Master's Thesis Defense by Mikael Hansen – University of Copenhagen

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Master's Thesis Defense by Mikael Hansen


The primary purpose of this study and thesis is to determine the tomography of the host galaxy of the gamma-ray burst (GRB) 161023A at a redshift of  by investigating the afterglow spectrum observed in three filters – ultra-violet, visual and near infrared – by X-shooter. The redshift is large enough to allow the detection of the full spectral range from the Lyman-Alpha line (1216Å) to the Lyman-limit (912Å) in the rest frame and small enough such that the Lyman-Alpha forest permits significant transmission at the location of these lines using X-Shooter. This allows for an investigation of a large number of metal absorption lines as well.

The main focus has been on determining the column densities of hydrogen and selected metal species followed by the metallicities of the three velocity components found in the GRB host system using various methods of different complexity – optically thin absorption lines, curve of growth fitting and multi-component fitting to multiple absorption lines. The methods and results are discussed and it is concluded that the host system of GRB 161023A is a complex three velocity component system with separation 180 km/s and a total hydrogen content of 9.42e20 per cm2 and metal contents of 1.73e15 cm-2 and 7.90e14 cm-2 for SiII and FeII, respectively. Furthermore the distribution of metals across the three components has been found not to be homogenous along the line of sight, which indicates that interesting events are taking place, such as star formation or possibly galaxy mergers.

Supervisor: Johan Fynbo, DARK Cosmology Centre