Antimatter in our Galaxy unveiled by Antimatter in our Galaxy unveiled by INTEGRAL INTEGRAL

Jürgen KnödlsederCentre d’Etude Spatiale des Rayonnements, Toulouse,

France

Antimatter annihilationAntimatter annihilation

E = m c2

Galactic positron annihilationGalactic positron annihilation

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

Purcell et al. 1997 OSSE, TGRS, SMM, …

Kinzer et al. 2001

Spectroscopy• centroid ~ 511 keV• Gaussian FWHM ~ 1.8-2.9 keV• positronium fraction 0.93 ± 0.04

The pre-INTEGRAL epoch

INTEGRALINTEGRALESA’s INTErnational Gamma-Ray Astrophysics Laboratory

Launch : 17 october 2002Mission duration : 2008Orbit : 72 h, excentricGuest observer time : 65-75 %

IBIS : Imager on Board the Integral Satellite 15 - 10000 keV, 12’, R ≈ 12SPI : SPectrometer onboard Integral 20 - 8000 keV, 2.5°, R ≈ 500JEM-X : Joint European Monitor for X-rays 3 - 35 keV, 3’, R ≈ 10OMC : Optical Monitoring Camera 550 nm (V band), 6"

SPISPISPectrometer onboard INTEGRAL

SPI all-sky exposure after ~ first yearSPI all-sky exposure after ~ first yearJürgen 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

107 cm2 s1 x 107 cm2 s = 133 ks

• 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

SPI 511 keV point-source sensitivitySPI 511 keV point-source sensitivity

10-4 ph cm-2 s-1

Background modelling

StepStep

11

511 keV background511 keV background

~ 5 % variations

511 keV background model511 keV background model

r(t) = rcont(t) + 1 + 2 x g(t) + 3 x ∫ g(t’) x exp((t’-t)/) dt’

rcont(t) : continuum background (from adjacent energies)

r(t) : predicted 511 keV line background rateg(t) : GEDSAT rate= 352 days1, 2, 3 : fitted coefficients (detector / orbit & detector)

rcont(t)

g(t)

∫ g(t’) x exp((t’-t)/) dt’constant

ResidualsResiduals

1 %

Model fitting

StepStep

22

511 keV bulge emission morphology511 keV bulge emission morphology

Modelling with a 2d GaussianModelling with a 2d Gaussian l0 -0.6° ± 0.3°

b0 +0.1° ± 0.3°

l (FWHM) 8.1° ± 0.9° b (FWHM) 7.2° ± 0.9° b / l 0.89 ± 0.14 511 keV flux 1.09 ± 0.04 (10-3 ph cm-2 s-

1)

Bulge/Halo modelsBulge/Halo models

SPI 511 keV bulge flux : (1.1-2.2) x 10-3 ph cm-2 s-

1

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

Bulge/Halo + Disk modelsBulge/Halo + Disk models

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

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

Comparison with tracer mapsComparison with tracer maps

FIRRadio NIRµ-waves V X-ray

Old stellar population

K+M giants XRBs

Young stellar population(free-free, CO, cold dust)

Step 2 : ConclusionsStep 2 : Conclusions

Bulge Halo DiskFlux (10-3 ph cm-2 s-1) 1.05 ± 0.07 1.6 ± 0.5 0.7 ± 0.5L511 (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 f* assuming fpp = 0.93 = 0.93

The 511 keV line emission is bulge dominated :B/D flux ratio : 1 - 3B/D luminosity ratio : 3 - 9

Imaging

StepStep

33

An all-sky image of 511 keV emissionAn 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

Choice of iterationChoice of iterationIteration 1 Exposure

Log likelihood

Flux

Choice of iterationChoice of iterationIteration 5 Exposure

Log likelihood

Flux

Choice of iterationChoice of iterationIteration 10 Exposure

Log likelihood

Flux

Choice of iterationChoice of iterationIteration 17 Exposure

Log likelihood

Flux

Choice of iterationChoice of iterationIteration 25 Exposure

Log likelihood

Flux

Choice of iterationChoice of iterationIteration 40 Exposure

Log likelihood

Flux

Choice of iterationChoice of iterationIteration 70 Exposure

Log likelihood

Flux

Choice of iterationChoice of iterationIteration 100 Exposure

Log likelihood

Flux

511 keV line and Ps continuum emission511 keV line and Ps continuum emission Galactic Centre

emission

Weidenspointner et al. (2005)

Positronium continuum • same morphology• Ps fraction ~98 %

Spectroscopy

StepStep

44

Galactic bulge spectrumGalactic bulge spectrumModel : 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 spectrumGalactic bulge spectrumModel : 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

Narrow Gauss (FWHM = 1.1 keV) :• ~65 % • Thermalised positronsBroad 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

Comparison with OSSEComparison with OSSE

• Results basically consistent with OSSEResults basically consistent with OSSE- emission centred on GC- emission centred on GC- bulge dominates emission- bulge dominates emission- flux consistent - flux consistent

• SPI bulge slightly larger than OSSE bulge SPI bulge slightly larger than OSSE bulge

• No PLE (fluxNo PLE (flux33 < 1.5 x 10 < 1.5 x 10-4-4 ph cm ph cm-2-2 s s-1-1))

QuantityQuantity SPI (1 yr)SPI (1 yr)OSSE (9 yr)OSSE (9 yr)l0 -0.6° ± 0.3° -0.25° ± 0.25°

b0 +0.1° ± 0.3° -0.3° ± 0.2°

l (FWHM) 8.1° ± 0.9° 6.3° ± 1.5°b (FWHM) 7.2° ± 0.9° 4.9° ± 0.7°511 keV flux (10-3 ph cm-2 s-1) 1.2 - 3.3 1 - 3B/D flux ratio 1 - 3 0.2 - 3.3

Constraints on the disk sourceConstraints on the disk source511 keV1809 keV (26Al)

• 26Al decays via + decay (85%)

• F511 = 0.5 x F1809 (fp = 0.93)

• Expected : 5 x 10-4 ph cm-2 s-1

• 44Sc decays via + 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

• Observed disk flux ~ (4-8) x 10Observed disk flux ~ (4-8) x 10-4-4 ph cm ph cm-2-2 s s-1-1

• 60% - 100% of the disk flux can be explained by 60% - 100% of the disk flux can be explained by 2626AlAl

• Rest (if any) is comfortably explained by Rest (if any) is comfortably explained by 4444TiTi• There seems to exist a pure bulge positron There seems to exist a pure bulge positron

source !source !

Constraints on the bulge sourceConstraints on the bulge source

Wolf-Rayet starsWolf-Rayet starsHypernovae / GRBHypernovae / GRB

Core-collapse SNeCore-collapse SNe

PulsarsPulsars

CR interactionsCR interactionswith ISMwith ISM Dark matterDark matter

SN IaSN Ia

NovaeNovae

HMXBHMXB

LMXBLMXB

Stellar flaresStellar flares

Constraints on the bulge sourceConstraints on the bulge source

Wolf-Rayet starsWolf-Rayet starsHypernovae / GRBHypernovae / GRB

Core-collapse SNeCore-collapse SNe

PulsarsPulsars

CR interactionsCR interactionswith ISMwith ISM Dark matterDark matter

SN IaSN Ia

NovaeNovae

HMXBHMXB

LMXBLMXB

Stellar flaresStellar flares

Strong disk component expectedStrong disk component expected

Constraints on the bulge sourceConstraints on the bulge source

Wolf-Rayet starsWolf-Rayet starsHypernovae / GRBHypernovae / GRB

Core-collapse SNeCore-collapse SNe

PulsarsPulsars

CR interactionsCR interactionswith ISMwith ISM Dark matterDark matter

SN IaSN Ia

NovaeNovae

HMXBHMXB

LMXBLMXB

Stellar flaresStellar flares

Constraints on the bulge sourceConstraints on the bulge source

Dark matterDark matter

SN IaSN Ia

NovaeNovaeLMXBLMXB

Low-mass X-ray binariesLow-mass X-ray binaries

Positron production Positron production processesprocesses• + e++ e- (pair jet)• N + N’ N* N + e+

UncertaintiesUncertainties• Yield• Line shape (broad versus narrow)

Grimm et al. 2002

Observed LMXB B/D ~ 1

Liu et al. 2000,2001

• B/D too small ? (completeness)B/D too small ? (completeness)• Why only LMXB and not Why only LMXB and not

HMXB ?HMXB ?

NovaeNovaePositron production Positron production processesprocesses• 13N 13C ( = 14 min, 100%)

• 18F 18O ( = 2.6 hr, 97%)

• 22Na 22Ne ( = 3.8 yr, 90%)

• 26Al 26Mg ( = 106 yr, 85%)

UncertaintiesUncertainties• 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)B/D probably OK (in particular if only CO novae contribute)• 1313N : if 100% escape N : if 100% escape bulge CO nova rate 25 century bulge CO nova rate 25 century-1-1 required required

(but models predict that (but models predict that 1313N eN e++ are absorbed in expanding shell) are absorbed in expanding shell)

YieldsYields 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 10-116 x 10-9

26Al 2 x 10-101 x 10-8

Hernanz et al. 2001

Type Ia supernovaeType Ia supernovaePositron production processesPositron production processes• 57Ni 57Co ( = 52 hr, 40%)

• 56Co 56Fe ( = 111 d, 19%)

• 44Sc 44Ca ( = 5.4 hr (87 yr), 99%)

UncertaintiesUncertainties• 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)

• 5757Ni : no chance for positrons to escapeNi : no chance for positrons to escape• 5656Co : 3% escape would require bulge rate of 0.6 centuryCo : 3% escape would require bulge rate of 0.6 century-1-1

• 4444Sc : always escape, Sub-Ch would require bulge rate of 0.5 - 2 Sc : always escape, Sub-Ch would require bulge rate of 0.5 - 2 centurycentury-1-1

(but : overproduces galactic (but : overproduces galactic 4444Ca abundance & makes bright Ca abundance & makes bright 4444Ti Ti bulge) bulge)

• Different types of SN Ia in bulge (underluminous) and disk Different types of SN Ia in bulge (underluminous) and disk (overluminous) ?(overluminous) ?

YieldsYields Ch Sub-Ch 57Ni 0.01 - 0.03 0.01 - 0.0356Co 0.4 - 1.1 0.3 - 0.944Sc (7-20) x 10-6 (1-4) x 10-3

Woosley 1997; Woosley & Weaver 1994

Dark matterDark matter

• Distribution not well Distribution not well knownknown

• No flux predictionNo flux prediction• Sgr dwarf not detectedSgr dwarf not detected

General conclusionsGeneral conclusions

• The 511 keV sky is bulge / halo dominated (B/D > 3)The 511 keV sky is bulge / halo dominated (B/D > 3)• Besides bulge / halo and disk, no further 511 keV Besides bulge / halo and disk, no further 511 keV

emission is observed (no PLE) emission is observed (no PLE) • The disk component can be entierly explained by The disk component can be entierly explained by ++

decay of radioactive decay of radioactive 2626Al and Al and 4444TiTi• The origin of the bulge component is still mysteriousThe origin of the bulge component is still mysterious

(LMXB, Novae, SN Ia, dark matter ?)(LMXB, Novae, SN Ia, dark matter ?)

• What is the bulge / halo eWhat is the bulge / halo e++ source ? source ?• Has the bulge / halo eHas the bulge / halo e++ source a disk component ? source a disk component ?• Can we learn something about SN Ia / Novae Can we learn something about SN Ia / Novae

distribution and types ?distribution and types ?

• Observe nearby candidate sources (SNR, LMXB)Observe nearby candidate sources (SNR, LMXB)• Deep observations at high galactic latitudes & galactic Deep observations at high galactic latitudes & galactic

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