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SUMMARY:Polarized H-alpha Emission from Supernova Remnant Shock Waves Effi
 ciently Accelerating Cosmic Rays - John M. Laming (NRL\, Washington DC)
DTSTART:20190513T130000Z
DTEND:20190513T140000Z
UID:TALK120868@talks.cam.ac.uk
CONTACT:Dr William Béthune
DESCRIPTION:It is frequently stated that over 99.999% of the visible unive
 rse is in the plasma "state". It is much less frequently commented that th
 e overwhelming majority of this plasma is collisionless\, in that particle
  mean free paths against Coulomb collisions are much longer than typical p
 lasma dimensions. The theory of shock waves propagating in such plasmas po
 ses special problems\, relying on plasma turbulence to compress and heat t
 he postshock gas\, and also to scatter and accelerate cosmic rays as a nec
 essary part of the shock dissipation.\n\nWe develop spectropolarimetry of 
 H alpha as a diagnostic of such phenomena. Neutral hydrogen in the interst
 ellar medium impacted by a collisionless shock "sees" an anisotropic distr
 ibution of scattering electrons and ions. In such circumstances line emiss
 ion excited by these scattering particles will in general be polarized\, a
 nd such polarization can be used to make inferences about collisionless pl
 asma processes at the shock. Following an initial prediction that such pol
 arization should exist (Laming 1990)\, and recent observational validation
  in the NW limb of SN 1006 (Sparks et al. 2015)\, we revisit the calculati
 ons with updated atomic data as a diagnostic of shock energy loss to cosmi
 c rays (Shimoda et al. 2018). Such energy loss has the effect of increasin
 g the mild "collimation" of the shocked flow\, increasing the degree of po
 larization expected. We make comparisons with existing observations of SN 
 1006 and for "knot g" in Tycho's supernova remnant\, attempting to infer t
 he shock energy losses to cosmic rays in each case. 
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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