March 2023 - Seminars-iihe - listserv.vub.be

IIHE invited seminar: Ultrahigh energy cosmic rays: an origin story,by Dr James Matthews, 31st of March
by MARIS Ioana Codrina 27 Mar '23

27 Mar '23

Invited Seminars <https://indico.iihe.ac.be/category/6/> IIHE invited seminar: Ultrahigh energy cosmic rays: an origin story //// byDrJames Matthews(University of Oxford) //Friday 31 Mar 2023, 15:00→16:30Europe/Brussels Description Understanding how ultrahigh energy cosmic rays (UHECRs) reach energies in excess of 1e20 eV stretches particle acceleration physics to its very limits. In this talk, I will discuss how such energies can be reached, using general arguments that can often be derived on the back of an envelope. I will review possible particle acceleration mechanisms, with special attention paid to shock acceleration. Informed by the arguments derived in the talk, and with insights from Galactic CR acceleration in supernova remnants, I will then discuss which classes of astrophysical sources might be UHECR sources, including my own (biased) perspective; generally, I favour radio galaxies, GRB afterglows and other sources which are not too compact and dissipate prodigious amounts of energy on large scales. Aided by hydrodynamic simulations, I will show that shocks in the backflows in radio galaxies are good accelerators of UHECRs, then present simulations in which the jet flickers and explore the impact on particle acceleration. I will explore a scenario in which a significant fraction of UHECRs originate from local radio galaxies like Centaurus A and Fornax A, arguing that they can explain the observed UHECR anisotropies. Finally, I will highlight the importance of variability in these potential UHECR sources, and explore the intiguing possibility that the UHECR arrival directions are partly a result of "UHECR echoes" or "reverberation" from magnetic structures in the local Universe. *About the speaker:*Dr. Matthews got his PhD in 2016 from the University of Southampton supervised by Christian Knigge, where he worked on radiative transfer modelling of accretion disc winds. He then moved to Oxford in 2016 for a postdoctoral position working on ultrahigh energy cosmic ray origins before taking up a Herchel Smith Fellowship in Cambridge from 2019-2022. He has recently returned to the Oxford astrophysics department as a Royal Society University Research Fellow, and his research lies at the intersection of theoretical and observational astrophysics, focusing mostly on outflows from accretion discs, astrophysical jets, particle acceleration and axion-like particles. Organised by Ioana Maris and Steven Lowette

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after-seminar beer, 17:00 in CoHop
by MARIS Ioana Codrina 24 Mar '23

24 Mar '23

Dear all, If you would like to join the seminar speaker for discussion and a beer after the seminar, you can do that at 17:00 in CoHop. https://cohop.be/en/ All the best, Ioana and Steven

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IIHE invited seminar: Relativistic Jets from Stellar Mass Black Holes in our galaxy by Prof. Rob Fender, 24th March
by MARIS Ioana Codrina 23 Mar '23

23 Mar '23

Invited Seminars<https://indico.iihe.ac.be/category/6/> IIHE invited seminar: Relativistic Jets from Stellar Mass Black Holes in our galaxy by Prof. Rob Fender (University of Oxford) Friday 24 Mar 2023, 15:00 → 16:30 Europe/Brussels G/0-G.0.20 - Neutrino Room (Building G) Description Astrophysical black holes are the purest manifestations of general relativity, and mark the frontier of our understanding of physics. When accreting gas into their gravitational potential, they can become the most luminous objects in the universe. The most poorly understood aspect of this accretion process is the formation of extremely powerful, highly collimated 'jets' which carry away a large fraction of the liberated gravitational potential energy at relativistic speeds. The most spectacular examples of this process are the supermassive black holes in the centres of giant elliptical galaxies, including M87, the site of the first direct image of a black hole event horizon. However, these supermassive black hole jets are almost frozen in time, and studying how they propagate from the event horizon to their ultimate termination in cluster gas many millions of years later, and how the liberated energy is deposited in the ambient medium, is simply impossible on humanly-accessible timescales. However, stellar mass black holes, the remnants of the most massive stars which lived fast and died young, pervade space, with an estimated 100 million in our galaxy alone. Some of these stellar mass black holes accrete at a high rate from orbiting binary companion stars, and mimic the relativistic accretion and jet formation observed in supermassive systems like M87. In this talk I will explore how rich new sets of observational data have allowed us to measure the state of the accretion flow at the moment of jet launch, and track the relativistically ejected material all the way to its termination in the interstellar medium on a timescale of one or two years. For the first time we are able to edge towards precise calorimetry of these ejections and connect this to the energy balance at the event horizon at the moment of launch. About the speaker: https://www.physics.ox.ac.uk/our-people/fender Organised by Ioana Maris and Steven Lowette

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