The all-sky distribution of 511 keV electron-positron annihilation emission Kn ö dlseder, J., Jean,...
-
date post
20-Dec-2015 -
Category
Documents
-
view
220 -
download
2
Transcript of The all-sky distribution of 511 keV electron-positron annihilation emission Kn ö dlseder, J., Jean,...
The all-sky distribution of 511 keV electron-positron annihilation emission
Knödlseder, J., Jean, P., Lonjou, V., et al. 2005, A&A, 441, 513
OutlineIntroductionDataBackground modellingResults1. Imaging2. Morphological characterisation3. Correlation with tracer maps4. Point-source search
Conclusions
Candidates for sources of positronscosmic-ray interactions with the interstellar medium (Ramaty et al. 1970)
Pulsars (Sturrock 1971)
compact objects housing either neutron stars or black holes (Ramaty & Lingenfelter 1979)
Gamma-ray bursts (Lingenfelter & Hueter 1984)
(light) dark matter (Rudaz & Stecker 1988; Boehm et al. 2004)
stars expelling radioactive nuclei produced by nucleosynthesissupernovae (Clayton 1973)
hypernovae (Cassé et al. 2004)
novae (Clayton & Hoyle 1974)
red giants (Norgaard 1980)
Wolf-Rayet stars (Dearborn & Blake 1985)
Introduction
INTEGRAL Mission SummaryLaunch date: 17 October 2002Dimensions: 5x3.7x3.7 metres.Launch dry mass: 3600 kgScience instruments mass: 2087 kgNominal mission lifetime: 2 yearsDesign lifetime: 5 yearsHighly eccentric orbitScientific PayloadMain instruments:
Spectrometer on Integral (SPI)Imager on Board the Integral Satellite (IBIS)
Monitors:Joint European X-Ray Monitor (JEM-X)
Optical Monitoring Camera (OMC)
OrbitHighly eccentric orbitPeriod: 72hInclination: 51.6 degTime above 40 000 km: ~90 %
SPI
IBIS detector
JEM-X coded mask
OMC
IBIS Coded Mask
JEM-X detectors
IMAGER IBISAccurate point source imagingBroad line spectroscopy & continuum
Coded Mask
Coolers
Veto
Veto
Ge detectors
SPECTROMETER SPIFine spectroscopy of narrow linesStudy of diffuse emission on large scales
X-RAY MONITOR JEM-XSource identificationMonitoring @ X-rays
OPTICAL MONITOR OMCOptical monitoring ofhigh energy sources
INTEGRAL payload: key parameters
dataDecember 10, 2004 public INTEGRAL data release (i.e. orbital revolutions 19−76, 79−80, 89−122)the INTEGRAL Science Working Team data of the Vela region observed during revolutions 81−88.covers approximately ~95% of the celestial sphere6821 pointed observationsExposure time: 15.3 Ms.instrumental energy resolution: 2.12 keV @ 511 keVEnergy interval: 507.5~514.5keVThe data have been analysed by sorting the events in a 3-dimensional data-space, spanned by the (calibrated) event energy, the detector number, and the SPI pointing number.
Map of the effective SPI exposure at 511 keV
SPI narrow line 3σ point-source sensitivity at 511 keV
Background modellingDETE
p: pointing number d: detector number e: energy bin
The background model for a given data-space bin
gp,d : the GEDSAT(saturated events in the germanium detectors) rateTp,d : the lifetime
∆e : the energy bin size for spectral bin eEadj : 523-545 keV
the continuum component of the instrumental background
the line component of the instrumental background
ORBIT-DETEadjust the model parameters β(2)
d,e
Residual count rate
ImagingRichardson-Lucy algorithm
Rij : the instrumental response matrixni : the measured number of countsi : data space binj : image space bink : iteration λk : acceleration factor
(the predicted number of counts)
Richardson-Lucy image of 511 keV gamma-ray line emission
Morphological characterisation
use a maximum likelihood multi-component model fitting algorithm.
Method
(Likelihood function)
log likelihood
fkj : sky intensity model
bi(β) : background model
αk and β are scaling factors
Maximum log likelihood-ratio
Reduced maximum log likelihood-ratio
detection of the bulge emission ~ 50σ
2d angular Gaussian surface brightness distribution
Galactic models
detection of the disk emission ~ 3−4σ
Correlation with tracer maps
None of the tracer maps is consistent with the data.
Point-source search
They looked for evidence of 511 keV gamma-ray line emission from a list of potential candidate objects.None of the sources which were searched for showed a significant 511 keV flux.
Summary of results511 keV emission is significantly (∼50σ) detected towards the galactic bulge region, and, at a very low level (∼4σ), from the galactic disk;
There is no evidence for a point-like source in addition to the diffuse emission, down to a typical flux limit of ∼10−4 ph cm−2 s−1;
There is no evidence for the positive latitude enhancement that has been reported from OSSE measurements (3σ upper flux limit ~1.5×10−4 ph cm−2 s−1).
The bulge emission is spherically symmetric and is centred on the galactic centre with an extension of ∼8◦ (FWHM); it is equally well described by models that represent the stellar bulge or the halo populations.
the bulge annihilation rate : (1.5 ± 0.1) × 1043 s−1
the disk annihilation rate : (0.3 ± 0.2) × 1043 s−1
the bulge-to-disk luminosity ratio : 3−9.
ConclusionsThe bulge emission arises from a different source which has only a weak or no disk component.
The disk emission can be attributed to the β+-decay of the radioactive species 26Al and 44Ti.
Type Ia supernovae and/or low-mass X-ray binaries are the prime candidates for the source of the galactic bulge positrons.
Light dark matter annihilation could also explain the observed 511 keV bulge emission characteristics.
Thank you