A5031781401- Astrophysical Phenomena and Observations
- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Stellar, planetary, and galactic studies
- Orthopedic Surgery and Rehabilitation
- Astronomical Observations and Instrumentation
- Bone fractures and treatments
- Oil and Gas Production Techniques
- Astrophysics and Cosmic Phenomena
- German Literature and Culture Studies
- Elbow and Forearm Trauma Treatment
- Reservoir Engineering and Simulation Methods
- Public Administration and Political Analysis
- Trauma and Emergency Care Studies
- Hip and Femur Fractures
- Radio Astronomy Observations and Technology
- Foot and Ankle Surgery
- Adaptive optics and wavefront sensing
- Digital Innovation in Industries
- Astrophysics and Star Formation Studies
- Musculoskeletal Disorders and Rehabilitation
- Technology, Environment, Urban Planning
- Pelvic and Acetabular Injuries
- Libraries and Information Services
University of Johannesburg
2016-2025
Durham University
2024
South African Radio Astronomy Observatory
1992-2021
Heidelberg University
1968-2019
University Hospital Heidelberg
2005-2019
Westpfalz Klinikum
2004-2016
Medizinische Fakultät Mannheim
2016
University Medical Centre Mannheim
2015
Johannes Gutenberg University Mainz
2002-2015
Texas Tech University
1994-2014
The thermal reprocessing hypothesis in active galactic nuclei (AGN), where extreme ultraviolet/X-ray photons are reprocessed by the accretion disc into optical/UV photons, predicts wavelength-dependent time-delays between optical continuum at different wavelengths. Recent photometric monitoring Sergeev et al. has shown that time-delay is observed 14 AGN, and generally seen to increase with increasing wavelength, as predicted scenario. We fit spectral energy distribution using a model. model...
We present the first results from an optical reverberation mapping campaign executed in 2014, targeting active galactic nuclei (AGN) MCG+08-11-011, NGC 2617, 4051, 3C 382, and Mrk 374. Our targets have diverse interesting observational properties, including a "changing look" AGN broad-line radio galaxy. Based on continuum-H$\beta$ lags, we measure black hole masses for all five targets. also obtain H$\gamma$ He{\sc ii}\,$\lambda 4686$ lags objects except 382. The indicate radial...
Spectroscopic observations of 36 southern Seyferts are presented. Most these also have been monitored photometrically over a period four years (Winkler et al.). The objects classified, line fluxes and widths measured peculiarities the spectra discussed. Many observed more than once changes in strengths profiles examined. Comparisons made with published by other investigators.
We present spectroscopic and photometric observations of SN 1987a in the Large Magellanic Cloud, made at Sutherland field station SAAO Cape Town for days 51–134 after Kamiokande-II neutrino event. During this period, both bolometric flux from supernova apparent angular radius photosphere reached a maximum subsequently declined. Some discussion is included based on comparison between derived fluxes those predicted by selected theoretical models.
We present spectroscopic and photometric observations of SN 1987a in the Large Magellanic Cloud made at Sutherland field station SAAO Cape Town during first 50 days after its discovery was announced.
We present a study of optical, UV and X-ray light curves the nearby changing look active galactic nucleus in galaxy NGC 1566 obtained with Neil Gehrels Swift Observatory MASTER Global Robotic Network over period 2007 - 2018. also report on our optical spectroscopy at South African Astronomical 1.9-m telescope night 2018 August 2-3. A substantial increase flux by 1.5 orders magnitude was observed following brightening bands during last year. After maximum reached beginning July fluxes all...
Abstract We present optical continuum lags for two Seyfert 1 galaxies, MCG+08-11-011 and NGC 2617, using monitoring data from a reverberation mapping campaign carried out in 2014. Our light curves span the ugriz filters over four months, with median cadences of 1.0 0.6 days respectively, combined roughly daily X-ray near-UV Swift 2617. find consistent geometrically thin accretion-disk models that predict lag-wavelength relation τ ∝ λ 4/3 . However, observed are larger than predictions based...
In this third paper of the series reporting on reverberation mapping (RM) campaign active galactic nuclei with asymmetric H$\beta$ emission-line profiles, we present results for 15 Palomar-Green (PG) quasars using spectra obtained between end 2016 to May 2021. This combines long time spans relatively high cadence. For 8 objects, both lags from entire light curves and measurements individual observing seasons are provided. Reverberation 9 our targets has been attempted first time, while 6...
Swift monitoring of NGC 4151 with ~6 hr sampling over a total 69 days in early 2016 is used to construct light curves covering five bands the X-rays (0.3-50 keV) and six ultraviolet (UV)/optical (1900-5500 A). The three hardest X-ray (>2.5 are all strongly correlated no measurable interband lag while two softer show lower variability weaker correlations. UV/optical significantly X-rays, lagging ~3-4 behind hard X-rays. within also correlated, UV appearing lead optical by ~0.5-1 day. This...
Abstract We study the long-term variability in optical monitoring database of Ark 120, a nearby radio-quiet active galactic nucleus (AGN) at distance 143 Mpc ( z = 0.03271). compiled historical archival photometric and spectroscopic data since 1974 conducted new two-year campaign 2015–2017, resulting total temporal baseline over four decades. The variations continuum exhibit wave-like pattern H β integrated flux series varies with similar behavior. broad profiles have asymmetric double...
Abstract In this work, we present the first results of long-term high-cadence spectroscopic monitoring 15 PG quasars with relatively strong Fe ii emission, as a part broader reverberation mapping campaign performed using Calar Alto Observatory’s 2.2 m telescope. The V -band, 5100 Å continuum, and H β broad emission line light curves are measured for set periods ranging from dozens to more than hundred epochs between 2017 May 2020 July. Accurate time lags variations broad-line fluxes optical...
We present the results of a four-year campaign to monitor variations 35 southern Seyfert galaxies, using |$UBV(RI)_\text C| multi-aperture photometry. Most galaxies are found be variable. The light curves displayed and some their more interesting details discussed. relationships between fluxes through different filters well described by straight lines, which suggests that spectral shape variable part optical continuum stays constant. values slopes used derive shapes continua, extinctions...
view Abstract Citations (103) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Steps toward Determination of the Size and Structure Broad-Line Region in Active Galactic Nuclei. VI. Variability NGC 3783 from Ground-based Data Stirpe, G. M. ; Winge, C. Altieri, B. Alloin, D. Aguero, E. L. Anupama, Ashley, R. Bertram, Calderon, J. H. Catchpole, Corradi, Covino, Dottori, A. Feast, W. Ghosh, K. Hutton, Gil Glass, I. S. Grebel, Jorda, Koen, Laney,...
Mining, mineral processing and industrial activities have long been linked to increased levels of radioanuclides in soil their vicinity. In this work, concentrations naturally occurring radionuclides samples collected around a rock phosphate storage facility Richards Bay South Africa were determined. A total 90 analyzed for 238U 232Th using neutron activation analysis 226Ra 4 K HPGe detector. The results revealed the average radioactivity 238U, 232Th, area 28.26 ± 11.40, 29.64 11.50, 32.18...
The Seyfert 1 galaxy Arp 151 was monitored as part of three reverberation mapping campaigns spanning $2008-2015$. We present modeling these velocity-resolved datasets using a geometric and dynamical model for the broad line region (BLR). By each independently, we infer evolution BLR structure in over total seven years constrain systematic uncertainties non-varying parameters such black hole mass. find that geometry thick disk viewed close to face-on is stable this time, although size grows...
We report on the results of a new spectroscopic monitoring campaign quasar PG 0026+129 at Calar Alto Observatory 2.2m telescope from July 2017 to February 2020. Significant variations in fluxes continuum and broad-emission lines, including H$\beta$ He II, were observed first third years, clear time lags between them are measured. The broad line profile consists two Gaussian components: an intermediate-width H$\beta_{\rm IC}$ with full width half-maximum (FWHM) 1964$\pm$18 $\rm km~s^{-1}$...
Abstract We present accretion disc size measurements for the well-known quasar 3C 273 using reverberation mapping (RM) performed on high-cadence light-curves in seven optical filters collected with Las Cumbres Observatory (LCO). Lag estimates obtained Javelin and PyROA are consistent each other yield sizes a factor of ∼2 − 7 larger than ‘thin disc’ theoretical expectations. This makes one growing number active galactic nuclei (AGN) to display so-called ‘accretion size’ problem usually...
Abstract As the deployment of solar power utilizing devices increases, accurate forecasts energy become increasingly important for managing and stabilizing electricity grid. This study investigates validity seven-day ahead Global Horizontal Irradiance ( GHI ) South Africa provided by Forecast System (GFS). The clear sky index was used to interpolate GFS mixed 3-hourly 6-hourly averages generate hourly forecasts. model's performance validated against radiometric data from 15 locations spread...
Supermassive black hole binaries (SMBHBs) with separations on (sub)pc scales represent one of the latest stages hierarchical galaxy assembly. However, many these objects are hidden behind large columns gas and dust at centers galaxies difficult to detect. In systems, accretion is expected take form two individual disks around holes, fed by a larger circumbinary disk. The X-ray UV emission in systems predicted vary regularly timescales that comparable orbital period binary. This first series...
The red and infrared intrinsic colours of B stars are derived from photometric observations through the UBV(RI)C JHK Hβ filters 257 early-type stars. Those for which UBV measurements match published spectral class, show no other signsof peculiarity, used to determine in infrared. From these interstellar reddening relationships evaluated, results compared with previous estimates quantities. values R, E(B — V) distance then determined individual R is confirmed be close 3.1 most cases, but was...
In Ergänzung zu früheren Arbeiten wurden die Inhaltsstoffe der Pygidialwehrblasen von 69 verschiedenen Laufkäferarten durch Dünnschichtchromatographie, Hochspannungs-Elektrophorese, Gaschromatographie, Massen- und IR-Spektroskopie untersucht. Es zeigte sich, daß neben Ameisensäure, Methacrylsäure Tiglinsäure auch n-Undecan sowie teilweise n-Decan n-Tridecan gespeichert werden kann. Als weitere Sekretbestandteile konnten iso-Valerian- iso-Buttersäure p-Benzochinon, 2-Methyl-p-benzochinon...
We present the first results from a reverberation-mapping campaign undertaken during half of 2012, with additional data on one AGN (NGC 3227) 2014 campaign. Our main goals are (1) to determine black hole masses continuum-Hbeta reverberation signatures, and (2) look for velocity-dependent time delays that might be indicators gross kinematics broad-line region. successfully measure Hbeta five AGNs, four which have previous mass measurements. The values measured here in agreement earlier...
Abstract We have recently initiated the first spectroscopic dust reverberation programme on active galactic nuclei in near-infrared. Spectroscopy enables measurement of properties, such as flux, temperature, and covering factor, with higher precision than photometry. In particular, it both luminosity-based radii response times. Here we report results from a 1 yr campaign NGC 5548. The hot responds to changes irradiating flux lag time ∼70 light-days, similar what was previously found...