haloes occur when X-rays are scattered at small angles
by dust concentrated in the dust clouds.
Only five GRB observations have previously been known to exhibit
these expanding haloes, two of which had two rings, indicating the presence
of two dust clouds. The most resent four of these GRBs have been
observed using the Swift, which has detected 477 GRBs to date. The
Swift XRT observations of these four GRBs are therefore used to develop
a strategy for reducing and analysing Swift observations of GRB afterglows.
The aim of this strategy is to detect similar dust scattered X-ray
haloes in other GRB observations. This strategy was developed into an
almost automated programme, using a combination of the .fits file manipulation
software package F T OOLS, the text processing programming
language P erl and the data analysis programming language IDL.
Using this programme, Swift observations of 55 GRBs within 10 ◦ of
the galactic plane, as well as 32 GRBs selected by other criteria, were
reduced and analysed. This led to the discovery of at least four previously
unknown dust scattered haloes, in the observations of GRB070704,
GRB071011, GRB090621a and GRB090807a. From the analysis I found
that the distances to the dust sheets causing these haloes are ∼ 380 pc,
∼ 100 pc, ∼ 900 pc and ∼ 81 pc, respectively.