Lizelke Klindt - Profile on Academia.edu (original) (raw)
Papers by Lizelke Klindt
Proceedings of Frontier Research in Astrophysics — PoS(FRAPWS2014), 2016
The Fermi gamma-ray telescope has detected a host of new gamma-ray sources since it began operati... more The Fermi gamma-ray telescope has detected a host of new gamma-ray sources since it began operation. While the 2LAC catalogue classifies 1017 extragalactic sources, there is still no clear association with approximately 18 per cent of them. We are undertaking a multi-wavelength campaign to identify the counter parts of these sources and search for potential Very High Energy (VHE) candidates. The project is focussing on southern hemisphere sources and undertaking observations from South African observatories. The early stages of this project have focussed on identifying candidate sources and undertaking optical spectroscopy observations with the Southern African Large Telescope (SALT) and the SAAO 1.9-m telescope located at the Southern African Astronomical Observatory (SAAO). We present an overview of this multi-wavelength project along with recent results obtained.
Proceedings of SALT Science Conference 2015 — PoS(SSC2015), 2016
The gamma-ray binary system PSR B1259-63 went through periastron on the 4th of May 2014. Approxim... more The gamma-ray binary system PSR B1259-63 went through periastron on the 4th of May 2014. Approximately 17 days before periastron the pulsar passes through or near the extended circumstellar disc of the Be companion star, as evidenced by the pulsar eclipse. The close interaction is expected to disturb the disc during this period. Approximately 30 days after the previous periastron passage, in 2010, an unusual flare event was observed by Fermi-LAT which showed no clear evidence of a corresponding multi-wavelength flare in e.g. optical, X-ray or TeV gammaray. During 2014 the system was the focus of multi-wavelength campaigns to monitor the system from radio to TeV gamma-ray energies. We report on optical spectroscopy undertaken with the Southern African Large Telescopes from 33 days before until 78 days after the 2014 periastron passage, focusing on the Hα and He-I emission lines. The lines, which originate from the circumstellar disc, present an orbital modulation, with an increase in their equivalent widths, which peaks after periastron, and an associated change in the V/R ratio of the He-I line. The variation of the lines is similar to what was previously reported around the 2010 periastron.
The Astrophysical Journal, 2022
The observed optical colors of quasars are generally interpreted in one of two frameworks: unifie... more The observed optical colors of quasars are generally interpreted in one of two frameworks: unified models that attribute the color to the random orientation of the accretion disk along the line of sight, and evolutionary models that invoke connections between quasar systems and their environments. We test these schemas by probing the dark matter halo environments of optically selected quasars as a function of g − i optical color by measuring the two-point correlation functions of ∼0.34 million eBOSS quasars as well as the gravitational deflection of cosmic microwave background photons around ∼0.66 million XDQSO photometric quasar candidates. We do not detect a trend of halo bias with optical color through either analysis, finding that optically selected quasars at 0.8 < z < 2.2 occupy halos of characteristic mass M h ∼ 3 × 1012 h −1 M ⊙ regardless of their color. This result implies that a quasar’s large-scale halo environment is not strongly connected to its observed optical ...
Certain selection criteria have been applied to sources listed in the Fermi-2LAC catalogue in ord... more Certain selection criteria have been applied to sources listed in the Fermi-2LAC catalogue in order to construct a target sample of twenty unidentified sources at high galactic latitudes with possible blazar characteristics. Blazars constitute the most violent and active astronomical objects which emit radiation at all wavelengths. Therefore multi-wavelength analysis provides the opportunity to construct a Spectral Energy Distribution (SED), which will allow the identification and modelling of the candidate sources. Preliminary spectroscopic results yield spectra of four observed targets which resemble that of BL Lac or flat spectrum radio quasars (FSRQs) with optical counterparts. Estimated redshifts are obtained within the range 0.11 < z < 0.37. Potential Ca II H&K, MgIb and/or NaD spectral lines have been detected in the spectra of four targets, which motivates further observations in order to identify spectral lines that are possibly present.
Unidentified Active Galactic Nuclei in the Fermi-2LAC catalogue: identification of candidate sources
A non-negligible fraction of quasars are red at optical wavelengths, indicating (in the vast majo... more A non-negligible fraction of quasars are red at optical wavelengths, indicating (in the vast majority of cases) that the accretion disc is obscured by a column of dust which extinguishes the shorter-wavelength blue emission. In this paper we summarise recent work by our group, where we find fundamental differences in the radio properties of SDSS optically selected red quasars. We also present new analyses, using a consistent colour-selected quasar parent sample matched to four radio surveys (FIRST, VLA Stripe 82, VLA COSMOS 3 GHz and LoTSS DR1) across a frequency range 150 MHz-3 GHz and four orders of magnitude in radio flux. We show this enhancement is driven by systems with small-scale radio emission (∼kpc) and peaks around the radio-quiet threshold (defined as the ratio of 1.4 GHz luminosity to 6μm luminosity) across the four radio samples. Exploring the potential mechanisms behind this enhancement, we rule out star-formation and propose either small-scale jets or dusty winds int...
Monthly Notices of the Royal Astronomical Society, 2020
Red quasi-stellar objects (QSOs) are a subset of the luminous end of the cosmic population of act... more Red quasi-stellar objects (QSOs) are a subset of the luminous end of the cosmic population of active galactic nuclei (AGNs), most of which are reddened by intervening dust along the line of sight towards their central engines. In recent work from our team, we developed a systematic technique to select red QSOs from the Sloan Digital Sky Survey, and demonstrated that they have distinctive radio properties using the Faint Images of the Radio Sky at Twenty centimetres radio survey. Here we expand our study using low-frequency radio data from the LOFAR Two-metre Sky Survey (LoTSS). With the improvement in depth that LoTSS offers, we confirm key results: Compared to a control sample of normal ‘blue’ QSOs matched in redshift and accretion power, red QSOs have a higher radio detection rate and a higher incidence of compact radio morphologies. For the first time, we also demonstrate that these differences arise primarily in sources of intermediate radio loudness: Radio-intermediate red QSOs...
Proceedings of SALT Science Conference 2015 — PoS(SSC2015), 2016
We are undertaking a multi-wavelength campaign to classify 19 unclassified Active Galactic Nuclei... more We are undertaking a multi-wavelength campaign to classify 19 unclassified Active Galactic Nuclei (AGN) in the 2nd Fermi-LAT catalogue of AGN, which includes optical spectroscopy to establish the targets optical properties and redshifts. With the addition of archival data, we are attempting to establish the Spectral Energy Distributions (SEDs) of these sources, and search for potential Very High Energy (VHE) candidates. The candidate sources all exhibit blazar-like characteristics, are at high galactic latitude (|b| > 10 •), and the optical/radio counterparts are within the Fermi 95% error circle. We present optical spectroscopy of 7 (V∼20 mag) targets undertaken with the Southern African Large Telescope (SALT) using the Robert Stobie Spectrograph (RSS). The target spectra are mainly featureless as are expected for BL Lac objects. However, we have detected broad emission lines, with equivalent widths greater than 5 Å in the spectra of 2FGL J0044.7-3702 and 2FGL J0201.5-6626, and Ca II K&H, G-band, MgI and/or NaD absorption lines from the host galaxy are present in 2FGL J0730.6-6607, 2FGL J1154.1-3242 and 2FGL J1218.8-4827, allowing for preliminary redshift measurements of 0.11 < z < 1.29. In addition, have obtained a Ca II depression depth value of K 4000 = 0.16. for 2FGL J0730.6-6607, which indicates the contribution from non-thermal jet emission and indicates that the source is of a BL Lac nature.
Proceedings of 3rd Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2015), 2016
BL Lacartae objects (BL Lacs) and flat spectrum radio quasars (FSRQs) exhibit variability in the ... more BL Lacartae objects (BL Lacs) and flat spectrum radio quasars (FSRQs) exhibit variability in the continuum flux at multiple wavelengths on timescales of hours to days. We report on optical photometric observations of 8 unidentified Active Galactic Nuclei (AGN) from the second Fermi-LAT catalogue of AGN, that shows potential blazar characteristics. We mainly focus our attention on the intra-day variability (IDV) with timescales of a few minutes to within a day and the short term variability (STV) on timescales of a few days to months. Variability on these timescales are known to be the result of the shock zones within the jet, hot spots and/or instabilities in the accretion disk. Preliminary differential photometric results, for the 8 target sources, obtained with the SAAO 1.9-m Sutherland High-Speed Optical Camera (SHOC) during December 2014 and May 2015, are discussed. Currently, optical long term monitoring of the entire target sample using the Watcher Robotic Telescope is undertaken to determine magnitudes in the RVi filters, as well as radio observations with the the HartRAO 26-m radio telescope to construct light curves in order to study the variability.
The Astrophysical Journal, 2018
The Nuclear Spectroscopic Telescope Array (NuSTAR) serendipitous survey has already uncovered a l... more The Nuclear Spectroscopic Telescope Array (NuSTAR) serendipitous survey has already uncovered a large number of active galactic nuclei (AGNs), providing new information about the composition of the cosmic X-ray background. For AGNs off the Galactic plane, it has been possible to use existing X-ray archival data to improve source localizations, identify optical counterparts, and classify the AGNs with optical spectroscopy. However, near the Galactic plane, better X-ray positions are necessary to achieve optical or near-IR identifications due to the higher levels of source crowding. Thus, we have used observations with the Chandra X-ray Observatory to obtain the best possible X-ray positions. With eight observations, we have obtained coverage for 19 NuSTAR serendips within 12°of the plane. One or two Chandra sources are detected within the error circle of 15 of the serendips, and we report on these sources and search for optical counterparts. For one source (NuSTAR J202421+3350.9), we obtained a new optical spectrum and detected the presence of hydrogen emission lines. The source is Galactic, and we argue that it is likely a cataclysmic variable. For the other sources, the Chandra positions will enable future classifications in order to place limits on faint Galactic populations, including high-mass X-ray binaries and magnetars.
Proceedings of Frontier Research in Astrophysics – II — PoS(FRAPWS2016), 2017
The Fermi Space Telescope has detected 1444 objects which in the Fermi-3LAC catalogue are associa... more The Fermi Space Telescope has detected 1444 objects which in the Fermi-3LAC catalogue are associated with extra-galactic sources (above galactic latitudes of |b| > 10 •). While most are already associated with Flat Spectrum Radio Quasars (FSRQs) and BL Lacs, a significant fraction are associated with blazar-like sources that remain unclassified. We have undertaken optical spectroscopy and photometry of a selection of these sources from South African based telescopes. Optical spectroscopy has been used to classify these sources into FSRQs and BL Lac type objects as well as establish their redshifts. Photometric observations have searched for intraday and short-term variability in these sources. The results for four sources, 2FGL J0044.7-3702, 2FGL J0201.5-6626, 2FGL J0644.2-671 and 2FGL J0730.6-6607 are presented. In addition, long-term optical monitoring of known and candidate TeV blazars is being performed with the Watcher Robotic Telescope and a new photometric pipeline is being developed to allow for automated alerts of flaring sources which may be used to trigger follow-up observations. The preliminary results from this pipeline for PKS 1510-089 during 2015 are presented.
Proceedings of 4th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA 2016), 2017
The Fermi-LAT telescope has provided an unprecedented view of the GeV gamma-ray sky since its lau... more The Fermi-LAT telescope has provided an unprecedented view of the GeV gamma-ray sky since its launch in 2008. The latest Fermi-LAT catalogue of Active Galactic Nuclei lists 1591 sources associated with AGN, of which 460 are classified as blazar candidates of uncertain type (BCU). The characterisation of the physical properties of these BCU sources is important for observational cosmology and fundamental physics, as these sources and their environments constitute a natural laboratory to study particle acceleration and matter/radiation interactions in extreme conditions. Of particular interest is the search for new and interesting/unusual sources that may be observable at very high energies by ground-based imaging atmospheric Cherenkov telescopes. Based on the observed gamma-ray properties, a number of machine learning techniques are being investigated to classify these sources. However, the classification of a blazar as a FSRQ or BL Lac depends on the optical spectral properties. Here we discuss the work that we have thus far undertaken to optically characterise a selection of sources as well as future plans to undertake classification to help calibrate an artificial neural network method.
Proceedings of Frontier Research in Astrophysics — PoS(FRAPWS2014), 2016
The Fermi gamma-ray telescope has detected a host of new gamma-ray sources since it began operati... more The Fermi gamma-ray telescope has detected a host of new gamma-ray sources since it began operation. While the 2LAC catalogue classifies 1017 extragalactic sources, there is still no clear association with approximately 18 per cent of them. We are undertaking a multi-wavelength campaign to identify the counter parts of these sources and search for potential Very High Energy (VHE) candidates. The project is focussing on southern hemisphere sources and undertaking observations from South African observatories. The early stages of this project have focussed on identifying candidate sources and undertaking optical spectroscopy observations with the Southern African Large Telescope (SALT) and the SAAO 1.9-m telescope located at the Southern African Astronomical Observatory (SAAO). We present an overview of this multi-wavelength project along with recent results obtained.
Proceedings of SALT Science Conference 2015 — PoS(SSC2015), 2016
The gamma-ray binary system PSR B1259-63 went through periastron on the 4th of May 2014. Approxim... more The gamma-ray binary system PSR B1259-63 went through periastron on the 4th of May 2014. Approximately 17 days before periastron the pulsar passes through or near the extended circumstellar disc of the Be companion star, as evidenced by the pulsar eclipse. The close interaction is expected to disturb the disc during this period. Approximately 30 days after the previous periastron passage, in 2010, an unusual flare event was observed by Fermi-LAT which showed no clear evidence of a corresponding multi-wavelength flare in e.g. optical, X-ray or TeV gammaray. During 2014 the system was the focus of multi-wavelength campaigns to monitor the system from radio to TeV gamma-ray energies. We report on optical spectroscopy undertaken with the Southern African Large Telescopes from 33 days before until 78 days after the 2014 periastron passage, focusing on the Hα and He-I emission lines. The lines, which originate from the circumstellar disc, present an orbital modulation, with an increase in their equivalent widths, which peaks after periastron, and an associated change in the V/R ratio of the He-I line. The variation of the lines is similar to what was previously reported around the 2010 periastron.
The Astrophysical Journal, 2022
The observed optical colors of quasars are generally interpreted in one of two frameworks: unifie... more The observed optical colors of quasars are generally interpreted in one of two frameworks: unified models that attribute the color to the random orientation of the accretion disk along the line of sight, and evolutionary models that invoke connections between quasar systems and their environments. We test these schemas by probing the dark matter halo environments of optically selected quasars as a function of g − i optical color by measuring the two-point correlation functions of ∼0.34 million eBOSS quasars as well as the gravitational deflection of cosmic microwave background photons around ∼0.66 million XDQSO photometric quasar candidates. We do not detect a trend of halo bias with optical color through either analysis, finding that optically selected quasars at 0.8 < z < 2.2 occupy halos of characteristic mass M h ∼ 3 × 1012 h −1 M ⊙ regardless of their color. This result implies that a quasar’s large-scale halo environment is not strongly connected to its observed optical ...
Certain selection criteria have been applied to sources listed in the Fermi-2LAC catalogue in ord... more Certain selection criteria have been applied to sources listed in the Fermi-2LAC catalogue in order to construct a target sample of twenty unidentified sources at high galactic latitudes with possible blazar characteristics. Blazars constitute the most violent and active astronomical objects which emit radiation at all wavelengths. Therefore multi-wavelength analysis provides the opportunity to construct a Spectral Energy Distribution (SED), which will allow the identification and modelling of the candidate sources. Preliminary spectroscopic results yield spectra of four observed targets which resemble that of BL Lac or flat spectrum radio quasars (FSRQs) with optical counterparts. Estimated redshifts are obtained within the range 0.11 < z < 0.37. Potential Ca II H&K, MgIb and/or NaD spectral lines have been detected in the spectra of four targets, which motivates further observations in order to identify spectral lines that are possibly present.
Unidentified Active Galactic Nuclei in the Fermi-2LAC catalogue: identification of candidate sources
A non-negligible fraction of quasars are red at optical wavelengths, indicating (in the vast majo... more A non-negligible fraction of quasars are red at optical wavelengths, indicating (in the vast majority of cases) that the accretion disc is obscured by a column of dust which extinguishes the shorter-wavelength blue emission. In this paper we summarise recent work by our group, where we find fundamental differences in the radio properties of SDSS optically selected red quasars. We also present new analyses, using a consistent colour-selected quasar parent sample matched to four radio surveys (FIRST, VLA Stripe 82, VLA COSMOS 3 GHz and LoTSS DR1) across a frequency range 150 MHz-3 GHz and four orders of magnitude in radio flux. We show this enhancement is driven by systems with small-scale radio emission (∼kpc) and peaks around the radio-quiet threshold (defined as the ratio of 1.4 GHz luminosity to 6μm luminosity) across the four radio samples. Exploring the potential mechanisms behind this enhancement, we rule out star-formation and propose either small-scale jets or dusty winds int...
Monthly Notices of the Royal Astronomical Society, 2020
Red quasi-stellar objects (QSOs) are a subset of the luminous end of the cosmic population of act... more Red quasi-stellar objects (QSOs) are a subset of the luminous end of the cosmic population of active galactic nuclei (AGNs), most of which are reddened by intervening dust along the line of sight towards their central engines. In recent work from our team, we developed a systematic technique to select red QSOs from the Sloan Digital Sky Survey, and demonstrated that they have distinctive radio properties using the Faint Images of the Radio Sky at Twenty centimetres radio survey. Here we expand our study using low-frequency radio data from the LOFAR Two-metre Sky Survey (LoTSS). With the improvement in depth that LoTSS offers, we confirm key results: Compared to a control sample of normal ‘blue’ QSOs matched in redshift and accretion power, red QSOs have a higher radio detection rate and a higher incidence of compact radio morphologies. For the first time, we also demonstrate that these differences arise primarily in sources of intermediate radio loudness: Radio-intermediate red QSOs...
Proceedings of SALT Science Conference 2015 — PoS(SSC2015), 2016
We are undertaking a multi-wavelength campaign to classify 19 unclassified Active Galactic Nuclei... more We are undertaking a multi-wavelength campaign to classify 19 unclassified Active Galactic Nuclei (AGN) in the 2nd Fermi-LAT catalogue of AGN, which includes optical spectroscopy to establish the targets optical properties and redshifts. With the addition of archival data, we are attempting to establish the Spectral Energy Distributions (SEDs) of these sources, and search for potential Very High Energy (VHE) candidates. The candidate sources all exhibit blazar-like characteristics, are at high galactic latitude (|b| > 10 •), and the optical/radio counterparts are within the Fermi 95% error circle. We present optical spectroscopy of 7 (V∼20 mag) targets undertaken with the Southern African Large Telescope (SALT) using the Robert Stobie Spectrograph (RSS). The target spectra are mainly featureless as are expected for BL Lac objects. However, we have detected broad emission lines, with equivalent widths greater than 5 Å in the spectra of 2FGL J0044.7-3702 and 2FGL J0201.5-6626, and Ca II K&H, G-band, MgI and/or NaD absorption lines from the host galaxy are present in 2FGL J0730.6-6607, 2FGL J1154.1-3242 and 2FGL J1218.8-4827, allowing for preliminary redshift measurements of 0.11 < z < 1.29. In addition, have obtained a Ca II depression depth value of K 4000 = 0.16. for 2FGL J0730.6-6607, which indicates the contribution from non-thermal jet emission and indicates that the source is of a BL Lac nature.
Proceedings of 3rd Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2015), 2016
BL Lacartae objects (BL Lacs) and flat spectrum radio quasars (FSRQs) exhibit variability in the ... more BL Lacartae objects (BL Lacs) and flat spectrum radio quasars (FSRQs) exhibit variability in the continuum flux at multiple wavelengths on timescales of hours to days. We report on optical photometric observations of 8 unidentified Active Galactic Nuclei (AGN) from the second Fermi-LAT catalogue of AGN, that shows potential blazar characteristics. We mainly focus our attention on the intra-day variability (IDV) with timescales of a few minutes to within a day and the short term variability (STV) on timescales of a few days to months. Variability on these timescales are known to be the result of the shock zones within the jet, hot spots and/or instabilities in the accretion disk. Preliminary differential photometric results, for the 8 target sources, obtained with the SAAO 1.9-m Sutherland High-Speed Optical Camera (SHOC) during December 2014 and May 2015, are discussed. Currently, optical long term monitoring of the entire target sample using the Watcher Robotic Telescope is undertaken to determine magnitudes in the RVi filters, as well as radio observations with the the HartRAO 26-m radio telescope to construct light curves in order to study the variability.
The Astrophysical Journal, 2018
The Nuclear Spectroscopic Telescope Array (NuSTAR) serendipitous survey has already uncovered a l... more The Nuclear Spectroscopic Telescope Array (NuSTAR) serendipitous survey has already uncovered a large number of active galactic nuclei (AGNs), providing new information about the composition of the cosmic X-ray background. For AGNs off the Galactic plane, it has been possible to use existing X-ray archival data to improve source localizations, identify optical counterparts, and classify the AGNs with optical spectroscopy. However, near the Galactic plane, better X-ray positions are necessary to achieve optical or near-IR identifications due to the higher levels of source crowding. Thus, we have used observations with the Chandra X-ray Observatory to obtain the best possible X-ray positions. With eight observations, we have obtained coverage for 19 NuSTAR serendips within 12°of the plane. One or two Chandra sources are detected within the error circle of 15 of the serendips, and we report on these sources and search for optical counterparts. For one source (NuSTAR J202421+3350.9), we obtained a new optical spectrum and detected the presence of hydrogen emission lines. The source is Galactic, and we argue that it is likely a cataclysmic variable. For the other sources, the Chandra positions will enable future classifications in order to place limits on faint Galactic populations, including high-mass X-ray binaries and magnetars.
Proceedings of Frontier Research in Astrophysics – II — PoS(FRAPWS2016), 2017
The Fermi Space Telescope has detected 1444 objects which in the Fermi-3LAC catalogue are associa... more The Fermi Space Telescope has detected 1444 objects which in the Fermi-3LAC catalogue are associated with extra-galactic sources (above galactic latitudes of |b| > 10 •). While most are already associated with Flat Spectrum Radio Quasars (FSRQs) and BL Lacs, a significant fraction are associated with blazar-like sources that remain unclassified. We have undertaken optical spectroscopy and photometry of a selection of these sources from South African based telescopes. Optical spectroscopy has been used to classify these sources into FSRQs and BL Lac type objects as well as establish their redshifts. Photometric observations have searched for intraday and short-term variability in these sources. The results for four sources, 2FGL J0044.7-3702, 2FGL J0201.5-6626, 2FGL J0644.2-671 and 2FGL J0730.6-6607 are presented. In addition, long-term optical monitoring of known and candidate TeV blazars is being performed with the Watcher Robotic Telescope and a new photometric pipeline is being developed to allow for automated alerts of flaring sources which may be used to trigger follow-up observations. The preliminary results from this pipeline for PKS 1510-089 during 2015 are presented.
Proceedings of 4th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA 2016), 2017
The Fermi-LAT telescope has provided an unprecedented view of the GeV gamma-ray sky since its lau... more The Fermi-LAT telescope has provided an unprecedented view of the GeV gamma-ray sky since its launch in 2008. The latest Fermi-LAT catalogue of Active Galactic Nuclei lists 1591 sources associated with AGN, of which 460 are classified as blazar candidates of uncertain type (BCU). The characterisation of the physical properties of these BCU sources is important for observational cosmology and fundamental physics, as these sources and their environments constitute a natural laboratory to study particle acceleration and matter/radiation interactions in extreme conditions. Of particular interest is the search for new and interesting/unusual sources that may be observable at very high energies by ground-based imaging atmospheric Cherenkov telescopes. Based on the observed gamma-ray properties, a number of machine learning techniques are being investigated to classify these sources. However, the classification of a blazar as a FSRQ or BL Lac depends on the optical spectral properties. Here we discuss the work that we have thus far undertaken to optically characterise a selection of sources as well as future plans to undertake classification to help calibrate an artificial neural network method.