D. R. Ballantyne
A5074133520- Astrophysical Phenomena and Observations
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Pulsars and Gravitational Waves Research
- Astronomy and Astrophysical Research
- High-pressure geophysics and materials
- Mechanics and Biomechanics Studies
- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Radio Astronomy Observations and Technology
- Particle Detector Development and Performance
- Adaptive optics and wavefront sensing
- Solar and Space Plasma Dynamics
- Scientific Measurement and Uncertainty Evaluation
- Dark Matter and Cosmic Phenomena
- Geophysics and Gravity Measurements
- Relativity and Gravitational Theory
- X-ray Spectroscopy and Fluorescence Analysis
- Cosmology and Gravitation Theories
- Magnetic confinement fusion research
- Advanced X-ray Imaging Techniques
- Astro and Planetary Science
- Spacecraft and Cryogenic Technologies
State Street (United States)
2015-2024
Georgia Institute of Technology
2015-2024
United States Naval Research Laboratory
2018
Institute for Space Astrophysics and Planetology
2018
Savannah Technical College
2017
Istituto Nazionale di Fisica Nucleare, Roma Tor Vergata
2016
University of Geneva
2016
Istituto Nazionale di Fisica Nucleare, Sezione di Cagliari
2010
University of Cagliari
2010
University of Palermo
2010
The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 2012 June 13, is the first focusing high-energy X-ray telescope in orbit. NuSTAR operates band from 3 to 79 keV, extending sensitivity of far beyond ∼10 keV cutoff achieved by all previous satellites. inherently low background associated with concentrating light enables probe hard sky a more than 100-fold improvement over collimated or coded mask instruments that have operated this bandpass. Using its unprecedented...
A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of exciting science opportunities next decade. The Large Synoptic Survey Telescope (LSST) have an effective aperture 6.7 meters and imaging camera field view 9.6 deg^2, be devoted ten-year 20,000 deg^2 south +15 deg. Each pointing imaged 2000 times fifteen second exposures six broad from 0.35 1.1 microns, total point-source depth r~27.5. LSST Science Book describes basic...
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 examine the ability of photoevaporative disk winds to explain low-velocity components observed in forbidden line spectra low-mass T Tauri stars. Using analytic model Shu and coworkers Hollenbach as a basis, we characteristics outflows with hydrodynamic simulations. General results from simulations agree well predictions, although some small differences are present. Most importantly, flow material surface develops at smaller radii than approximations, velocity is only one-third sound...
We present high-precision JHK photometry with the 3.8-m UK Infrared Telescope (UKIRT) of 82 standard stars, 28 from widely used preliminary list known as 'UKIRT Faint Standards', referred to here Fundamental List, and 54 additional stars Extended List. The have 9.4<K<15.0 all or most should be readily observable imaging array detectors in normal operating modes on telescopes up 10-m aperture. Many are accessible southern hemisphere. Arcsec-accuracy positions (J2000, epoch ∼1998) given,...
ABSTRACT We present ≃0.″4 resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at z = 1.3–3.0. These are selected from sensitive blank-field surveys the 2′ × Hubble Ultra-Deep Field λ 5 cm 1.3 mm using Karl G. Jansky Very Large Array Atacama Millimeter/submillimeter Array. They have rates (SFRs), stellar masses, properties representative massive main-sequence SFGs ∼ 2. Morphological classification performed on spatially resolved mass...
ABSTRACT We present a new metric that uses the spectral curvature (SC) above 10 keV to identify Compton-thick active galactic nuclei (AGNs) in low-quality Swift /Burst Alert Telescope (BAT) X-ray data. Using NuSTAR , we observe nine high SC-selected AGNs. find high-sensitivity spectra show majority are (78% or 7/9) and remaining two nearly ( N H ≃ (5–8) × 23 cm −2 ). SC BAT measurements consistent, suggesting this technique can be applied future telescopes. tested method on well-known AGNs...
We report on a NuSTAR and XMM-Newton program that has observed sample of three extremely luminous, heavily obscured WISE-selected AGN at z~2 in broad X-ray band (0.1 - 79 keV). The parent sample, selected to be faint or undetected the WISE 3.4um (W1) 4.6um (W2) bands but bright 12um (W3) 22um (W4), are rare, with only ~1000 so-called W1W2-dropouts across extragalactic sky. Optical spectroscopy reveals typical redshifts for this population, implying rest-frame mid-IR luminosities L(6um)~6e46...
We present X-ray spectral analyses for three Seyfert 2 active galactic nuclei, NGC 424, 1320, and IC 2560, observed by NuSTAR in the 3-79 keV band. The high quality hard spectra allow detailed modeling of Compton reflection component first time these sources. Using quasi-simultaneous Swift/XRT data, as well archival XMM-Newton we find that all nuclei are obscured Compton-thick material with column densities excess ~5 x $10^{24}$ cm$^{-2}$, their above 3 dominated intrinsic continuum on...
We present the analysis of first NuSTAR observations ($\sim 220$ ks), simultaneous with last SUZAKU 50$ active galactic nucleus bright Seyfert 1 galaxy Mrk 509. The time-averaged spectrum in $1-79$ keV X-ray band is dominated by a power-law continuum ($\Gamma\sim 1.8-1.9$), strong soft excess around keV, and signatures reflection form Fe K emission 6.4$ keV), an absorption edge 7.1$ Compton hump due to electron scattering 20-30$ keV). show that these data can be described two very different...
Calculations of X-ray reflection spectra from ionized, optically thick material are an important tool in investigations accretion flows surrounding compact objects. We present the results calculations that treat relevant physics with a minimum assumptions. The temperature and ionization structure top five Thomson depths illuminated disc calculated while also demanding atmosphere is hydrostatic equilibrium. In agreement Nayakshin, Kazanas & Kallman, we find there rapid transition hot to cold...
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...
A number of neutron star low-mass X-ray binaries (LMXBs) have recently been discovered to show broad, asymmetric Fe K emission lines in their spectra. These are generally thought be the most prominent part a reflection spectrum, originating inner accretion disk where strong relativistic effects can broaden lines. We present comprehensive, systematic analysis Suzaku and XMM-Newton spectra 10 LMXBs, all which display broad Of sources, 4 Z atolls, 2 accreting millisecond pulsars (also atolls)....
MCG−6-30-15, at a distance of 37 Mpc (z = 0.008), is the archetypical Seyfert 1 galaxy showing very broad Fe Kα emission. We present results from joint NuSTAR and XMM-Newton observational campaign that, for first time, allows sensitive, time-resolved spectral analysis 0.35 keV up to 80 keV. The strong variability source best explained in terms intrinsic X-ray flux variations context light-bending model: primary, variable emission reprocessed by accretion disk, which produces secondary, less...
We present a broad band spectral analysis of the joint XMM-Newton and NuSTAR observational campaign Narrow Line Seyfert 1 SWIFT J2127.4+5654, consisting 300 ks performed during three orbits. detect relativistic broadened iron K$\alpha$ line originating from innermost regions accretion disc surrounding central black hole, which we infer an intermediate spin $a$=$0.58^{+0.11}_{-0.17}$. The intrinsic spectrum is steep ($\Gamma=2.08\pm0.01$) as commonly found in galaxies, while cutoff energy...
We present a spectral analysis of four coordinated NuSTAR+XMM-Newton observations the Seyfert galaxy NGC 1365. These exhibit an extreme level variability, which is primarily due to variable line-of-sight absorption, revealing relatively unobscured states in this source for first time. Despite diverse range absorption states, each displays same characteristic signatures relativistic reflection from inner accretion disk. Through time-resolved spectroscopy we find that strength iron line and...
We perform an X-ray spectral analysis of the brightest and cleanest bare AGN known so far, Ark 120, in order to determine process(es) at work vicinity SMBH. present data from extensive campaign observing 120 X-rays with XMM-Newton (4$\times$120 ks, 2014 March 18-24), NuSTAR (65.5 22). During this very deep campaign, source was caught a high flux state similar earlier 2003 observation, about twice as bright lower-flux observation 2013. The confirms "softer when brighter" behaviour 120. four...
We report on the first ten identifications of sources serendipitously detected by NuSTAR to provide sensitive census cosmic X-ray background (CXB) source population at >10 keV. find that these NuSTAR-detected are ~100x fainter than those previously keV and have a broad range in redshift luminosity (z=0.020-2.923 L_10-40 keV~4x10^{41}-5x10^{45} erg/s); median z~0.7 keV~3x10^{44} erg/s, respectively. characterize basis broad-band ~0.5-32 spectroscopy, optical ultraviolet-to-mid-infrared SED...
We have obtained a deep, simultaneous observation of the bright, nearby Seyfert galaxy IC 4329A with Suzaku and NuSTAR. Through detailed spectral analysis, we are able to robustly separate continuum, absorption distant reflection components in spectrum. The absorbing column is found be modest at $N_H = 6 \times 10^{21}$ cm$^2$, does not introduce any significant curvature Fe K band. place strong constraint on presence broadened K{\alpha} line: $E 6.46^{+0.08}_{-0.07}$ keV rest frame...
We present Nustar 3-40 keV observations of the optically selected Type 2 quasar (QSO2) SDSS J1034+6001 or Mrk 34. The high-quality hard X-ray spectrum and archival XMM-Newton data can be fitted self-consistently with a reflection-dominated continuum strong Fe Kalpha fluorescence line equivalent-width >1 keV. Prior spectral fitting below 10 showed source to consistent being obscured by Compton-thin column densities gas along line-of-sight, despite evidence for much higher columns from...
The covering factor of Compton-thick obscuring material associated with the torus in active galactic nuclei (AGN) is at present best understood through fraction sources exhibiting absorption along line sight ($N_{H}>1.5\times10^{24}$ cm$^{-2}$) X-ray band, which reveals average factor. Determining this difficult however, due to extreme obscuration. With its spectral coverage hard X-rays ($>$10 keV), NuSTAR sensitive AGN since Compton scattering off optically thick dominates these energies....
Aims. We study the connection between masing disk and obscuring torus in Seyfert 2 galaxies.
The intrinsic column density (NH) distribution of quasars is poorly known. At the high obscuration end quasar population and for redshifts z < 1, X-ray spectra can only be reliably characterized using broad-band measurements that extend to energies above 10 keV. Using hard observatory NuSTAR, along with archival Chandra XMM-Newton data, we study nine optically selected (from SDSS), candidate Compton-thick (NH > 1.5 × 1024 cm−2) type 2 (CTQSO2s); five new NuSTAR observations are reported...
We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear Spectroscopic Telescope Array (NuSTAR) Suzaku observations the Seyfert 1.5 galaxy NGC 4151. disentangle continuum emission, absorption, reflection properties active galactic nucleus (AGN) by applying inner accretion disk absorption-dominated models. With a time-averaged analysis, we find strong evidence for relativistic from disk. that emission arises highly ionized with steep emissivity profile, which suggests an...
ABSTRACT Hot dust-obscured galaxies (hot DOGs), selected from Wide-Field Infrared Survey Explorer ’s all-sky infrared survey, host some of the most powerful active galactic nuclei known and may represent an important stage in evolution galaxies. Most hot DOGs are located at <?CDATA $z\gt 1.5$?> , due part to a strong bias against identifying them lower redshift related selection criteria. We present new method that identifies 153 DOG candidates $z\sim 1$?> where they significantly brighter...