Speakers and Topics

From Cargese School 2016 - Astrophysical Jets
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  • Introduction to the inflow/outflow connection in accreting black holes (3 hrs)

Speaker: Sera Markoff (UvA, NL)

Abstract: Accreting black holes are thought to play a major role in the Universe, from influencing the growth of their host galaxies to altering local gas conditions, today as well as during the Epoch of Reionization. Their jets are also copious particle accelerators, potentially the source of ultra-high energy cosmic rays. We still do not fully understand how to account for all of these effects, however, because we still lack a complete theoretical understanding of the so-called “inflow/outflow” problem: how do the properties of what falls in determine the properties of what comes out (jets/winds)? I will review the current state of our understanding, including the issues we are still struggling with, particularly focusing on the weak-accretion state associated with steady jets. I will also cover how approaching black holes as uniform class, regardless of mass, holds promise for understanding some of these outstanding questions.

Slides: File:Sera cargese.pdf

  • X-ray binaries and microquasars (3 hrs)

Speaker: Elena Gallo (Michigan University, USA)

Abstract: To some extent, all Galactic binary systems hosting a compact object are potential “microquasars”, so much as all Galactic nuclei may have been quasars, once upon a time. The necessary ingredients for a compact object of stellar mass to qualify as a microquasar seem to be: accretion, rotation, and magnetic field. The presence of a black hole may help, but is not strictly required, since neutron star X-ray binaries and dwarf novae can be powerful jet sources as well. The above issues are broadly discussed throughout these lectures, with a rather trivial question in mind: Why do we care? In other words: are jets a negligible phenomenon in terms of accretion power, or do they contribute significantly to dissipating gravitational potential energy? How do they influence their surroundings? The latter point is especially relevant in a broader context, as there is mounting evidence that outflows powered by supermassive black holes in external galaxies may play a crucial role in regulating the evolution of cosmic structures. Microquasars can also be thought of as a form of quasars for the impatient: what makes them appealing, despite their low number statistics with respect to quasars, are the fast variability timescales. In the first approximation, the physics of the jet-accretion coupling in the innermost regions should be set by the mass/size of the accretor: stellar mass objects vary by 105-108 times shorter timescales, making it possible to study variable accretion modes and related ejection phenomena over average Ph.D. timescales. At the same time, allowing for a systematic comparison between different classes of compact objects - black holes, neutron stars, and white dwarfs - microquasars hold the key to identify and characterize properties that may be unique to, e.g., the presence (or the lack) of an event horizon.

Slides part 1: File:Gallo-Cargese-part1.pdf

Slides part 2: File:Gallo-Cargese-part2.pdf

  • Astrophysical particle acceleration (3 hrs)

Speaker: John Kirk (MPI, D)

Abstract: Starting from basic electrodynamics, I will introduce and explain the basic mechanisms thought to be responsible for particle acceleration in astrophysical contexts, including stochastic (turbulent) acceleration, shock-drift acceleration, diffusive shock acceleration and acceleration at relativistic shocks. I will also describe some open questions regarding the application of these mechanisms in jets, and briefly discuss recent developments.

Slides: File:John Kirk handout slides.pdf

  • Active Galactic Nuclei (3 hrs)

Speaker: Volker Beckmann (APC, F)

Abstract: AGN are able to launch the most powerful jets in the Universe. Fed by the central engine that is powered by a super massive black hole, AGN jets can extend up to hundreds of kiloparsec. The jet launching mechanism is, similar to the situation we face for Galactic black holes, not fully understood yet, but certainly the accretion disk, the magnetic field and the black hole parameters play a vital role. After a general introduction into the topic of accreting super massive black holes, we will investigate some of the open questions concerning jets in the context of AGN. How do jets of AGN appear throughout the different wavelengths, what physics can be studied in the radio, optical, UV, X-ray and gamma-ray domain? Which AGN produce jets, and what parameters are the most important in this respect? Is the central black whole rapidly spinning and can we observe this? The jets plough through the interstellar medium — so what is the effect on the star formation in the host galaxy, and what impact does the surrounding matter have on the AGN itself? How did super massive black holes and their jets evolve through the observable cosmos, from redshift z=7 until today, and what do we know about the quasar seeds? I will outline the status of related research and describe research projects able to tackle these fundamental topics.

Slides part 1: File:AGN Cargese Beckmann session1 handout 2016.pdf

Slides part 2: File:AGN Cargese Beckmann session2 handout 2016.pdf

  • Radiation processes in high energy astrophysics (3+3 hrs)

Speaker: Gabriele Ghisellini (INAF OAB, I)

Abstract: I will present the relativistic beaming, the synchrotron and the inverse Compton processes. I will present the phenomena that happen when a source of radiation is moving relativistically with respect to the observer. This is an important addition to classic special relativity, leading to somewhat unexpected results. With these basis, it will be easier to explain the basics of the synchrotron process, where a charge emits because of the Lorentz force exerted by a magnetic field. Finally I will present the fundamental interaction between photons and matter: the scattering, focussing on the case in which the electrons are more energetic than the photons.

Slides: File:Ghisellini cargese.pptx

  • The SVOM mission (1 hr)

Speaker: Diego Götz (CEA Saclay, F)

Abstract: SVOM (Space based multi band astronomical Variable Objects Monitor) is a Sino-French mission dedicated to Gamma-Ray Bursts and more generally to time domain astronomy to be launched in 2021. I will describe the SVOM multi wavelength payload and its scientific objectives, and specifically focus on the imaging techniques used at X-ray and hard X-ray wavelengths.

Slides: File:SVOM GOTZ-Cargese.pdf

  • Revealing the sites of particle acceleration with Very-High-Energy gamma rays (1 hr)

Speaker: Karl Kosack (CEA Saclay, F)

Abstract: Because Very-High-Energy (VHE) gamma rays are produced only via non-thermal processes associated with the most extreme objects in the universe, the "VHE gamma-ray sky" provides a direct image of the sites where cosmic rays are being accelerated. By studying the spectra, morphology, and variability of VHE gamma ray sources, we can better understand the environments in which they are produced: from the shocks that form after supernovae or around pulsars, to those within accretion-powered jets in AGN and microquasars. In this lecture we will cover a selection the most interesting results from the relatively new field of ground-based VHE gamma ray astronomy (HESS, VERITAS, MAGIC), learn what they can tell us about extreme environments, and provide prospectives for what we can expect in the future from instruments like CTA.

Slides: File:Kosack-cargese-2016.pdf

  • Simulation of particle acceleration (3 hrs)

Speaker: Benoît Cerutti (IPAG, F)

Abstract: While analytical methods provide powerful insights into the physics of particle acceleration, numerical simulations are needed to capture the full complexity of the non-linear processes at work. In this lecture, we will first review the numerical methods usually employed, with a special emphasis on the "Particle-In-Cell" (PIC) technique. The PIC method is particularly well-suited for modeling collisionless plasmas at the kinetic level, which allows to capture the microphysics involved in particle acceleration self-consistently. In the second part of this lecture, we will review some applications in high-energy astrophysics, ranging from shock acceleration in supernovae remnants and gamma-ray bursts, to relativistic reconnection in pulsars, pulsar wind nebulae, and relativistic jets.

Slides part 1: File:Bcerutti Cargese PartI.pdf

Slides part 2: File:Bcerutti Cargese PartII.pdf

Slides part 2: File:Bcerutti Cargese PartIII.pdf

  • Gamma-Ray Bursts (3 hrs)

Speaker: Giancarlo Ghirlanda (INAF OAB, I)

Abstract: In the last 10 years our understanding of GRBs have have been changing and revolutionized. I will review the main observational properties of GRBs such as their global properties (energetics, spectra, distance scale, host galaxies). Some of these facts nicely fit in the standard model but several issues have been raised by the recent discoveries. I will discuss the progenitor nature, energy extraction and dissipation mechanisms, jet geometry and dynamics, radiative process which can reproduce some of the observational properties of GRBs. The critical points of this model will be discussed in light of alternative scenarios. GRBs as probes of the early Universe is one challenging perspective which will be discussed in light of forthcoming experiments/missions.

Slides: File:Ghirlanda-grbs.pdf

  • Facts and conjectures about magnetically driven jets from accretion discs (3 hrs)

Speaker: Johnatan Ferreira (IPAG, F)

Abstract: Jets from compact objects are commonly thought as being magnetized outflows carrying mass, angular momentum and energy from an underlying rotating object on which a large scale vertical magnetic field is anchored to. For black holes, two possible mechanisms are at stand: either jets are emitted from the ergosphere of a rotating black hole and are tapping its rotational power (Blandford-Znajek or BZ process) or they are emitted from a larger radial extent in the accretion disc and are powered by accretion (Blandford-Payne or BP process). For neutron stars, no BZ process can be at work but a star-disc magnetic interaction (X-wind) might be invoked. In this lecture, I will focus only on the last two scenario, both related to the accretion disc. I will thus review what is known, from analytical and numerical studies, about these magnetized outflows and their feedback on the underlying disc. I will then elaborate on pending issues such as the required MHD turbulence that needs to be active within magnetized disks according to these models. All models so far, including BZ winds, require the existence of a large scale vertical magnetic field. The question of its existence and possible evolution in time will be finally discussed, within the context of outbursting black hole binaries.

Slides: File:Ferreira Cargese2016.pdf

  • ATHENA (1hr)

Speaker: Jérôme Rodriguez (CEA Saclay, F)

Abstract: Athena has been selected as a L2 mission by ESA and is the next major X-ray observatory to be launch at the horizon 2030. Its current design comprises two main instrument an X-ray polarimeter and a wide field imager. I will present the core scientific themes of the Athena project and I will review the capabilities of both instruments.

Slides: File:Athena JR.pdf

  • The Square Kilometer Array (1 hr)

Speaker: Stéphane Corbel (Université Paris Diderot, F)

Abstract: The SKA is the next generation radio telescope. It is currently in the design phase under a consortium of 11 partners countries. The SKA Observatory will be build on two sites in Australia and South Africa, with the SKA HQ located in the UK. In this talk, I will provide an update on the status of the SKA and its key science drivers, including a specific focus on jets with the SKA.

Slides: File:2016 SKA Cargese Corbel.pdf

  • The multi-messenger approach to Astrophysical Jets (3 hrs)

Speaker: Silvia Piranomonte (INAF OAB, I)

Abstract: Gravitational waves (GW) and neutrinos from astrophysical objects such as cosmic explosions and compact object binary mergers may soon be detected by the joint search of advanced LIGO and VIRGO (aLIGO and aVIRGO) interferometers together with high-energy neutrinos detectors like KM3NET. These events are expected to be associated with fast electromagnetic (EM) transients connected with accretion disks and jets phenomena. While GWs trace the bulk motion of mass within a source, EM signals typically come about after the interaction of matter with the interstellar medium or from out-flows and neutrinos are created in the innermost part of the jets. In these lessons I will show how the joint GW-EM-neutrinos observations will give complementary information and could help us in better understanding the nature of these sources.

Slides: File:Spiranomonte cargese.pdf

  • Outflows from Young Stars: What They Can Tell Us About Astrophysical Jets (3 hrs)

Speaker: Tom Ray (Dublin University, IE)

Abstract: Jets are ubiquitous in the Universe and are seen from a large number of astrophysical objects including active galactic nuclei, gamma ray bursters, micro-quasars, proto-planetary nebulae, young stars and even brown dwarfs. In every case they seem to be accompanied by an accretion disk and, while the detailed physics may change, it is thought that the same basic mechanism is responsible for their generation. Although we do not understand what that mechanism is, it is thought to involve the centrifugal ejection of matter from the disk along magnetic field lines. For a number of reasons, in particular their proximity and the abundant range of diagnostics to determine their characteristics, outflows from young stars offer us the best opportunity of discovering how jets are generated and the nature of the link between outflows and their accretion disks. Theory predicts that the jet is initially launched from within 0.1 to a few au of the star and focused on scales that are at most ten times larger. Thus, even for the nearest star formation region, we need high spatial resolution to image the “central engine” and test current models. After reviewing what is known, I will describe in my lecture course how new observational resources (e.g. the next generation of interferometers and forthcoming missions such as JWST) can be used to investigate the origin of YSO jets, and the jet/accretion zone link.

Slides Part 1: File:TR Ajaccio1.pdf

Slides Part 2: File:TR Ajaccio1.pdf

  • Computer simulations of astrophysical jets (3 hrs)

Speaker: Manel Perucho Pla (University of Valencia, E)

Abstract: Numerical simulations of relativistic outflows in microquasars and active galaxies represent our only possible approach to their physics. In my talk I will summarize the basics of numerical methods to solve the conservation equations of relativistic magneto-hydrodynamics. I will also review the main results obtained in this challenging task, including different topics of jet studies from a numerical perspective, such as jet launching, acceleration, stability and long-term evolution.

Slides: File:Perucho Cargese.pdf

  • How to apply for stuff: demystifying the academic job search (1.5 hrs)

Speaker: Sera Markoff (UvA, NL)

Abstract: Dr. Sera Markoff runs a research group of ~10 people, and has sat in multiple selection committees for, e.g., graduate school admission, top US and European postdoc Fellowship and grants, and faculty hires at several universities. When she started at University of Amsterdam she was shocked at how unprepared students and postdocs were for the (academic) job market and started giving a seminar to help give them some guidance. This seminar has now grown into an annual event involving Dutch Astronomy and Physics students and postdocs across the country, and so she also often gives this seminar when she travels to other countries, like now!

Sera will give a talk of ~1 hour full of information and practical advice about the steps involved in the academic job search and application process. The aim is to de-mystify and de-stress, and she'll emphasize how there's actually a lot one can do to improve one's chances. She promises it will mostly be a pep talk and even if you're a few years away from job apps, it is very important to start thinking about what is coming and strategize. In fact, the earlier you start, the better, since that allows time to "course correct" if necessary. Sera also notes that those who think they don't need the advice are (in her experience) the ones who need it the most!

Bring your questions as well, because after the presentation will be an open discussion where you can get advice on specific situations.

Slides: File:How2apply cargese.pdf