Roger Blandford (KIPAC/Stanford University - EUA)


Black Holes as Cosmic Dynamos

Recent, remarkable observations involving all of the astronomical channels - electromagnetic, gravitational radiation, neutrino and cosmic ray - support the view that spinning magnetized black holes power many of the most extreme phenomena observed in the universe. Our understanding of the underlying mechanisms is improving through a combination of simulation and analysis and many new ideas await testing by upcoming observations. In this talk I will give an introduction to some of the basic ideas and list some unsolved problems. I will then introduce some speculative notions including magnetoluminescence, magnetic lampposts, TeV synchrotron emission and jet boundary layers. I will also argue that, by contrast, Ultra High Energy Cosmic Rays may not be accelerated by relativistic jets.

 

 

Ioannis Contopoulos (Academy of Athens - Greece)


A Cosmic Battery in accretion flows around astrophysical black holes

I will present my views on the immediate environment of an astrophysical black hole. In particular, I will discuss the origin of the electron-positron and large scale electron-proton jets, and the origin of the large scale magnetic field. I will show how the aberrated radiation field (as viewed by the rotating plasma) generates an electric field, the curl of which yields a secular (steady) magnetic field growth over a few hundred million dynamical times (that corresponds to days-weeks for stellar mass black holes, and few million years for super-massive black holes in AGN). I will present recent axisymmetric radiation GR MHD simulations and Faraday RM observations that confirm the action of a Cosmic Battery in accretion flows around astrophysical black holes.

 

 

Bernardo Fraga (CBPF - Brazil)


MAGIC and the very high energy gamma-ray sky

MAGIC is a system of two 17m Cherenkov telescopes for very high energy gamma-ray and cosmic-ray astrophysics and currently one of the best performing in the field. Through the discovery of more than 50 extragalactic and galactic sources including blazars, radiogalaxies, pulsars, supernovae remnants and binary systems (among other types) a broad range of topics can be studied: accretion to black holes, relativistic jets, shocks and their connection to the acceleration of cosmic rays. In addition, MAGIC tries to answer fundamental physics questions, such as the search for dark matter. In this talk I will discuss some selected highlights from MAGIC, especially the recent detection of very high energy gamma-rays from the blazar TXS 0506+056, which could potentially be the source of the high-energy extragalactic neutrino recently detected by Icecube.

 

 

Igor Felix Mirabel (CONICET/UBA - Argentina)


Microquasar Jets and Gamma-ray emission

I will review the observational results obtained so far on the powerful relativistic jets in milky way microquasars and their associated high energy radiation. I will show that in addition to a particular geometry of the radio jets relative to the observer, the nature of the donor stars are an important ingredient in producing gamma-rays. The hot radiation field and dense winds from massive stars provide soft seed photons and protons with which the jet particles can interact to produce gamma-rays.

 

 

Carola Dobrigkeit (UNICAMP - Brazil)


Recent highlights from the Pierre Auger Observatory

The Pierre Auger Observatory is the largest facility ever built aiming the study of ultra-high energy cosmic rays. Operating continuously since the beginning of 2004, it has permitted outstanding breakthroughs in our knowledge about these most energetic particles. We will briefly review what we have achieved to learn about their energy spectrum and mass composition and focus on the distribution of their arrival directions and their extragalactic origin. We will discuss recently published results on anisotropy studies in large and intermediate angular scale and briefly refer to the search for neutrinos in correlation with the events GW170817 and IceCube-170922A.

 

 

Will Potter (University of Oxford/Department of Physics - UK)


Determining Jet Properties Using a Fluid Jet Emission Model

Black hole jets are one of the most powerful and luminous phenomena in our universe, however, despite multiwavelength observations many of their basic properties such as their shape, speed and magnetisation are not well known. I will show that it is possible to determine these properties by fitting with unprecedented accuracy to the entire multiwavelength spectra of blazar jets, using a new relativistic fluid jet emission model. This allows us to understand how the power of the jet determines its dynamical properties, such as the length of the magnetised accelerating region of the jet and its terminal bulk Lorentz factor.

 

 

Daniel Supanitsky (IAFE/CONICET - Argentina)


Implications of gamma-ray and neutrino observations on source models of ultrahigh energy cosmic rays

The origin and nature of the ultrahigh energy cosmic rays (UHECRs) is still unknown. However, a big progress have been achieved in past years due to the observations performed by the Pierre Auger Observatory and Telescope Array. Above 1 EeV the observed energy spectrum presents two features: a hardening of the slope at about 4 EeV, which is known as the ankle and a suppression at approximately 40 EeV. The composition inferred from the experimental data, interpreted by using the current high energy hadronic interaction models, seems to be light below the ankle, showing a trend to heavier nuclei for increasing values of the primary energy. Current high energy hadronic interaction models, updated by using the Large Hadron Collider data, are still subject to large systematic uncertainties, which makes difficult the interpretation of the experimental data in terms of composition. On the other hand, it is very well known that gamma rays and neutrinos are produced by UHECRs during propagation from their sources, as a consequence of their interactions with the radiation field present in the universe. The flux at Earth of these secondary particles is correlated with the UHECR composition. Therefore, both gamma-ray and neutrino observations can be used to constrain the composition, by using models of the sources, in an independent way of the high energy hadronic interaction models. In this lecture I will review recent results obtained by using latest gamma-ray and neutrino observations.

 

 

Manel Perucho (Observatori Astronòmic/Universitat de València - Spain)


Radio source evolution and the interplay with the host galaxy

There is compelling evidence showing that extragalactic jets are a crucial ingredient in the evolution of host galaxies and their environments. Extragalactic jets are well collimated and relativistic, both in terms of thermodynamics and kinematics. They generate strong shocks in
the ambient medium, associated with observed hotspots in FRII radio galaxies, and carve cavities that are filled with the shocked jet flow, dragging larga amount of interstellar gas along in the form of slow, massive outflows. In my talk, I will discuss jet evolution basing on 2D and 3D RHD long-term simulations of extragalactic jets developing in galactic atmospheres. In addition, I will talk about the role that mass load by stellar winds in galaxies can play in FRI jet deceleration based on RMHD simulations. Jet/star interaction can actually be also responsible for the production of hugh energy radiation and cosmic rays.

 

 

Vitor de Souza (USP/IFSC - Brazil)


The Cherenkov Telescope Array

In this presentation, we will discuss the capabilities of Cherenkov Telescope Array (CTA) and its potential to help forward the understanding of black holes as cosmic accelerators. CTA, which will be constructed over the next few years, will be devoted to the detection of high energy gamma rays. Through a wide energy range (from 20 GeV to more than 300 TeV) and improved angular resolution it will provide a significant improvement in sensitivity over the current generation of instruments. The telescopes will be deployed in two arrays, one in the Southern and one in the Northern hemisphere, providing full-sky coverage from one gamma-ray observatory for the first time. Currently, groups across the world are testing prototype cameras and telescopes. In this talk, an overview of the instrumentation and key science projects will be given with special attention to the connection between high energy gamma rays and cosmic ray acceleration.

 

 

Carlos Henrique Coimbra Araújo (UFPR - Brazil)


Rotating black holes with magnetic fields as accelerators of charged particles

We are concerned to analyze the circumstances under which charged particles can escape black hole gravitational fields after its collision with another particle. Here we examine the dynamics of a charge particle interactig with a rapid rotating Kerr black hole in the presence of magnetic fields. In this respect, it is possible to show that rotating black holes may act as particle accelerators. Axially symmetric magnetic field homogeneous at infinity and other type of configurations are discussed. Here it is discussed expressions for the effective potential of the system, the total energy and te escape velocity of the particle. Leading results appointed by many examples in the literature are that the intensity of the magnetic fields induce the innermost stable circular orbit (ISCO) to be closer to the black hole horizon. The present investigation on particle escape velocity can possibly contribute, for example, to constrain AGN dynamic properties to properly understand the acceleration mechanisms of the highest energy cosmic rays.

 

 

Elisabete Maria de Gouveia Dal Pino (IAG/USP - Brazil)


Magnetic reconnection, Cosmic Ray Acceleration, and Gamma-Ray emission around Black Holes and Relativistic Jets

Particle acceleration by magnetic reconnection is currently regarded as an important process in magnetically dominated regions of galactic and extragalactic black hole sources. This process may help to solve current puzzles specially related to the origin of the very high energy emission in these sources. In this talk, I will review briefly this acceleration process and show recent analytical studies and multidimensional numerical MHD and GRMHD (general relativistic magnetohydrodynamical) simulations that probe this process both in the relativistic jets and in the core regions of these sources.

 

 

Gustavo Esteban Romero (IAR - Argentina)


The first micro-quasars

The first astrophysical black holes in the universe were the result of the collapse of Population III stars, which were formed from the primordial gas after the recombination era. Current simulations show that fragmentation of the original clouds was common, so most of these stars formed binary or multiple systems. Since binary systems are not disrupted by direct collapse of one of the stars, then a rich population of black holes orbiting very massive stars of zero metallicity can be expected at high-redshifts. These stars do not have stellar winds so mass transfer to the compact object should occur exclusively through overflowing the Roches lobe. The rate of accretion should be extremely super-Eddington, with an intense mass loss from the system in the form of winds and jets. In this talk I will discuss the properties of these first accreting black holes, their accretion regime in close binaries, the jets they produced, and their effects on the early universe.