Universitat de - Departament d'Astronomia i Meteorologia ...

1.1. X-ray binaries 7
Galactic latitude [deg]
90
60
30
0
−30
−60
Low Mass X−ray Binaries
−90
180 120 60 0 300 240 180
Galactic longitude [deg]
Figure 1.2: Distribution of catalogued LMXBs in galactic coordinates. LMC stands for
Large Magellanic Cloud. The dashed line represents the galactic plane.
Fig. 1.1, these systems do not trace the galactic disk, and are located in the galactic
bulge and in globular clusters at relatively high galactic latitudes, because are old
stellar systems of Population II. Only two LMXBs are catalogued in the LMC, and
none in the SMC.
In Table 1.2 we list the number of different types of LMXBs within the SMC,
the LMC, the Galaxy and total values. There are only 5 XPs, i.e., ∼ 3% of the
149 catalogued LMXBs, compared to the ∼ 54% in HMXBs. This fact tells us that
most of LMXBs are low magnetic field NSs or BHs. Two of these XPs are also X-ray
bursters. There are 63 X-ray bursters, all of them containing NS compact objects.
A total of 6 Z sources have been found in the Galaxy, while 1 is suspected in the
LMC (omitted here). There are 18 Atoll sources, of which 16 are X-ray bursters,
LMC