Investigating the Faint X-ray Sources in Globular Clusters with XMM-Newton Natalie Webb Centre d’Etude Spatiale des Rayonnements, Toulouse D. Barret, B. Gendre

Globular clusters - Dense group of old stars - Stable on dynamical timescales - Unstable on thermal timescales - Binaries may be responsible for delaying core collapse - Binaries are difficult to detect because of high stellar density M 22 - optical M 22 - X-rays

Two types of X-ray source : Bright X-ray sources (Lx > 1036 ergs s-1) – X-ray binaries Faint X-ray sources (Lx < 1034.5 ergs s-1) - X-ray binaries - cataclysmic variables - active binaries - back- and foreground sources - millisecond pulsars

Globular clusters: - large cores - close - low absorption Observations with XMM-Newton MOS + PN imaging  Centauri M 22 NGC 6366 M 13

RS CVn  Centauri CV, bremsstrahlung fit kT=17.3±6.2 keV 2=0.84 (30 dof) Lx=4.7±0.2x1032 erg s-1 (0.5-10.0keV)

M 22 =2.03±0.21 Gaussian, centre=1.0 keV L=8.1x1031ergs s-1 2=1.08, 36  Pulsar like 1E1207.4-52 MEKAL, z=0.10±0.02 kT=2.25±0.21 keV Abundance=0.44±0.18 solar Lbol=5.4x1042ergs s-1 R= 0.2-0.4Mpc

M 13 T = 76±3 eV R = 12.8±0.4 km With a mass of 1.4Msolar

Do we expect so many Neutron Star Low Mass X-ray Binaries? Theory predicts that the number of NSLMXBs scales with the collision rate (Verbunt 2002) XMM-Newton and Chandra observations of globular clusters are deep enough to observe all NSLMXBs NSLMXBs easily identified by VERY soft spectrum and well fitted by hydrogen atmosphere model

Number of neutron star X-ray binaries Normalised collision rate

Results and Conclusions Faint X-ray sources are many different types of binaries (and fore-/background objects) Confirmed Neutron Star Low Mass X-ray Binary (NSLMXB) in  Centauri + detected a new one in M 13 Observations support that NSLMXBs are formed via collisions NSLMXBs in globular clusters are excellent objects to use to eventually constrain the NS equation of state