INTEGRAL Observations ofthe Galactic 511 keV Emission andMeV Gamma-ray Astrophysics
K. Watanabe, NASA/Goddard Space Flight Center
On behalf of the INTEGRAL/SPI Science TeamRironkon Seminar, 12/26/05

MeV Gamma-ray Astrophysics• Nucleosynthesis-e.g. 26Al (1.809MeV), 60Fe (1.172,1.333MeV), 44Ti(1.156MeV fromCasA&Vela)• Supernovae- e.g. 56Co-->56Fe (t1/2 = 79 d, E =0.847, 1.238 MeV)

• Neutron Star Binaries-e.g. Neutron-Proton recombination line at 2.223 MeV (Bildsten, Salpeter & Wasserman 1993)• Cosmic Ray Interactions-e.g 12C excitation line (4.439 MeV), and 16O excitation line (6.129 MeV)

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Gamma-Ray Bursts/Hypernovae
PROBLEM:Black Holes
Small S/N ~ less than 1%Pulsars
Solar FlaresAGNsSeminar, 12/26/05
Cosmic Gamma-ray Rironkon
Background,etc.

26Al Sky Map

Rironkon Seminar, 12/26/05

26Al Line Width• Inner-Galaxy Line is Probably “Narrow” (~1 keV)
• Cygnus Region (young stars, WR-dominated) ?
Courtesy of R. Diehl

Rironkon Seminar, 12/26/05

Galactic Rotation•••

Doppler Shift of the Centroid
The Sources are not Localized
Steady-State Mass of 26Al = 2.8 (±0.8) Mo

Courtesy of R. Diehl

Rironkon Seminar, 12/26/05

60Fe-Marginal (3-4σ) detections of the 1.172 and 1.333 MeV lines
RHESSI (Smith 2004)

INTEGRAL/SPI (Harris et al. 2005)

3.6±1.4 x 10-5 ph cm-2s-1 (2.6σ)(3σ)- the 60Fe/26Al ratio ~ 0.11 ± 0.03 [INTEGRAL/SPI(Harris et al. 2005)]
Rironkon Seminar, 12/26/05

Some other source of 26Al besides explosive
nucleosynthesis in core-collapse SNe are required!
Rironkon Seminar, 12/26/05

Cosmic Gamma-ray Background-SNIa can not makethis contribution?
(Zhang et al. 2004)-Is Dark Matter
responsible?
(Ahn et al. 2005)-A future mission(e.g. ACT) couldanswer.
(Watanabe et al. 1999)-the decay chain 56Ni

56Co

56Fe

Rironkon Seminar, 12/26/05

INTEGRAL Mission Description• European Space Agency (ESA) mission– Launched 17 Oct., 2002

• Mission Science– Gamma-ray astronomy in 15 keV - 10 MeV range– Supporting x-ray and optical monitoring• Payload– Main Instruments• SPI: germanium spectrometer• IBIS: CdTe + CsI imager– Monitor Instruments• JEM-X: x-ray monitor• OMC: optical monitor
Rironkon Seminar, 12/26/05

Mission Description (cont.)• Follow-on to Compton Gamma-Ray Observatory(CGRO).
• New technologies result in significant
improvements in performance over CGRO.
– Germanium detectors ⇒ ~ 50 x better energy resolution– CdTe detectors ⇒ ~ 15 x better angular resolution• Forms complementary set with SWIFT (gammaray bursts) and GLAST (high-energy gammarays).

Rironkon Seminar, 12/26/05

INTEGRAL Spacecraft

Rironkon Seminar, 12/26/05

Detectors
EnergyRange

SPI(SPectrometeron INTEGRALIBIS(Imager onBoard theIntegralSatellite)

JEM-X(JointEuropean Xray Monitor)

EnergyField ofResolution View

Angular
Detector
Resolution Area

18 keV - 2.2keV
8 MeV@1.3MeV

16 deg
2.5 degfully coded FWHM

15 keV - 8%
10 MeV @100keV
10%
@1MeV

8.3 x 8.0deg fully
coded

12 arcmin
FWHM

500 cm2 (19hexagonal Gedetectors)

2600 cm2(4x4x2mm CdTe pixels)

ISGRI, 3000 cm2(9x9x30 mm CsIpixels)PICsIT

3-35keV 1.3keV@10keV

4.8deg3 arcminfully coded

Rironkon Seminar, 12/26/05

500 cm2 (2 imaging
microstrip gas
chambers (90%Xenon + 10%Methane)

IBIS
SPI
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.

CodedMask

BGO
ActiveShieldJEM-X

Ge Detector
Array
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.

BGO
ActiveShieldRironkon Seminar, 12/26/05

MechanicalCoolerCoded Aperture Imaging (SPI, IBIS

and JEM-X)
IBIS fullycoded Crabshadowgram
Mask
Mask

IBIS off-axis
Crabshadowgram
Detector
Detector
Array
Array
Rironkon Seminar, 12/26/05

Some Highlights•Discoveries of various new sources
HMXB:IGR J16318-4848, IGR J16320-4751, IGR J17391-3021, Seyfert: IGR J18027-1455
LMXB:IGR J16358-4726, IGR J16418-4532, IGR J17464-3213, Neutron star: IGR J17597-2201
γ-ray Sources: IGR J00291+5934,IGR J06074+2205,IGR J07597-3842,IGR J11305-6256,
IGR J16167-4957,IGR J16479-4514, IGR J16558-5203,IGR J17252-3616,
IGR J18325-0756,IGR J18450-0435,IGR J18483-0311,IGR J21247+5058•A faint persistent source within 1’ of Sgr A* (Bélanger et al., 2005, astro-ph/0508128)•Identification of the Galactic TeV (H.E.S.S. ) sources: IGRJ18135-1751 & AX J1838.0-065(Ubertini et al., ApJ 629, L109, 2005; Malizia et al., ApJ 630, L157, 2005)•Fast X-ray transients of just a few hours duration: XTE J1739-302(Sguera et al., astro-ph/0508018; Smith et al., astro-ph/0510658)•ms pulsar IGR J00291+5934: the fastest known accreting X-ray pulsar(1.67ms, Porb= 2.46h) (e.g. Falanga et al., A&A 436, 647, 2005)•Anomalous X-ray Pulsar 4U 0142+614 (den Hartog et al., 2004,ATel #293)•Gamma-RayBursts or X-ray flashes(e.g. GCN #3059, 3323, 3348, 3430, 3446, 3472, 3552, 3607, 4002, 4007, 4192).
Rironkon Seminar, 12/26/05

511 keV Emission

Rironkon Seminar, 12/26/05

Possible Positron Sources• Massive stars (e.g. Wolf-Rayet)– Positrons created by nucleosynthesis in stellar interior, convectedto surface and transported into interstellar medium (ISM) by stellarwind.

• Hypernovae– Asymmetric explosion of a massive (> 30 Msun) star. Positrons canbe efficiently transported outward by strong jets and escape into
low optical depth regions where they subsequently annihilate.

• Black Holes (BH)
– Pair plasmas believed to exist in BH jets.
– Could either be aggregate emission from many BHs in Galactic
Center region or from a single massive BH at Galactic Center.

• Type Ia Supernovae– Beta-decay of radioactive nuclei created in SN explosion andtransported into ISM)in expanding shell.
Rironkon Seminar, 12/26/05

Possible Positron Sources• Dark Matter– There has been recent speculation on the possible existence oflight (mc2 < 100 MeV) dark matter particles which would decay orannihilate primarily through the formation of electrons and positrons.

• Superconducting Strings– Positron production proportional to Galactic magnetic field.

Rironkon Seminar, 12/26/05

511 keV Spectroscopy• Measured line energy
consistent with rest energy,
mc2 = 511.00 keV.
• Narrow line width (2.3 keV)consistent with annihilation inwarm interstellar clouds.

• Step in continuum frompositronium (ps). Orthopositronium is formed 3/4 ofthe time and undergoes 3photon decay.

511 keV Line Flux
(10-3 cm-2 s-1)

1.35 ± 0.11

Line Energy (keV)

511.14 ± 0.08

FWHM (keV)

2.34 ± 0.24

Positronium
Continuum Flux
(10-3 cm-2 s-1)

4.7 - 10.2

Ps fraction

Rironkon Seminar, 12/26/05> 0.88

Annihilation Processes
T ~ 106 yrs(due to Coulomb collisions)

Guessoum et al.(1991)

Rironkon Seminar, 12/26/05

511 keV Line Profile(Churazov et al., 2005)•Positrons probably
migrate far from source
and annihilate
somewhere in ISM.

•511 keV line profile andpositronium fraction are
diagnostic ofannihilation region.

•Annihilation probably
takes place in warm
(T ~ 104 K) partiallyionized region of ISM.

Thermalized
Ps annihilation
Ps in-flightannihilation

Ps 3γ
continuum

Rironkon Seminar, 12/26/05

Thermalized e+
directannihilation

Courtesy of P. JeanBest spectral modelParam.
InΓnIbΓbI3γ
Ac

Measured values(0.72 ± 0.12 ± 0.02) x 10-3 s-1 cm-21.32 ± 0.35 ± 0.02 keV(0.35 ± 0.11 ± 0.02) x 10-3 s-1 cm-2
5.36 ± 1.22 ± 0.06 keV(4.23 ± 0.32 ± 0.03) x 10-3 s-1 cm-2
(7.17 ± 0.80 ± 0.06) x 10-6 s-1 cm-2 keV-1

χ2 ~ 171.3 (d.o.f. 148)
Broad line detected (3.2σ)
Ib ~1/3 of the 511 keV flux
Total 511 keV flux :(1.07±0.03) x 10-3 γ s-1 cm-2
Ps fraction : 96.7±2.2 %(systematic error ~ 0.2%)
Remark :- s = 1.75 (fixed)
Kinzer et al., 1999
- line centroïds are fixed
Rironkon Seminar, 12/26/05

CGRO/OSSE 511 keV Map(Purcell et al., ApJ, 1997)

Gal. Lat.

Fountain?

Bulge

Gal. Long.
Rironkon Seminar, 12/26/05

PlaneMapping 511 keV line emission: OSSE/SMM/TGRS
Richardson-Lucy
Algorithm

Singular Value
Decomposition
Algorithm

Rironkon Seminar, 12/26/05

Courtesy of P. MilneINTEGRAL/SPI vs. CGRO/OSSE
OSSE

INTEGRAL/SPI

BackgroundLow-earth orbit.
Variablebackground.

High orbit outside
magnetosphere.
Stable background.

ImagingSimple 4° x 11°
collimator.

Coded aperture.
3° resolution.

EnergyResolution(E/∆E @ 511keV) LineNarrow~ 10~ 250~ 5 x 10-5 cm-2 s-1~ 5 x 10-5 cm-2 s-1

Sensitivity(511 keV, 106sec)
Rironkon Seminar, 12/26/05

511 keV Spatial Distribution
Knodlseder et al., 2005

• Bulge distribution– Data are reasonably well
fit by symmetric gaussianwith FWHM = 8° ± 1°
– No evidence for OSSE
“fountain”– Ensemble of point
sources cannot be ruledout• Concentration of flux
at GC suggests older
population.
Rironkon Seminar, 12/26/05

Teegarden, Watanabe et al., 2005

511 keV Bulge + Disk Model• INTEGRAL marginally detects 511 keV galactic diskcomponent at 3-4 σ significance.
– F511 = (7±5) x 10-4 cm-2 s-1 (Knodlseder et al., 2005)– Bulge/disk ratio = 1 - 3
Rironkon Seminar, 12/26/05

CGRO/COMPTEL 26AL (1809 keV) Map•

26Al in the Galaxy is most likely produced by nucleosynthesis in

massive stars.
– Eγ = 1809 keV– Half-life = 7.2 x 105 yr
Rironkon Seminar, 12/26/05

511 keV from 26Al
• 511 kev disk component could be accounted
for by 26Al decay– 26Al(β+)26Mg,• fdecay = 82% (β+ decay fraction)– F1809 ≈ 7 x 10-4 cm-2 s-1– F511 = fdecay x f511 x F1809= 3.5 x 10-4 cm-2 s-1(f511 = no. of 511 keV ph/annihilation≈ 0.65)Predicted 511 keV disk component flux from 26Al
decay is ~ 50% of observed value but still withinerror bar.

Rironkon Seminar, 12/26/05

Positronium Map
Weidenspointner et al.,2005•More difficult measurement due to broader energy range.
––••Smaller signal-to-background ratio
More complex background

Similar morphology to 511 keV narrow line.
Consistent with OSSE results.

Rironkon Seminar, 12/26/05

Searching for Tracer of 511 keV Emission
Reduced Maximum log Likelihood-Ratio

Courtesy of J.Knodlseder
K + M giants
nuclearbulge

compact
objects

relativistic
electrons

ISM

zodiacallight pollution

atomic HRadioµ-waves

FIR
Rironkon Seminar, 12/26/05

NIR

extinction

VX-rayγLikelihood vs. Bulge-to-Disk Ratio

RMLR

Courtesy of J.Knodlseder• Data favour large B/D ratio• HEAO-1 traces X-ray binaries• Low-mass X-ray binaries show a strong
concentration towards GC (B/D ~ 1.8)

Origin of positrons• LMXB ?
• Old stellar population (SN Ia) ?
• Dark Matter ?

Rironkon Seminar, 12/26/05

LMXB 511 keV Limits
No smoking gun
Knodlseder et al., 2005
Sourcel(degb(deg)Distance(kpc)

3 σ Flux Limit(10-4 ph cm-2 s-1)

GX 5-15.08°-1.02°

~ 8?

< 0.7

GRS 1915+105

45.37°-0.22°

12.5< 1.0A 0620-00

209.96°295.30°322.12°332.24°349.10°359.09°-6.54°

1.5 - 2.5

< 3.8-7.07°

5.5< 2.00.04°>8< 1.123.89°?

< 1.72.75°?

< 0.823.78°

0.7< 1.5Nova Muscae
Cir X-1
Cen X-4
GX 349+2
Sco X-1•Also a Comprehensive Line Search (Teegarden & Watanabe 2005)
does not find any 511 keV point sources
Rironkon Seminar, 12/26/05

Conclusions(511 keV Emission)• INTEGRAL/SPI has measured the spatial and spectral profilesof the Galactic 511 keV emission.
• Spatial distribution:––––~10° symmetric bulge component in the direction of the Galactic Center.
Weakly detected disk component, possibly from 26Al decay.
Positronium spatial distribution similar to narrow line spatial distribution.
Favors older population, e. g. LMXB or SNIa, or perhaps dark matter origin.

• Spectral distribution:––––Narrow line: FWHM ~ 2 keVLine energy = electron rest energy within errors
Positronium step: ps fraction > ~ 0.9
Indicates that annihilation takes place in warm (~ 104 K) partially ionizedregion of the ISM.

Rironkon Seminar, 12/26/05