A5004039041- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Astrophysics and Star Formation Studies
- Stellar, planetary, and galactic studies
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- High-pressure geophysics and materials
- Astronomical Observations and Instrumentation
- Astro and Planetary Science
- Radio Astronomy Observations and Technology
- Atmospheric Ozone and Climate
- Spectroscopy and Laser Applications
- Mechanics and Biomechanics Studies
- Molecular Spectroscopy and Structure
- Atomic and Molecular Physics
- Ionosphere and magnetosphere dynamics
- Calibration and Measurement Techniques
- Dark Matter and Cosmic Phenomena
- Particle Accelerators and Free-Electron Lasers
- Adaptive optics and wavefront sensing
- Solar and Space Plasma Dynamics
- Relativity and Gravitational Theory
- Scientific Research and Discoveries
University of Crete
2015-2024
Foundation for Research and Technology Hellas
2015-2024
Max Planck Institute for Extraterrestrial Physics
2011
FORTH Institute of Astrophysics
2000-2008
National Observatory of Athens
2005
Max Planck Society
2001
Max Planck Innovation
2001
California Institute of Technology
1981-1982
University of Illinois Urbana-Champaign
1979-1981
University of Illinois System
1980
We present new calculations of the attenuation stellar light from spiral galaxies using geometries for stars and dust which can reproduce entire spectral energy distribution ultraviolet (UV) to Far-infrared (FIR)/submillimeter (submm) also account surface brightness in both optical/Near-infrared (NIR) FIR/submm. The are based on model Popescu et al. ([CITE]), incorporates a dustless bulge, disk old with associated diffuse dust, thin young clumpy component star-forming regions disk....
We present a self-consistent model of the spectral energy distributions (SEDs) spiral galaxies from ultraviolet (UV) to mid-infrared (MIR)/far-infrared (FIR)/submillimeter (submm) based on full radiative transfer calculation propagation starlight in galaxy disks. This predicts not only total integrated absorbed UV/optical and re-emitted infrared/submm, but also colours dust emission an explicit strength colour radiation fields heating dust, incorporating stochastic small grains PAH molecules.
We present first results on polarization swings in optical emission of blazars obtained by RoboPol, a monitoring program an unbiased sample gamma-ray bright specially designed for effective detection such events. A possible connection swing events with periods high activity gamma rays is investigated using the dataset during season operation. It was found that brightest flares tend to be located closer time rotation events, which may indication two separate mechanisms responsible rotations....
We present average R-band optopolarimetric data, as well variability parameters, from the first and second RoboPol observing season. investigate whether gamma-ray-loud gamma-ray-quiet blazars exhibit systematic differences in their optical polarization properties. find that have a systematically higher fraction (0.092) than (0.031), with hypothesis of two samples being drawn same distribution fractions rejected at 3σ level. not found any evidence this discrepancy is related to redshift...
We study Compton upscattering of low-frequency photons in a converging flow thermal plasma. The escape diffusively, and electron scattering is the dominant source opacity. solve equation radiative transfer case spherical, steady state accretion into black holes numerically approximately analytically. Unlike previous work on this subject, we consider inner boundary at finite radius, has significant effect emergent spectrum. It shown that bulk motion more efficient than Comptonization,...
view Abstract Citations (142) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On mapping the magnetic field direction in molecular clouds by polarization measurements Goldreich, P. ; Kylafis, N. D. It is predicted that interstellar radio-frequency lines possess a few percent linear polarization, provided (1) radiative transition rate at least comparable to collision rate, (2) optical depth moderate and anisotropic, (3) number of extrema...
view Abstract Citations (162) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dust Distribution in Spiral Galaxies Kylafis, Nikolaos D. ; Bahcall, John N. A method for determining the dust distribution edge-on, late Hubble type, spiral galaxies from their surface photometry is described. The assumes that both stars and are distributed isothermally direction perpendicular to galactic plane with scale heights z(s) z(d) respectively,...
We present measurements of rotations the optical polarization blazars during second year operation RoboPol, a monitoring programme an unbiased sample gamma-ray bright specially designed for effective detection such events, and we analyse large set rotation events discovered in two years observation. investigate patterns variability parameters total flux density compare them to behaviour non-rotating state. have searched possible correlations between average polarization-plane polarization,...
We use results of our 3 yr polarimetric monitoring programme to investigate the previously suggested connection between rotations polarization plane in optical emission blazars and their gamma-ray flares GeV band. The homogeneous set 40 rotation events 24 sources detected by RoboPol is analysed together with data provided Fermi-LAT. confirm that are indeed related closest time lags these consistent zero. Amplitudes anticorrelated amplitudes flares. This presumably caused higher relativistic...
The fast variability observed in the X-ray emission from black-hole binaries has a very complex phenomenology, but offers possibility to investigate directly properties of inner accretion flow. In particular, type-B oscillations 2-8 Hz range, Soft-Intermediate state, have been associated relativistic jet. We present results timing and spectral analysis set observations bright transient MAXI J1348-630 made with NICER telescope. are brightest part outburst all feature strong QPO at ~4.5 Hz....
We have used Rossi X-Ray Timing Explorer data to measure the lags between soft (2-5 keV) and hard (5-13 photons study aperiodic variability of superluminal black hole candidate GRS 1915+105 during low-flux states. The power density spectra exhibit quasi-periodic oscillations (QPO) whose frequency increases with increasing count rate varies in range 0.6-8 Hz. A correlation QPO phase lag is reported for first time. This found both continuum at frequency. find that as moves higher values...
view Abstract Citations (89) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Linear polarization of radio frequency lines in molecular clouds and circumstellar envelopes Goldreich, P. ; Kylafis, N. D. It is predicted that interstellar possess a few percent linear provided the optical depth source region both anisotropic order unity radiative rates are at least comparable to collision rates. These conditions expected be met many sources which...
We present first results from RoboPol, a novel-design optical polarimeter operating at the Skinakas Observatory in Crete. The data, taken during May - June 2013 commissioning of instrument, constitute single-epoch linear polarization survey sample gamma-ray loud blazars, defined according to unbiased and objective selection criteria, easily reproducible simulations, as well comparison of, otherwise similar, quiet blazars. As such, this are appropriate for both phenomenological population...
We describe the data reduction pipeline and control system for RoboPol project. The project is monitoring optical R-band magnitude linear polarization of a large sample active galactic nuclei that dominated by blazars. calibrates reduces each exposure frame, producing measurement every source in 13 arcmin × field view. combines dynamic scheduler, real-time reduction, telescope automation to allow high-efficiency unassisted observations.
We present a new set of optical polarization plane rotations in blazars, observed during the third year operation RoboPol. The entire rotation events discovered three years observations is analysed with aim determining whether these are inherent all blazars. It found that frequency varies widely among This variation cannot be explained either by difference relativistic boosting or selection effects caused average fractional polarization. conclude characteristic subset blazars and they occur...
ABSTRACT We present the design and performance of RoboPol, a four-channel optical polarimeter operating at Skinakas Observatory in Crete, Greece. RoboPol is capable measuring both relative linear Stokes parameters q u (and total intensity I) one sky exposure. Though primarily used to measure polarization point sources R band, instrument features additional filters (B, V, I), enabling multiwavelength imaging polarimetry over large field view (13.6′ × 13.6′). demonstrate accuracy stability...
We present uniformly reprocessed and re-calibrated data from the RoboPol programme of optopolarimetric monitoring active galactic nuclei (AGN), covering observations between 2013, when instrument was commissioned, 2017. In total, dataset presented in this paper includes 5068 222 AGN with Dec > -25 deg. describe current version pipeline that used to process calibrate entire dataset, we make publicly available for use by astronomical community. Average quantities summarising behaviour (average...
Using tools previously described and applied to the prototype galaxy NGC 891, we model optical far-infrared spectral energy distributions (SED) of four additional edge-on spiral galaxies, namely 5907, 4013, UGC 1082 2048. Comparing predictions with IRAS and, where available, sub-millimeter millimeter observations, determine respective roles old young stellar populations in grain heating. In all cases, population dominates, contribution being at most 40% , as found for 891. After...
view Abstract Citations (120) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Diagnostics of Dust in Spiral Galaxies: Numerical Simulations Radiative Transfer Byun, Y. I. ; Freeman, K. C. Kylafis, N. D. In order to find the best observable diagnostics for amount internal extinction within spiral galaxies, we have constructed realistic models disk galaxies with immersed dust layers. The radiative transfer including both scattering and...