dynamical formation of lmxbs in the inner bulge of m31 by rasmus voss with marat gilfanov x-rays...
TRANSCRIPT
Dynamical formation of LMXBs
in the inner bulge of M31
by
Rasmus Vosswith
Marat Gilfanov
X-rays from nearby galaxies ESAC September 2007
OverviewOverview
Introduction: LMXBsWhat are they, how are they formed
Observations: LMXBs in M31The spatial distribution
Theory: Dynamical formation of LMXBs
Conclusions: Dynamical formation of LMXBs is important in the bulge of M31
LMXBsLMXBs
NS or BH accreting from a companion star < 1 Msol
Mass transfer driven by angular momentum lossfrom magnetic braking and gravitational radiation
Formation of (primordial) LMXBsFormation of (primordial) LMXBs
Only weaklydependent onthe stellarenvironment.
LMXBs trace the mass in galaxies
ObservationsObservationsGilfanov (2004):
LMXBs do follow the stellar mass in nearby galaxies
ObservationsObservationsGilfanov (2004):
LMXBs do follow the stellar mass in nearby galaxies
Centaurus A Voss & Gilfanov (2006)with Chandra
LMXBs in globular clustersLMXBs in globular clusters
Out of ~150 LMXBs inthe Milky Way13 LMXBs reside in globular clusters
Globular clusters contain <0.1% of the mass of the Milky Way
Improbable that they can be primordial LMXBs
Due to stellar encounters(dynamical formationof LMXBs)
M31M31
M31M31
ObservationsObservations
M31 with Chandra
Something wrong!
Dynamical formation?
Dynamical LMXB formation channelsDynamical LMXB formation channelsTidal capture Exchange reactionCollision
A few equationsA few equations
encounter rate per unit volume:
Two body encounters
Important: Gravitational focusing
A few equationsA few equations
Two body encounters
Kroupa IMF
Padova stellar isochrones (Girardi et al. 2002)
M31 versus globular clustersM31 versus globular clusters
Density: 102 -5·105 Msol
/pc3 103-104 Msol
/pc3
Velocity dispersion: 1-20 km/s 150 km/s
Metallicity: 0.01-1.0 solar 1.5-2.0 solar
Globular clusters M31 inner bulge
Mass segregation: strong not effective
Black holes: No Yes
Neutron stars: 10% retention 100% retention
Mass <107 Msol
>1010Msol
Dynamical LMXB formation channelsDynamical LMXB formation channelsTidal capture Exchange reactionCollision
Predictions for M31Predictions for M31
•24 BH LMXBs• 5 NS LMXBs• 3 UCXBs
Conclusions: M31Conclusions: M31•First evidence of dynamical formation of LMXBs in M31! •First theoretical investigation of DF in this environment! •Theory works •Mainly short period systems •Mainly BH accretors
Predictions for globular clustersPredictions for globular clusters
Metal-rich With lifetimes:
•2 “normal” LMXB•3 LMXB with ~0.1 M
sol comp.
•1.5 UCXB
Observed:
•2 LMXB P>5hr•4 with P unknown•2 UCXB (P<1hr)
An extra piece of evidenceAn extra piece of evidenceThe luminosity function of the LMXBs:The luminosity function of the LMXBs:
MW globularclusters
M31 globularclusters
M31 inner1 arcmin