The Experts below are selected from a list of 17049 Experts worldwide ranked by ideXlab platform
Robert Hanus - One of the best experts on this subject based on the ideXlab platform.
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Applicability of time-domain feature extraction methods and artificial intelligence in two-phase flow meters based on Gamma-Ray Absorption technique
Measurement, 2021Co-Authors: Mohammad Amir Sattari, Gholam Hossein Roshani, Robert Hanus, E. NazemiAbstract:Abstract Determining the type of flow pattern and gas volumetric percentage with high precision is one of the vital topics for researchers in this field. For this, in this paper, three different types of liquid–gas two-phase flow regimes, namely annular, stratified, and homogenous were simulated in various gas volumetric percentages ranging from 5% to 90%. Simulations were performed by Monte Carlo N Particle (MCNP) code. Metering system includes one 137Cs sources, one Pyrex glass, and two NaI detectors to register the transmitted photons. Because the signals which are received from the MCNP simulations contain high-frequency noises, the Savitzky-Golay filter has been applied to solve this problem. Then, thirteen characteristics in time domain were extracted from the recorded data of both detectors. Since none of features were capable of completely separating the flow regimes, two methods as “extracting two different features from the recorded data of both detectors” and “extracting three features from the recorded data of both detectors” were proposed. Using these methods, many different separator cases were found and the best separator cases were distinguished via S parameter. Finally, two artificial neural network (ANN) models of multilayer perceptron (MLP) were implemented for each method to identify the flow regimes and approximate the gas volumetric percentages. The proposed methodology and networks could diagnose all flow patterns properly, and also predict the volumetric percentage with a root mean square error (RMSE) of less than 0.60. Increasing the precision of two-phase flow meter by extracting time-domain features and signal processing techniques is the most important advantage of this study.
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Evaluation of the structures size in the liquid-gas flow by Gamma-Ray Absorption
Epj Web of Conferences, 2018Co-Authors: Marcin Zych, Robert Hanus, Marek Jaszczur, Dariusz Świsulski, Leszek Petryka, Paweł Jodłowski, Piotr ZychAbstract:The rapid development of tomography methods particularly electrical, X and Gamma Rays allows for a wide range of the information about flow structure. However, all of such methods are quite complicated. At the same time much simpler systems as the measuring system of Gamma Rays Absorption, allows to obtain a all key flow information which describe the two-phase flow. In the article the results of analyzes of radiometric signal that not only allow to recognize the type of flow, but also the assessment of forming structures are presented. Calculation and interpretation of the data were based on the crosscorrelation and cross-spectral density function. In order to verify the calculations the photographic documentation made during the measurements was used.
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identification of liquid gas flow regime in a pipeline using Gamma Ray Absorption technique and computational intelligence methods
Flow Measurement and Instrumentation, 2018Co-Authors: Robert Hanus, Marcin Zych, Marek Jaszczur, Maciej Kusy, Leszek PetrykaAbstract:Abstract Liquid-gas flows in pipelines occur frequently in the mining, nuclear, and oil industry. One of the non-contact techniques useful for studying such flows is the Gamma Ray Absorption method. An analysis of the signals from scintillation detectors allows us to determine the number of flow parameters and to identify the flow structure. In this work, four types of liquid-gas flow regimes as a slug, plug, bubble, and transitional plug – bubble were evaluated using computational intelligence methods. The experiments were carried out for water-air flow through a horizontal pipeline. A sealed Am-241 Gamma Ray source and a NaI(Tl) scintillation detector were used in the research. Based on the measuring signal analysis in the time domain, nine features were extracted which were used at the input of the classifier. Six computational intelligence methods (K-means clustering algorithm, single decision tree, probabilistic neural network, multilayer perceptron, radial basic function neural network and support vector machine) were used for a two-phase flow structure identification. It was found that all the methods give good recognition results for the types of flow examined. These results confirm the usefulness of Gamma Ray Absorption in combination with artificial intelligence methods for liquid-gas flow regime classification.
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application of the hilbert transform to measurements of liquid gas flow using Gamma Ray densitometry
International Journal of Multiphase Flow, 2015Co-Authors: Robert HanusAbstract:Abstract Measuring parameters of two-phase flows usually requires contactless measuring techniques to be used together alongside advanced methods of signal processing. One of these techniques, which has been employed for many years in measurements of liquid–gas, liquid–solids and gas–solid flows is a method of Gamma-Ray densitometry. Frequently in such measurements mutually delayed stochastic signals are received from the scintillation detectors. For the analysis of such signals a well-known cross-correlation function (CCF) is used due to the random nature of the signals and the presence of disturbances. This paper applies the Hilbert Transform to the time delay estimation in measurements of two-phase flow performed by using Gamma-Ray Absorption. It presents the selected results of study of the modified CCFHT cross-correlation method, in which a Hilbert Transform of one measured signal is used. The experiments have been carried out for two-phase water–air flow through a horizontal pipeline of 30 mm inner diameter. A sealed 241Am Gamma Ray source of 59.5 keV energy has been used in the experiments mentioned above, together with scintillation detectors based on NaI(Tl) crystals. Based on obtained values of time delay the mean velocity of gaseous phase transported by liquid was calculated. It is stated, that the CCFHT method provides better metrological properties than the classical CCF. In the presented experiments combined uncertainties of the gas phase average velocity did not exceed 3.1% for CCF and 0.05% for CCFHT.
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velocity measurement of the liquid solid flow in a vertical pipeline using Gamma Ray Absorption and weighted cross correlation
Flow Measurement and Instrumentation, 2014Co-Authors: Robert Hanus, Leszek Petryka, Marcin ZychAbstract:Abstract Developing technology for the deep-sea mining of polymetallic nodules requires, theoretical analyses, simulation and numerous experimental studies. In this paper authors focused on nuclear methods adoption to velocity of solid phase measurement in an extremely hard and varying environment. Selected results of the experimental studies of two-phase liquid–solid particles flow in a vertical pipeline obtained by probing with photon beams are presented. With the use of the sealed 241Am isotopes emitting Gamma radiation of 59.5 keV, and the scintillation probes with NaI(TI) detectors, the average transport velocity for ceramic models representing natural polymetallic nodules were determined. In the paper for analysis of the signals coming from the probes, the cross correlation function (CCF) and its modifications consisting in the combination of the CCF with such procedures as the average square difference function (ASDF) and the average magnitude difference function (AMDF) were used. An example of measurement is presented and its resulting uncertainties determined. In described experiment the relative values of the combined uncertainty of solid particles average velocity estimation are equal to: 3.2% for the CCF, 3.0% for the CCF/AMDF and 2.8% for the CCF/ASDF.
Tomonori Totani - One of the best experts on this subject based on the ideXlab platform.
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extragalactic background light from hierarchical galaxy formation Gamma Ray attenuation up to the epoch of cosmic reionization and the first stars
The Astrophysical Journal, 2013Co-Authors: Yoshiyuki Inoue, Susumu Inoue, Masakazu A R Kobayashi, Ryu Makiya, Yuu Niino, Tomonori TotaniAbstract:We present a new model of the extragalactic background light (EBL) and corresponding γγ opacity for intergalactic Gamma-Ray Absorption from z = 0 up to z = 10, based on a semi-analytical model of hierarchical galaxy formation that reproduces key observed properties of galaxies at various redshifts. Including the potential contribution from Population III stars and following the cosmic reionization history in a simplified way, the model is also broadly consistent with available data concerning reionization, particularly the Thomson scattering optical depth constraints from Wilkinson Microwave Anisotropy Probe (WMAP). In comparison with previous EBL studies up to z ~ 3-5, our predicted γγ opacity is in general agreement for observed Gamma-Ray energy below 400/(1 + z) GeV, whereas it is a factor of ~2 lower above this energy because of a correspondingly lower cosmic star formation rate, even though the observed ultraviolet (UV) luminosity is well reproduced by virtue of our improved treatment of dust obscuration and direct estimation of star formation rate. The horizon energy at which the Gamma-Ray opacity is unity does not evolve strongly beyond z ~ 4 and approaches ~20 GeV. The contribution of Population III stars is a minor fraction of the EBL at z = 0, and is also difficult to distinguish through Gamma-Ray Absorption in high-z objects, even at the highest levels allowed by the WMAP constraints. Nevertheless, the attenuation due to Population II stars should be observable in high-z Gamma-Ray sources by telescopes such as Fermi or the Cherenkov Telescope ArRay and provide a valuable probe of the evolving EBL in the rest-frame UV. The detailed results of our model are publicly available in numerical form at http://www.slac.stanford.edu/~yinoue/Download.html.
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extragalactic background light from hierarchical galaxy formation Gamma Ray attenuation up to the epoch of cosmic reionization and the first stars
arXiv: Cosmology and Nongalactic Astrophysics, 2012Co-Authors: Yoshiyuki Inoue, Susumu Inoue, Masakazu A R Kobayashi, Ryu Makiya, Yuu Niino, Tomonori TotaniAbstract:We present a new model of the extragalactic background light (EBL) and corresponding Gamma-Gamma opacity for intergalactic Gamma-Ray Absorption from z = 0 up to z = 10, based on a semi-analytical model of hierarchical galaxy formation that reproduces key observed properties of galaxies at various redshifts. Including the potential contribution from Population III stars and following the cosmic reionization history in a simplified way, the model is also broadly consistent with available data concerning reionization, particularly the Thomson scattering optical depth constraints from WMAP. In comparison with previous EBL studies up to z ~ 3-5, our predicted Gamma-Gamma opacity is in general agreement for observed Gamma-Ray energy below 400/(1 + z) GeV, whereas it is a factor of ~ 2 lower above this energy because of a correspondingly lower cosmic star formation rate, even though the observed UV luminosity is well reproduced by virtue of our improved treatment of dust obscuration and direct estimation of star formation rate. The horizon energy at which the Gamma-Ray opacity is unity does not evolve strongly beyond z ~ 4 and approaches ~ 20 GeV. The contribution of Population III stars is a minor fraction of the EBL at z = 0, and is also difficult to distinguish through Gamma-Ray Absorption in high-z objects, even at the highest levels allowed by the WMAP constraints. Nevertheless, the attenuation due to Population II stars should be observable in high-z Gamma-Ray sources by telescopes such as Fermi or CTA and provide a valuable probe of the evolving EBL in the rest-frame UV. The detailed results of our model are publicly available in numerical form at the URL this http URL
Dmitry Khangulyan - One of the best experts on this subject based on the ideXlab platform.
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non thermal radiation from a pulsar wind interacting with an inhomogeneous stellar wind
Astronomy and Astrophysics, 2017Co-Authors: Victor M De La Cita, V Boschramon, Dmitry Khangulyan, X Paredesfortuny, M PeruchoAbstract:Context. Binaries hosting a massive star and a non-accreting pulsar are powerful non-thermal emitters owing to the interaction of the pulsar and the stellar wind. The winds of massive stars are thought to be inhomogeneous, which could have an impact on the non-thermal emission. Aims. We study numerically the impact of the presence of inhomogeneities or clumps in the stellar wind on the high-energy non-thermal radiation of high-mass binaries hosting a non-accreting pulsar. Methods. We compute the trajectories and physical properties of the streamlines in the shocked pulsar wind without clumps, with a small clump, and with a large clump. This information is used to characterize the injection and the steady state distribution of non-thermal particles accelerated at shocks formed in the pulsar wind. The synchrotron and inverse Compton emission from these non-thermal particles is calculated, accounting also for the effect of Gamma-Ray Absorption through pair creation. A specific study is done for PSR B1259-63/LS2883. Results. When stellar wind clumps perturb the two-wind interaction region, the associated non-thermal radiation in the X-Ray band, of synchrotron origin, and in the GeV–TeV band, of inverse Compton origin, is affected by several equally important effects: (i) strong changes in the plasma velocity direction that result in Doppler boosting factor variations; (ii) strengthening of the magnetic field that mainly enhances the synchrotron radiation; (iii) strengthening of the pulsar wind kinetic energy dissipation at the shock, potentially available for particle acceleration; and (iv) changes in the rate of adiabatic losses that affect the lower energy part of the non-thermal particle population. The radiation above 100 GeV detected, presumably, during the post-periastron crossing of the Be star disc in PSR B1259-63/LS2883, can be roughly reproduced assuming that the crossing of the disc is modelled as the encounter with a large inhomogeneity. Conclusions. Because of the likely diverse nature of clumps in the stellar wind, and hydrodynamical instabilities, the non-thermal radiation of high-mass binaries with a non-accreting pulsar is expected to be boosted somewhat chaotically, and to present different superimposed variability patterns. Some of the observed variability in Gamma Rays from PSR B1259-63/LS2883 is qualitatively reproduced by our calculations.
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non thermal radiation from a pulsar wind interacting with an inhomogeneous stellar wind
arXiv: High Energy Astrophysical Phenomena, 2016Co-Authors: Victor M De La Cita, V Boschramon, Dmitry Khangulyan, X Paredesfortuny, M PeruchoAbstract:Binaries hosting a massive star and a non-accreting pulsar are powerful non-thermal emitters due to the interaction of the pulsar and the stellar wind. The winds of massive stars are thought to be inhomogeneous, which could have an impact on the non-thermal emission. We study numerically the impact of the presence of inhomogeneities or clumps in the stellar wind on the high-energy non-thermal radiation of high-mass binaries hosting a non-accreting pulsar. We compute the trajectories and physical properties of the streamlines in the shocked pulsar wind without clumps, with a small clump, and with a large one. This information is used to compute the synchrotron and inverse Compton emission from the non-thermal populations, accounting also for the effect of Gamma-Ray Absorption through pair creation. A specific study is done for PSR B1259-63/LS2883. When stellar wind clumps perturb the two-wind interaction region, the associated non-thermal radiation in the X-Ray band,of synchrotron origin, and in the GeV-TeV band, of inverse Compton origin, is affected by several effects: (i) strong changes in the the plasma velocity direction that result in Doppler boosting factor variations, (ii) strengthening of the magnetic field that mainly enhances the synchrotron radiation, (iii) strengthening of the pulsar wind kinetic energy dissipation at the shock, potentially available for particle acceleration, and (iv) changes in the rate of adiabatic losses that affect the lower energy part of the non-thermal particle population. The radiation above 100 GeV detected, presumably, during the post-periastron crossing of the Be star disc in PSR B1259-63/LS2883, can be roughly reproduced assuming that the crossing of the disc is modeled as the encounter with a large inhomogeneity.
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formation of hard very high energy Gamma Ray spectra of blazars due to internal photon photon Absorption
Monthly Notices of the Royal Astronomical Society, 2008Co-Authors: F Aharonian, Dmitry Khangulyan, L CostamanteAbstract:The energy spectra of TeV Gamma-Rays from blazars, after being corrected for intergalatic Absorption in the Extragalactic Background Light (EBL), appear unusually hard, a fact that poses challenges to the conventional models of particle acceleration in TeV blazars and/or to the EBL models. In this paper we show that the internal Absorption of Gamma-Rays caused by interactions with dense narrow-band radiation fields in the vicinity of compact Gamma-Ray production regions can lead to the formation of Gamma-Ray spectra of an almost arbitrary hardness. This allows significant relaxation of the current tight constraints on particle acceleration and radiation models, although at the expense of enhanced requirements to the available nonthermal energy budget. The latter, however, is not a critical issue, as long as it can be largely compensated by the Doppler boosting, assuming very large (> 30) Doppler factors of the relativistically moving Gamma-Ray production regions. The suggested scenario of formation of hard Gamma-Ray spectra predicts detectable synchrotron radiation of secondary electronpositron pairs which might require a revision of the current “standard paradigm” of spectral energy distributions of Gamma-Ray blazars. If the primary Gamma-Rays are of hadronic origin related to pp or pγ interactions, the “internal Gamma-Ray Absorption” model predicts neutrino fluxes close to the detection threshold of the next generation high energy neutrino detectors.
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formation of hard vhe Gamma Ray spectra of blazars due to internal photon photon Absorption
arXiv: Astrophysics, 2008Co-Authors: F Aharonian, Dmitry Khangulyan, L CostamanteAbstract:The energy spectra of TeV Gamma-Rays from blazars, after being corrected for intergalatic Absorption in the Extragalactic Background Light (EBL), appear unusually hard, a fact that poses challenges to the conventional models of particle acceleration in TeV blazars and/or to the EBL models. In this paper we show that the internal Absorption of Gamma-Rays caused by interactions with dense narrow-band radiation fields in the vicinity of compact Gamma-Ray production regions can lead to the formation of Gamma-Ray spectra of an almost arbitrary hardness. This allows significant relaxation of the current tight constraints on particle acceleration and radiation models, although at the expense of enhanced requirements to the available nonthermal energy budget. The latter, however, is not a critical issue, as long as it can be largely compensated by the Doppler boosting, assuming very large ($\geq 30$) Doppler factors of the relativistically moving Gamma-Ray production regions. The suggested scenario of formation of hard Gamma-Ray spectra predicts detectable synchrotron radiation of secondary electron-positron pairs which might require a revision of the current ``standard paradigm'' of spectral energy distributions of Gamma-Ray blazars. If the primary Gamma-Rays are of hadronic origin related to $pp$ or $p \Gamma$ interactions, the ``internal Gamma-Ray Absorption'' model predicts neutrino fluxes close to the detection threshold of the next generation high energy neutrino detectors.
M Perucho - One of the best experts on this subject based on the ideXlab platform.
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non thermal radiation from a pulsar wind interacting with an inhomogeneous stellar wind
Astronomy and Astrophysics, 2017Co-Authors: Victor M De La Cita, V Boschramon, Dmitry Khangulyan, X Paredesfortuny, M PeruchoAbstract:Context. Binaries hosting a massive star and a non-accreting pulsar are powerful non-thermal emitters owing to the interaction of the pulsar and the stellar wind. The winds of massive stars are thought to be inhomogeneous, which could have an impact on the non-thermal emission. Aims. We study numerically the impact of the presence of inhomogeneities or clumps in the stellar wind on the high-energy non-thermal radiation of high-mass binaries hosting a non-accreting pulsar. Methods. We compute the trajectories and physical properties of the streamlines in the shocked pulsar wind without clumps, with a small clump, and with a large clump. This information is used to characterize the injection and the steady state distribution of non-thermal particles accelerated at shocks formed in the pulsar wind. The synchrotron and inverse Compton emission from these non-thermal particles is calculated, accounting also for the effect of Gamma-Ray Absorption through pair creation. A specific study is done for PSR B1259-63/LS2883. Results. When stellar wind clumps perturb the two-wind interaction region, the associated non-thermal radiation in the X-Ray band, of synchrotron origin, and in the GeV–TeV band, of inverse Compton origin, is affected by several equally important effects: (i) strong changes in the plasma velocity direction that result in Doppler boosting factor variations; (ii) strengthening of the magnetic field that mainly enhances the synchrotron radiation; (iii) strengthening of the pulsar wind kinetic energy dissipation at the shock, potentially available for particle acceleration; and (iv) changes in the rate of adiabatic losses that affect the lower energy part of the non-thermal particle population. The radiation above 100 GeV detected, presumably, during the post-periastron crossing of the Be star disc in PSR B1259-63/LS2883, can be roughly reproduced assuming that the crossing of the disc is modelled as the encounter with a large inhomogeneity. Conclusions. Because of the likely diverse nature of clumps in the stellar wind, and hydrodynamical instabilities, the non-thermal radiation of high-mass binaries with a non-accreting pulsar is expected to be boosted somewhat chaotically, and to present different superimposed variability patterns. Some of the observed variability in Gamma Rays from PSR B1259-63/LS2883 is qualitatively reproduced by our calculations.
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non thermal radiation from a pulsar wind interacting with an inhomogeneous stellar wind
arXiv: High Energy Astrophysical Phenomena, 2016Co-Authors: Victor M De La Cita, V Boschramon, Dmitry Khangulyan, X Paredesfortuny, M PeruchoAbstract:Binaries hosting a massive star and a non-accreting pulsar are powerful non-thermal emitters due to the interaction of the pulsar and the stellar wind. The winds of massive stars are thought to be inhomogeneous, which could have an impact on the non-thermal emission. We study numerically the impact of the presence of inhomogeneities or clumps in the stellar wind on the high-energy non-thermal radiation of high-mass binaries hosting a non-accreting pulsar. We compute the trajectories and physical properties of the streamlines in the shocked pulsar wind without clumps, with a small clump, and with a large one. This information is used to compute the synchrotron and inverse Compton emission from the non-thermal populations, accounting also for the effect of Gamma-Ray Absorption through pair creation. A specific study is done for PSR B1259-63/LS2883. When stellar wind clumps perturb the two-wind interaction region, the associated non-thermal radiation in the X-Ray band,of synchrotron origin, and in the GeV-TeV band, of inverse Compton origin, is affected by several effects: (i) strong changes in the the plasma velocity direction that result in Doppler boosting factor variations, (ii) strengthening of the magnetic field that mainly enhances the synchrotron radiation, (iii) strengthening of the pulsar wind kinetic energy dissipation at the shock, potentially available for particle acceleration, and (iv) changes in the rate of adiabatic losses that affect the lower energy part of the non-thermal particle population. The radiation above 100 GeV detected, presumably, during the post-periastron crossing of the Be star disc in PSR B1259-63/LS2883, can be roughly reproduced assuming that the crossing of the disc is modeled as the encounter with a large inhomogeneity.
G Barbiellini - One of the best experts on this subject based on the ideXlab platform.
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minute timescale 100 mev γ Ray variability during the giant outburst of quasar 3c 279 observed by fermi lat in 2015 june
The Astrophysical Journal, 2016Co-Authors: M Ackermann, Richard Anantua, Katsuaki Asano, L Baldini, G Barbiellini, D Bastieri, Becerra J GonzalezAbstract:On 2015 June 16, Fermi-LAT observed a giant outburst from the flat spectrum radio quasar 3C 279 with a peak $>100$ MeV flux of $\sim3.6\times10^{-5}\;{\rm photons}\;{\rm cm}^{-2}\;{\rm s}^{-1}$ averaged over orbital period intervals. It is the historically highest $\Gamma$-Ray flux observed from the source including past EGRET observations, with the $\Gamma$-Ray isotropic luminosity reaching $\sim10^{49}\;{\rm erg}\;{\rm s}^{-1}$. During the outburst, the Fermi spacecraft, which has an orbital period of 95.4 min, was operated in a special pointing mode to optimize the exposure for 3C 279. For the first time, significant flux variability at sub-orbital timescales was found in blazar observations by Fermi-LAT. The source flux variability was resolved down to 2-min binned timescales, with flux doubling times less than 5 min. The observed minute-scale variability suggests a very compact emission region at hundreds of Schwarzschild radii from the central engine in conical jet models. A minimum bulk jet Lorentz factor ($\Gamma$) of 35 is necessary to avoid both internal $\Gamma$-Ray Absorption and super-Eddington jet power. In the standard external-radiation-Comptonization scenario, $\Gamma$ should be at least 50 to avoid overproducing the synchrotron-self-Compton component. However, this predicts extremely low magnetization ($\sim5\times10^{-4}$). Equipartition requires $\Gamma$ as high as 120, unless the emitting region is a small fraction of the dissipation region. Alternatively, we consider $\Gamma$ Rays originating as synchrotron radiation of $\Gamma_{\rm e}\sim1.6\times10^6$ electrons, in magnetic field $B\sim1.3$ kG, accelerated by strong electric fields $E\sim B$ in the process of magnetoluminescence. At such short distance scales, one cannot immediately exclude production of $\Gamma$ Rays in hadronic processes.
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early fermi Gamma Ray space telescope observations of the quasar 3c 454 3
The Astrophysical Journal, 2009Co-Authors: M Ajello, M Ackermann, L Baldini, G Barbiellini, A A Abdo, W B Atwood, M Axelsson, J BalletAbstract:This is the first report of Fermi Gamma-Ray Space Telescope observations of the quasar 3C 454.3, which has been undergoing pronounced long-term outbursts since 2000. The data from the Large Area Telescope (LAT), covering 2008 July 7 - October 6, indicate strong, highly variable Gamma-Ray emission with an average flux of ~3 x 10^{-6} photons cm^{-2} s^{-1}, for energies above 100 MeV. The Gamma-Ray flux is variable, with strong, distinct, symmetrically-shaped flares for which the flux increases by a factor of several on a time scale of about three days. This variability indicates a compact emission region, and the requirement that the source is optically thin to pair-production implies relativistic beaming with Doppler factor delta > 8, consistent with the values inferred from VLBI observations of superluminal expansion (delta ~ 25). The observed Gamma-Ray spectrum is not consistent with a simple power-law, but instead steepens strongly above ~2 GeV, and is well described by a broken power-law with photon indices of ~2.3 and ~3.5 below and above the break, respectively. This is the first direct observation of a break in the spectrum of a high luminosity blazar above 100 MeV, and it is likely direct evidence for an intrinsic break in the energy distribution of the radiating particles. Alternatively, the spectral softening above 2 GeV could be due to Gamma-Ray Absorption via photon-photon pair production on the soft X-Ray photon field of the host AGN, but such an interpretation would require the dissipation region to be located very close (less than 100 gravitational radii) to the black hole, which would be inconsistent with the X-Ray spectrum of the source.
