1 / 14

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

This study investigates the possibility of pulsars as a source for the observed cosmic ray electron/positron data. It analyzes the effects of continuous electron/positron injection from astrophysical objects on the observed electron/positron spectrum and examines the constraints already placed by H.E.S.S. on pulsar models. High-resolution spectra from future missions may help discriminate between different models.

cornwelll
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

  2. 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)

  3. ATIC/PPB-BETS ~10GeV-3TeV (Chang et al. 2008) Sharp spectral cutoff around ~600GeV m~600GeV dark matter annihilation/decay?

  4. H.E.S.S. ~1-10TeV (H.E.S.S. collaboration 2008)

  5. Astrophysical source(s)? • Electrons/Positrons are cooled via synchrotron & inverse Compton scattering during the propagation. • electron energy~10GeV-1TeV  Sources should be within Rd~kpc (< Galactic disk~10kpc) • diffusion time~Rd2/K ~107yr (~birth rate of the source) • Etot ~1050 erg is needed. (Lavalle et al. 2007)

  6. 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…

  7. e± propagation • Diffusion equation injection diffusion cooling (synchrotron, IC)  Green’s 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)

  8. The case of transient source (e.g. GRB) t=5.6x105yr … age r=1kpc Etot=1x1050erg a=1.8 ? Epeak~1/bt~600GeV

  9. Continuous injection (expected in pulsars, MQs, etc.) The spectral peak around Ee~1/bt will be broadened! Case 1:pulsar-type decay cf.) Case 2:exponential decay

  10. Results: Electron/Positron Flux solid line :exponential decay (t0~105yr) thick: total (source+2nd) DE: effect of finite t0 pure secondary t=5.6x105yr r=1kpc Etot=2x1050erg a=1.4 Emax=3TeV K0=3.2x1028cm2s-1 d=0.6 transient source Epeak~1/bt~600GeV (NK, Ioka and Nojiri in prep.) pure source

  11. Spin down time should not be too long? * A significant fraction of observed electrons are emitted recently. pulsar type: t0=105yr t=5.6x105yr r=1kpc Etot=2x1050erg a=1.4 Emax=3TeV K0=3.2x1028cm2s-1 d=0.6 H.E.S.S. pulsar type: t0=104yr (NK, Ioka and Nojiri in prep.) pure source

  12. 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 (<2×1050 erg)? (= P0 >~10msec) • Only the pulsars with low B (=long tau0) and low Emax (avoiding HE tail) should contribute? H.E.S.S. t=3.0x104 yr r=1 kpc Etot=6x1047 erg a=1.4 (NK, Ioka and Nojiri in prep.)

  13. Results: Positron Fraction Total contribution from old pulsars (birth rate~1 per 5x105yr) thin solid lines: old pulsars with a=1.4 thin dashed lines: a=1.6 (NK, Ioka and Nojiri in prep.)

  14. 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 @ 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.

More Related