480 citations · 6k across the 156 of their papers we have counts for
55 papers · 1 filter
55 Cancri: A Laboratory for Testing Numerous Conjectures about Planet Formation
Dimitris M. Christodoulou, Demosthenes Kazanas
Five planets are presently believed to orbit the primary star of 55 Cnc, but there exists a large 5 AU gap in their distribution between the two outermost planets. This gap has att…
A novel method for measuring the extragalactic background light: Fermi application to the lobes of Fornax A
Markos Georganopoulos, Rita M. Sambruna, Demosthenes Kazanas +5
We describe a new method for measuring the extragalactic background light (EBL) through the detection of -ray inverse Compton (IC) emission due to scattering of the EBL photons…
A multi-zone model for simulating the high energy variability of TeV blazars
Philip B. Graff, Markos Georganopoulos, Eric S. Perlman +1
We present a time-dependent multi-zone code for simulating the variability of Synchrotron-Self Compton (SSC) sources. The code adopts a multi-zone pipe geometry for the emission re…
Cosmological Inflation: A Personal Perspective
Demosthenes Kazanas
We present a brief review of Cosmological Inflation from the personal perspective of the author who almost 30 years ago proposed a way of resolving the problem of Cosmological Hori…
Light Echoes in Kerr Geometry: A Source of High Frequency QPOs from Random X-ray Bursts
Keigo Fukumura, Demosthenes Kazanas
We propose that high frequency quasi-periodic oscillations (HFQPOs) can be produced from randomly-formed X-ray bursts (flashes) by plasma interior to the ergosphere of a rapidly-ro…
Compton dragged supercritical piles: The GRB prompt and afterglow scenario
A. Mastichiadis, D. Kazanas
We examine the prompt and afterglow emission within the context of the Supercritical Pile model for GRBs. For this we have performed self-consistent calculations, by solving three…
Mass Outflows from Dissipative Shocks in Hot Accretion Flows
Keigo Fukumura, Demosthenes Kazanas
We consider stationary, axisymmetric hydrodynamic accretion flows in Kerr geometry. As a plausible means of efficiently separating a small population of nonthermal particles from t…
Simulations of the Poynting--Robertson Cosmic Battery in Resistive Accretion Disks
Dimitris M. Christodoulou, Ioannis Contopoulos, Demosthenes Kazanas
We describe the results of numerical "2.5--dimensional" MHD simulations of an initially unmagnetized disk model orbiting a central point--mass and responding to the continual gener…
Exact Solutions of the Isothermal Lane--Emden Equation with Rotation and Implications for the Formation of Planets and Satellites
Dimitris M. Christodoulou, Demosthenes Kazanas
We have derived exact solutions of the isothermal Lane--Emden equation with and without rotation in a cylindrical geometry. The corresponding hydrostatic equilibria are most releva…
Accretion Disk Illumination in Schwarzschild and Kerr Geometries: Fitting Formulae
Keigo Fukumura, Demosthenes Kazanas
We describe the methodology and compute the illumination of geometrically thin accretion disks around black holes of arbitrary spin parameter exposed to the radiation of a poin…
High Energy Variability Of Synchrotron-Self Compton Emitting Sources: Why One Zone Models Do Not Work And How We Can Fix It
Philip B. Graff, Markos Georganopoulos, Eric S. Perlman +1
With the anticipated launch of GLAST, the existing X-ray telescopes, and the enhanced capabilities of the new generation of TeV telescopes, developing tools for modeling the variab…
Fourier-Resolved Spectroscopy of AGN using XMM-Newton data: I. The 3-10 keV band results
I. E. Papadakis, Z. Ioannou, D. Kazanas
We present the results from the Fourier Resolved Spectroscopy of archival XMM-Newton data of five AGN, namely, Mrk 766, NGC 3516, NGC 3783, NGC 4051 and Ark 564. This work suppleme…
The "Supercritical Pile" GRB Model: Afterglows and GRB, XRR, XRF Unification
Demosthenes Kazanas, Apostolos Mastichiadis, Markos Georganopoulos
We present the general notions and observational consequences of the "Supercritical Pile" GRB model; the fundamental feature of this model is a detailed process for the conversion…
Quasar X-ray jets: Gamma-ray diagnostics of the synchrotron and inverse Compton hypotheses, the case of 3C 273
Markos Georganopoulos, Eric S. Perlman, Demosthenes Kazanas +1
The process responsible for the Chandra-detected X-ray emission from the large scale jets of powerful quasars is a matter of ongoing debate. The two main contenders are external Co…
Hubble Space Telescope Ultraviolet Spectroscopy of Fourteen Low-Redshift Quasars
Rajib Ganguly, Michael S. Brotherton, Nahum Arav +35
We present low-resolution ultraviolet spectra of 14 low redshift (z<0.8) quasars observed with HST/STIS as part of a Snap project to understand the relationship between quasar outf…
The Cosmic Battery Revisited
Ioannis Contopoulos Demosthenes Kazanas Dimitris M. Christodoulou
We reinvestigate the generation and accumulation of magnetic flux in optically thin accretion flows around active gravitating objects. The source of the magnetic field is the azimu…
Fourier resolved spectroscopy of 4U 1543-47 during the 2002 outburst
P. Reig, I. E. Papadakis, C. R. Shrader +1
We have obtained Fourier-resolved spectra of the black-hole binary 4U 1543-47 in the canonical states (high/soft, very high, intermediate and low/hard) observed in this source duri…
The Supercritical Pile Model for GRBs
A. Mastichiadis, D. Kazanas
We present the spectral and temporal radiative signatures expected within the "Supercritical Pile" model of Gamma Ray Bursts (GRB). This model is motivated by the need for a proces…
Is the core of M87 the source of its TeV emission? Implications for unified schemes
Markos Georganopoulos, Eric S. Perlman, Demosthenes Kazanas
M87 has been recently shown to be a TeV source which is likely to be variable. Based on this, and on contemporaneous optical and X-ray monitoring, we argue that the source of the T…
How is the blazar GeV emission really produced?
Markos Georganopoulos, Eric Perlman, Demosthenes Kazanas +1
We show that the external Compton (EC) model for the production of the GeV emission in blazars makes specific predictions for the spectrum and variability of those blazars characte…
Fourier Resolved Spectroscopy of the XMM-Newton Observations of MCG -6-30-15
I. E. Papadakis, D. Kazanas, A. Akylas
We study the Frequency Resolved Spectra of the Seyfert galaxy MCG -6-30-15 obtained during two recent XMM-Newton observations. Splitting the Fourier spectra in soft (<2 keV) and ha…
Long-lag, Wide-Pulse Gamma-Ray Bursts
J. P. Norris, J. T. Bonnell, D. Kazanas +3
Currently, the best available probe of the early phase of gamma-ray burst (GRB) jet attributes is the prompt gamma-ray emission, in which several intrinsic and extrinsic variables…
Bulk Comptonization of the Cosmic Microwave Background by Extragalactic Jets as a Probe of their Matter Content
Markos Georganopoulos, Demosthenes Kazanas, Eric Perlman +1
We propose a method for estimating the composition, i.e. the relative amounts of leptons and protons, of extragalactic jets which exhibit X-ray bright knots in their kpc scale jets…
Witnessing the gradual slow-down of powerful extragalactic jets: The X-ray -- optical -- radio connection
Markos Georganopoulos, Demosthenes Kazanas
A puzzling feature of the {\it Chandra}--detected quasar jets is that their X-ray emission decreases faster along the jet than their radio emission, resulting to an outward increas…