A5046904691- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Pulsars and Gravitational Waves Research
- Advanced X-ray Imaging Techniques
- Gamma-ray bursts and supernovae
- Mechanics and Biomechanics Studies
- Epistemology, Ethics, and Metaphysics
- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Theology and Philosophy of Evil
- Crystallography and Radiation Phenomena
- Astronomical Observations and Instrumentation
- Particle Accelerators and Free-Electron Lasers
- Atomic and Subatomic Physics Research
- Adaptive optics and wavefront sensing
- Statistical and numerical algorithms
- Radio Astronomy Observations and Technology
- High-pressure geophysics and materials
- Philosophy and Theoretical Science
- Biblical Studies and Interpretation
- Indian and Buddhist Studies
- Solar and Space Plasma Dynamics
- Relativity and Gravitational Theory
- Karl Barth and Christian Theology
University of Hertfordshire
2023-2025
Syracuse University
1994-2023
European Space Astronomy Centre
2018-2023
University of Michigan
2023
University of Illinois Urbana-Champaign
2023
Rutgers, The State University of New Jersey
2023
University of Cambridge
2014-2021
University of Maryland, College Park
2018
Montana State University
2018
Cornell University
2018
There have recently been several reports of apparently periodic variations in the light curves quasars, e.g. PG 1302-102 by Graham et al. (2015a). Any quasar showing oscillations brightness would be a strong candidate to close binary supermassive black hole and, turn, for gravitational wave studies. However, normal quasars -- powered accretion onto single, usually show stochastic variability over wide range timescales. It is therefore important carefully assess methods identifying candidates...
X-ray reverberation, where light-travel time delays map out the compact geometry around inner accretion flow in supermassive black holes, has been discovered several of brightest, most variable and well-known Seyfert galaxies. In this work, we expand study reverberation to all galaxies XMM–Newton archive above a nominal rms variability exposure level (a total 43 sources). Approximately 50 per cent sources exhibit iron K that broad emission line responds rapid continuum. We also find on long...
We report the detection of weak pulsations from archetypal ultraluminous X-ray source (ULX) NGC 1313 X-2. Acceleration searches reveal sinusoidal in segments two out six new deep observations this object, with a period $\sim$ 1.5 s and pulsed fraction 5%. use Monte Carlo simulations to demonstrate that individual detections are unlikely originate false Poisson noise given their very close frequencies; strong similarity other detected ULXs also argues they real. The presence large bubble...
We present simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR ) and Suzaku observations of the X-ray binary Cygnus X-1 in hard state. This is first time this state has been observed Cyg with NuSTAR, which enables us to study reflection broadband spectra unprecedented detail. confirm that iron line cannot be fit a combination narrow lines absorption features, instead requiring relativistically blurred profile from companion wind. use models García et al. simultaneously measure black...
In recent work with high-resolution grating spectrometers (RGS) aboard XMM-Newton Pinto et al. (2016) have discovered that two bright and archetypal ultraluminous X-ray sources (ULXs) strong relativistic winds in agreement theoretical predictions of high accretion rates. It has been proposed such can become optically thick enough to block reprocess the disk photons almost entirely, making source appear as a soft thermal emitter or supersoft (ULS). To test this hypothesis we studied ULX where...
We present a detailed spectral analysis of the recent 1.5\,Ms XMM-Newton observing campaign on narrow line Seyfert 1 galaxy IRAS~13224$-$3809, taken simultaneously with 500\,ks NuSTAR data. The X-ray lightcurve shows three flux peaks, registering at about 100 times minimum seen during campaign, and rapid variability time scale kiloseconds. spectra are well fit primary powerlaw continuum, two relativistic-blurred reflection components from inner accretion disk very high iron abundance, simple...
Epistemic Justification collects twelve distinguished and influential essays in epistemology by William P. Alston taken from a body of work spanning almost two decades. They represent the gradual development Alston's thought epistemology.He concentrates on topics that are central to contemporary provides much-needed useful map these issues be explicitly distinguishing interrelating concepts justification used epistemology. More important, he develops defends his own distinctive epistemic...
We report the discovery of an ∼1.5 × 10−4 Hz (∼2 h) X-ray quasi-periodic oscillation (QPO) in active galaxy MS 2254.9−3712, using ∼70 ks XMM–Newton observation. The QPO is significantly detected (∼3.3σ) 1.2–5.0 keV band only, connecting its origin with primary power-law continuum. detect a highly coherent soft lag between 0.3–0.7 and energy bands at frequency 3:2 ratio, strongly suggesting presence harmonic. An iron Kα reverberation found harmonic frequency, indicating reflecting material...
Ultrafast outflows (UFOs) are the most extreme winds launched by active galactic nuclei (AGN) due to their mildly-relativistic speeds (~0.1-0.3c) and thought significantly contribute evolution via AGN feedback. Their nature launching mechanism however not well understood. Recently, we have discovered presence of a variable UFO in narrow-line Seyfert 1 IRAS 13224-3809. The varies response brightness source. In this work perform flux-resolved X-ray spectroscopy study variability found that...
We present a detailed X-ray timing analysis of the highly variable NLS1 galaxy, IRAS 13224-3809. The source was recently monitored for 1.5 Ms with XMM-Newton which, combined 500 ks archival data, makes this best studied galaxy in X-rays to date. apply standard time- and Fourier-domain order understand underlying variability process. flux is not distributed lognormally, as would be expected accreting sources. first non-linear rms-flux relation any waveband found, $\mathrm{rms} \propto...
Most ULXs are believed to be powered by super-Eddington accreting neutron stars and, perhaps, black holes. Above the Eddington rate disc is expected thicken and launch powerful winds through radiation pressure. Winds have been recently discovered in several ULXs. However, it yet unclear whether thickening of or wind variability causes switch between classical soft supersoft states observed some In order understand such phenomenology overall mechanism, we undertook a large (800 ks) observing...
Abstract We present the first results from a 100-day Swift, NICER, and ground-based X-ray–UV–optical reverberation mapping campaign of Narrow-line Seyfert 1 Mrk 335, when it was in an unprecedented low X-ray flux state. Despite dramatic suppression variability, we still observe UV–optical lags as expected disk reverberation. Moreover, are consistent with archival observations luminosity >10 times higher. Interestingly, both low- high-flux states reveal that 6–11 longer than thin disk....
We present an analysis of the long-term X-ray variability extreme narrow-line Seyfert 1 (NLS1) galaxy IRAS 13224-3809 using principal component (PCA) and fractional excess (Fvar) spectra to identify model-independent spectral components. a series peaks in both first PCA Fvar spectrum which correspond strongest predicted absorption lines from ultra-fast outflow (UFO) discovered by Parker et al. (2017). also find higher order components, soft reflection features. The subtle differences between...
We analyse a sample of 21 active galactic nuclei using data from the Swift satellite to study variability properties population in X-ray, UV and optical band. find that variable part UV–optical emission has spectrum consistent with power law, an average index −2.21 ± 0.13, as would be expected central illumination thin disc (index −7/3). also calculate slope law X-ray emission, αOX, Var; for this is Var = −1.06 0.04. The anticorrelation αOX luminosity, LUV, previously found present part: ( −...
Abstract The X-ray quasi-periodic oscillation (QPO) at ∼2.6 × 10−4 Hz in RE J1034+396 has been robustly observed the 0.2–10 keV band of one ∼90 ks XMM–Newton observation, but was not detected subsequent observations. Here, we investigate power spectral density (PSD) eight archival observations J1034+396, and search for presence QPOs three energy bands: soft (0.3–0.8 keV); hard (1.0–4.0 keV) total (0.2–10.0 keV). We find a significant detection QPO feature hard-band PSD five...
We present a qualitative search for ultra-fast outflows (UFOs) in excess variance spectra of radio-quiet active galactic nuclei (AGN). analyse 42 sources from the Tombesi et al. (2010) spectroscopic UFO detection sample, and an additional 22 different Kara (2016) variability sample. A total 58 have sufficient observational data XMM-Newton EPIC-pn spectrum to be calculated. examine these peaks corresponding variable blue-shifted H- He-like ion absorption lines UFOs. find good evidence such...
ABSTRACT SS433 is the only Galactic binary system known to persistently accrete at highly super-critical (or hyper-critical) rates, similar those in tidal disruption events, and likely needed explain rapid growth of very high redshift quasars containing massive SMBHs. Probing inner regions X-rays crucial understanding this system, accretion general, but challenging due obscuration by surrounding wind, driven from flow. NuSTAR observed hard X-ray band across multiple phases its 162 d...
We analyse a sample of 26 active galactic nuclei with deep XMM-Newton observations, using principal component analysis (PCA) to find model independent spectra the different variable components. In total, we identify at least 12 qualitatively patterns spectral variability, involving several mechanisms, including five sources which show evidence relativistic reflection (MCG-6-30-15, NGC 4051, 1H 0707-495, 3516 and Mrk 766) three varying partial covering neutral absorption (NGC 4395, 1365,...
We present the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X), a probe-class mission concept selected study by NASA. It combines huge collecting area, high throughput, broad energy coverage, and excellent spectral temporal resolution in single facility. STROBE-X offers an enormous increase sensitivity X-ray timing, extending these techniques to extragalactic targets first time. is also agile capable of rapid response transient events, making it essential...
We present results from the major coordinated X-ray observing program on ULX NGC 1313 X-1 performed in 2017, combining $XMM$-$Newton$, $Chandra$ and $NuSTAR$, focusing evolution of broadband ($\sim$0.3-30.0 keV) continuum emission. Clear unusual spectral variability is observed, but this markedly suppressed above $\sim$10-15 keV, qualitatively similar to Holmberg IX X-1. model multi-epoch data with two-component accretion disc models designed approximate super-Eddington accretion, allowing...
Most ultraluminous X-ray sources (ULXs) are thought to be powered by neutron stars and black holes accreting beyond the Eddington limit. If compact object is a hole or star with magnetic field $\lesssim10^{12}$ G, accretion disc expected thicken launch powerful winds driven radiation pressure. Evidence of such has been found in ULXs through high-resolution spectrometers onboard XMM-Newton, but several unknowns remain, as geometry launching mechanism these winds. In order better understand...