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THE RIDDLE OF P0SITRONS IN THE GALACTIC BULGE M.Cassé

THE RIDDLE OF P0SITRONS IN THE GALACTIC BULGE M.Cassé Service d’Astrophysique,CEA, Institut d’Astrophysique de Paris. OUTLINE SPI /INTEGRAL OBSERVATIONS POSITRON INJECTION RATE & MORPHOLOGY POSITRON SOURCE(S) SNIa fall short Hypernovae, GRB, LMXB, microquasars & NEUTRALINOS

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THE RIDDLE OF P0SITRONS IN THE GALACTIC BULGE M.Cassé

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  1. THE RIDDLE OF P0SITRONS IN THE GALACTIC BULGE M.Cassé Service d’Astrophysique,CEA, Institut d’Astrophysique de Paris OUTLINE SPI /INTEGRAL OBSERVATIONS POSITRON INJECTION RATE & MORPHOLOGY POSITRON SOURCE(S) SNIafall short Hypernovae, GRB, LMXB, microquasars & NEUTRALINOS even less convincing Pave the way to LIGHT DARK M ATTER (P. Fayet) Treated by J. Knödlseder M.Cassé@iap.fr

  2. OSSE/GRO map M.Cassé@iap.fr

  3. M.Cassé@iap.fr

  4. Knödlseder et al 2005 M.Cassé@iap.fr

  5. SPI Observation of 511 keV line from the Galactic bulge INTEGRAL/SPI • Centroid: • 511.06+0.17/-0.10 keV • Line width: • 2.95+0.45/-0.51 keV (FWHM) Flux: (1.05±0.06)×10-3 ph cm-2 s-1 M.Cassé@iap.fr

  6. ANNIHILATION MEDIUM P.Jean et al 2005 M.Cassé@iap.fr

  7. Positronium Fraction • Annihilation of e+ in the gas after thermalisation • direct annihilation e+ e- : 2g (511keV) • formation of Positronium (para) • 1/4 of the Ps (s=0) • annihilation via 2g (511keV line) • formation of Ps (s=1) • 3/4 of the Ps (triplet) • annihilation via 3g (0 - 511 keV) • fraction de positronium : • fPs= 2 / (1.5 + 2.25 F511 / F3g) • CGRO/OSSE • Kinzer et al, ApJ 559 (2001) • thin line  3 keV • fPs= 0.93 ± 0.04 • Annihilation in a warm medium • (~5×104 K). • L511 =(2-1.5 fp) L e+ • Positron injection rate: (1.5 ± 0.1)1043 s-1 GRO/OSSE data M.Cassé@iap.fr

  8. M.Cassé@iap.fr

  9. 26Al map (1809 keV) CGRO/COMPTEL Knödlseder, 1999, Proceedings 'Astronomy with Radioactivities’ M.Cassé@iap.fr

  10. FLUX & MORPHOLOGY (summary) Jean et al, 2003, A&A, 407 Knödlseder et al 2003, A&A, 407 Knödlseder et al 2005, astro-ph/0506026 Bulge Flux = (1.09 ± 0.04) ph cm-2 s-1 fp = 93±0.04 Le+ = (2-1.5fp).L511 Annihilation rate = (1.5±0.1) 1043 e+ s-1 No evidence for a point like source Δl (FWHM) = 8.1°± 0.9° Δb (FWHM) =7.2 ± 0.9° No other sources (Cygnus, Vela, LMC…) WHAT IS THE SOURCE OF POSITRONS? M.Cassé@iap.fr

  11. GAS DENSITY(rough estimate) Gaz density (through dE/dx) determines behaviour of positrons in the GB together with Diffusion coefficient D, both poorly known No clear observation of HI, H2(foreground disk), except in the CMZ Bulge = elliptical galaxy in a spiral (see models by Wyse &Silk ) Age of stars ~ 10 Gyr, Metallicity ~ solar IMF dN/dm =k Ma (Gould 2000) (a =-2.0 for M>0.7Mo, a= -1.3 for M<0.7Mo) 1Mo<M<8Mo stars WD: 22% Each WD ejects (PN phase) ~ 0.5 Mo  Mg ~109 Mo Bulge Radius ~ 2 kpc Gas Density ~ 1 cm-3 (upper limit) Accretion by stars? Sinking in CMZ  new stars Necessity dedicated calculations M.Cassé@iap.fr

  12. PROPAGATION OF LOW E POSITONS Diffusion + Ionisation losses D ~ 3 1027 cm2s-1 (Parizot et al 2005) TENTATIVE (Bykov) Ionisation dE/dt ~ 2 10-8 (Ln gamma +6.6)nH eVs-1 tD =R2/D 108 ans tstop = E/(dE/dt) 1 0.1 0.01 cm-3 1 2.2 105 2.2 106 2.2 107 10 1.7 106 1.7 1071.7 108 100 1.4 1071.4 1081.4 109 MeV Escape M.Cassé@iap.fr

  13. Potential sources of e+ • ACTIVE OBJECTS WITH A BLACK HOLE OR A NEUTRON STAR INSIDE • Microquasars: to few, not powerful enough • LMXRB (Prantzos 2004) No 511 keV emission detected • HN/GRB(Schanne et al 2204,Parizot et al 2005): • Central Source • Pb of diffusion des positons: • D~3 1027cm2s-1 • Rate of HN/GRB? Disk emission • NO GOOD CANDIDATE • +RADIOACTIVITY by order of importance • 22NaNovae very small amounts • 26AlSN et WR(1809 keV emission) not sufficient • 44TiSN: smaller contribution than 26Al • 56Ni SN II MNi=0.1 M Thick envelope (10Mo) • positrons released~ 0% • SN IaMNi= 0.6 M Thinner envelope (1 Mo) • positrons released ? M.Cassé@iap.fr

  14. Production of positrons by SNIa (Milne et al, Schanne et al ) • TYPICAL PARAMETERS OF SNIa: • M=1.34 Moejected mass • E=1.17×1051 erg Kineticenergy (E=1/2 M v2) • MNi = 0.6 Mo mass of56Ni synthesized • ENERGY SOURCE : • 56Ni  56Co (t1/2=6.1 j)  56Fe (t1/2=77j) + e+ • SimpleModel ofexplosion(spherical symmetry ) • - free homologous expansion : R = v t • radioactivenuclei (56Ni) deeply buried • - productionof positrons:56Co  56Fe + e+ (19%) • - absorption:r R = l = mean free path l ~ 0.6 g cm-2 • -Escape time:M E-1/2 • t~390 dconsistent with inflexion of L.C.. • 3.3% of 56Co remaining • Number of positrons released Ne+= 8×1052 M.Cassé@iap.fr

  15. RATE OF SNIa IN THE BULGE Calibration with M (1010Mo) and B-K (+4.8) ;Schanne et al 2004, 2005) : 0.03±0.02/century, in agreement with theoretical models (Matteucci, Nomoto…) M.Cassé@iap.fr

  16. HYPERNOVA SN2003dh • SNIA: • PUREMELY RADIOACTIVE OBJECTS • L.C. fed by gammas & positrons • 56Ni  56Co (t1/2=6.1 j)  56Fe (t1/2=77j) + e+ • Eg=847 keV, • <Ee+>=640 keV (19%), Emax=1.4 MeV Envelope dense & opaque to g & e+ , then progressive leak out • Light curve of SN2003dh declines faster than typical SNIa •  faster ejection (earlier transparency) •  faster escape of g and e+ •  larger numberof released positrons • 25 times morethan in SNIa • ~ 0.02/century required • BUT: Rate? Diffusion of positrons? Disk/Bulge ratio? Time (days since max) Magnitude difference (V-band) 56Ni  56Co (t1/2=6.1 j)  56Fe (t1/2=77j)+ e+(Br=19%) M.Cassé@iap.fr Schanne et al 2004

  17. hypothesis :ANNIHILATION OF DARK MATTER NATURE ? NEUTRALINOS (favorite candidate of particle physicists) 551keVEMISSIONDOUBLE ANNIHILATION e+e- or   = a + b Z + cHo,1 + d Ho,2 photino higgsino MAJORANAPARTICULE (particle = antiparticle) Positrons producedby different channels  WW,ZZ,tt,+- (qq-) (bb-) ° 2 ++e+ --e-  final product , (e+,e-), (, -), (p,p-) ~ ~ ~ ~ M.Cassé@iap.fr

  18. NEUTRALINO m = 500GeV – 10TeV e+ injectedar high Energy Hooper et al., 2004 Energy ~ 1043 Ee+ ergs-1 if Ee+ ~ 1 GeV Lbol > 1040 erg s-1>> Lbol(non thermal)  Radio-synchrotron + Bremmstrahlung Not observed Branching (e+ e-)/ ~ 1 huge flux of HE  Not observed GB Positrons do not emanate from the annihilation of neutralinos E>30 MeV excluded by bremmstrahlung (EGRET 30-100 MeV) M.Cassé@iap.fr

  19. Hunter et al 1997 BREMMSTRAHLUNG (EGRET) No hint of a bulge Lb(bulge) < 2 1036 erg/s Thick target Lb =τb/τi Li Li = 5 1039 erg/s Lb (100-0 MeV) ~1039 erg/s Lb(100-30 MeV) ~2 1038 erg/s Mx < 100 MeV Ionisation Bremsstrahlung M.Cassé@iap.fr

  20. CONCLUSION OTHER SOURCE(S) OF POSITRONS NEEDED LIGHT DARK MATTER (TO AVOID PRODUCTION OF π° and HIGH ENERGY GAMMA RAYS)  Pierre Fayet M.Cassé@iap.fr

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