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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-1444
DTSTART:20090305T220000Z
DURATION:PT1H0M0S
DTSTAMP:20260420T041534Z
LAST-MODIFIED:20090225T001120Z
LOCATION:4274 Chamberlin
SUMMARY:Active Galactic Nuclei: Sources for ultra high energy cosmic r
 ays?\, NPAC (Nuclear/Particle/Astro/Cosmo) Forum\, Peter L. Biermann\,
  MPI Bonn
DESCRIPTION:Particles near $10^{20}$ eV are the most energetic particl
 es known to us in the universe\, also called ultra high energy cosmic 
 rays. Their observations have led us to build the largest detector sys
 tems in the world\, in the South the Auger air-shower array\, and in t
 he North the Telescope Array\, and perhaps soon Auger-North.  With the
 se and earlier arrays events have been detected of an energy up to $3 
 \, 10^{20}$ eV\, which is a macroscopic energy.  There have been two p
 redictions: one that due to interaction with the microwave background 
 the spectrum should show a turnoff near $5 \, 10^{19}$ eV\; a turn-off
  has been confirmed by two experiments\, HiRes and Auger.  Second\, th
 at active galactic nuclei\, possibly radio galaxies\, should be the ac
 celerators\, based on the non-thermal optical spectra of knots and hot
  spots in radio galaxies\; this is now tentatively confirmed by Auger\
 , but contradicted by HiRes. I will go through some fundamental proble
 ms with the predictions\, which teach us about active galactic nuclei 
 and starburst galaxies. Apart from differentiating various remaining o
 ptions\, such as gamma ray bursts\, how to generate these particles\, 
 and their source population\, there is one major difficulty: the lack 
 of understanding of the cosmological web of magnetic fields\, which ma
 y influence the propagation of high energy particles\; here it is espe
 cially important to understand the role of our local cosmic neighborho
 od and a possible galactic magnetic wind.  It appears from MHD simulat
 ions that magnetic scattering leads to a steep distribution function o
 f scattering angles of the deviation from a straight line path for the
  arriving particles\, and also to a substantial delay time distributio
 n. I will list and debate the merits of the closest candidate sources\
 , Cen A\, Vir A and For A.  I will discuss the observational and theor
 etical limits for an exemplary set of models\, the predictions like ch
 emical abundances\, that result from these models\, and how present an
 d future observations will test our conclusions\, especially with the 
 the Auger Array\, the Telescope Array (TA)\, the neutrino observatory 
 IceCube\, the TeV Cherenkov $gamma$-ray telescopes\, and the future sp
 ace observatory EUSO.  We face a number of exciting challenges for pla
 sma physics\, particle physics\, cosmology\, astronomy\, and may attai
 n better tools for our deep understanding of matter.
URL:https://www.physics.wisc.edu/events/?id=1444
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