{"id":{"repo_id":"cape-town","oai_identifier":"oai:open.uct.ac.za:11427/40880"},"canonical_url":"https://search.dev.ndltd.org/etd/cape-town/oai:open.uct.ac.za:11427/40880","repository":{"repo_id":"cape-town","name":"University of Cape Town","base_url":"https://open.uct.ac.za/oai/request"},"display":{"title":"Gamma-ray bursts with MeerLICHT","abstract":"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.","abstract_html":"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.","abstract_has_math":false,"creators":["De Wet, Simon"],"institution":"Department of Astronomy","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Groot, Paul Joseph"],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024","date_published":"2024","updated_at":"2026-07-22T22:23:19Z","subjects":["astronomy"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/11427/40880","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Groot, Paul Joseph"]},{"key":"dc:creator","label":"Author","values":["De Wet, Simon"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2025-02-04T14:05:34Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2025-02-04T14:05:34Z"]},{"key":"dc:date.issued","label":"Date","values":["2024"]},{"key":"dc:publisher.department","label":"Dc Publisher Department","values":["Department of Astronomy"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cape Town"]},{"key":"dc:type","label":"Dc Type","values":["Thesis / Dissertation"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral","PhD"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["astronomy"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/11427/40880"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["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."]},{"key":"dc:title","label":"Title","values":["Gamma-ray bursts with MeerLICHT"]}]}],"canonical_facts":{"dc:contributor.advisor":["Groot, Paul Joseph"],"dc:creator":["De Wet, Simon"],"dc:date.accessioned":["2025-02-04T14:05:34Z"],"dc:date.available":["2025-02-04T14:05:34Z"],"dc:date.issued":["2024"],"dc:description.abstract":["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."],"dc:identifier.uri":["http://hdl.handle.net/11427/40880"],"dc:publisher.department":["Department of Astronomy"],"dc:publisher.institution":["University of Cape Town"],"dc:subject":["astronomy"],"dc:title":["Gamma-ray bursts with MeerLICHT"],"dc:type":["Thesis / Dissertation"],"dc:type.qualificationlevel":["Doctoral","PhD"]},"updated_at":"2026-07-22T22:23:19Z"}