Injections of e from Nearby Pulsars and their GeV/TeV Spectral Features

(NK, Ioka & Nojiri 2010a, ApJ, 710, 958)(Kashiyama, Ioka & NK 2010, arXiv:1009.1141)(NK, Ioka, Ohira & Kashiyama 2010b, arXiv:1009.1142)Norita Kawanaka (KEK/IPNS)

COSMO/CosPA@University of Tokyo2010/9/27

Electron/Positron Excess(Adriani et al. 2009)PAMELA: e+e-+e+ positron fraction (PAMELA) rising in 10-100GeV, contrary to the conventional theory electron+positron spectrum the excess in 100GeV-1TeV (Fermi/HESS) or the possible peak at ~500GeV (ATIC/PPB-BETS) Additional e sources? Dark Matter annihilation/decay? Astrophysical sources? forthcoming experiments (AMS-02, CALET, CTA etc.) will explore >~TeV spectrum more precisely.(Abdo et al. 2009)

Astrophysical OriginPulsarAharonian+ 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, Ioka & Nojiri 10; NK, Ioka, Ohira & Kashiyama 10Supernova RemnantPohl & 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 09Microquasar (Galactic BH)Heinz & Sunyaev 02Gamma-Ray Burst Ioka 10 White Dwarfs Kashiyama, Ioka & NK 10 (see the poster D2)What kind of electron/positron spectrum can we expect from astrophysical sources?

CR Propagation Equation and Solution diffusion equationinjection Spectrum from instantaneous injection from a point source (Atoyan+ 1995)energy loss (synchrotron, inverse Compton scattering)diffusiondiffusion length: electron energy at t0In the Thomson limit,cutoff energy: ee~1/btage

The case of transient source: e spectrum(a)E=0.9x1050ergage=2x105yra=2.5(b)E=0.8x1050ergage=5.6x105yra=1.8(c)E=3x1050ergage=3x106yra=1.8d=1kpcThe cutoff energy corresponds to the age of the source.Ioka 2010

Continuous Injection: Broadened PeakbackgroundBurst-like event (e.g. GRB)Flux without backgroundt=5.6x105yrr=1kpcEe+ ~Ee-~1050erga=1.7Emax=5TeVEpeak~1/bt~600GeVt0~105yrNK+ 2010a

e Injection from Multiple SourcesTotal injection energy required to account for the peak of ATIC/PPB-BETS ~ 1050erg ~ Rotation energy of a pulsar with P0~10msecToo efficient?Local pulsar birth rate ~10-5 yr-1 kpc-2(Narayan 1985; Lorimer+1994) Pulsars which have not been observed via EM radiation may contribute significantly. Young pulsars (age

Average e Spectrum and Its DispersionAverage flux from nearby sources with a birth rate of R:Number of sources which contribute to the energy bin of ee NK+ 2010a; Kashiyama, Ioka & NK 2010Assuming the Poisson statistics of the source distribution,Flux per source

e+ fractionespectrumsolid lines fave(ee)dashed lines fave(ee) DfaveR~0.7x10-5/yr/kpc2Ee+=Ee-~1048erg a~1.9Average 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.

Spectral Features in >TeV BandWill be explored by CALET, CTA etc.Large theoretical dispersion We can expect to observe the contributions from a single young and nearby source.Vela pulsar (age~104year, distance~290pc), Cygnus loop, or undiscovered compact objects10TeV100TeV?

A young PSR/PWN is surrounded by a SNR. CR electrons/positrons from a pulsar should go through the SNR shock.Kennel & Coroniti 93Low energy particles are trapped around the shock (i.e. have a smaller diffusion length).

Escape condition:rshock frontxLescLE CRHE CR

Escape-Limited ModelIn the Sedov phase, higher energy particles escape the SNR shock earlier (Ptuskin & Zirakashivili 03, 05; Caprioli+ 09; Gabici+ 09; Ohira+ 10) Age-limited model (Higher energy particles require a longer time for acceleration)

Predict (1) the softening of the CR spectrum from the injection and (2) the spectral break in the g-ray spectrum consistent with observations but NO DIRECT EVIDENCEModels of eesc(t)Nesceesc(t)eObserved CR spectrum

TeV e spectrum can prove the CR escape!eesc(t) from Ptuskin & Zirakashvili 03 Electron spectrum from Vela SNR/PSR (d=290pc, tage~104yr, Etot=1048erg) Only e with ee>eesc(tage) can run away from the SNR. Low Energy Cutoff 5yr obs. by CALET (SWT=220m2sr days) may detect it.Without energy-dependent escapeDirect Evidence of Escape-Limited Model for CR accelerators (=SNR)!

SummaryGeV/TeV spectral features of CR e from pulsars.Continuous injection from a single source comparison with the ATIC/PPB-BETS data peak widthduration of the source may be measured by CALETMultiple injections: average flux and its dispersion average e spectrum 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 sourcesCR escape from the SNR shock, which is the most important process in determining the CR spectrum, has been never probed directly from observations. The electron flux from a young pulsar may have the low energy cutoff in >~TeV band, which can be the probe of CR escape from SNRs.

CALorimetric Electron TelescopeCALETWith 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.)A Dedicated Detector for Electron Observation in 1GeV 20,000 GeVRed points/errorbars: expected from 5yr obs. by CALETEnergy resolution: ~2% (>100GeV)e/p selection power: ~105

International Collaboration Team

Waseda University : S.Torii, K.Kasahara, S.Ozawa, Y.Aakaike, H.Murakami , J.Kataoka, N.Hasebe, N.Yamashita JAXA/ISAS: M.Takayanagi, H. Tomida, S. Ueno, J. Nishimura, Y. Saito H. Fuke, K.EbisawaM.HareyamaKanagawa University : T.Tamura, N.Tateyama, K.Hibino, S.Okuno, S.Udo, T.Yuda Aoyama Gakuin University:A.Yoshida, K.Yamaoka, T.Kotani Shibaura Institute of Technology: K.Yoshida , A.Kubota, E.KamiokaYokohama National University: Y.Katayose, M.ShibataICRR, University of Tokyo: Y.Shimizu, M.Takita KEK: K.Ioka, N.KawanakaNational Inst. of Radiological Sciences : Y. Uchihori, H. Kitamura S.KodairaHirosaki University: S. Kuramata, M. Ichimura T okyo Technology Inst.: T.Terasawa, Y. TsunesadaKanagawa University of Human Services : Y.Komori Saitama University: K.Mizutani Shinshu University : K.Munekata Nihon University: A.Shiomi

NASA/GSFC: J.W.Mitchell, A.J.Ericson, T.Hams, A.A.Moissev, J.F.Krizmanic, M.SasakiLouisiana State University: M. L. Cherry, T. G. Guzik, J. P. WefelWashington University in St Louis: W. R. Binns, M. H. Israel, H. S. KrawzczynskiUniversity of Denver: J.F.Ormes

University of Siena and INFN: P.S.Marrocchesi , M.G.Bagliesi, G.Bigongiari, A.Caldaroe, M.Y.Kim, R.Cesshi, P.Maestro, V.Millucci , R.Zei University of Florence and INFN: O. Adriani, P. Papini, L. Bonechi, E.VannucciniUniversity of Pisa and INFN: C.Avanzini, T.Lotadze, A.Messineo, F.Morsani

Purple Mountain Observatory: J. Chang, W. Gan, J. YangInstitute of High Energy Physics: Y.Ma, H.Wang,G.Chen

Thank you. Today I will talk about the cosmic-ray electrons and positrons originated from astrophysical sources and their spectral features. The excess of CR positrons is implied by PAMELA satellite 2 years ago. The data shows the rising of the positron fraction with energy and such a feature cannot be explained by the conventional model. In addition, several experiments such as Fermi implied the electron+positron flux excess from the conventional model. The spectrum implied by Fermi observations is flat and smooth, and on the other hand Here we show part of the candidates of astrophysical electron and positron sources.What is interesting is that in the energy range where the Thomson approximation for Compton scattering can apply this spectrum will have a high energy cutoff determined by the age of the source. In other words, this is the most important energy scale in the models of astrophysical electron sources. The older the source is, the smaller the cutoff energy becomes.Assuming the age of source and the power-law injection with the index like this, the Fermis flat and smooth spectrum can be fitted. On the other hand the ATICs spiky spectral structure around 500GeV can be fitted by assuming the source with the age of 5-6x10^5yr and relatively harder spectral index. Anyway we can see that the cutoff energy scale is determined by the age of the source.In general the source do not emit CR electrons and positrons instantaneously but emit with a certain finite duration. Then as a result the spiky spectral structure will have a finite width. Assuming such electron injection with a duration timescale of 10^5 yr, the theoretical spectrum can mimic not only the peak but the gradual decline above the peak around here. Especially the peak width can be written by the function of this duration and the age of the source like this. The typical energy resolution required to resolve this broadening is around 10% and this will be able to be attained by the future experiments such as CALET.In practice the sources contributing to the observed flux should be young and located in the vicinity of the Earth, so it is enough to integrate up to the diffusion length within the energy loss time scale.