Cosmic Rays & Supernova Remnants Collaborator: D.C.Ellison Cosmic particle accelerators: Galactic Cosmic Rays (CRs) origin problem (100 years old) Cosmic Rays in Supernova Remnants (80 years old problem) Physics of plasma in extreme non-equilibrium state with particle SED which is dominated by the highest energy end Diffusive Shock Acceleration (DSA) in Supernova Remnants (also called first-order Fermi mechanism) (40 years old problem) Ø Ø Ø Ø strong turbulent magnetic field amplification (observed in X-rays) relativistic outflows in SNRs nonlinear DSA collisionless shocks Spectra and radiation expected from CR sources and diffuse component needed to search for dark matter related signatures Fermi images of young SNRs L! ~ 10 34 !10 36 erg / s Thompson Baldini Uchiyama 2012 W51C (filled circles) W44 (open circles); IC 443 (filled rectangles); W28 (open rectangles) Cassiopeia A (filled diamonds). Observed gamma-ray spectra of SNRs S. Funk • How to get PeV energy CRs? SNR in Molecular Clouds: Hadronic CR signatures M.Ackermann 2013 Pion-Decay Signatures see: Tavani + 2010, Uchiyama+ 2010, Giuliani+ 2011, Ackermann+ 2013, Cardillo+ 2014 IC 443: electron bremsstrahlung constrains SNR in Molecular Clouds M.Ackermann 2013 What do MeV-TeV observations tell us? Cas A SNR brems IC Chandra CXO Hwang et al 2004 P-P Tycho’s SNR See Morlino+ , Rico Fermi paper, ApJL 2010 Where PeV CRs are accelerated? ASTROGAM SNR perspective M. Cardillo Cas A MeV regime continuum electron injection constrains (Renaud et al. 06) IBIS/ISGRI AB+ Shock wave SN explosion Diffusive Shock Acceleration: Shocks set up converging flows of ionized plasma Interstellar medium (ISM), cool with speed VISM ~ 0 VDS Vsk = u0 shock frame flow speed, u0 charged particle moving through turbulent B-field Post-shock gas à Hot, compressed, dragged along with speed VDS < Vsk shock u2 Upstream DS X u2 = Vsk - VDS Particles make nearly elastic collisions with background plasma è gain energy when cross shock è bulk kinetic energy of converging flows put into individual particle energy p4 f(p) [f(p) is phase space distr.] Temperature If acceleration is efficient, shock becomes smooth from backpressure of CRs p4 f(p) test particle shock Flow speed Lose universal power law subshock X NL TP: f(p) ∝ p-4 ► Concave spectrum ► Compression ratio, rtot > 4 ► Low shocked temp. rsub < 4 In efficient acceleration, entire particle spectrum must be described consistently, including escaping particles and turbulent magnetic field è challenging mathematically (multi-scale problem) BUT, connects photon emission across spectrum from radio to γ-rays For efficient DSA, a large fraction of CR energy can be in Qesc Protons trapped in shock Escaping CRs For this example 20% of SN explosion energy goes into CRs after 1000 yr 1/2 of this is in escaping particles Very different spectral shape from trapped CRs Escaping CRs produce gamma-rays if impact dense material TeV observations can test escaped CRs MeV-TeV observations test trapped CRs Relativistic SNR – GRB afterglow D.Warren, Ellison, Bykov, Lee 15 Relativistic SNR D.Warren, Ellison, Bykov, Lee 15 Relativistic SNR (non-linear DSA) Relativistic SNR: what about fion? Warren, Ellison, Bykov, Lee 15 A day long emission after prompt GRB MeV afterglow could be detected at 1Mpc Fermi image of Cygnus superbubble Ackermann + 2011 Fermi spectrum of Cygnus superbubble Ackermann + 2011 Gamma-line spectra of a SB Sensitivity of ~ 5 10(-7) ph cm-2 s-1 Field of view ~ a few degrees Galactic Inner Radian Spectrum Benhabiles-Mezhoud + 2013 A.W.Strong 2013 Fermi 30 Dor spectra model SED starburst 1041 Starbursts NGC 1068 NGC 1068 (H.E.S.S.) M82 M82 (VERITAS) NGC 4945 NGC 253 NGC 253 (H.E.S.S.) E2 dN/dE (erg s-1) 1040 1039 1038 1037 Local Group Milky Way Global Model M31 LMC SMC 1036 103 Ackermann + 12 105 107 Energy (MeV) 109
© Copyright 2024