Electron and positron cosmic-ray astrophysics

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Electron and positron cosmic-ray astrophysics Powered By Docstoc
					On cosmic-ray positron origin
 and the role of circumpulsar
                  debris disks
                             Catia Grimani
              University of Urbino and INFN Florence
Discovery of cosmic rays
Characteristics of cosmic rays
Electrons and positrons (the lowest
 mass particles in cosmic rays)
Origin of electrons and positrons
Electrons, positrons and pulsar physics
                            The discovery
1911-12 cosmic-ray discovery
         Victor F. Hess

What cosmic rays are made of?
No, energetic positive charged
 particles (protons and ions)!
 Latitude effect and east-west
        Cosmic-ray composition
90% protons
8% helium nuclei
1% electrons
1% heavy nuclei
<1% positrons, antiprotons
        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)
   Cosmic-ray overall
   Above a few GeV
   Part./(m2 sr s GeV)

         o the knee (3x1015 eV)
          o 1018 eV
   above the ankle (3x1018 eV)
           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.
                     Electron energy losses
(dE/dt)I = 7.6 10-18 n[3 ln(E/mc2)+18.8] GeV/s
 n=1 atom/cm3
(dE/dt)B = 8 10-16 n E GeV/s
 (dE/dt)s =3.8 10-18 HT2 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
  These interactions imply that
Electrons are less abundant than
A spectral break is present at the
 source for electrons only…
    Interplanetary electron flux
     Origin of               CG et al., to be submitted to CQG
 1<E<30 MeV
  Jupiter magnetosphere
 30<E<100 MeV
 Secondary Galactic origin
 E>100 MeV
 Primary Galactic origin

 Near Earth
 Above a few GeV
 Part./(m2 sr s GeV)
   
About the e- galactic component…
Various authors assume electron spectrum break at the

Moskalenko and Strong:
=2.1 E≤ 10 GeV =2.4 E≥10 GeV
 Best agreement to data!

=1.54 E≤ 4.5 GeV =2.54 E≥4.5 GeV
Plerion-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
Galactic electron flux estimates
Solar electrons
     November 3rd and
     September 7th 1973
     solar events

     Solar electron
     can be used to
     forecast incoming

     Posner, 2007
Positron flux observations and calculations

             Moskalenko & Strong, 1998
              Stephens, 2001a,b
         Positron fraction
measurements before 1995

                   Protheroe, 1982
             Origin of positrons
Secondary particles produced in the
 interstellar medium as final products
 of proton interactions.
 pp                    
 e + +   
 pp                          e-
   +    Black Hole Annihilation
 56Co decay in also…
But possibly Supernova Remnants
  Supersymmetric particle annihilation
   interaction
  Pulsar magnetosphere
    (Polar Cap - Outer Gap Models)
           POLAR CAP MODEL

                                                                     Goldreich & Julian, 1969
                                                                     Harding & Ramaty, 1987
                                                                     •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)

Figure from

                                                                              Cheng, Ho & Ruderman, 1986
                                                                              *Electrons are accelerated in the
                                                                              outer magnetosphere in vacuum
                                                                              gaps within a charge separated
                                                                              *Electrons interact through
                                                                              syncrotron radiation or inverse
                                                                              Compton scattering
                                                                              *e+e- pairs are produced by 

Different cut-off energies are predicted by polar
cap and outer gap models in the pulsed
gamma-ray spectra (GLAST)!
  Figures from

                              C. Grimani ECRS Florence August 31st - September 3rd 2004
 How to distinguish among
       different hypotheses?
It is mandatory to discriminate
       among various models of
              secondary e+ - e-
     Solar modulation of cosmic-
                     ray spectra

D. Hathaway and Dikpati M.

Positive SOL MIN              Positive SOL MAX

                               Negative SOL MIN
BESS proton data
 Solar Modulation of Galactic Cosmic Rays

                    J(r,E,t)             J(∞,E+)
                    E2-Eo2              (E)2-Eo2
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)
                                         Gleeson and Axford, Ap. J., 154, 1011, 1968

                           Ok for positive polarity epoch data only!
Solar polarity effect on GCR p and He
                      @ solar minimum
             p                            Negative Polarity

        He                                -40% @ 100
                                          -30%@ 200
                                          -25%@ 1 GeV(/n)
                                          -a few % up to 4

                     Boella G. et al., J. Geophys. Res. 106:355 2001
        LEE and AESOP data

      A>0                    Thick dot-dashed lines:
                             Protheroe, 1982 SLBM
                             Clem & Evenson, 2004

Positron measurements during the last two solar
                                        CG, A&A, 2007
                          Secondary calculations by M&S, 1998
               A>0                                              A<0
PAMELA data…

 CG, A&A, 2007 - 550 MV/c

            before PAMELA

            CG, A&A, 2004
Positron Flux measurement
                 flux excess
                 (continuous thick line)
                 respect to the
                 component (dot-dashed line
                 -Moskalenko&Strong, 1998):
                 same trend
                 than H&R87
                 with 1/PB=35 years (dotted line)

                       CG, ICRC2005
Positron Flux from Young Pulsar Polar Caps
                                            Harding & Ramaty, 1987
                                            Maximum pulsar age for
                                            e+ production: 104 years
                                            1/PB=30 years
                                            Crab and Vela pulsar
                                     Spectral index
                                     above 20 GeV:
                                  Rate of positron emission per pulsar
                                   Le+ (E)  B12 P-1.7 E-2.2 s-1 GeV-1
                                  Measurements before 1995
                                  1/PB=60 years
                                   CG, Ap&SS, 241, 295, 1996
Positron fraction data after 1995 and calculation uncertainties

                                                       Harding & Ramaty, 1987

                                                     Top region corresponds
                                                     to the secondary component
                                                     + H&R with a 1/PB of 30 yrs

                                                     Dashed region corresponds
                                                     to the secondary component
                                                     + H&R with a 1/PB of 200 yrs
                                                     BEST FIT:
                                                     1/PB=200+/-100 years

                                                     Bottom region corresponds
                                                     to the secondary component
                                                     + H&R with a 1/PB of 250 yrs
                                                            CG, A&A, 418, 649, 2004
Positron flux

      Spectral index
      above 20 GeV
      PAMELA data
      Implies 1.9-2.0
      at the source (?)
Yuksel, Kistler & Stanev

                   LMT-1985: Lyne, Manchester &
                   Taylor, 1985
                   L-1993: Lorimer, 1993
                   H-1999: Hansen, 1999
                   R-2001: Regimbeau, 2001
                   CET-1999: Cappellaro, Evans &
                   Turatto, 1999

                             35.7 years

                   Fucher-Giguère and Kaspi,
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 pulsars
have an age ranging between
0 and 104 years

                                     Arzoumanian, astro-ph/0106159
          What it was proposed:
Positrons and electrons observed near
 Earth are generated by Geminga e
Positrons and electrons fluxes are
 generated by galactic middle aged
Observed gamma-ray pulsar characteristics
         Pulsar        Age     Magnetic Field         Period
                     (years)   B     (1012 G)          (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
               3.8  1012 G H&R87

                                    Radio pulsar observed
                                    magnetic field distribution

                                     Observed gamma-ray
                                     pulsar magnetic field
                                     (3.92  1.97)  1012 G

Figure from Gonthier et al., 2002
Pulsars from e+ measurements
200-300 ms                            Radio pulsar observed
                                      period distribution
                                        Average observed gamma-ray
                                        pulsar period
                                        121  29 ms

                                  Figure from Gonthier et al., 2002

              pulsars from Harding&Ramaty
              33 ms

Different cut-off energies are predicted by polar
cap and outer gap models in the pulsed
gamma-ray spectra (GLAST)!

                                   Figure from
Is the proposed scenario
  consistent with overall
    pulsar observations?
   Pulsar energy loss processes
           and braking indeces

n= -( d2/dt2 )/ (ddt)2
Electromagnetic (n=3)
Gravitational (n=5)
Supernova fallback debris disk friction
     Observed young pulsar
           braking indeces
 Pulsar        n

J1846-0258   2.65
B0531+21     2.51
B1509-58     2.839
J1119-6127   2.91
B0540-69     2.140
B0833-45     1.4
   Pulsar gravitational wave energy

 …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
            Fallback 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)
      Energy losses due to
Electromagnetic processes
          and debris disk
 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).
                        An exercise:
      estimate of gravitational wave
    emission from pulsar+debris disk

 Disk dimensions (theory): 2000 - 200000
 Disk dimensions (observed): 2.02x106-
  6.75x106 km
 Disk mass: 10 Earth mass = 5.97 1025 kg
 Pulsar mass = 2.8 1030 kg
     Might gravitational waves
   produced by debris disks be
Planetary systems
Disk precession
      Gravitational energy loss from pulsar
                         planetary systems

LGW = (32/5) G4/c5 M3 2/a5


 M1M2/(M1+M2)

Planetary disk dimensions > 8 105 km
  < 6.04 10-4 Hz
LGW < 1.24 x 1016 J/s
LISA sensitivity curve

         Vocca et al., CQG, 2004
   Gravitational wave amplitude
          from pulsar planetary
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
            Gravitational waves from
         internal parts of precessing
                             disks (?)
 I3= 1/2 M (R12 + R22)
 = I3/(I1 cos) 
P=(2G)/(5c5)  ) sin2 (cos2 +16 sin2 )
  (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

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.
 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
 The hypothesis of fallback debris disks around young pulsars is
  compatible with positron origin from pulsar polar cap.
Thank you!
ATIC electron data
 Supersymmetry and the positron excess
                        in cosmic rays
Kane, Wang & Wells, 2001 hep-ph/0108138
Cirelli, Kadastik, Raidal, Strumia,
Kamionkowski and Turner, 1991
Neutralino annihilation

 Cheng et al, 2002
 Kaluza-Klein DM annihilation

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