A5114376594- Astrophysical Phenomena and Observations
- Galaxies: Formation, Evolution, Phenomena
- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Astronomy and Astrophysical Research
- Advanced X-ray Imaging Techniques
- Stellar, planetary, and galactic studies
- Adaptive optics and wavefront sensing
- Astronomical Observations and Instrumentation
- Astrophysics and Star Formation Studies
- Mechanics and Biomechanics Studies
- Statistical and numerical algorithms
- Astro and Planetary Science
- Particle Detector Development and Performance
- SAS software applications and methods
- Scientific Measurement and Uncertainty Evaluation
- History and Developments in Astronomy
- High-pressure geophysics and materials
- Statistics Education and Methodologies
- Plant Water Relations and Carbon Dynamics
- Geology and Paleoclimatology Research
- Black Holes and Theoretical Physics
- Tree-ring climate responses
- Calibration and Measurement Techniques
University of Leicester
2013-2025
Centrum Badań Kosmicznych
2016
Consejo Superior de Investigaciones Científicas
2016
Goddard Space Flight Center
2015
Deleted Institution
2015
Institut de Recherche en Astrophysique et Planétologie
2012-2014
Institut d'Estudis Espacials de Catalunya
2014
Swiss Institute of Comparative Law
2012
National Hospital for Neurology and Neurosurgery
2011
University College London
2011
We review some practical aspects of measuring the amplitude variability in `red noise' light curves typical those from Active Galactic Nuclei (AGN). The quantities commonly used to estimate AGN curves, such as fractional rms amplitude, F_var, and excess variance, sigma_XS^2, are examined. Their statistical properties, relationship power spectrum, uses for investigating nature processes discussed. demonstrate that sigma_XS^2 (or similarly F_var) shows large changes one part curve next, even...
We show that the rms–flux relation recently discovered in X-ray light curves of active galactic nuclei (AGN) and binaries (XRBs) implies have a formally non-linear, exponential form, provided applies to variations on all time-scales (as it appears to). This phenomenological model stationary data will lognormal flux distribution. confirm this result using an observation Cyg X-1, further demonstrate our predicts existence powerful millisecond flares observed X-1 low/hard state, explains...
The bright, soft X-ray spectrum Seyfert 1 galaxies Ark 564 and Ton S180 were monitored for 35 days 12 days, respectively, with ASCA RXTE (and EUVE S180). These represent the most intensive monitoring of any such soft-spectrum to date. Light curves constructed in six bands spanning 0.1-10 keV five 0.7-10 keV. short-timescale (hours-days) variability patterns very similar across energy bands, no evidence lags between studied. fractional amplitude was almost independent band, unlike...
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...
We present the first results from a 325-ks observation of Seyfert 1 galaxy MCG–6-30-15 with XMM-Newton and BeppoSAX. The strong, broad, skewed iron line is clearly detected well characterized by steep emissivity profile within 6rg (i.e. 6GM/c2) flatter beyond. inner radius emission appears to lie at about 2rg, consistent reported both an earlier Wilms et al. part ASCA Iwasawa when source was in lower flux state. do depend however on assumed incident power-law continuum lack complex...
We demonstrate a simple method for testing the significance of peaks in periodogram red noise data. The procedure was designed to test spurious periodicities X-ray light curves active galaxies, but can be used quite generally periodic components against background spectrum assumed have power law shape. provides and fast candidate signals short, well-sampled time series such as those obtained from XMM-Newton observations Seyfert without need Monte Carlo simulations. A full account is made...
We present observations of the early X-ray emission for a sample 40 gamma-ray bursts (GRBs) obtained using Swift satellite which narrow-field instruments were pointed at burst within 10 minutes trigger. Using data from Burst Alert and X-Ray Telescopes, we show that light curve can be well described by an exponential relaxes into power law, often with flares superimposed. The transition time between law provides physically defined timescale duration. In most breaks to shallower decay first...
By combining complementary monitoring observations spanning long, medium and short time scales, we have constructed power spectral densities (PSDs) of six Seyfert~1 galaxies. These PSDs span $\gtrsim$4 orders magnitude in temporal frequency, sampling variations on scales ranging from tens minutes to over a year. In at least four cases, the PSD shows "break," significant departure law, typically order few days. This is similar behavior Galactic X-ray binaries (XRBs), lower mass compact...
AGN, powered by accretion onto SMBHs, are thought to be scaled up versions of Galactic black hole X-ray binaries (BH-XRBs). In the past few years evidence such correspondence include similarities in broadband shape variability power spectra, with characteristic bend times-scales scaling mass. We have performed a uniform analysis spectrum densities (PSDs) 104 nearby (z<0.4) AGN using 209 XMM-Newton/pn observations. The PSDs been estimated three energy bands: 0.2-10, 0.2-2, and 2-10 keV....
Recent intensive Swift monitoring of the Seyfert 1 galaxy NGC 5548 yielded 282 usable epochs over 125 days across six UV/optical bands and X-rays. This is densest extended AGN continuum sampling ever obtained, with a mean rate <0.5 day. Approximately daily HST UV was also obtained. The light curves show strong correlations (r_max = 0.57 - 0.90) clearest measurement to date interband lags. These lags are well-fit by \tau propto \lambda^4/3 wavelength dependence, normalization that indicates...
Abstract Swift intensive accretion disk reverberation mapping of four AGN yielded light curves sampled ∼200–350 times in 0.3–10 keV X-ray and six UV/optical bands. Uniform reduction cross-correlation analysis these data sets yields three main results: (1) The X-ray/UV correlations are much weaker than those within the UV/optical, posing severe problems for lamp-post reprocessing model which variations a central corona drive power surrounding disk. (2) interband lags generally consistent with...
We describe the first results from a six-month long reverberation-mapping experiment in ultraviolet based on 170 observations of Seyfert 1 galaxy NGC 5548 with Cosmic Origins Spectrograph Hubble Space Telescope. Significant correlated variability is found continuum and broad emission lines, amplitudes ranging ~30% to factor two lines three continuum. The variations all strong lag behind those continuum, He II 1640 lagging by ~2.5 days Lyman alpha 1215, C IV 1550, Si 1400 ~5-6 days....
The bright Seyfert 1 galaxy MCG—6-30-15 has provided some of the best evidence to date for existence supermassive black holes in active galactic nuclei. Observations with ASCA revealed an X-ray iron line profile shaped by strong Doppler and gravitational effects. In this paper shape line, its variability characteristics robustness spectral interpretation are examined using long XMM–Newton observation taken 2001. A variety models, both including excluding effects gravity, compared data a...
This paper presents a comprehensive examination of the X-ray continuum variability bright Seyfert 1 galaxy MCG-6-30-15. The source clearly shows strong, linear correlation between rms amplitude and flux first seen in Galactic binaries. high-frequency power spectral density (PSD) MCG-6-30-15 is examined detail using Monte Carlo fitting procedure found to be well represented by steep law at high frequencies (with power-law index α≈ 2.5), breaking flatter slope (α≈ 1) below fbr≈ 0.6–2.0 × 10−4...
We apply a reflection‐dominated model to the second XMM–Newton observation of narrow‐line Seyfert 1 galaxy 1H 0707–495. As in first observation, sharp spectral drop is detected with energy that has shifted from 7 7.5 keV two years. The interpreted terms relativistically blurred ionized reflection accretion disc, while shift can be accounted for by changes ionization state and, more importantly, emissivity profile on disc. A flatter during higher flux reduces gravitational redshift effects,...
A model for the inner regions of accretion flows is presented where, owing to disc instabilities, cold and dense material clumped into deep sheets or rings. Surrounding these density enhancements hot, tenuous gas where coronal dissipation processes occur. We expect this situation be most relevant when rate close Eddington radiation-pressure-dominated, so may apply narrow-line Seyfert 1 (NLS1) galaxies. In scenario, hard X-ray source obscured observers, detected emission would dominated by...
This paper discusses Swift observations of the gamma-ray burst GRB 050315 (z=1.949) from 80 s to 10 days after onset burst. The X-ray light curve displayed a steep early decay (t^-5) for ~200 and several breaks. However, both prompt hard X-ray/gamma-ray emission (observed by BAT) first ~ 300 XRT) can be explained exponential decays, with similar constants. Extrapolating BAT into XRT band suggests rapidly decaying, was simply continuation fading emission; this strong similarity between may...
Many astrophysical sources, especially compact accreting show strong, random brightness fluctuations with broad power spectra in addition to periodic or quasi-periodic oscillations (QPOs) that have narrower spectra. The nature of the dominant source variance greatly complicates process searching for possible weak signals. We addressed this problem using tools Bayesian statistics; particular Markov chain Monte Carlo techniques approximate posterior distribution model parameters, and...
We discuss the detection of cyclic signals in stratigraphic ‘time series’ using spectral methods. The dominant source variance record is red noise, which greatly complicates process searching for weak periodic signals. highlight two issues that are more significant than generally appreciated. first lack a correction ‘multiple tests’ – many independent frequencies examined periods but significance test appropriate examination single frequency. second problem poor choice null hypothesis used...
The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions the supermassive that power active galactic nuclei. However, if physics accretion is universal, it should also possible extend this scaling other types accreting systems, irrespective accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding white dwarfs young stellar objects. Every object in sample displays same linear correlation between...
ABSTRACT We present results of time-series analysis the first year Fairall 9 intensive disc-reverberation campaign. used Swift and Las Cumbres Observatory global telescope network to continuously monitor from X-rays near-infrared at a daily subdaily cadence. The cross-correlation function between bands provides evidence for lag spectrum consistent with τ ∝ λ4/3 scaling expected an optically thick, geometrically thin blackbody accretion disc. Decomposing flux into constant variable...
We report the first detection of a sharp spectral feature in narrow-line Seyfert 1 galaxy. Using XMM-Newton we have observed 1H and find drop flux by factor more than 2 at rest-frame energy ∼7keV without any detectable narrow Fe Kα line emission. The this suggests connection with neutral iron K photoelectric edge, but lack obvious absorption spectrum lower energies makes interpretation challenging. explore two alternative explanations for unusual feature: (i) partial-covering clouds...
The lack of variability the broad iron line seen in Seyfert 1 galaxy MCG—6-30-15 is studied using EPIC pn data obtained from a 2001 observation 325 ks, during which count rate source varied by factor 5.The spectrum 80 ks when was bright, lowest 10 as background, well fitted over 3–10 keV band with simple power law photon index Γ= 2.11.The can therefore be decomposed into an approximately constant component, containing strong emission line, and variable component.Assuming that power-law...