Mining MeerKAT data for minute to hour timescale transients and variable sources
- Authors: Gcilitshana, Sihle
- Date: 2024-10-11
- Subjects: MeerKAT , Astronomy Data processing , Radio astronomy , Pipelining (Electronics) , Active galactic nuclei
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/464886 , vital:76554
- Description: In radio astronomy, minute-to-hour timescale transients and variable sources present an understudied population. We now have an unprecedented view of the transient radio sky due to the advent of new telescopes (such as the MeerKAT) with high instantaneous sensitivity, excellent snapshot imaging capabilities, and a large field of view. We can now probe into this population. This thesis presents the search for minute-to-hour timescale transient and variable sources in two of MeerKAT archival observations: the COSMOS and MACS J2140.2−2339 fields. The fields were observed for eight and five hours at the UHF band, respectively. We employed the PARROT transient and variable search pipeline currently being developed by the RATT group at Rhodes University. The pipeline’s input is a cross-calibrated measurement set, and its outputs are light curves extracted from all the sources in the restored image of the field. Using the light curves from the pipeline, we detected two variable sources in the COSMOS field, scintillating Active Galactic Nuclei (AGNs), which are most likely caused by the turbulent plasma in the interstellar medium. Due to persistent ionospheric diffraction, no variable sources were detected in the MACS J2140.2−2339 field, and no transients were detected in either field. The thesis also highlights areas where improvements to the PARROT pipeline can be implemented. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Authors: Gcilitshana, Sihle
- Date: 2024-10-11
- Subjects: MeerKAT , Astronomy Data processing , Radio astronomy , Pipelining (Electronics) , Active galactic nuclei
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/464886 , vital:76554
- Description: In radio astronomy, minute-to-hour timescale transients and variable sources present an understudied population. We now have an unprecedented view of the transient radio sky due to the advent of new telescopes (such as the MeerKAT) with high instantaneous sensitivity, excellent snapshot imaging capabilities, and a large field of view. We can now probe into this population. This thesis presents the search for minute-to-hour timescale transient and variable sources in two of MeerKAT archival observations: the COSMOS and MACS J2140.2−2339 fields. The fields were observed for eight and five hours at the UHF band, respectively. We employed the PARROT transient and variable search pipeline currently being developed by the RATT group at Rhodes University. The pipeline’s input is a cross-calibrated measurement set, and its outputs are light curves extracted from all the sources in the restored image of the field. Using the light curves from the pipeline, we detected two variable sources in the COSMOS field, scintillating Active Galactic Nuclei (AGNs), which are most likely caused by the turbulent plasma in the interstellar medium. Due to persistent ionospheric diffraction, no variable sources were detected in the MACS J2140.2−2339 field, and no transients were detected in either field. The thesis also highlights areas where improvements to the PARROT pipeline can be implemented. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
SolarKAT: a solar imaging pipeline for MeerKAT
- Samboco, Victória da Graça Gilberto
- Authors: Samboco, Victória da Graça Gilberto
- Date: 2024-10-11
- Subjects: MeerKAT , Radio interferometers , Solar activity , Radio Interference , Data processing
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/465102 , vital:76573
- Description: Solar interference poses a significant challenge in radio interferometric observations, particularly with the increasing sensitivity of modern new-generation telescopes. This thesis presents the SolarKAT pipeline, a novel approach designed to mitigate solar interference in MeerKAT observations. The pipeline incorporates a series of steps, including self-calibration (second generation calibration or 2GC), precise determination of the Sun’s position, phase centre adjustments, creation of region-based masks, deconvolution, prediction, solar model subtraction, and peeling. We applied the SolarKAT pipeline to three datasets that feature the Sun in different conditions (frequency band and angular distance from the Sun to the telescope pointing position). These observations were obtained from three MeerKAT telescope surveys: ThunderKAT, MIGHTEE and LADUMA. We compared the visual images, peak fluxes, flux density, RMS and pixel distribution to evaluate the pipeline. Our results showed a notable reduction in solar interference. This is evidenced by the improved image quality, reduction in RMS and pixel distribution values, and consistent peak flux measurements after applying the pipeline. SolarKAT has not only improved the data quality but also demonstrated to be a valuable tool in producing high-quality solar images, which can be a helpful resource for solar physics and space weather forecasts. This study showcases the potential of the SolarKAT pipeline in enabling high-quality radio interferometric observations, even in the presence of solar interference. Unlike conventional methods that often discard corrupted visibilities (e.g. flagging), our approach focuses on recovering them. Additionally, the SolarKAT pipeline naturally delivers detailed images of the Sun. Our findings contribute to advancing the field of radio interferometry, providing a valuable tool for researchers seeking to enhance the accuracy of their observations and conduct studies in solar physics and space weather. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Authors: Samboco, Victória da Graça Gilberto
- Date: 2024-10-11
- Subjects: MeerKAT , Radio interferometers , Solar activity , Radio Interference , Data processing
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/465102 , vital:76573
- Description: Solar interference poses a significant challenge in radio interferometric observations, particularly with the increasing sensitivity of modern new-generation telescopes. This thesis presents the SolarKAT pipeline, a novel approach designed to mitigate solar interference in MeerKAT observations. The pipeline incorporates a series of steps, including self-calibration (second generation calibration or 2GC), precise determination of the Sun’s position, phase centre adjustments, creation of region-based masks, deconvolution, prediction, solar model subtraction, and peeling. We applied the SolarKAT pipeline to three datasets that feature the Sun in different conditions (frequency band and angular distance from the Sun to the telescope pointing position). These observations were obtained from three MeerKAT telescope surveys: ThunderKAT, MIGHTEE and LADUMA. We compared the visual images, peak fluxes, flux density, RMS and pixel distribution to evaluate the pipeline. Our results showed a notable reduction in solar interference. This is evidenced by the improved image quality, reduction in RMS and pixel distribution values, and consistent peak flux measurements after applying the pipeline. SolarKAT has not only improved the data quality but also demonstrated to be a valuable tool in producing high-quality solar images, which can be a helpful resource for solar physics and space weather forecasts. This study showcases the potential of the SolarKAT pipeline in enabling high-quality radio interferometric observations, even in the presence of solar interference. Unlike conventional methods that often discard corrupted visibilities (e.g. flagging), our approach focuses on recovering them. Additionally, the SolarKAT pipeline naturally delivers detailed images of the Sun. Our findings contribute to advancing the field of radio interferometry, providing a valuable tool for researchers seeking to enhance the accuracy of their observations and conduct studies in solar physics and space weather. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
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Studying the brightest radio sources in the southern sky
- Authors: Sejake, Precious Katlego
- Date: 2022-04-06
- Subjects: Galaxies Formation , Galaxies Evolution , Active galaxies , Radio galaxies , Radio sources (Astronomy) , Southern sky (Astronomy)
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/455350 , vital:75423
- Description: Active Galactic Nuclei (AGN) are among the most remarkable and powerful extragalactic radio sources in the Universe. The study of AGN enables us to understand better the critical mechanisms leading to the launch of radio jets, and its link to the central engine. Radio jets are thought to impact their host galaxy by promoting or suppressing star formation. By studying AGN, we can better understand their formation, evolution, and environment. The host galaxy cross-identification is a crucial step to be carried out to build a multi-wavelength analysis of powerful radio sources; AGN. The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) 4Jy (G4Jy) Sample comprises 1,863 of the powerful radio sources in the southern sky. However, 140 sources from the G4Jy Sample were followed-up with the Open Time on MeerKAT. Of these 140 sources, 126 had an ambiguous host galaxy, and 13 had an identified host galaxy; however, there were some discrepancies in the literature concerning the host galaxy. The host-galaxy identification of these sources is limited by the poor resolution of radio data at 25" to 45". This study aims to assess the radio morphology of these 140 sources and identify their host galaxy using the ⇠ 7” resolution images from MeerKAT in conjunction with datasets at other wavelengths. This analysis is carried out by visually inspecting the overlays. The overlays comprise radio contours from 150 MHz, 200 MHz, 843/1400 MHz and 1300 MHz overlaid on the mid-infrared image (3.4 μm). The MeerKAT images reveal sources with various radio morphologies. While most of the sources have radio morphology of typical symmetric lobes, 10 radio sources have head-tail morphology, 14 are wide-angle tail (WAT), and 5 have X-, S- /Z-shaped morphology. Overall, we find host galaxies for 70% of the sources in the sample, with the remainder comprising sources with ambiguous host galaxy (20.7%) and sources with a faint mid-infrared host galaxy (9.3%). These results highlight the importance of angular resolution and sensitivity for morphological classification and host galaxy cross-identification. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2022
- Full Text:
- Authors: Sejake, Precious Katlego
- Date: 2022-04-06
- Subjects: Galaxies Formation , Galaxies Evolution , Active galaxies , Radio galaxies , Radio sources (Astronomy) , Southern sky (Astronomy)
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/455350 , vital:75423
- Description: Active Galactic Nuclei (AGN) are among the most remarkable and powerful extragalactic radio sources in the Universe. The study of AGN enables us to understand better the critical mechanisms leading to the launch of radio jets, and its link to the central engine. Radio jets are thought to impact their host galaxy by promoting or suppressing star formation. By studying AGN, we can better understand their formation, evolution, and environment. The host galaxy cross-identification is a crucial step to be carried out to build a multi-wavelength analysis of powerful radio sources; AGN. The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) 4Jy (G4Jy) Sample comprises 1,863 of the powerful radio sources in the southern sky. However, 140 sources from the G4Jy Sample were followed-up with the Open Time on MeerKAT. Of these 140 sources, 126 had an ambiguous host galaxy, and 13 had an identified host galaxy; however, there were some discrepancies in the literature concerning the host galaxy. The host-galaxy identification of these sources is limited by the poor resolution of radio data at 25" to 45". This study aims to assess the radio morphology of these 140 sources and identify their host galaxy using the ⇠ 7” resolution images from MeerKAT in conjunction with datasets at other wavelengths. This analysis is carried out by visually inspecting the overlays. The overlays comprise radio contours from 150 MHz, 200 MHz, 843/1400 MHz and 1300 MHz overlaid on the mid-infrared image (3.4 μm). The MeerKAT images reveal sources with various radio morphologies. While most of the sources have radio morphology of typical symmetric lobes, 10 radio sources have head-tail morphology, 14 are wide-angle tail (WAT), and 5 have X-, S- /Z-shaped morphology. Overall, we find host galaxies for 70% of the sources in the sample, with the remainder comprising sources with ambiguous host galaxy (20.7%) and sources with a faint mid-infrared host galaxy (9.3%). These results highlight the importance of angular resolution and sensitivity for morphological classification and host galaxy cross-identification. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2022
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Neutral Atomic Hydrogen in Gravitationally Lensed Systems
- Authors: Blecher, Tariq Dylan
- Date: 2021-10-29
- Subjects: Uncatalogued
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/192776 , vital:45263
- Description: Thesis (PhD) -- Faculty of Law, Law, 2021
- Full Text:
- Authors: Blecher, Tariq Dylan
- Date: 2021-10-29
- Subjects: Uncatalogued
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/192776 , vital:45263
- Description: Thesis (PhD) -- Faculty of Law, Law, 2021
- Full Text:
Advanced radio interferometric simulation and data reduction techniques
- Authors: Makhathini, Sphesihle
- Date: 2018
- Subjects: Interferometry , Radio interferometers , Algorithms , Radio telescopes , Square Kilometre Array (Project) , Very Large Array (Observatory : N.M.) , Radio astronomy
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/57348 , vital:26875
- Description: This work shows how legacy and novel radio Interferometry software packages and algorithms can be combined to produce high-quality reductions from modern telescopes, as well as end-to-end simulations for upcoming instruments such as the Square Kilometre Array (SKA) and its pathfinders. We first use a MeqTrees based simulations framework to quantify how artefacts due to direction-dependent effects accumulate with time, and the consequences of this accumulation when observing the same field multiple times in order to reach the survey depth. Our simulations suggest that a survey like LADUMA (Looking at the Distant Universe with MeerKAT Array), which aims to achieve its survey depth of 16 µJy/beam in a 72 kHz at 1.42 GHz by observing the same field for 1000 hours, will be able to reach its target depth in the presence of these artefacts. We also present stimela, a system agnostic scripting framework for simulating, processing and imaging radio interferometric data. This framework is then used to write an end-to-end simulation pipeline in order to quantify the resolution and sensitivity of the SKA1-MID telescope (the first phase of the SKA mid-frequency telescope) as a function of frequency, as well as the scale-dependent sensitivity of the telescope. Finally, a stimela-based reduction pipeline is used to process data of the field around the source 3C147, taken by the Karl G. Jansky Very Large Array (VLA). The reconstructed image from this reduction has a typical 1a noise level of 2.87 µJy/beam, and consequently a dynamic range of 8x106:1, given the 22.58 Jy/beam flux Density of the source 3C147.
- Full Text:
- Authors: Makhathini, Sphesihle
- Date: 2018
- Subjects: Interferometry , Radio interferometers , Algorithms , Radio telescopes , Square Kilometre Array (Project) , Very Large Array (Observatory : N.M.) , Radio astronomy
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/57348 , vital:26875
- Description: This work shows how legacy and novel radio Interferometry software packages and algorithms can be combined to produce high-quality reductions from modern telescopes, as well as end-to-end simulations for upcoming instruments such as the Square Kilometre Array (SKA) and its pathfinders. We first use a MeqTrees based simulations framework to quantify how artefacts due to direction-dependent effects accumulate with time, and the consequences of this accumulation when observing the same field multiple times in order to reach the survey depth. Our simulations suggest that a survey like LADUMA (Looking at the Distant Universe with MeerKAT Array), which aims to achieve its survey depth of 16 µJy/beam in a 72 kHz at 1.42 GHz by observing the same field for 1000 hours, will be able to reach its target depth in the presence of these artefacts. We also present stimela, a system agnostic scripting framework for simulating, processing and imaging radio interferometric data. This framework is then used to write an end-to-end simulation pipeline in order to quantify the resolution and sensitivity of the SKA1-MID telescope (the first phase of the SKA mid-frequency telescope) as a function of frequency, as well as the scale-dependent sensitivity of the telescope. Finally, a stimela-based reduction pipeline is used to process data of the field around the source 3C147, taken by the Karl G. Jansky Very Large Array (VLA). The reconstructed image from this reduction has a typical 1a noise level of 2.87 µJy/beam, and consequently a dynamic range of 8x106:1, given the 22.58 Jy/beam flux Density of the source 3C147.
- Full Text:
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