Description: In both maps, the Galactic Centre is at the origin, the
Galactic plane is along the equator; Galactic longitude and
latitude are shown in degrees. a, The 511-keV line map. The
bright bulge region is prominent, as is the distinct
asymmetry in the flux from the inner disk; contours
correspond to intensity levels of 10-3 and 10-2 photons cm-2
s-1 sr-1. The map is based on observations with the imaging
spectrometer SPI on board the INTEGRAL satellite, and uses
data obtained during 'guaranteed time' for the first 4.3
years of the mission and publicly available data from 'guest
observer' observations for the first 3.3 years, supplemented
by observing time awarded to the authors. The map was
obtained using a MREM (Multi-Resolution Expectation
Maximization) image deconvolution algorithm28. During the
iterative image reconstruction, a filter is applied to the
image correction to suppress artefacts due to statistics
noise. Such filtering implies that low surface brightness
emission which is still detectable by model fitting may not
be present in the image, as is the case for some of the disk
emission. b, The sky distribution of the hard LMXBs detected
at energies above 20 keV with INTEGRAL/IBIS24, showing the
resemblance to that of the 511-keV annihilation line in a.