Radiation Spectra

14,000,000 Leading Edge Experts on the ideXlab platform

Scan Science and Technology

Contact Leading Edge Experts & Companies

Scan Science and Technology

Contact Leading Edge Experts & Companies

The Experts below are selected from a list of 86583 Experts worldwide ranked by ideXlab platform

Thomas Pappas - One of the best experts on this subject based on the ideXlab platform.

  • effective temperatures and Radiation Spectra for a higher dimensional schwarzschild de sitter black hole
    Physical Review D, 2017
    Co-Authors: Panagiota Kanti, Thomas Pappas
    Abstract:

    The absence of a true thermodynamical equilibrium for an observer located in the causal area of a Schwarzschild--de Sitter spacetime has repeatedly raised the question of the correct definition of its temperature. In this work, we consider five different temperatures for a higher-dimensional Schwarzschild--de Sitter black hole: the bare ${T}_{0}$, the normalized ${T}_{\mathrm{BH}}$, and three effective ones given in terms of both the black-hole and cosmological horizon temperatures. We find that these five temperatures exhibit similarities but also significant differences in their behavior as the number of extra dimensions and the value of the cosmological constant are varied. We then investigate their effect on the energy emission Spectra of Hawking Radiation. We demonstrate that the Radiation Spectra for the normalized temperature ${T}_{\mathrm{BH}}$---proposed by Bousso and Hawking over twenty years ago---leads to the dominant emission curve, while the other temperatures either support a significant emission rate only in a specific $\mathrm{\ensuremath{\Lambda}}$ regime or have their emission rates globally suppressed. Finally, we compute the bulk-over-brane emissivity ratio and show that the use of different temperatures may lead to different conclusions regarding the brane or bulk dominance.

  • hawking Radiation Spectra for scalar fields by a higher dimensional schwarzschild de sitter black hole
    Physical Review D, 2016
    Co-Authors: Thomas Pappas, Panagiota Kanti, N Pappas
    Abstract:

    In this work, we study the propagation of scalar fields in the gravitational background of a higher-dimensional Schwarzschild--de Sitter black hole as well as on the projected-on-the-brane four-dimensional background. The scalar fields have also a nonminimal coupling to the corresponding, bulk or brane, scalar curvature. We perform a comprehensive study by deriving exact numerical results for the greybody factors, and study their profile in terms of particle and spacetime properties. We then proceed to derive the Hawking Radiation Spectra for a higher-dimensional Schwarzschild--de Sitter black hole, and we study both bulk and brane channels. We demonstrate that the nonminimal field coupling, which creates an effective mass term for the fields, suppresses the energy emission rates while the cosmological constant assumes a dual role. By computing the relative energy rates and the total emissivity ratio for bulk and brane emission, we demonstrate that the combined effect of a large number of extra dimensions and value of the field coupling gives to the bulk channel the clear domination in the bulk-brane energy balance.

Panagiota Kanti - One of the best experts on this subject based on the ideXlab platform.

  • effective temperatures and Radiation Spectra for a higher dimensional schwarzschild de sitter black hole
    Physical Review D, 2017
    Co-Authors: Panagiota Kanti, Thomas Pappas
    Abstract:

    The absence of a true thermodynamical equilibrium for an observer located in the causal area of a Schwarzschild--de Sitter spacetime has repeatedly raised the question of the correct definition of its temperature. In this work, we consider five different temperatures for a higher-dimensional Schwarzschild--de Sitter black hole: the bare ${T}_{0}$, the normalized ${T}_{\mathrm{BH}}$, and three effective ones given in terms of both the black-hole and cosmological horizon temperatures. We find that these five temperatures exhibit similarities but also significant differences in their behavior as the number of extra dimensions and the value of the cosmological constant are varied. We then investigate their effect on the energy emission Spectra of Hawking Radiation. We demonstrate that the Radiation Spectra for the normalized temperature ${T}_{\mathrm{BH}}$---proposed by Bousso and Hawking over twenty years ago---leads to the dominant emission curve, while the other temperatures either support a significant emission rate only in a specific $\mathrm{\ensuremath{\Lambda}}$ regime or have their emission rates globally suppressed. Finally, we compute the bulk-over-brane emissivity ratio and show that the use of different temperatures may lead to different conclusions regarding the brane or bulk dominance.

  • hawking Radiation Spectra for scalar fields by a higher dimensional schwarzschild de sitter black hole
    Physical Review D, 2016
    Co-Authors: Thomas Pappas, Panagiota Kanti, N Pappas
    Abstract:

    In this work, we study the propagation of scalar fields in the gravitational background of a higher-dimensional Schwarzschild--de Sitter black hole as well as on the projected-on-the-brane four-dimensional background. The scalar fields have also a nonminimal coupling to the corresponding, bulk or brane, scalar curvature. We perform a comprehensive study by deriving exact numerical results for the greybody factors, and study their profile in terms of particle and spacetime properties. We then proceed to derive the Hawking Radiation Spectra for a higher-dimensional Schwarzschild--de Sitter black hole, and we study both bulk and brane channels. We demonstrate that the nonminimal field coupling, which creates an effective mass term for the fields, suppresses the energy emission rates while the cosmological constant assumes a dual role. By computing the relative energy rates and the total emissivity ratio for bulk and brane emission, we demonstrate that the combined effect of a large number of extra dimensions and value of the field coupling gives to the bulk channel the clear domination in the bulk-brane energy balance.

N Pappas - One of the best experts on this subject based on the ideXlab platform.

  • hawking Radiation Spectra for scalar fields by a higher dimensional schwarzschild de sitter black hole
    Physical Review D, 2016
    Co-Authors: Thomas Pappas, Panagiota Kanti, N Pappas
    Abstract:

    In this work, we study the propagation of scalar fields in the gravitational background of a higher-dimensional Schwarzschild--de Sitter black hole as well as on the projected-on-the-brane four-dimensional background. The scalar fields have also a nonminimal coupling to the corresponding, bulk or brane, scalar curvature. We perform a comprehensive study by deriving exact numerical results for the greybody factors, and study their profile in terms of particle and spacetime properties. We then proceed to derive the Hawking Radiation Spectra for a higher-dimensional Schwarzschild--de Sitter black hole, and we study both bulk and brane channels. We demonstrate that the nonminimal field coupling, which creates an effective mass term for the fields, suppresses the energy emission rates while the cosmological constant assumes a dual role. By computing the relative energy rates and the total emissivity ratio for bulk and brane emission, we demonstrate that the combined effect of a large number of extra dimensions and value of the field coupling gives to the bulk channel the clear domination in the bulk-brane energy balance.

H Loos - One of the best experts on this subject based on the ideXlab platform.

  • coherent Radiation spectroscopy of few femtosecond electron bunches using a middle infrared prism spectrometer
    Physical Review Letters, 2013
    Co-Authors: T Maxwell, C Behrens, Yuantao Ding, A Fisher, J Frisch, Zhirong Huang, H Loos
    Abstract:

    Modern, high-brightness electron beams such as those from plasma wakefield accelerators and free-electron laser linacs continue the drive to ever-shorter bunch durations. In low-charge operation (� 20 pC), bunches shorter than 10 fs are reported at the Linac Coherent Light Source (LCLS). Though suffering from a loss of phase information, Spectral diagnostics remain appealing as compact, low-cost bunch duration monitors suitable for deployment in beam dynamics studies and operations instrumentation. Progress in middle-infrared (MIR) imaging has led to the development of a single-shot, MIR prism spectrometer to characterize the corresponding LCLS coherent beam Radiation power spectrum for fewfemtosecond scale bunch length monitoring. In this Letter, we report on the spectrometer installation as well as the temporal reconstruction of 3 to 60 fs-long LCLS electron bunch profiles using single-shot coherent transition Radiation Spectra.

  • coherent Radiation spectroscopy of few femtosecond electron bunches using a middle infrared prism spectrometer
    Physical Review Letters, 2013
    Co-Authors: T Maxwell, C Behrens, Yuantao Ding, A Fisher, J Frisch, Zhirong Huang, H Loos
    Abstract:

    Modern, high-brightness electron beams such as those from plasma wakefield accelerators and free-electron laser linacs continue the drive to ever-shorter bunch durations. In low-charge operation ($\ensuremath{\sim}20\text{ }\text{ }\mathrm{pC}$), bunches shorter than 10 fs are reported at the Linac Coherent Light Source (LCLS). Though suffering from a loss of phase information, Spectral diagnostics remain appealing as compact, low-cost bunch duration monitors suitable for deployment in beam dynamics studies and operations instrumentation. Progress in middle-infrared (MIR) imaging has led to the development of a single-shot, MIR prism spectrometer to characterize the corresponding LCLS coherent beam Radiation power spectrum for few-femtosecond scale bunch length monitoring. In this Letter, we report on the spectrometer installation as well as the temporal reconstruction of 3 to 60 fs-long LCLS electron bunch profiles using single-shot coherent transition Radiation Spectra.

A. Rozanska - One of the best experts on this subject based on the ideXlab platform.

  • Radiation Spectra of warm and optically thick coronae in AGNs
    Astronomy and Astrophysics - A&A, 2020
    Co-Authors: Pierre-olivier Petrucci, D. Gronkiewicz, A. Rozanska, R. Belmont, S. Bianchi, B. Czerny, G. Matt, J. Malzac, R. Middei, A. De Rosa
    Abstract:

    A soft X-ray excess above the 2–10 keV power-law extrapolation is generally observed in the X-ray Spectra of active galactic nuclei. The origin of this excess is still not well understood. Presently there are two competitive models: blurred ionized reflection and warm Comptonization. In the case of warm Comptonization, observations suggest a corona temperature in the range 0.1–2 keV and a corona optical depth of about 10–20. Moreover, radiative constraints from Spectral fits with Comptonization models suggest that most of the accretion power should be released in the warm corona and the disk below is basically non-dissipative, radiating only the reprocessed emission from the corona. However, the true radiative properties of such a warm and optically thick plasma are not well known. For instance, the importance of the Comptonization process, the potential presence of strong absorption and/or emission features, and the Spectral shape of the output spectrum have been studied only very recently. Here, we present simulations of warm and optically thick coronae using the TITAN radiative transfer code coupled with the NOAR Monte-Carlo code, the latter fully accounting for Compton scattering of continuum and lines. Illumination from above by hard X-ray emission and from below by an optically thick accretion disk are taken into account, as well as (uniform) internal heating. Our simulations show that for a large part of the parameter space, the warm corona with sufficient internal mechanical heating is dominated by Compton cooling and neither strong absorption nor emission lines are present in the outgoing Spectra. In a smaller part of the parameter space, the calculated emission agrees with the Spectral shape of the observed soft X-ray excess. Remarkably, this also corresponds to the conditions of radiative equilibrium of an extended warm corona covering a non-dissipative accretion disk almost entirely. These results confirm that warm Comptonization is a valuable model that can explain the origin of the soft X-ray excess.

  • Radiation Spectra of warm and optically thick coronae in agn
    arXiv: High Energy Astrophysical Phenomena, 2020
    Co-Authors: Pierre-olivier Petrucci, D. Gronkiewicz, A. Rozanska, R. Belmont, S. Bianchi, B. Czerny, G. Matt, J. Malzac, R. Middei, A. De Rosa
    Abstract:

    A soft X-ray excess above the 2-10 keV power law extrapolation is generally observed in AGN X-ray Spectra. Presently there are two competitive models to explain it: blurred ionized reflection and warm Comptonisation. In the latter case, observations suggest a corona temperature $\sim$ 1 keV and a corona optical depth $\sim$ 10. Moreover, radiative constraints from Spectral fits with Comptonisation models suggest that most of the accretion power should be released in the warm corona. The disk below is basically non-dissipative, radiating only the reprocessed emission from the corona. The true radiative properties of such a warm and optically thick plasma are not well-known, however. For instance, the importance of the Comptonisation process, the potential presence of strong absorption/emission features or the Spectral shape of the output spectrum have been studied only very recently. We present in this paper simulations of warm and optically thick coronae using the TITAN radiative transfer code coupled with the NOAR Monte-Carlo code, the latter fully accounting for Compton scattering of continuum and lines. Illumination from above by a hard X-ray emission and from below by an optically thick accretion disk is taken into account as well as (uniform) internal heating. Our simulations show that for a large part of the parameter space, the warm corona with sufficient internal mechanical heating is dominated by Compton cooling and neither strong absorption nor emission lines are present in the outgoing Spectra. In a smaller part of the parameter space, the calculated emission agrees with the Spectral shape of the observed soft X-ray excess. Remarkably, this also corresponds to the conditions of radiative equilibrium of an extended warm corona covering almost entirely a non-dissipative accretion disk. These results confirm the warm Comptonisation as a valuable model for the soft X-ray excess.

  • the structure and x ray Radiation Spectra of illuminated accretion disks in agn iii modeling fractional variability
    Astronomy and Astrophysics, 2006
    Co-Authors: B. Czerny, R W Goosmann, M Mouchet, G Ponti, M Dovciak, Vladimir Karas, A. Rozanska
    Abstract:

    Context. Random magnetic flares above the accretion disks of Active Galactic Nuclei can account for the production of the primary Radiation and for the rapid X-ray variability that have been frequently observed in these objects. The primary component is partly reprocessed in the disk atmosphere, forming a hot spot underneath the flare source and giving rise to distinct Spectral features. Aims. Extending the work of Czerny et al. (2004, AA the black hole’s angular momentum is a free parameter and is subject to the fitting procedure. Results. We confirm that the rms-variability Spectra involve intrinsic randomness at a significant level when the number of flares appearing during the total observation time is too small. Furthermore, the fractional variability expressed by Fvar is not always compatible with Fpp. In the special case of MCG-6-30-15, we can reproduce the short-timescale variability and model the suppressed variability in the energy range of the Kα line without any need to postulate reprocessing farther away from the center. The presence of the dip in the variability spectrum requires an increasing rate of energy production by the flares toward the center of the disk. The depth of the feature is well represented only if we assume a fast rotation of the central black hole and allow for considerable suppression of the primary flare emission. The modeled line remains consistent with the measured equivalent width of the iron Kα line complex. The model can reproduce the frequently observed suppression of the variability in the Spectral range around 6.5 keV, thereby setting constraints on the black hole spin and on the disk inclination.

  • the structure and x ray Radiation Spectra of illuminated accretion disks in agn iii modeling fractional variability
    arXiv: Astrophysics, 2006
    Co-Authors: R W Goosmann, A. Rozanska, B. Czerny, M Mouchet, G Ponti, M Dovciak, Vladimir Karas, A M Dumont
    Abstract:

    [abridged] Extending the work of Czerny et al. (2004), we model the fractional variability amplitude due to distributions of hot spots co-orbiting on the accretion disk around a supermassive black hole. From defined radial distributions, our code samples random positions for the hot spots across the disk. The local spot emission is computed as reprocessed Radiation coming from a compact primary source above the disk. The structure of the hot spot and the anisotropy of the re-emission are taken into account. We compute the fractional variability Spectra expected from such spot ensembles and investigate dependencies on the parameters describing the radial spot distribution. We consider the fractional variability F_var with respect to the Spectral mean and also the so-called point-to-point F_pp. Our method includes relativistic corrections for the curved space-time; the black hole angular momentum is a free parameter and subject to the fitting procedure. We confirm that the rms-variability Spectra involve intrinsic randomness at a significant level when the number of flares appearing during the total observation time is too small. Furthermore, F_var is not always compatible with F_pp. For MCG -6-30-15, we can reproduce the short-timescale variability and model the suppressed variability in the energy range of the Kalpha line without any need to postulate reprocessing farther away from the center. An increasing rate of energy production by the flares toward the center of the disk, a fast rotation of the central black hole, and considerable suppression of the primary flare emission are required. The modeled line remains consistent with the measured equivalent width of the iron Kalpha line complex.

  • the structure and Radiation Spectra of illuminated accretion disks in agn ii flare spot model of x ray variability
    arXiv: Astrophysics, 2004
    Co-Authors: B. Czerny, A. Rozanska, M Dovciak, Vladimir Karas, A M Dumont
    Abstract:

    We discuss a model of X-ray variability of active galactic nuclei (AGN). We consider multiple spots which originate on the surface of an accretion disk following intense irRadiation by coronal flares. The spots move with the disk around the central black hole and eventually decay while new spots continuously emerge. We construct time sequences of the Spectra of the spotted disk and compute the corresponding energy-dependent fractional variability amplitude. We explore the dependence on the disk inclination and other model parameters. AGN seen at higher inclination with respect to the observer, such as Seyfert 2 galaxies, are expected to have fractional variability amplitude of the direct emission by a factor of a few higher than objects seen face on, such as the Seyfert 1s.