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Author: Publisher: ISBN: Category : Languages : en Pages : 5
Book Description
A search for emission of ultra-high energy gamma radiation from 13 active galactic nuclei that were detected by EGRET, using the CYGNUS extensive air-shower array, is described. The data set has been searched for continuous emission, emission on the time scale of one week, and for on the time scale of out day. No evidence for emission from any of the AGN on any of the time scales examined was found. The 90% C.L. upper limit to the continuous flux from Mrk 421 above 50 TeV is 7.5 [times] 10[sup [minus]14] cm[sup [minus]2]s[sup [minus]1].
Author: Publisher: ISBN: Category : Languages : en Pages : 5
Book Description
A search for emission of ultra-high energy gamma radiation from 13 active galactic nuclei that were detected by EGRET, using the CYGNUS extensive air-shower array, is described. The data set has been searched for continuous emission, emission on the time scale of one week, and for on the time scale of out day. No evidence for emission from any of the AGN on any of the time scales examined was found. The 90% C.L. upper limit to the continuous flux from Mrk 421 above 50 TeV is 7.5 [times] 10[sup [minus]14] cm[sup [minus]2]s[sup [minus]1].
Author: Felix A. Aharonian Publisher: World Scientific ISBN: 9789812561732 Category : Science Languages : en Pages : 516
Book Description
Gamma ray astronomy, the branch of high energy astrophysics that studies the sky in energetic ?-ray photons, is destined to play a crucial role in the exploration of nonthermal phenomena in the Universe in their most extreme and violent forms. The great potential of this discipline offers impressive coverage of many OC hot topicsOCO of modern astrophysics and cosmology, such as the origin of galactic and extragalactic cosmic rays, particle acceleration and radiation processes under extreme astrophysical conditions, and the search for dark matter."
Author: Publisher: ISBN: Category : Languages : en Pages : 72
Book Description
We show that accretion disks around Active Galactic Nuclei (AGNs) could account for the enormous power in observed ultra high energy cosmic rays ≈102° eV (UHEs). In our model, cosmic rays are produced by quasi-steady acceleration of ions in magnetic structures previously proposed to explain jets around Active Galactic Nuclei with supermassive black holes. Steady acceleration requires that an AGN accretion disk act as a dynamo, which we show to follow from a modified Standard Model in which the magnetic torque of the dynamo replaces viscosity as the dominant mechanism accounting for angular momentum conservation during accretion. A black hole of mass M{sub BH} produces a steady dynamo voltage V ∝ √M{sub BH} giving V ≈ 102° volts for M{sub BH} ≈ 108 solar masses. The voltage V reappears as an inductive electric field at the advancing nose of a dynamo-driven jet, where plasma instability inherent in collisionless runaway acceleration allows ions to be steadily accelerated to energies ≈ V, finally ejected as cosmic rays. Transient events can produce much higher energies. The predicted disk radiation is similar to the Standard Model. Unique predictions concern the remarkable collimation of jets and emissions from the jet/radiolobe structure. Given MBH and the accretion rate, the model makes 7 predictions roughly consistent with data: (1) the jet length; (2) the jet radius; (3) the steady-state cosmic ray energy spectrum; (4) the maximum energy in this spectrum; (5) the UHE cosmic ray intensity on Earth; (6) electron synchrotron wavelengths; and (7) the power in synchrotron radiation. These qualitative successes motivate new computer simulations, experiments and data analysis to provide a quantitative verification of the model.
Author: Matteo Cerruti Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
. In this thesis manuscript we tried to summarize the research work done during the last three years in the high-energy group of the LUTh laboratory, as well as in the H.E.S.S. collaboration. The project deals with the study of high-energy emission from active galactic nuclei (AGN), where, with high energy, we refer here to X and y-rays. The thesis covers in fact two différent aspects of the physics of AGN, firstly the study of the X-ray emission from Seyfert galaxies (radio-quiet AGN), and then of the y-ray emission from blazars (radio-loud AGN).We start then by providing a short introduction to the scientific context of AGN physics (by present- ing the unified AGN model), as well as of TeV astronomy. In the first part we first describe the problem of the soft-X-ray excess in Seyfert galaxies (Chapter 1), before entering in the details of the study of Suzaku observations of two particular objects (Mrk 509 and Mrk 841, Chapter 2), presenting the data analysis and their modelling. The second part starts with an introduction on the blazar physics (Chapter 3), before showing the results achieved by the H.E.S.S. telescope array on AGN (Chapter 4). A detailed study has been done on a particular blazar detected at TeV energies (1RXS J101015.9 - 311909), and is presented in Chapter 5. The following chapters are more theoretical, and discuss the modelling of the observed blazar emis- sion. In particular, in Chapter 6 we discuss the constrains on the synchrotron-self-Compton model, presenting a new numerical algorithm to determine the best-fit solution, while in Chapter 7 we present a new stationary lepto-hadronic code, which can be used to model the blazar emission in leptonic, hadronic and mixed scenarios.In Chapter 8 we present the problem of the spectral break observed in the GeV spectrum of 3C 454.3, and we model it consistently in an external-inverse-Compton scenario.Finally we present a perspective for the detection of high-redshift sources with the future telescope CTA (Appendix A).
Author: Felix A Aharonian Publisher: World Scientific ISBN: 981449139X Category : Science Languages : en Pages : 511
Book Description
Gamma ray astronomy, the branch of high energy astrophysics that studies the sky in energetic γ-ray photons, is destined to play a crucial role in the exploration of nonthermal phenomena in the Universe in their most extreme and violent forms. The great potential of this discipline offers impressive coverage of many “hot topics” of modern astrophysics and cosmology, such as the origin of galactic and extragalactic cosmic rays, particle acceleration and radiation processes under extreme astrophysical conditions, and the search for dark matter. The recent observational results and exciting theoretical predictions provide a strong rationale for a deep study of cosmic radiation with forthcoming satellite-borne and ground-based detectors in the so-called very high energy domain of the electromagnetic spectrum above 1010 eV.This invaluable book presents the motivations and highlights the principal objectives of the field, as well as demonstrates its intrinsic links to other branches of high energy astrophysics. Preference is given to three topical areas: (i) origin of cosmic rays; (ii) physics and astrophysics of relativistic jets; (iii) observational gamma ray cosmology. Also, an essential part of the book is devoted to the discussion of the principal mechanisms of production and absorption of energetic γ-rays in different astrophysical environments, as well as to the description of the detection methods of high energy cosmic γ-radiation.
Author: Publisher: ISBN: Category : Languages : en Pages : 11
Book Description
Data collected by the Pierre Auger Observatory provide evidence for anisotropy in the arrival directions of cosmic rays (CRs) with energies>57 EeV that suggests a correlation with the positions of active galactic nuclei (AGN) located within H"5 Mpc. However, this analysis does not take into account AGN morphology. A detailed study of the sample of AGN whose positions correlate with the CR events shows that most of them are classified as Seyfert 2 and low-ionization nuclear emission-line region (LINER) galaxies which do not differ from other local AGN of the same types. Therefore, the claimed correlation between the CR events observed by the Pierre Auger Observatory and local active galaxies should be considered as resulting from a chance coincidence, if the production of the highest energy CRs is not episodic in nature, but operates in a single object on long (e"Myr) timescales. Additionally, most of the selected sources do not show significant jet activity, and hence--in the framework of the jet paradigm--there are no reasons for expecting them to accelerate CRs up to the highest energies, H"02° eV, at all. If the extragalactic magnetic fields and the sources of these CRs are coupled with matter, it is possible that the deflection angle is larger than expected in the case of a uniform source distribution due to effectively larger fields. A future analysis has to take into account AGN morphology and may yield a correlation with a larger deflection angle and/or more distant sources. We further argue that Cen A alone could be associated with at least 4 events due to its large radio extent, and Cen B can be associated with more than 1 event due to its proximity to the Galactic plane and, correspondingly, the stronger Galactic magnetic field the ultra high energy CRs (UHECRs) encounter during propagation. If the UHECRs associated with these events are indeed accelerated by Cen A and Cen B, their deflection angles may provide information on the structure of the magnetic field in the direction of these putative sources. Future -ray observations (by, e.g., Gamma-Ray Large Area Space Telescope [GLAST], High Energy Stereoscopic System [HESS]) may provide additional clues to the nature of the accelerators of the UHECRs in the local Universe.
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Author: Peter L. Biermann
Author: Yannick Giraud-Héraud
Author: Wai-Ying Mak
Author: Wai-ying Mak
Author: Felix A. Aharonian
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Author: Matteo Cerruti
Author: Felix A Aharonian
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