Continuous Injection of High Energy Positrons from an Astrophysical Object: Can a Pulsar Account for

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Continuous Injection of High Energy Positrons
from an Astrophysical Object Can a Pulsar
Account for the Cosmic Ray Electron/Positron Data?

• Norita Kawanaka
• Kunihito Ioka Mihoko M. Nojiri
• (KEK, Japan)
• Rencontres de Moriond 04/02/09

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Positron Excess PAMELA

• Observed positron flux seems to exceed that
  expected in the context of secondary positron
  production.
• Similar trend had been observed (AMS, HEAT etc.)
• Some primary sources are needed!

1-100GeV
(Adriani et al. 2008)
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ATIC/PPB-BETS
10GeV-3TeV
(Chang et al. 2008)
Sharp spectral cutoff around 600GeV
m600GeV dark matter annihilation/decay?
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H.E.S.S.
1-10TeV
(H.E.S.S. collaboration 2008)
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Astrophysical source(s)?

• Electrons/Positrons are cooled via synchrotron
  inverse Compton scattering during the
  propagation.
• electron energy10GeV-1TeV ? Sources should be
  within Rdkpc (lt Galactic disk10kpc)
• diffusion timeRd2/K 107yr (birth rate of the
  source)
• Etot 1050 erg is needed.

(Lavalle et al. 2007)
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Candidates

• Pulsars
• e pairs are produced in the magnetosphere and
  accelerated by the electric fields and/or the
  pulsar wind. (Chi 1996 Zhang Cheng 2001
  Grimani 2007 Hooper 2008 Profumo 2008 etc.)
• Gamma-Ray Bursts
• Pair creations between TeV photons and soft
  photons (eV) far outside the GRB remnant (Ioka
  2008)
• Microquasars
• Pair creations in the internal shock in the
  jet? (Heinz Sunyaev 2002 etc.)
• and so on

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e propagation

• Diffusion equation

injection
diffusion
cooling (synchrotron, IC)
? Greens function with respect to r and t
(Atoyan 1995)
This is just the observed spectrum in the case of
a transient point source (e.g. GRB)
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The case of transient source (e.g. GRB)
t5.6x105yr age r1kpc Etot1x1050erg a1.8
?
Epeak1/bt600GeV
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Continuous injection (expected in pulsars, MQs,
etc.)
The spectral peak around Ee1/bt will be
broadened!
Case 1 pulsar-type decay
cf.)
Case 2 exponential decay
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Results Electron/Positron Flux
solid line exponential decay (t0105yr) thick
total (source2nd)
DE effect of finite t0
pure secondary
t5.6x105yr r1kpc Etot2x1050erg a1.4 Emax3TeV
K03.2x1028cm2s-1 d0.6
transient source
Epeak1/bt600GeV
(NK, Ioka and Nojiri in prep.)
pure source
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Spin down time should not be too long?
pulsar type t0105yr
A significant fraction of observed electrons
are emitted recently.
t5.6x105yr r1kpc Etot2x1050erg a1.4 Emax3TeV
K03.2x1028cm2s-1 d0.6
H.E.S.S.
pulsar type t0104yr
(NK, Ioka and Nojiri in prep.)
pure source
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Young pulsars should not have any contribution?

• Why so rare?
• Local birth rate is intrinsically low?
• HE pairs are confined in the pulsar wind nebula?
• Most pulsars have lower Etot (lt21050 erg)? ( P0
  gt10msec)
• Only the pulsars with low B (long tau0) and low
  Emax (avoiding HE tail) should contribute?

H.E.S.S.
t3.0x104 yr r1 kpc Etot6x1047 erg a1.4
(NK, Ioka and Nojiri in prep.)
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Results Positron Fraction
Total contribution from old pulsars (birth rate1
per 5x105yr)
thin solid lines old pulsars with a1.4 thin
dashed lines a1.6
(NK, Ioka and Nojiri in prep.)
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Summary

• We investigate the effects of continuous
  electron/positron injection from astrophysical
  objects on the observed electron/positron
  spectrum.
• Epeak ?? tage of the source
• DE _at_ Epeak ?? the duration of electron injection
• Assuming pulsar spin down type injection, high
  energy tail in the electron spectrum would be
  enhanced if t0 is long. ? H.E.S.S. has already
  put serious constraints on pulsar models?
• High resolution spectra will be obtained by
  Fermi, CALET etc., and we may be able to
  discriminate models.