Cosmic-Ray Electron Excess from Pulsars is Spiky or Smooth?: Continuous and Multiple Electron/Positron Injections(arXiv:0903.3782, submitted to ApJ) Norita Kawanaka (KEK) Kunihito Ioka (KEK) Mihoko M. Nojiri (KEK/IPMU) KEK Theory Center Cosmophysics Group Workshop on High Energy Astrophysics Nov. 12, 2009
Positron Excess: PAMELA • Observed cosmic-ray 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)
Electron+Positron Flux ATIC/PPB-BETS ee~100-600GeV bump+sharp cutoff (Chang et al. 2008) H.E.S.S. ~1-5TeV spectral drop (H.E.S.S. collaboration 2008)
Recent Results H.E.S.S. (340GeV~) Fermi LAT Abdo et al. (arXiv:0905.0025) Aharonian et al. (arXiv:0905.0105) ATIC/PPB-BETS peak has not been confirmed.
What is the Origin of e± Excess? • Dark Matter Particles annihilation/decay e± Cutoff ~600GeV in the ATIC/PPB-BETS corresponds to the mass of DM particles annihilation: <su>required~O(10-23)cm3s-1 >> <su>thermal Overproductions of anti-proton should be avoided. • Astrophysical Sources Compact objects in our Galaxy (NS, SNR, BH…) Cutoff ~600GeV in the ATIC/PPB-BETS corresponds to the cooling time for e± Required energy ~ 10-3x1050erg/SN ~ 1047erg/SN ~ CR nucleon energy
Astrophysical Origin • Pulsar • Shen 70; Aharonian+ 95; Atoyan et al. 95; Chi+ 96; Zhang & Cheng 01; Grimani 07; Yuksel+ 08; Buesching+ 08; Hooper+ 08; Profumo 08; Malyshev+ 09; Grasso+ 09; NK+ 09 • Supernova Remnant • Shen & Berkey 68; Pohl & Esposito 98; Kobayashi+ 04; Shaviv+ 09; Hu+ 09; Fujita, Kohri, Yamazaki & Ioka 09; Blasi 09; Blasi & Serpico 09; Mertsch&Sarkar 09; Biermann+ 09; Ahlers, Mertsch & Sarkar 09 • Microquasar (Galactic BH) • Heinz & Sunyaev 02 • Gamma-Ray Burst Ioka 08 • Propagation Effect • Delahaye+ 08; Cowsik & Burch 09; Stawarz+09; Schlickeiser & Ruppel 09
Any characteristic features in the e± spectrum from astrophysical sources? Can we give any constraints on models by the future missions? • Effects of continuous e± injections on the spectrum • Effects of multiple sources • Constraints in >TeV range by H.E.S.S. • Astrophysical Sources? Or Dark Matter? Can We Discriminate them from the Spectrum?
e± propagation in ISM Propagation effects 1. Random walk due to the Galactic magnetic field diffusion approx. 2. Synchrotron + inverse Compton scattering energy loss e± g ？
CR Propagation Equation and Solution • diffusion equation injection diffusion energy loss (synchrotron, inverse Compton scattering) B/C ratio Galactic Magnetic Fields & Radiation Fields Spectrum from instantaneous injection from a point source(Atoyan+ 1995) cutoff energy: ee~1/btage ：diffusion length
The case of transient source: e+ fraction The cutoff energy corresponds to the age of the source. d=1kpc (a) E=0.9x1050erg age=2x105yr a=2.5 (b) E=0.8x1050erg age=5.6x105yr a=1.8 (c) E=3x1050erg age=3x106yr a=1.8 Ioka 2008
The case of transient source: e± spectrum The cutoff energy corresponds to the age of the source. d=1kpc (a) E=0.9x1050erg age=2x105yr a=2.5 (b) E=0.8x1050erg age=5.6x105yr a=1.8 (c) E=3x1050erg age=3x106yr a=1.8 Ioka 2008
Continuous injection (expected in pulsars, SNRs, etc.) The spectral peak around Ee~1/bt will be broadened! Case 1:pulsar-type decay cf.) Case 2:exponential decay
Continuous Injection (e++e-) exponential decay,t0~105yr background t=5.6x105yr r=1kpc Ee+ ~Ee-~1050erg a=1.7 Emax=5TeV Burst-like event (e.g. GRB) Epeak~1/bt~600GeV NK+ 2009 Flux without background
Constraints on pulsar-type decay time * A significant fraction of observed electrons are emitted recently. pulsar type: t0=105yr H.E.S.S. pulsar type: t0=104yr
e± Injection from Multiple Sources • Total injection energy required to account for the peak of ATIC/PPB-BETS ~ 1050erg ~ Rotation energy of a pulsar with P0~10msec Too efficient? • Local pulsar birth rate ~10-5 yr-1 kpc-2(Narayan 1985; Lorimer+1994) Pulsars which have not observed (e.g. off-beam) should contribute significantly. Young pulsars (age<5x105yr) should exist. • The peak might be made by a pulsar with an extraordinary large amount of energy. • Then, what is the spectrum like on average?
Average e± Spectrum and Its Dispersion NK+ 2009 Average flux from nearby sources with a birth rate of R: Flux per source Number of sources which contribute to the energy bin of ee Assuming the Poisson statistics of the source distribution,
solid lines： fave(ee) dashed lines： fave(ee) ±Dfave e+ fraction • Average spectra are consistent with PAMELA, Fermi & H.E.S.S. • ATIC/PPB-BETS peak is largely separated from the average flux to the 10s level. Such a peak is hardly to produce by the sum of multiple pulsars. • Large dispersion in the TeV range due to the small N(ee) possible explanation for the cutoff inferred by H.E.S.S. R~1/(1.5x105)/yr/kpc2 Ee+=Ee-~1048erg a~1.9 e±spectrum
CALorimetric Electron Telescope (Torii-san’s talk) A Dedicated Detector for Electron Observation in 1GeV – 20,000 GeV Energy resolution: ~2% (>100GeV) e/p selection power: ~105 CALET With the high energy resolution and statistics of the CALET observations, we will be able to discriminate models of injection. (duration, the functional form of Q0(t), etc.) Red points/errorbars: expected from 5yr obs. by CALET
Summary • We investigate the spectral features of CR e± from continuous/multiple sources (e.g. pulsars). • Continuous injection from a single source comparison with the ATIC/PPB-BETS data peak width：duration of the source TeV tail：upper limit for the duration (B>~1011G for a pulsar) may be measured by CALET • Multiple injections: average flux and its dispersion average e± spectrum should be quite FLAT & SMOOTH. seen in the Fermi data ATIC/PPB-BETS peak is hardly to produce by multiple pulsars, and requires a single (or a few) energetic source(s). spectral cutoff at ~a few TeV seen in the H.E.S.S. data : due to the small number of young and nearby sources