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Gamma-ray bursts with MeerLICHT
The subject of this thesis is the multi-wavelength observational study of gamma-ray burst (GRB) afterglows. The driving force behind this work is the fully robotic MeerLICHT optical telescope which is able to rapidly slew to the position of a GRB in the sky and obtain multi-lter follow-up observatio...
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| Format: | Thesis |
| Language: | English |
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Department of Astronomy
2025
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| _version_ | 1867613301280604160 |
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| access_status_str | Open Access |
| author | De Wet, Simon |
| author2 | Groot, Paul Joseph |
| author_browse | De Wet, Simon Groot, Paul Joseph |
| author_facet | Groot, Paul Joseph De Wet, Simon |
| author_sort | De Wet, Simon |
| collection | Thesis |
| description | The subject of this thesis is the multi-wavelength observational study of gamma-ray burst (GRB) afterglows. The driving force behind this work is the fully robotic MeerLICHT optical telescope which is able to rapidly slew to the position of a GRB in the sky and obtain multi-lter follow-up observations of the early phases of the afterglow, when non-standard behaviour may occur. Following the introduction, the thesis consists of four main chapters: a chapter outlining the more than two year GRB follow-up programme undertaken with MeerLICHT in which we followed-up 29 bursts, and three chapters presenting detailed studies on individual GRBs. The rst of these studies focuses on GRB 210731A. Starting 286 seconds post-trigger, MeerLICHT obtained a highly unusual light curve consisting of three peaks, which we interpreted as being due to energy injection. Through multi-wavelength theoretical modeling we found that a forward shock model within a stellar wind medium could explain all of our X-ray, optical and radio data, but not our 1.4 GHz upper limits. We suggested that a possible thermal electron population might explain the additional opacity at lower radio frequencies. The subject of the second detailed study is GRB 220627A, a rare burst consisting of two gamma-ray emission episodes separated by almost 1000 s. The discovery of the optical afterglow by MeerLICHT led to spectroscopic observations which secured the burst redshift to z=3.08, making this the most distant ultra-long GRB to date. Our modelling and afterglow analysis showed that GRB 220627A does not appear to have a dierent progenitor compared to the wider long GRB propulation. The third detailed study encompasses GRB 210702A. This burst was unique for being the rst GRB with a clear rebrightening in its millimeter light curve which we attempted to explain via energy injection or a reverse shock from a late-time shell collision. Prior to the millimeter rebrightening, we found that the X-ray, optical and millimeter data could be reconciled within a standard forward shock model in a stellar wind medium, however, similar to other bursts with extensive radio data sets, no standard model could explain all of our radio data. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/40880 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:33:57.504Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Department of Astronomy |
| publisherStr | Department of Astronomy |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/40880 Gamma-ray bursts with MeerLICHT De Wet, Simon Groot, Paul Joseph astronomy The subject of this thesis is the multi-wavelength observational study of gamma-ray burst (GRB) afterglows. The driving force behind this work is the fully robotic MeerLICHT optical telescope which is able to rapidly slew to the position of a GRB in the sky and obtain multi-lter follow-up observations of the early phases of the afterglow, when non-standard behaviour may occur. Following the introduction, the thesis consists of four main chapters: a chapter outlining the more than two year GRB follow-up programme undertaken with MeerLICHT in which we followed-up 29 bursts, and three chapters presenting detailed studies on individual GRBs. The rst of these studies focuses on GRB 210731A. Starting 286 seconds post-trigger, MeerLICHT obtained a highly unusual light curve consisting of three peaks, which we interpreted as being due to energy injection. Through multi-wavelength theoretical modeling we found that a forward shock model within a stellar wind medium could explain all of our X-ray, optical and radio data, but not our 1.4 GHz upper limits. We suggested that a possible thermal electron population might explain the additional opacity at lower radio frequencies. The subject of the second detailed study is GRB 220627A, a rare burst consisting of two gamma-ray emission episodes separated by almost 1000 s. The discovery of the optical afterglow by MeerLICHT led to spectroscopic observations which secured the burst redshift to z=3.08, making this the most distant ultra-long GRB to date. Our modelling and afterglow analysis showed that GRB 220627A does not appear to have a dierent progenitor compared to the wider long GRB propulation. The third detailed study encompasses GRB 210702A. This burst was unique for being the rst GRB with a clear rebrightening in its millimeter light curve which we attempted to explain via energy injection or a reverse shock from a late-time shell collision. Prior to the millimeter rebrightening, we found that the X-ray, optical and millimeter data could be reconciled within a standard forward shock model in a stellar wind medium, however, similar to other bursts with extensive radio data sets, no standard model could explain all of our radio data. 2025-02-04T14:05:34Z 2025-02-04T14:05:34Z 2024 2025-02-04T14:03:17Z Thesis / Dissertation Doctoral PhD http://hdl.handle.net/11427/40880 eng application/pdf Department of Astronomy Faculty of Science University of Cape Town |
| spellingShingle | astronomy De Wet, Simon Gamma-ray bursts with MeerLICHT |
| thesis_degree_str | Doctoral |
| title | Gamma-ray bursts with MeerLICHT |
| title_full | Gamma-ray bursts with MeerLICHT |
| title_fullStr | Gamma-ray bursts with MeerLICHT |
| title_full_unstemmed | Gamma-ray bursts with MeerLICHT |
| title_short | Gamma-ray bursts with MeerLICHT |
| title_sort | gamma ray bursts with meerlicht |
| topic | astronomy |
| url | http://hdl.handle.net/11427/40880 |
| work_keys_str_mv | AT dewetsimon gammarayburstswithmeerlicht |