Burning Plasma Research Group, Politecnico di Torino, Italy




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PARTICLE ACCELERATION: FROM GALAXIES TO LARGE SCALE STRUCTURES


Peter L. Biermann*

Max Planck Institute for Radioastronomy, and Dept for Physics and Astronomy

University of Bonn Bonn, Germany


Energetic particles exist almost everywhere in the Universe, usually in cohabitation with magnetic fields; and although we have some ideas where these energetic particles and magnetic fields come from, we are not certain at all. Here we discuss on both Galactic and extragalactic cosmic ray particles, and focus on the simplest models in debate. Standard shock acceleration in the Interstellar Medium leads to energies below the feature in the cosmic ray spectrum usually referred to as the knee, at 3 1015 eV, where the spectrum bends down by about 1/3. There is one proposal published that links this feature to the explosion of very massive stars, especially Wolf Rayet stars. The observed features, at knee and ankle are so well defined that the critical E/Z ratio must be very well defined in Nature, and be common to all sites contributing to our cosmic ray population. This then leads back to the argument by Bisnovatyi-Kogan (1970) that supernovae are powered by potential energy, and that the energy is transmitted from rotation via magnetic fields to the outside; this argument can be made quantitative. Considering then the abundances of cosmic rays this proposal requires that very massive stars explode with 1052 ergs, just what the hypernova model of Paczynski suggested, providing a clear connection in the physical model to Gamma Ray Bursts. These explosions may provide a new standard candle in cosmology, if we found a way to correct for non-sphericity. The origin of Galactic magnetic fields may also lie with the powerful winds of Wolf Rayet stars; however, we still do not know the origin of the large scale order of the magnetic fields. Radiogalaxies and Gamma Ray Bursts provide possible sources for the ultrahigh energy cosmic rays. The topology of the large scale magnetic fields, first in a putative Galactic magnetic wind, and then in the supergalactic plane, are key to check on all such proposals. The prominent shock waves in the large scale structure itself are yet another source for energetic particles, albeit probably not for the highest energies. The most conservative candidate for the locally observed ultra high energy cosmic ray particles is the Virgo cluster radio galaxy M87.


MAGNETIC FIELDS AND ULTRA HIGH ENERGY COSMIC RAYS


Angela V. Olinto*

University of Chicago, USA


The observation of cosmic rays at the highest energies will help to determine cosmic magnetic fields on the largest scales. We review the state of ultra-high energy cosmic ray observations and the ability of next generation observatories to test cosmic magnetic fields.


ACCELERATION AND PROPAGATION OF UHECRS


P. Blasi*

Observatory of Arcetri, Italy


MAGNETIC LENSING AND CLUSTERING OF ULTRA HIGH ENERGY COSMIC RAYS


Diego Harari, Silvia Mollerach, Esteban Roulet

CONICET - Centro Atomico Bariloche, Argentina


Ultra high energy cosmic ray (UHECR) astronomy is inevitably tied to the magnetic fields along the line of sight towards the most powerful sources if the bulk of their emission is in the form of charged particles. The behaviour of the transition from a diffusive regime towards quasirectilinear propagation at the highest energies is a very rich source of information, both on the source properties as well as on the magnetic fields. We summarize strategies to reconstruct the parameters of intervening magnetic fields based on the lensing phenomena that take place around a characteristic energy at which it is likely to observe strongly magnified multiple images of single UHECR sources. We discuss properties of the clustering of arrival directions that may be expected from lensing effects. We identify tools that may help to characterize the nature of cosmic ray sources based on the clustering properties of observed events.


EVOLUTION OF THE ISM OF STARBURST GALAXIES AND THE FORMATION

OF GALACTIC SUPERWINDS


Claudio Melioli, Elisabete M. de Gouveia Dal Pino

Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Brazil


The interstellar medium heated by supernova explosions (SN) may acquire an expansion velocity larger than the escape velocity and leave the galaxy through a supersonic wind. Galactic winds are effectively observed in many local starburst galaxies. SN ejecta are transported out of the galaxies by such winds, therefore affecting the chemical evolution of those galaxies. The effectiveness of the processes mentioned above depends on the heating efficiency (HE) of the SNe, i.e., on the fraction of the SNe explosion energy that is effectively stored in the ISM gas, in the form of kinetic and internal energy to produce the wind, and that is not radiated away. The value of HE, in particular in starburst (SB) galaxies, is still a matter of debate. Considering the essential ingredients of a SB environment we have developed a semi-analytic model, which is able to qualitatively trace the thermalisation history of the ISM in a SB region and determine the HE evolution. Our study has been also accompanied by full 3-D radiative cooling hydrodynamical simulations of SNR-SNR and SNR- clouds interactions. We have found that the heating efficiency of the SNe is very sensitive to the amount of ambient gas and clouds of the SB, and may remain very small at least during part of the SB lifetime, therefore preventing or postponing the formation of a superwind (Melioli & de Gouveia Dal Pino 2004, Melioli & de Gouveia Dal Pino, Raga 2004). As long as the efficiency remains small, the cooled gas remains confined to the system and can promote new generations of star-formation, or increase the gas in-fall to the central regions of the SB. As the ambient density decreases, the gas can finally heat and expand very rapidly and abandon the galaxy as a superwind. A magneto-centrifugal mechanism to accelerate and collimate these superwinds as a function of the SNe heating efficiency is also discussed.


- C. Melioli & E. M. de Gouveia Dal Pino, A&A, 424, 817 (2004)

- C. Melioli, E. M. de Gouveia Dal Pino, & A. Raga (2004), in prep.

XIV. Magnetic Fields in Galaxies and the IGM


MHD GAS FLOW IN THE GALAXY: MODELING THE BAR AND

THE SPIRAL PATTERNS


M. Martos*

University of California & Universidad Autonoma de Mexico


Collisions of High Velocity Clouds with a Magnetized Galactic Disk


Alfredo Santillán*

Cómputo Aplicado-DGSCA, UNAM, México


High-velocity clouds are large flows of neutral hydrogen, located at high galactic latitudes, with large velocities (| VLSR |  100 km/s) that do not match a simple model of circular rotation for our Galaxy. Numerical simulations have been performed during many years to study the details of their evolution, and their possible interaction with the interstellar disk. Here we present a brief review of the models that have been already published, and describe three-dimensional magneto hydrodynamical simulations of the HVC-Magnetized Galactic Disk interaction.


DETECTION OF NUMEROUS LINEAR FILAMENTS IN THE GALACTIC

CENTER REGION


F. Yusef-Zadeh

Northwestern University, USA


Based on our recent 20cm survey of the Galactic center region with the VLA, we show the evidence for an order of magnitude increase in the number of faint linear filaments with typical lengths of few arcminutes. Many of the filaments show morphological characteristics similar to the Galactic center magnetized radio filaments. The linear filaments are not isolated but are generally clustered in star forming regions where prominent nonthermal radio filaments had been detected previously. The extensions of many of these linear filaments appear to terminate at either a compact source or a resolved shell-like thermal source. We discuss that a relationship between the filaments, the compact and extended thermal sources as well as a lack of preferred orientation for many radio filaments should constrain models that are proposed to explain the origin of nonthermal radio filaments in the Galactic center.


THE SOUTHERN OPTICAL/INFRARED SURVEY OF INTERSTELLAR

POLARIZATION IN THE GALAXY


Antonio Mário Magalhães, Antonio Pereyra, Rocío Melgarejo, Luciana de Matos, Flaviane F. C. Benedito, Rodolfo Valentim and Viviana S. Gabriel

Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Brazil


We describe the status of the on-going Optical/IR Survey of Interstellar Polarization in the Galaxy. The aim is to improve the knowledge of the magnetic field structure of the diffuse Interstellar Medium, the ratio between the random and uniform components of the field and the scale length of the field fluctuations. The Survey has been gathering high accuracy optical imaging polarimetry data of selected directions and regions along the Southern Galactic Plane. Data towards clouds at high galactic latitudes and across open clusters have been also obtained. These observations allow mapping of the magnetic field on small scales. We present both an account of the directions observed and representative data and their interpretation. We have started an IR extension of the Survey, concentrated on the Galactic Plane. The IR data will include data on both point source and extended objects. Plans include IR imaging polarimetry with the Spartan Camera on SOAR. The Survey is being carried out with the IAG-Univ. São Paulo 60-cm telescope at the LNA observatory.

This research is supported by Brazilian agencies FAPESP, CAPES and CNPq.


STAR FORMATION IN THE LOCAL SPIRAL ARM


Jacques R.D. Lépine (1), Wilton S. Dias (1,2)

(1)Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Brazil

(2) Instituto de Física de Sao Carlos, University of Sao Paulo, Brazil


We analyze the dynamics of the young stellar clusters belonging to the local spiral arm, based on the proper motions, radial velocities and ages of the clusters, which are compiled in our Catalog of Open Clusters. By computing the orbits of the clusters, we obtain their initial velocity components at the instant of formation. In general, the clusters present systematic perturbations (non-circular orbits) that can be understood in the frame of the classical theory of spiral arms. This theory predicts that the galactic material is decelerated by the spiral shock waves inside corotation radius, and accelerated outside corotation radius (the corotation radius being the radius which the interstellar gas and the spiral patterns have the same rotation velocity). While the velocity components (U, V), within the galactic plane are easily understood, the W velocity components (perpendicular to the plane) of the clusters also present systematic trends, which would require 3D models of the spiral arms to be understood.


XV. Magnetic Fields in Galaxies, the IGM,

and the Early Universe


PRIMORDIAL MAGNETIC FIELDS


M. Shaposhnikov*

Inst. Theor. Phys., Swiss Federal Institute of Technology, Switzerland


PRIMORDIAL MAGNETIC FIELDS FROM COSMOLOGICAL PHASE TRANSITIONS


H. J. de Vega*

LPTHE-Univ. Paris VI, France


Different mechanisms may be responsible of the generation of large scale primordial magnetic fields. We study cosmological phase transition during the radiation dominated era where charged scalar fields undergo a phase transition. During this phase transition the fields are out of equilibrium and a large number of charged particles are produced. They emit an abundant number of photons which may be the seed for large scale magnetic fields. The dynamics after the transition features two distinct stages: a spinodal regime dominated by linear long-wavelength instabilities, and a scaling stage in which the non-linearities and backreaction of the scalar fields are dominant. This second stage describes the growth of horizon sized domains. The non-equilibrium Schwinger-Dyson equations are used to obtain the spectrum of magnetic fields that includes the dissipative effects of the plasma. We find that large scale magnetogenesis is efficient during the scaling regime. Charged scalar field fluctuations with wavelengths of the order of the Hubble radius induce large scale magnetogenesis via loop effects. The leading processes are: pair production, pair annihilation and low energy bremsstrahlung, these processes while forbidden in equilibrium are allowed strongly out of equilibrium. The ratio between the energy density on scales larger than L and that in the background radiation r(L,T)= B(L,T)/ cmb(T) is r(L,T)  10-34 at the Electroweak scale and r(L,T) sim 10-14 at the QCD scale for L sim 1 Mpc.The resulting spectrum is insensitive to the magnetic diffusion length and equipartition between electric and magnetic fields does not hold. We conjecture that a similar mechanism could be operative after the QCD chiral phase transition.


MAGNETIC FIELDS AND THE FIRST OBJECTS


Reuven Opher*

Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Brazil


Magnetic Fields are important in star formation at low redshifts. Thus, we may assume that a primordial magnetic field was important in the formation of the first objects. We discuss our work on the origin of the primordial magnetic field due to nonminimal gravitational-electromagnetic coupling, primordial density fluctuations, and primordial supernovae explosions. Our work on the amplification of the primordial magnetic field by helical turbulence and the magnetization of the intergalactic medium as well as the effects of the magnetized intergalactic medium on the formation of the first objects is also discussed.


MAGNETIC FIELDS AND CMB ANISOTROPIES


Eduardo Battaner, Estrella Florido, Beatriz Ruiz

University of Granada, Spain


Assuming that magnetic fields were produced before recombination they could constitute a source of anisotropies actually present in the Cosmic Microwave background. We integrate the relativistic linear perturbed equations of fluids, Maxwell and Einstein to follow the evolution of a primordial magnetic filament. Magnetic fields equivalent to present 10-9 Gauss should have observable effects on CMB anisotropies. The identification of magnetic anisotropies will be discussed.


GRAVITATIONAL WAVES DRIVEN BY BARDEEN-PETTERSON EFFECT AND SUSPENDED ACCRETION IN AGN AS TARGETS FOR LISA


Herman Mosquera Cuesta (1), Anderson Caproni (2) and Zulema Abraham (2)

(1) CBPF-ICRA-Brazil

(2)Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Brazil


We have shown that the Bardeen-Peterson (B-P) effect may be responsible for the precession of the jet inlets in a sample of active galactic nuclei (AGN). We show here that for the dynamical conditions in those systems a suspended accretion state could have developed, too, in the region between the supermassive black hole innermost stable orbit and the B-P radius, where a massive torus orbits. The strong coupling of the magnetic field; generated in the accretion torus, to the supermassive black hole (SMBH) angular momentum makes that most of the SMBH rotational energy to be given off as gravitational radiation rather than electromagnetic waves. Thus, any AGN driven by the Lense-Thirring effect (or spin-induced precession) and a suspended accretion state turn out to be a powerful source of gravitational waves (GWs) that could be detected by LISA. The concommitant detection of GWs together with optical and radio emissions from these AGN may decisively help in picturing a consistent scenario of those cosmic sources.

1* Invited Speakers

*


*

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