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Antimatter in our Galaxy unveiled by INTEGRAL

Antimatter in our Galaxy unveiled by INTEGRAL. Jürgen Knödlseder Centre d’Etude Spatiale des Rayonnements, Toulouse, France. The pre-INTEGRAL epoch. Galactic positron annihilation. OSSE, TGRS, SMM, …. Purcell et al. 1997. Morphology & Flux 3 components : - bulge - disk - PLE

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Antimatter in our Galaxy unveiled by INTEGRAL

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  1. Antimatter in our Galaxy unveiled by INTEGRAL Jürgen Knödlseder Centre d’Etude Spatiale des Rayonnements, Toulouse, France

  2. The pre-INTEGRAL epoch Galactic positron annihilation OSSE, TGRS, SMM, … Purcell et al. 1997 • Morphology & Flux • 3 components : - bulge - disk - PLE • Bulge morphology highly uncertain • Total flux : (1-3) x 10-3 ph cm-2 s-1 • Bulge / Disk flux ratio : 0.2 - 3.3 • Spectroscopy • centroid ~ 511 keV • Gaussian FWHM ~ 1.8-2.9 keV • positronium fraction 0.93 ± 0.04 Kinzer et al. 2001

  3. SPI/INTEGRAL image of 511 keV emission OSSE image (to scale) Knödlseder et al. 2005astro-ph/0506026 • Iteration 17 of accelerated Richardson-Lucy algorithm • 5° x 5° boxcar smoothing • Integrated 511 keV flux : 1.4 x 10-3 ph cm-2 s-1

  4. 511 keV bulge emission morphology Modelling with a 2d Gaussian l0 -0.6° ± 0.3° b0 +0.1° ± 0.3° Dl (FWHM) 8.1° ± 0.9° Db (FWHM) 7.2° ± 0.9° Db / Dl 0.89 ± 0.14 511 keV flux 1.09 ± 0.04 (10-3 ph cm-2 s-1)

  5. Galaxy models compatible with SPI data 1.17 x 10-3 ph cm-2 s-1 2.15 x 10-3 ph cm-2 s-1 1.62 x 10-3 ph cm-2 s-1 2.04 x 10-3 ph cm-2 s-1 B/D ratio : 1-3 (flux) / 3-9 (luminosity)

  6. Comparison with tracer maps Old stellar population K+M giants XRBs Young stellar population(free-free, CO, cold dust) Radio µ-waves FIR NIR V X-ray g

  7. Model : Gauss + positronium + continuum Energy 511.00 ± 0.03 keV FWHM 2.07 ± 0.10 keV Flux 10.0 x 10-4 ph cm-2 s-1 Galactic bulge spectrum

  8. Model : 2 Gauss + positronium + cont. Energy 510.98 ± 0.03 keV FWHM1 1.14 ± 0.40 keV FWHM2 5.08 ± 1.11 keV Flux1 6.9 x 10-4 ph cm-2 s-1 Flux2 3.8 x 10-4 ph cm-2 s-1 Galactic bulge spectrum • Narrow Gauss (FWHM = 1.1 keV) : • ~65 % • Thermalised positrons • Broad Gauss (FWHM = 5.1 keV) : • ~35 % • Inflight positronium formation (quenched if fully ionised) Consistent with 8000 K ISM with ionisation fraction of ~ 0.07-0.17 Churazov et al. 2005

  9. 1809 keV (26Al) 511 keV Constraints on the disk source • 44Sc decays via b+ decay (99%) • M44 ~ 4 x 10-6 M yr-1 (chem. evol.) • Morphology and escape fraction unknown • Expected : 8 x 10-4 ph cm-2 s-1 • 26Al decays via b+ decay (85%) • F511 = 0.5 x F1809 (fp = 0.93) • Expected : 5 x 10-4 ph cm-2 s-1 • Observed disk flux ~ (4-8) x 10-4 ph cm-2 s-1 • 60% - 100% of the disk flux can be explained by 26Al • Rest (if any) is comfortably explained by 44Ti • There seems to exist a pure bulge positron source !

  10. Constraints on the bulge source Wolf-Rayet stars Hypernovae / GRB Pulsars Core-collapse SNe Stellar flares CR interactionswith ISM Dark matter HMXB SN Ia LMXB Novae

  11. Constraints on the bulge source Wolf-Rayet stars Hypernovae / GRB Pulsars Core-collapse SNe Stellar flares CR interactionswith ISM Dark matter HMXB SN Ia LMXB Novae Strong disk component expected

  12. Constraints on the bulge source Wolf-Rayet stars Hypernovae / GRB Pulsars Core-collapse SNe Stellar flares CR interactionswith ISM Dark matter HMXB SN Ia LMXB Novae

  13. Constraints on the bulge source Dark matter SN Ia LMXB Novae

  14. Low-mass X-ray binaries • Positron production processes • g + g e++ e- (pair jet) • N + N’  N*  N + e+ • Uncertainties • Yield • Line shape (broad versus narrow) Observed LMXB B/D ~ 1 Grimm et al. 2002 Liu et al. 2000,2001 • B/D too small ? (completeness) • Why only LMXB and not HMXB ?

  15. Novae • Positron production processes • 13N  13C (t = 14 min, 100%) • 18F  18O (t = 2.6 hr, 97%) • 22Na  22Ne (t = 3.8 yr, 90%) • 26Al  26Mg (t = 106 yr, 85%) Yields CO (0.8 M) ONe (1.25 M) 13N 2 x 10-7 4 x 10-8 18F 2 x 10-9 5 x 10-9 22Na 7 x 10-11 6 x 10-9 26Al 2 x 10-10 1 x 10-8 Hernanz et al. 2001 • Uncertainties • B/D ratio (values up to 4 proposed for M31) M31 : 2 types of novae (bulge & disk) bulge : slow-dim, associated with CO disk : fast-bright, associated with ONe • Nova rate (20-40 per year) • Escape fractions (important for 13N and 18F) • B/D probably OK (in particular if only CO novae contribute) • 13N : if 100% escape  bulge CO nova rate 25 century-1 required(but models predict that 13N e+ are absorbed in expanding shell)

  16. Type Ia supernovae • Positron production processes • 57Ni  57Co (t = 52 hr, 40%) • 56Co  56Fe (t = 111 d, 19%) • 44Sc  44Ca (t = 5.4 hr (87 yr), 99%) Yields Ch Sub-Ch 57Ni 0.01 - 0.03 0.01 - 0.03 56Co 0.4 - 1.1 0.3 - 0.9 44Sc (7-20) x 10-6 (1-4) x 10-3 Woosley 1997; Woosley & Weaver 1994 • Uncertainties • B/D ratio (poorly known) • SN Ia explosion mechanism • SN Ia rate (0.3 - 1.1 per century) • Escape fraction (important for 57Ni and 56Co) • 57Ni : no chance for positrons to escape • 56Co : 3% escape would require bulge rate of 0.6 century-1 • 44Sc : always escape, Sub-Ch would require bulge rate of 0.5 - 2 century-1(but : overproduces galactic 44Ca abundance & makes bright 44Ti bulge) • Different types of SN Ia in bulge (underluminous) and disk (overluminous) ?

  17. Dark matter • Distribution not well known • No flux prediction • Sgr dwarf not detected

  18. General conclusions • The 511 keV sky is bulge / halo dominated (B/D > 3) • Besides bulge / halo and disk, no further 511 keV emission is observed (no PLE) • The disk component can be entierly explained by b+ decay of radioactive 26Al and 44Ti • The origin of the bulge component is still mysterious(LMXB, Novae, SN Ia, dark matter ?) • What is the bulge / halo e+ source ? • Has the bulge / halo e+ source a disk component ? • Can we learn something about SN Ia / Novae distribution and types ? • Observe nearby candidate sources (SNR, LMXB) • Deep observations at high galactic latitudes & galactic plane

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