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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. Antimatter annihilation. E = m c 2. The pre-INTEGRAL epoch. Galactic positron annihilation. OSSE, TGRS, SMM, …. Purcell et al. 1997. Morphology & Flux

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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. Antimatter annihilation E = m c2

  3. 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

  4. ESA’s INTErnational Gamma-Ray Astrophysics Laboratory INTEGRAL Launch : 17 october 2002 Mission duration : 2008 Orbit : 72 h, excentric Guest observer time : 65-75 % IBIS : Imager on Board the Integral Satellite 15 - 10000 keV, 12’, R ≈ 12 SPI : SPectrometer onboard Integral 20 - 8000 keV, 2.5°, R ≈ 500 JEM-X : Joint European Monitor for X-rays 3 - 35 keV, 3’, R ≈ 10 OMC : Optical Monitoring Camera 550 nm (V band), 6"

  5. SPectrometer onboard INTEGRAL SPI

  6. Jürgen Knödlseder, Pierre Jean, Vincent Lonjou, Georg Weidenspointner, Nidhal Guessoum,William Gillard, Gerry Skinner, Peter von Ballmoos, Gilbert Vedrenne, Jean-Pierre Roques, Stéphane Schanne, Bonnard Teegarden, Volker Schönfelder, C. Winkler,submitted to A&A SPI all-sky exposure after ~ first year 107 cm2 s 1 x 107 cm2 s = 133 ks

  7. SPI 511 keV point-source sensitivity 10-4 ph cm-2 s-1 • maximum : 5 x 10-5 ph cm-2 s-1 at GC • large parts of galactic plane better than 2 x 10-4 ph cm-2 s-1 • several high latitude regions better than 2 x 10-4 ph cm-2 s-1

  8. Step1 Background modelling

  9. 511 keV background ~ 5 % variations

  10. 511 keV background model g(t) rcont(t) ∫ g(t’) x exp((t’-t)/t) dt’ constant r(t) = rcont(t) + b1 + b2 x g(t) + b3 x ∫ g(t’) x exp((t’-t)/t) dt’ rcont(t) : continuum background (from adjacent energies) r(t) : predicted 511 keV line background rate g(t) : GEDSAT rate t = 352 days b1, b2, b3 : fitted coefficients (detector / orbit & detector)

  11. Residuals 1 %

  12. Step2 Model fitting

  13. 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)

  14. Bulge/Halo models 1.17 x 10-3 ph cm-2 s-1 1.09 x 10-3 ph cm-2 s-1 1.13 x 10-3 ph cm-2 s-1 2.15 x 10-3 ph cm-2 s-1 SPI 511 keV bulge flux : (1.1-2.2) x 10-3 ph cm-2 s-1

  15. Bulge/Halo + Disk models 1.62 x 10-3 ph cm-2 s-1 2.04 x 10-3 ph cm-2 s-1 2.05 x 10-3 ph cm-2 s-1 2.43 x 10-3 ph cm-2 s-1 SPI flux (imaging) (1.6-2.4) x 10-3 ph cm-2 s-1 SMM flux (wide FOV) (1.5-2.8) x 10-3 ph cm-2 s-1

  16. 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

  17. Step 2 : Conclusions Bulge Halo Disk Flux (10-3 ph cm-2 s-1) 1.05 ± 0.07 1.6 ± 0.5 0.7 ± 0.5 L511 (1043 ph s-1) 0.90 ± 0.06 1.2 ± 0.3 0.2 ± 0.1 Lp (1043 s-1)* 1.50 ± 0.10 2.0 ± 0.5 0.3 ± 0.2 * assuming fp = 0.93 The 511 keV line emission is bulge dominated : B/D flux ratio : 1 - 3 B/D luminosity ratio : 3 - 9

  18. Step3 Imaging

  19. An all-sky image of 511 keV emission • 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

  20. Iteration 1 Exposure Choice of iteration Flux Log likelihood

  21. Iteration 5 Exposure Choice of iteration Flux Log likelihood

  22. Iteration 10 Exposure Choice of iteration Flux Log likelihood

  23. Iteration 17 Exposure Choice of iteration Flux Log likelihood

  24. Iteration 25 Exposure Choice of iteration Flux Log likelihood

  25. Iteration 40 Exposure Choice of iteration Flux Log likelihood

  26. Iteration 70 Exposure Choice of iteration Flux Log likelihood

  27. Iteration 100 Exposure Choice of iteration Flux Log likelihood

  28. Galactic Centre emission 511 keV line and Ps continuum emission • Positronium continuum • same morphology • Ps fraction ~98 % Weidenspointner et al. (2005)

  29. Step4 Spectroscopy

  30. 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

  31. 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

  32. Comparison with OSSE Quantity SPI (1 yr) OSSE (9 yr) l0 -0.6° ± 0.3° -0.25° ± 0.25° b0 +0.1° ± 0.3° -0.3° ± 0.2° Dl (FWHM) 8.1° ± 0.9° 6.3° ± 1.5° Db (FWHM) 7.2° ± 0.9° 4.9° ± 0.7° 511 keV flux (10-3 ph cm-2 s-1) 1.2 - 3.3 1 - 3 B/D flux ratio 1 - 3 0.2 - 3.3 • Results basically consistent with OSSE- emission centred on GC- bulge dominates emission- flux consistent • SPI bulge slightly larger than OSSE bulge • No PLE (flux3s < 1.5 x 10-4 ph cm-2 s-1)

  33. 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 !

  34. 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

  35. 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

  36. 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

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

  38. 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 ?

  39. 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)

  40. 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) ?

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

  42. 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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