On cosmic-ray positron origin and the role of circumpulsar debris disks
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On cosmic-ray positron origin and the role of
circumpulsar debris disks
Catia GrimaniUniversity of Urbino and INFN Florence
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ContentsContents
Discovery of cosmic raysCharacteristics of cosmic raysElectrons and positrons (the lowest
mass particles in cosmic rays)Origin of electrons and positronsElectrons, positrons and pulsar
physics
Discovery of cosmic raysCharacteristics of cosmic raysElectrons and positrons (the lowest
mass particles in cosmic rays)Origin of electrons and positronsElectrons, positrons and pulsar
physics
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The discoveryThe discovery1911-12 cosmic-ray discovery Victor F. Hess
What cosmic rays are made of?Photons? No, energetic positive charged particles (protons and ions)! Latitude effect and east-west asymmetry
1911-12 cosmic-ray discovery Victor F. Hess
What cosmic rays are made of?Photons? No, energetic positive charged particles (protons and ions)! Latitude effect and east-west asymmetry
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Cosmic-ray compositionCosmic-ray composition
90% protons8% helium nuclei1% electrons1% heavy nuclei<1% positrons, antiprotons
90% protons8% helium nuclei1% electrons1% heavy nuclei<1% positrons, antiprotons
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Rare particle discovery in cosmic rays
Rare particle discovery in cosmic rays
1932 Positrons (ground)1937 Muons (ground)1947 Pions (ground)1961 Electrons (Galactic cosmic rays)1964 Positrons (Galactic cosmic rays)1979 Antiprotons (Galactic cosmic
rays)
1932 Positrons (ground)1937 Muons (ground)1947 Pions (ground)1961 Electrons (Galactic cosmic rays)1964 Positrons (Galactic cosmic rays)1979 Antiprotons (Galactic cosmic
rays)
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Cosmic-ray overallspectrum
Above a few GeVF(E)=AE-
Part./(m2 sr s GeV)
o the knee (3x1015 eV)o 1018 eVabove the ankle (3x1018 eV)
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That special interest in e- and e+…
That special interest in e- and e+…
Electrons and positrons interact with magnetic field and background and stellar photons.
Comparison between proton and electron fluxes (rigidity and velocity propagation processes).
Exotic origin.
Electrons and positrons interact with magnetic field and background and stellar photons.
Comparison between proton and electron fluxes (rigidity and velocity propagation processes).
Exotic origin.
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Electron energy lossesElectron energy lossesIonization (dE/dt)I = 7.6 10-18 n[3 ln(E/mc2)+18.8] GeV/s n=1 atom/cm3
Bremsstrahlung (dE/dt)B = 8 10-16 n E GeV/sSynchrotron (dE/dt)s =3.8 10-18 HT
2 E2 GeV/s
<HT>=3 G
H= 1.23 <HT>Inverse Compton Blackbody radiation Stellar photons (dE/dt)c = 10-16 w E2 GeV/s
w=0.7 eV/cm3
Ionization (dE/dt)I = 7.6 10-18 n[3 ln(E/mc2)+18.8] GeV/s n=1 atom/cm3
Bremsstrahlung (dE/dt)B = 8 10-16 n E GeV/sSynchrotron (dE/dt)s =3.8 10-18 HT
2 E2 GeV/s
<HT>=3 G
H= 1.23 <HT>Inverse Compton Blackbody radiation Stellar photons (dE/dt)c = 10-16 w E2 GeV/s
w=0.7 eV/cm3
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These interactions imply that …
These interactions imply that …
Electrons are less abundant than protons
A spectral break is present at the source for electrons only…
Electrons are less abundant than protons
A spectral break is present at the source for electrons only…
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Interplanetary electron flux
Interplanetary electron flux
Origin of electronsOrigin of
electrons
1<E<30 MeV Jupiter
magnetosphere 30<E<100 MeV Secondary Galactic
origin E>100 MeV Primary Galactic origin
1<E<30 MeV Jupiter
magnetosphere 30<E<100 MeV Secondary Galactic
origin E>100 MeV Primary Galactic originNear Earth
Above a few GeVF(E)=AE-
Part./(m2 sr s GeV)
CG et al., to be submitted to CQG
Primaries
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About the e- galactic component…
About the e- galactic component…
Various authors assume electron spectrum break at the source:
Moskalenko and Strong: =2.1 E≤ 10 GeV =2.4 E≥10 GeV Best agreement to data!
Stephens: =1.54 E≤ 4.5 GeV =2.54 E≥4.5 GeVPlerion-like input spectrum
Above 1 TeV descrete sources (for example nearby SNR- Vela, Monogem, Cygnus Loop -Kobayashi et al., 2004) are expected to produce electrons observed near Earth
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Galactic electron flux estimates
Galactic electron flux estimates
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Solar electronsSolar electrons
November 3rd and September 7th 1973 solar events
Solar electron detectioncan be used to forecast incoming SEPs
Posner, 2007
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Positron flux observations and calculations
Moskalenko & Strong, 1998Stephens, 2001a,b
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Positron fraction measurements before
1995
Positron fraction measurements before
1995
Protheroe, 1982
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Origin of positrons Origin of positrons
Secondary particles produced in the interstellar medium as final products of proton interactions.
pp e++
pp e-
+
But possibly also…
Secondary particles produced in the interstellar medium as final products of proton interactions.
pp e++
pp e-
+
But possibly also… Primordial Black Hole Annihilation56Co decay in Supernova RemnantsSupersymmetric particle annihilation interactionPulsar magnetosphere (Polar Cap - Outer Gap Models)
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POLAR CAP MODEL
Goldreich & Julian, 1969Harding & Ramaty, 1987
Figure from http://cossc.gsfc.nasa.gov/images/epo/gallery/pulsars/
•Strong electric fields are induced by the rotating neutron star
•Electrons are extracted from the star outer layer and accelerated
•Open field lines originate at polar caps (rpc= 8 x 102 m)
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OUTER GAP MODEL
C. Grimani ECRS Florence August 31st - September 3rd 2004
Cheng, Ho & Ruderman, 1986*Electrons are accelerated in the outer magnetosphere in vacuumgaps within a charge separatedplasma*Electrons interact through syncrotron radiation or inverseCompton scattering*e+e- pairs are produced by interaction
Different cut-off energies are predicted by polar cap and outer gap models in the pulsed gamma-ray spectra (GLAST)!
Figures from http://cossc.gsfc.nasa.gov/images/epo/gallery/pulsars/
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How to distinguish among different
hypotheses?It is mandatory to
discriminate among various models of secondary e+ - e-
calculations…
How to distinguish among different
hypotheses?It is mandatory to
discriminate among various models of secondary e+ - e-
calculations…
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Solar modulation of cosmic-ray spectra
D. Hathaway and Dikpati M. http://science.nasa.gov/headlines/y2006/10may_lagrange.htm
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SOLAR POLARITY
Positive SOL MIN Positive SOL MAX
Negative SOL MIN
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BESS proton dataBESS proton data
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Solar Modulation of Galactic Cosmic Rays
Solar Modulation of Galactic Cosmic Rays
Gleeson and Axford, Ap. J., 154, 1011, 1968
J(r,E,t) J(∞,E+)=
E2-Eo2 (E2-Eo
2
J: particle flux
r: distance from Sun
E: particle total energy
t: time
Eo= particle mass
= particle energy loss from infinity (different for each species)
Ok for positive polarity epoch data only!
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Solar polarity effect on GCR p and He @ solar minimum
p
He
Boella G. et al., J. Geophys. Res. 106:355 2001
Negative Polarity
-40% @ 100 MeV(/n)
-30%@ 200 MeV(/n)
-25%@ 1 GeV(/n)
-a few % up to 4 GeV(/n)
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LEE and AESOP data
A>0
A<0
Thick dot-dashed lines:Protheroe, 1982 SLBMClem & Evenson, 2004
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Positron measurements during the last two solar Positron measurements during the last two solar cyclescycles
CG, A&A, 2007
Secondary calculations by M&S, 1998
A>0 A<0
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PAMELA data…PAMELA data…
Best-fit before PAMELA
0.064+/-0.003CG, A&A, 2004
CG, A&A, 2007 - 550 MV/c
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Positron Flux measurementPositron Flux
measuremente+
flux excess (continuous thick line) withrespect to thesecondary component (dot-dashed line-Moskalenko&Strong, 1998):same trendthan H&R87with 1/PB=35 years (dotted line)
CG, ICRC2005
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Positron Flux from Young Pulsar Polar CapsHarding & Ramaty, 1987
Measurements before 1995
1/PB=60 years CG, Ap&SS, 241, 295, 1996
Maximum pulsar age for e+ production: 104 years
1/PB=30 years
Crab and Vela pulsar parameters
Le+ (E) B12 P-1.7 E-2.2 s-1 GeV-1
Rate of positron emission per pulsar
Spectral index above 20 GeV:
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Positron fraction data after 1995 and calculation uncertainties
Harding & Ramaty, 1987
Top region correspondsto the secondary component+ H&R with a 1/PB of 30 yrs
Dashed region correspondsto the secondary component+ H&R with a 1/PB of 200 yrsBEST FIT:
1/PB=200+/-100 years
Bottom region correspondsto the secondary component+ H&R with a 1/PB of 250 yrs
CG, A&A, 418, 649, 2004
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Positron fluxPositron flux
Spectral index above 20 GeVPAMELA datapoints:Implies 1.9-2.0at the source (?)
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Yuksel, Kistler & Stanevastro-ph/0810.2784V2
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PULSAR BIRTHRATE ESTIMATES
LMT-1985: Lyne, Manchester & Taylor, 1985L-1993: Lorimer, 1993H-1999: Hansen, 1999R-2001: Regimbeau, 2001CET-1999: Cappellaro, Evans & Turatto, 1999
35.7 years
Fucher-Giguère and Kaspi,astro-ph/0512585
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However… middle aged pulsars are favoured over young ones in producing positrons reaching the interstellar medium as an increasing fraction of them lies outside their host remnants as a function of age.
0.0625 % of pulsarshave an age ranging between 0 and 104 years
Arzoumanian, astro-ph/0106159
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What it was proposed:What it was proposed:
Positrons and electrons observed near Earth are generated by Geminga e B0656+14
Positrons and electrons fluxes are generated by galactic middle aged pulsars
Positrons and electrons observed near Earth are generated by Geminga e B0656+14
Positrons and electrons fluxes are generated by galactic middle aged pulsars
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Pulsar Age (years)
Magnetic Field B (1012 G)
Period (ms)
Crab 1300 3.8 33
B1509-58 1500 15.4 150
Vela 11000 3.4 89
B1706-44 17000 1.165 102
B1951+32 110000 1.1 40
Geminga 340000 1.6 237
B1055-52 530000 0.97 197
Observed gamma-ray pulsar characteristics
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Radio pulsar observedmagnetic field distribution
Figure from Gonthier et al., 2002
Observed gamma-raypulsar magnetic field(3.92 1.97) 1012 G
3.8 1012 G H&R87
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Radio pulsar observedperiod distribution
Average observed gamma-raypulsar period121 29 ms
Gamma-rayPulsars from e+ measurements200-300 ms
Gamma-raypulsars from Harding&Ramaty33 ms
Figure from Gonthier et al., 2002
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ELECTRON
FLUx
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Different cut-off energies are predicted by polar cap and outer gap models in the pulsed gamma-ray spectra (GLAST)!
Figure from http://cossc.gsfc.nasa.gov/images/epo/gallery/pulsars/
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Is the proposed scenario consistent with overall pulsar
observations?
Is the proposed scenario consistent with overall pulsar
observations?
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Pulsar energy loss processes
and braking indeces
Pulsar energy loss processes
and braking indeces
n= -(d2/dt2 )/ (ddt)2
Electromagnetic (n=3)Gravitational (n=5)Supernova fallback debris disk
friction (n<3)
n= -(d2/dt2 )/ (ddt)2
Electromagnetic (n=3)Gravitational (n=5)Supernova fallback debris disk
friction (n<3)
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Observed young pulsar braking indeces
Observed young pulsar braking indeces
J1846-0258 2.65B0531+21 2.51B1509-58 2.839J1119-6127 2.91B0540-69 2.140B0833-45 1.4
J1846-0258 2.65B0531+21 2.51B1509-58 2.839J1119-6127 2.91B0540-69 2.140B0833-45 1.4
Pulsar n
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Pulsar gravitational wave energy losses…
Pulsar gravitational wave energy losses…
…cannot be the only answer however electromagnetic AND gravitational wave energy losses can explain observed braking indeces (LIGO shows Crab loses at most 6% of energy in gws; Abbott et al., 2008).
Debris disks lead to braking indeces compatible with observations
…cannot be the only answer however electromagnetic AND gravitational wave energy losses can explain observed braking indeces (LIGO shows Crab loses at most 6% of energy in gws; Abbott et al., 2008).
Debris disks lead to braking indeces compatible with observations
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Fallback Debris disksFallback Debris disks
It was suggested that protoplanetary disks might form around pulsars from remnant fallback material
A debris disk has been observed around the young pulsar 4U 0142+61
(brightest known 8.7 s AXP)
It was suggested that protoplanetary disks might form around pulsars from remnant fallback material
A debris disk has been observed around the young pulsar 4U 0142+61
(brightest known 8.7 s AXP)
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Energy losses due to Electromagnetic processes
and debris disk
Energy losses due to Electromagnetic processes
and debris disk
MP&H01
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At most 12%-29% is lost by a young pulsar such as Crab because of a debris disk surrounding the pulsar
This leads to a wrong estimate of pulsar dP/dt due to em processes and therefore to wrong estimates of pulsar magnetic fields between 6% and 16% (B2 prop P dP/dt) and age. Positron flux calculations are affected similarly (Le+ prop. B).
… however, present positron measurements are still consistent with this scenario within uncertainties (a factor of two on the magnetic field).
At most 12%-29% is lost by a young pulsar such as Crab because of a debris disk surrounding the pulsar
This leads to a wrong estimate of pulsar dP/dt due to em processes and therefore to wrong estimates of pulsar magnetic fields between 6% and 16% (B2 prop P dP/dt) and age. Positron flux calculations are affected similarly (Le+ prop. B).
… however, present positron measurements are still consistent with this scenario within uncertainties (a factor of two on the magnetic field).
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An exercise:estimate of gravitational wave
emission from pulsar+debris
disk systems
An exercise:estimate of gravitational wave
emission from pulsar+debris
disk systems
Disk dimensions (theory): 2000 - 200000 km
Disk dimensions (observed): 2.02x106- 6.75x106 km
Disk mass: 10 Earth mass = 5.97 1025
kgPulsar mass = 2.8 1030 kg
Disk dimensions (theory): 2000 - 200000 km
Disk dimensions (observed): 2.02x106- 6.75x106 km
Disk mass: 10 Earth mass = 5.97 1025
kgPulsar mass = 2.8 1030 kg
Assumptions:
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Might gravitational waves produced by debris disks
be detected?
Might gravitational waves produced by debris disks
be detected?Planetary systemsDisk precession
Planetary systemsDisk precession
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Gravitational energy loss from pulsar planetary systems
Gravitational energy loss from pulsar planetary systems
LGW = (32/5) G4/c5 M3 2/a5
M=M1+M2
M1M2/(M1+M2)
Planetary disk dimensions > 8 105 km < 6.04 10-4 Hz
LGW < 1.24 x 1016 J/s
LGW = (32/5) G4/c5 M3 2/a5
M=M1+M2
M1M2/(M1+M2)
Planetary disk dimensions > 8 105 km < 6.04 10-4 Hz
LGW < 1.24 x 1016 J/s
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LISA sensitivity curveLISA sensitivity curve
Vocca et al., CQG, 2004
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Gravitational wave amplitude from pulsar
planetary systems
Gravitational wave amplitude from pulsar
planetary systems Signals might lie in the LISA band (r>c/):
ho=-1/r (G2/c4) (4M1M2/a)ho=-1/r (4.59x10-7) At 3x10-4 Hz LISA can detect gw with
amplitudes larger than 5.07x10-23 Sources will lie within a light year in 10
years of data taking
Signals might lie in the LISA band (r>c/):
ho=-1/r (G2/c4) (4M1M2/a)ho=-1/r (4.59x10-7) At 3x10-4 Hz LISA can detect gw with
amplitudes larger than 5.07x10-23 Sources will lie within a light year in 10
years of data taking
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Gravitational waves from internal parts of
precessing disks (?)
Gravitational waves from internal parts of
precessing disks (?) I3= 1/2 M (R1
2 + R22)
= I3/(I1 cos
P=(2G)/(5c5)sin2 (cos2 +16 sin2 s
(0.01) x GW frequencies are similar to those produced by pulsar
planetary systems (in the LISA band).Decay time are very long! d/dt=-1/ 1/ =(2G)/(5c5)/I1
I3= 1/2 M (R12 + R2
2)
= I3/(I1 cos
P=(2G)/(5c5)sin2 (cos2 +16 sin2 s
(0.01) x GW frequencies are similar to those produced by pulsar
planetary systems (in the LISA band).Decay time are very long! d/dt=-1/ 1/ =(2G)/(5c5)/I1
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Consequences…Consequences…
Even if the frequencies lie in the LISA band, ten years of integration would not allow the detection of planetary systems beyond one light years. The role of disk precession in generating gravitatonal waves must be investigated further.
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ConclusionsConclusions
Electrons and positrons are unique tools for cosmic-ray and interstellar medium investigation.
Data seem to indicate the model by M&S as the best reproducing e+ and e-data trend.
A positron excess is present above a few GeV. The positron excess is compatible with a model of pair
production at the polar cap of middle aged pulsars extrapolated from a model of pair production at the polar cap of young pulsars.
The hypothesis of fallback debris disks around young pulsars is compatible with positron origin from pulsar polar cap.
Electrons and positrons are unique tools for cosmic-ray and interstellar medium investigation.
Data seem to indicate the model by M&S as the best reproducing e+ and e-data trend.
A positron excess is present above a few GeV. The positron excess is compatible with a model of pair
production at the polar cap of middle aged pulsars extrapolated from a model of pair production at the polar cap of young pulsars.
The hypothesis of fallback debris disks around young pulsars is compatible with positron origin from pulsar polar cap.
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Thank you!Thank you!
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ATIC electron data
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Supersymmetry and the positron excess in cosmic rays
Supersymmetry and the positron excess in cosmic rays
Kane, Wang & Wells, 2001 hep-ph/0108138
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Cirelli, Kadastik, Raidal, Strumia,2008
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Kamionkowski and Turner, 1991Neutralino annihilation
Cheng et al, 2002Kaluza-Klein DM annihilation