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)
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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