1. M.Cassé@iap.fr1 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 even less convincing Pave the way to LIGHT DARK M ATTER (P. Fayet) Treated by J. Knödlseder

2. M.Cassé@iap.fr2 OSSE/GRO map

3. M.Cassé@iap.fr3

4. 4 Knödlseder et al 2005

5. M.Cassé@iap.fr5 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 SPI Observation of 511 keV line from the Galactic bulge INTEGRAL/SPI

6. M.Cassé@iap.fr6 ANNIHILATION MEDIUM P.Jean et al 2005

7. M.Cassé@iap.fr7 Positronium Fraction Annihilation of e + in the gas after thermalisation direct annihilation e + e - : 2  (511keV) formation of  Positronium (para) 1/4 of the Ps (s=0) annihilation via 2  (511keV line) formation of  Ps (s=1) 3/4 of the Ps (triplet) annihilation via 3  (0 - 511 keV) fraction de positronium : f Ps = 2 / (1.5 + 2.25  511 /  3  ) CGRO/OSSE Kinzer et al, ApJ 559 (2001) thin line  3 keV f Ps = 0.93 ± 0.04 Annihilation in a warm medium (~5×10 4 K). L 511 =(2-1.5 f p ) L e+ Positron injection rate: (1.5 ± 0.1)10 43 s-1 GRO/OSSE data

8. M.Cassé@iap.fr8

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

10. M.Cassé@iap.fr10 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 f p = 93±0.04 L e+ = (2-1.5f p ).L 511 Annihilation rate = (1.5±0.1) 10 43 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? FLUX & MORPHOLOGY (summary)

11. M.Cassé@iap.fr11 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, H 2 (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 M a (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  M g ~10 9 Mo Bulge Radius ~ 2 kpc Gas Density ~ 1 cm -3 (upper limit) Accretion by stars? Sinking in CMZ  new stars Necessity dedicated calculations

12. M.Cassé@iap.fr12 PROPAGATION OF LOW E POSITONS Diffusion + Ionisation losses D ~ 3 10 27 cm 2 s -1 (Parizot et al 2005) TENTATIVE (Bykov) Ionisation dE/dt ~ 2 10 -8 (Ln gamma +6.6)n H eVs -1 t D =R 2 /D  10 8 ans t stop = E/(dE/dt) 10.10.01 cm -3 12.2 10 5 2.2 10 6 2.2 10 7 101.7 10 6 1.7 10 7 1.7 10 8 1001.4 10 7 1.4 10 8 1.4 10 9 MeV Escape

13. M.Cassé@iap.fr13 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 10 27 cm 2 s -1 Rate of HN/GRB? Disk emission NO GOOD CANDIDATE  + RADIOACTIVITY by order of importance 22 NaNovae  very small amounts 26 AlSN et WR  (1809 keV emission) not sufficient 44 TiSN: smaller contribution than 26 Al 56 NiSN IIM Ni =0.1 M  Thick envelope (10Mo) positrons released~ 0% SN Ia M Ni = 0.6 M  Thinner envelope (1 Mo) positrons released ? Potential sources of e +

14. M.Cassé@iap.fr14 TYPICAL PARAMETERS OF SNIa: M=1.34 Mo ejected mass E=1.17×10 51 erg Kinetic energy (E=1/2 M v 2 ) M Ni = 0.6 Mo mass of 56 Ni synthesized ENERGY SOURCE : 56 Ni  56 Co (t 1/2 =6.1 j)  56 Fe (t 1/2 =77j) + e + Simple Model of explosion ( spherical symmetry ) - free homologous expansion : R = v t - radioactive nuclei ( 56 Ni) deeply buried - production of positrons: 56 Co  56 Fe + e + (19%) - absorption:  R =  = mean free path  ~ 0.6 g cm -2 -Escape time: M E -1/2 t~390 d  consistent with inflexion of L.C.. 3.3% of 56 Co remaining Number of positrons released N e+ = 8×10 52 Production of positrons by SN I a (Milne et al, Schanne et al )

15. M.Cassé@iap.fr15 RATE OF SNIa IN THE BULGE Calibration with M (10 10 Mo) and B-K (+4.8) ; Schanne et al 2004, 2005) : 0.03±0.02/century, in agreement with theoretical models (Matteucci, Nomoto…)

16. M.Cassé@iap.fr16 HYPERNOVA SN2003dh SNIA: PUREMELY RADIOACTIVE OBJECTS L.C. fed by gammas & positrons 56 Ni  56 Co (t 1/2 =6.1 j)  56 Fe (t 1/2 =77j) + e + E  =847 keV, = 640 keV (19%), E max =1.4 MeV Envelope dense & opaque to  & e +, then progressive leak out Light curve of SN2003dh declines faster than typical SNIa  faster ejection (earlier transparency)  faster escape of  and e +  larger number of released positrons 25 times more than in SNIa ~ 0.02/century required BUT: Rate? Diffusion of positrons? Disk/Bulge ratio? Magnitude difference (V-band) Time (days since max) 56 Ni  56 Co (t 1/2 =6.1 j)  56 Fe (t 1/2 =77j) + e + (Br=19%) Schanne et al 2004

17. M.Cassé@iap.fr17 hypothesis : ANNIHILATION OF DARK MATTER NATURE ? NEUTRALINOS (favorite candidate of particle physicists) 551keV EMISSION DOUBLE ANNIHILATION   e + e -   or   = a  + b Z + c Ho,1 + d Ho,2 photino higgsino MAJORANA PARTICULE (particle = antiparticle) Positrons produced by different channels   WW,ZZ,tt,  +  - (qq-) (bb - )    °  2   +   +  e +  -   -  e - final product , (e +,e - ), (, - ), (p,p - ) ~~~~

18. M.Cassé@iap.fr18 Energy ~ 10 43 E e+ ergs -1 if E e+ ~ 1 GeV L bol > 10 40 erg s -1 >> L bol (non thermal)  Radio-synchrotron + Bremmstrahlung Not observed Branching (e+ e-)/  ~ 1  huge flux of HE  Not observed NEUTRALINO m  = 500GeV – 10TeV e + injected ar high Energy GB Positrons do not emanate from the annihilation of neutralinos E>30 MeV excluded by bremmstrahlung (EGRET 30-100 MeV) Hooper et al., 2004

19. M.Cassé@iap.fr19 BREMMSTRAHLUNG (EGRET) Ionisation Bremsstrahlung No hint of a bulge L b (bulge) < 2 10 36 erg/s Thick target L b =τ b /τ i L i L i = 5 10 39 erg/s L b (100-0 MeV) ~10 39 erg/s L b (100-30 MeV) ~2 10 38 erg/s M x < 100 MeV Hunter et al 1997

20. M.Cassé@iap.fr20 CONCLUSION OTHER SOURCE(S) OF POSITRONS NEEDED LIGHT DARK MATTER (TO AVOID PRODUCTION OF π° and HIGH ENERGY GAMMA RAYS)  Pierre Fayet