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HIGH ENERGY ASTROPHYSICS -ray emission from galactic radioactivity

HIGH ENERGY ASTROPHYSICS -ray emission from galactic radioactivity. Relevant radioactive nuclei for galactic -ray line emission : how and where they are synthesized: nucleosynthesis (hydrostatic and explosive), in stars interaction with cosmic rays, in the interstellar medium

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HIGH ENERGY ASTROPHYSICS -ray emission from galactic radioactivity

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  1. HIGH ENERGY ASTROPHYSICS-ray emission from galactic radioactivity • Relevant radioactive nuclei for galactic -ray line emission: • how and where they are synthesized: • nucleosynthesis (hydrostatic and explosive), in stars • interaction with cosmic rays, in the interstellar medium • Electron-positron annihilation emission (line and continuum): • e+ from +- unstable nuclei • BUT other sources of e+ ( radioactivity) exist • Type of emission: point-source or diffuse

  2. Electron-positron annihilation emission • Electron-positron annihilation emission (line and continuum): • e+ from +- unstable nuclei (nucleosynthesis or interaction with cosmic rays) • pion decay (interaction of cosmic rays with ISM) • e+ -e- creation in compact objects

  3. Origin of galactic positrons • Stellar nucleosynthesis (mainly explosive): +-unstable nuclei • 56Co(56Ni)(SNe) ~ 1043 e+/s • 44Sc (44Ti) (SNe) ~ 2x1042 e+/s • 26Al (SNe, WR, AGB, novae) ~ 2x1042 e+/s • 22Na (novae) ~ (0.5-2) x1041 e+/s • Interaction with cosmic rays: • production of +-unstable nuclei by nuclear collisions: 12C(p,pn)11C(+), 16O(p,a)13N(+) • pp: production of pions +: p+p  + + X < E(e+)> ~ 30 (+) – 70 (0) MeV • pp: production of pions 0: p + p  X + p0  2g  e--e+(t=1,810-16 s)

  4. Radioactive isotopes relevant for -ray line astronomy: e+-emitters Supernovae mainly Novae mainly e- capture +-

  5. Origin of galactic positrons • Stellar nucleosynthesis (mainly explosive): +-unstable nuclei • 56Co (56Ni) (SNe) ~ 1043 e+/s • 44Sc (44Ti) (SNe) ~ 2x1042 e+/s • 26Al (SNe, WR, AGB, novae) ~ 2x1042 e+/s • 22Na (novae) ~ (0.5-2) x1041 e+/s • Interaction with cosmic rays: • production of +-unstable nuclei by nuclear collisions: 12C(p,pn)11C(+), 16O(p,a)13N(+) • pp: production of pions+: p+p  + + X < E(e+)> ~ 30 (+) – 70 (0) MeV • pp: production of pions0: p + p  X + p0  2g  e--e+(t=1,810-16 s)

  6. Excitation of nuclei by interaction with cosmic rays (parenthesis) • p + 12C  12C*  12C + 4.439 MeV • p + 16O  16O*  16O + 6.130 MeV • Broad (p at rest) or narrow (atom at rest) lines • p p • not observed yet (CGRO/COMPTEL reported their detection in Orion, but later deduced they were background lines)

  7. Origin of galactic positrons •   e+ e-(around black holes ) • Active Galactic Nuclei (AGNs) • “great annihilator” (1E 1740.7-2942) in the Galactic Center • Gamma Ray Bursts (GRBs) •  (B): (x-gamma) + (IR-x) → e+ e-(large magnetic fields: pulsars, B: 1012G) • Light dark matter (different from neutralinos), E~1-100 MeV; see recent papers: Boehm & Fayet 2003, hep-ph/0305261; Boehm et al., 2004, Phys. Rev. Lett, 92, 101301 (astro-ph/0309686)

  8. Positron propagation • Slowing down, thermalization, formation of Ps in flight • e+ + e- e+ + e-Coulomb energy loss (ionised gaz) • e+ + H  e+ + H*excitation (neutral or ionized gas) • e+ + H  e+ + H+ + e-ionization energy loss(neutral gas: H2, HI) • e+ + H  Ps + H+charge exchange • Timescales for slowing-down: ~105 years, E(e+)1MeV, n=1cm-3 • Direct annihilation is negligible

  9. Positron annihilation processes: 2 and 3 • Thermalized positrons • Direct annihilation: • 2: 511 keV line • Positronium “atom” formation (Ps): • ¼ singlet state (parapositronium) • 2: 511 keV line • 3/4 triplet state (orthopositronium) • 3 2=1.25x10-10 s 3=1.4x10-7 s

  10. 1991 Positron propa-gationand annihila-tion f1~90%

  11. Annihilation of positrons: summary • 2 of 511 keV: 511 keV line radiation • 3 with positronium, Ps, continuum spectrum • Probe of the ISM (interstellar medium)

  12. Observations of Galactic electron-positron annihilation: historical overview The line at 511 keV longest known and most studied extra-solar -ray line A -ray line at E<0.5 MeV was first detected from the direction of the GC, with a scintillator detector (NaI) onboard a ballon, thus with poor energetic resolution (Johnson et al 1973): RICE experiments

  13. Observations of Galactic electron-positron annihilation: historical overview The line at 511 keV longest known and most studied extra-solar -ray line A -ray line at E<0.5 MeV was first detected from the direction of the GC, with a scintillator detector (NaI) onboard a ballon, thus with poor energetic resolution (Johnson et al 1973): RICE experiments In 1977, observations with Ge detectors (higher energetic resolution) were performed: narrow line with E=511 keV (Leventhal et al. 1978). Bell/Sandia experiments interpretation of lower E resolution experiments: 511 keV line convolved with Ps continuum

  14. Leventhal et al. 1978

  15. Observations of Galactic electron-positron annihilation: historical overview • Main results before “COMPTON era” (i.e., before CGRO observations): • Flux increases with aperture of instrument (FOV) • extended source (scale: some 10 degrees) • Flux is variable with time (controversial): deduced from sharp drop in flux in ~1980 ... • reported by HEAO3 observations (but later shown to be not statistically significant) and various balloon flights (1977-1986)

  16. Smith et al., 1997

  17. Observations of Galactic electron-positron annihilation: historical overview • Main results before “COMPTON era” (i.e., before CGRO observations): • Flux increases with aperture of instrument (FOV) • extended source (scale: some 10 degrees) • Flux is variable with time (controversial): deduced from sharp drop in flux in ~1980 ... • reported by HEAO3 observations (but later shown to be not statistically significant) and various balloon flights (1977-1986)

  18. Historical summary of the 511 keV line flux from the Galactic center region, as observed by various balloon and satellite instruments Purcell et al 1997

  19. HEAO-3, like HEAO-1, was a survey mission involving several independent but complementary instruments. This satellite was launched by NASA on September 20, 1979 into an orbit of 500 km altitude, 43.6 degrees inclination. The mission included two cosmic ray experiments, the Heavy Nuclei Experiment, the Cosmic Ray Isotope Experiment, and the Gamma-Ray Spectroscopy Experiment. The Gamma Ray Spectroscopy Experiment on HEAO-3 consisted of four p-type, high purity germanium detectors. These detectors had an energy range of 50 keV-10 MeV. An initial energy resolution of 3 keV at 1.46 MeV was achieved for each detector. The instrument had a 30 degree (FWHM) field of view

  20. Observations of Galactic electron-positron annihilation: historical overview • Main results before “COMPTON era” (i.e., before CGRO observations) • PROBLEM: extended source and rapid variability are not compatible: • light travel (too large to vary globally on timescales of years): variability on a scale of 0.5 yr size ~ 0.5 light-years • time required for e+ slow down before annihilation in the ISM: around 105 years (Guessoum et al. 1991) SOLUTION: two-component model; extended source + variable point source close to the GC (Lingenfelter & Ramaty, 1989)

  21. Lingenfelter & Ramaty, 1989

  22. Lingenfelter & Ramaty, 1989

  23. October 1990 Energy spectrum of 1E 1740.7-2942, as observed by SIGMA onboard GRANAT Bouchet et al., 1991 But some transients detected by SIGMA have not been confirmed by CGRO monitoring observations (BATSE) March/April 1990

  24. Granat was launched on 1 December1989 aboard a Russian PROTON rocket. It was placed in a highly eccentric 96 hour orbit with an initial apogee of 200,000 km and a perigee of 2000 km. Over time the orbit circularized so that by 1991 the perigee had increased to 20,000 km. Three days of the four day orbit were devoted to observations. After an initial period of pointed observations, Granat was placed in survey mode in September 1994, when the attitude control gas was exhausted. Granat ceased transmissions on 27 November 1998

  25. The SIMGA telescope was a collaboration between CESR (Toulouse), CEA (Saclay), and IKI (Moscow). It covered the energy range 30-1300 keV with an effective area of 800 cm2and a maximum sensitivity field of view of ~5° x5°. The maximum angular resolution was 10 arcmin. Its imaging capabilities were derived from the association of a coded mask and a position sensitive detector based on the Anger camera principle.

  26. Compton Gamma-Ray Observatory CGRO (1991-2000)

  27. Compton Gamma-Ray Observatory instruments

  28. CGRO/OSSE (Oriented Scintillation Spectrometer Experiment)

  29. OSSE observations of Galactic e--e+ annihilation • OSSE (11.4  3.8) • VP 16 of the Galactic Center Region • E= 509(5) keV • f2g = 2.4 0.310-4g cm-2 s-1 • f3g = 10.0 0.7010-4g cm-2 s-1 • (f=0.98 0.04 is adopted) 511 keV line power law Total 2g flux f2g = 28 (4)10-4g cm-2 s-1 Total Galactic annihilation rate 4p (8 kpc)2f2g21043 g s-1 One e+ produces 2[(1-f)+ (f/4)] 0.511 MeV photons; f is fraction that decay via positronium f 0.9 31043 e+ s-1in the Milky Way positronium

  30. CGRO/OSSE observations of Galactic electron-positron annihilation: map OSSE+SMM+TGRS data: map of Galactic 511 keV line central bulge + galactic plane + positive latitude enhancement • Purcell et al., 1997 • Fluxes(10-4 phot/cm2/s) • central bulge: 3.3 (size 4o) • Galactic plane: 10 (size lat.~12o, long.~30o) • Positive-latitude excess: 9 (~16o; centroid b~12o, l~-2o) • No time variability

  31. CGRO/OSSE observations of Galactic electron-positron annihilation: new maps Milne et al., 2000, 2002; Fluxes(10-4 phot/cm2/s): central bulge: 3.5-24; Galactic plane: 17.4-7.3; Positive-latitude excess: 0.7-1.1 Bulge/Disk: 0.2-3.3

  32. INTEGRAL satellite. Launched on October 17th, 2002

  33. Jean, 2004

  34. Jean, 2004

  35. Jean, 2004

  36. Jean et al., 2004

  37. Other all-sky maps in gamma-ray astronomy (COMPTEL & EGRET)

  38. COMPTEL all-sky map (E: 1-30 MeV) Strong et al., 1999

  39. EGRET (Energetic Gamma-Ray Experiment Telescope) EGRET detected gamma rays using a spark chamber for direction measurement and a NaI(Tl) calorimeter, the Total Absorption Shower Counter (TASC), for energy measurement. The spark chamber had interleaved tantalum foils and tracking layers. A fraction of the incoming gamma rays (about 35% above 200 MeV) interacted in the foils to produce high-energy positron-electron pairs, which were tracked through subsequent layers of the spark chamber and absorbed by the TASC at the bottom of the tracker. Reconstruction of the energies and directions of the positron-electron pairs yielded the energies and directions of the incident photons.

  40. EGRET all-sky map (E>100 MeV)

  41. Schönfelder, 2001

  42. Source types detected by COMPTEL & EGRET Schönfelder, 2001

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