Antimatter in our Galaxy unveiled by
INTEGRAL
Jürgen Knödlseder
Centre d’Etude Spatiale des Rayonnements, Toulouse, France
Antimatter annihilation
E = m
2
c
Galactic positron annihilation
The pre-INTEGRAL epoch
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
INTEGRAL
ESA’s INTErnational Gamma-Ray Astrophysics Laboratory
Launch : 17 october 2002
Mission duration : 2008
Orbit : 72 h, excentric
Guest observer time : 65-75 %
IBIS : Imager on Board the Integral Satellite
SPI : SPectrometer onboard Integral
JEM-X : Joint European Monitor for X-rays
OMC : Optical Monitoring Camera
15 - 10000 keV, 12’, R ≈ 12
20 - 8000 keV, 2.5°, R ≈ 500
3 - 35 keV, 3’, R ≈ 10
550 nm (V band), 6"
SPI
SPectrometer onboard INTEGRAL
SPI all-sky exposure after ~ first year
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
107 cm2 s
1 x 107 cm2 s = 133 ks
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
Step 1
Background modelling
511 keV background
~ 5 % variations
511 keV background model
g(t)
rcont(t)
constant
∫ g(t’) x exp((t’-t)/t) dt’
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)
Residuals
1%
Step 2
Model fitting
511 keV bulge emission morphology
Modelling with a 2d Gaussian
l0
b0
Dl (FWHM)
Db (FWHM)
Db / Dl
511 keV flux
-0.6° ± 0.3°
+0.1° ± 0.3°
8.1° ± 0.9°
7.2° ± 0.9°
0.89 ± 0.14
1.09 ± 0.04 (10-3 ph cm-2 s-1)
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
Bulge/Halo + Disk models
1.62 x 10-3 ph cm-2 s-1
2.05 x 10-3 ph cm-2 s-1
SPI flux (imaging)
SMM flux (wide FOV)
2.04 x 10-3 ph cm-2 s-1
2.43 x 10-3 ph cm-2 s-1
(1.6-2.4) x 10-3 ph cm-2 s-1
(1.5-2.8) x 10-3 ph cm-2 s-1
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
Step 2 : Conclusions
Flux (10-3 ph cm-2
L511 (1043 ph s-1)
Lp (1043 s-1)*
Bulge
s-1) 1.05 ± 0.07
0.90 ± 0.06
1.50 ± 0.10
Halo
1.6 ± 0.5
1.2 ± 0.3
2.0 ± 0.5
* assuming fp = 0.93
The 511 keV line emission is bulge dominated :
B/D flux ratio
: 1 - 3
B/D luminosity ratio
: 3 - 9
Disk
0.7 ± 0.5
0.2 ± 0.1
0.3 ± 0.2
Step 3
Imaging
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
Choice of iteration
Iteration 1
Flux
Exposure
Log likelihood
Choice of iteration
Iteration 5
Flux
Exposure
Log likelihood
Choice of iteration
Iteration 10
Flux
Exposure
Log likelihood
Choice of iteration
Iteration 17
Flux
Exposure
Log likelihood
Choice of iteration
Iteration 25
Flux
Exposure
Log likelihood
Choice of iteration
Iteration 40
Flux
Exposure
Log likelihood
Choice of iteration
Iteration 70
Flux
Exposure
Log likelihood
Choice of iteration
Iteration 100
Flux
Exposure
Log likelihood
511 keV line and Ps continuum emission
Galactic Centre emission
Positronium continuum
• same morphology
• Ps fraction ~98 %
Weidenspointner et al. (2005)
Step 4
Spectroscopy
Galactic bulge spectrum
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
Model : 2
Energy
FWHM1
FWHM2
Flux1
Flux2
Gauss + positronium + cont.
510.98 ± 0.03 keV
1.14 ± 0.40 keV
5.08 ± 1.11 keV
6.9 x 10-4 ph cm-2 s-1
3.8 x 10-4 ph cm-2 s-1
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
Comparison with OSSE
Quantity
SPI (1 yr)
OSSE (9 yr)
l0
b0
Dl (FWHM)
Db (FWHM)
511 keV flux (10-3 ph cm-2 s-1)
B/D flux ratio
-0.6° ± 0.3°
+0.1° ± 0.3°
8.1° ± 0.9°
7.2° ± 0.9°
1.2 - 3.3
1 - 3
-0.25° ± 0.25°
-0.3° ± 0.2°
6.3° ± 1.5°
4.9° ± 0.7°
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)
Constraints on the disk source
1809 keV (26Al)
• 26Al decays via b+ decay (85%)
• F511 = 0.5 x F1809 (fp = 0.93)
• Expected : 5 x 10-4 ph cm-2 s-1
•
•
•
•
511 keV
• 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
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 !
Constraints on the bulge source
Wolf-Rayet stars
Pulsars
Core-collapse SNe
Hypernovae / GRB
Stellar flares
CR interactions
with ISM
Dark matter
HMXB
SN Ia
LMXB
Novae
Constraints on the bulge source
Wolf-Rayet stars
Pulsars
Hypernovae / GRB
Core-collapse SNe
Stellar flares
CR interactions
with ISM
Dark matter
HMXB
SN Ia
LMXB
Novae
Strong disk component expected
Constraints on the bulge source
Wolf-Rayet stars
Pulsars
Core-collapse SNe
Hypernovae / GRB
Stellar flares
CR interactions
with ISM
Dark matter
HMXB
SN Ia
LMXB
Novae
Constraints on the bulge source
Dark matter
SN Ia
LMXB
Novae
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 ?
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
13N
18F
22Na
26Al
CO (0.8 M)
2 x 10-7
2 x 10-9
7 x 10-11
2 x 10-10
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)
•
•
ONe (1.25 M)
4 x 10-8
5 x 10-9
6 x 10-9
1 x 10-8
Hernanz et al. 2001
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)
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
57Ni
56Co
44Sc
Ch
0.01 - 0.03
0.4 - 1.1
(7-20) x 10-6
Sub-Ch
0.01 - 0.03
0.3 - 0.9
(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
•
•
•
•
57Ni
56Co)
: 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) ?
Dark matter
•
•
•
Distribution not well known
No flux prediction
Sgr dwarf not detected
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