Download Understanding LMXBs in Elliptical Galaxies

Understanding LMXBs
in Elliptical Galaxies
Vicky Kalogera
Low-Mass X-Ray Binaries
Accretors: NS or BH
CXC Image Archive
RLOF Donors:
MS, RG, WD/degenerate
low-mass:
< 1Mo
Binary Periods:
minutes to ~10 days
LMXBs form in both
galactic fields (isolated binaries)
globulars (dynamical interactions)
Ages:
old, ~ 0.1 - 10 Gyr
Persistent X-rays:
~10 Myr - ~1 Gyr
How do
Low-Mass
X-ray binaries
form in
galactic fields ?
primordial binary
Common Envelope:
orbital contraction
and mass loss
NS or BH formation
courtesy
Sky & Telescope
Feb 2003 issue
X-ray binary
at Roche Lobe
overflow
LMXB Population Modeling
Population Synthesis Calculations: necessary
Basic Concept of a Statistical Description:
evolution of an ensemble of binary and
single stars with focus on XRB formation and
their evolution through the X-ray phase
(ideally in both galactic field and globulars).
Population Synthesis Elements
Star formation conditions:
> time and duration, metallicity, IMF, binary properties
Population Synthesis Elements
Star formation conditions:
> time and duration, metallicity, IMF, binary properties
Modeling of single and binary evolution
> mass, radius, core mass, wind mass loss
> orbital evolution: e.g., tidal synchronization and
circularization, mass loss, mass transfer
> mass transfer modeling:
stable driven by nuclear evolution or angular momentum loss
thermally unstable or dynamically unstable
> compact object formation: masses and supernova kicks
> X-ray phase: evolution of mass-transfer rate
and X-ray luminosity
Population Synthesis Elements
Star formation conditions:
> time and duration, metallicity, IMF, binary properties
Modeling of single and binary evolution
> mass, radius, core mass, wind mass loss
> orbital evolution: e.g., tidal synchronization and
circularization, mass loss, mass transfer
> mass transfer modeling:
stable driven by nuclear evolution or angular momentum loss
thermally unstable or dynamically unstable
> compact object formation: masses and supernova kicks
> X-ray phase: evolution of mass-transfer rate
and X-ray luminosity
Population Synthesis Elements
Star formation conditions:
> time and duration, metallicity, IMF, binary properties
Modeling of single and binary evolution
> mass, radius, core mass, wind mass loss
> orbital evolution: e.g., tidal synchronization and
circularization, mass loss, mass transfer
> mass transfer modeling:
stable driven by nuclear evolution or angular momentum loss
thermally unstable or dynamically unstable
> compact object formation: masses and supernova kicks
> X-ray phase: evolution of mass-transfer rate
and X-ray luminosity
Population Synthesis Elements
Star formation conditions:
> time and duration, metallicity, IMF, binary properties
Modeling of single and binary evolution
> mass, radius, core mass, wind mass loss
> orbital evolution: e.g., tidal synchronization and
circularization, mass loss, mass transfer
> mass transfer modeling:
stable driven by nuclear evolution or angular momentum loss
thermally unstable or dynamically unstable
> compact object formation: masses and supernova kicks
> X-ray phase: evolution of mass-transfer rate
and X-ray luminosity
Population Synthesis Elements
Star formation conditions:
> time and duration, metallicity, IMF, binary properties
Modeling of single and binary evolution
> mass, radius, core mass, wind mass loss
> orbital evolution: e.g., tidal synchronization and
circularization, mass loss, mass transfer
> mass transfer modeling:
stable driven by nuclear evolution or angular momentum loss
thermally unstable or dynamically unstable
> compact object formation: masses and supernova kicks
> X-ray phase: evolution of mass-transfer rate
and X-ray luminosity
Population Synthesis Elements
Star formation conditions:
> time and duration, metallicity, IMF, binary properties
Modeling of single and binary evolution
> mass, radius, core mass, wind mass loss
population
synthesis
code:
> orbitalOur
evolution:
e.g., tidal
synchronization
and
circularization, mass
loss, mass transfer
StarTrack
> mass transfer modeling:
Belcynski et al. 2006
stable driven by nuclear evolution or angular momentum loss
thermallyincluding
unstable (simple)
or dynamically
unstable
cluster
dynamics:
> compact object formation:
masses
and supernova kicks
Ivanova et
al. 2005
> X-ray phase: evolution of mass-transfer rate
and X-ray luminosity
XLFs in Elliptical Galaxies
Fabbiano et al., Kim et al. 2006
(3-4)x1036 - (5-6)x1038 erg/s
XLF slope: 0.9 +- 0.1
Field LMXB models for NGC 3379 and NGC4278
Fragos, VK, Belczynski, et al. 2007
Star Formation:
delta-function at t=0
Population Age:
9-10 Gyr
Metallicity:
Z=0.03
(1.5 x solar)
Total Stellar Mass:3 x 1010 Mo
Binary Fraction:
Initial Mass Fn:
CE efficiency:
also:
100%
50%
power-law index -2.7
(Scalo/Kroupa)
also -2.35
(Salpeter)
50%
See poster by Fragos et al. (#155.01)
Field LMXB models for NGC 3379 and NGC4278
NS accretors
dominate over BHs
Transients in outburst
more numerous than
Persistent sources
best-fit XLF slope: 0.9
XLF shape depends on
transient Duty Cycle:
Lout=min (LX/DC,
2LEDD)
i.e., empty disk mass
accumulated during
quiescence
Field LMXB models for NGC 3379 and NGC 4278
NS accretors
dominate over BHs
Transients in outburst
more numerous than
Persistent sources
Lout=min (LX/DC,
2LEDD)
DC ~ 15-20% favored
Lout dependent on Porb
(claimed for MW BHs)
clearly inconsistent
with data
Field LMXB models for NGC 3379 and NGC 4278
Dominant LMXB
Donor Types:
< ~5x1036 erg/s
transient LMXBs with
MS donors
5x1036 - 2x1037
persistent LMXBs with
RG donors
> ~2x1037
transient LMXBs with
RG donors
(not just transient RG
as in Piro & Bildsten 2002)
Field LMXB models for NGC 3379 and NGC 4278
LMXBs contributing
to the observed XLF:
LX > 5x1036 erg/s
Field LMXB models for NGC 3379 and NGC 4278
Short & old (10Gyr ago)
star formation episode
does NOT lead to
similar LMXB formation
pattern
LMXB formation rate:
very high at ~500Myr
but continues at
lower levels
for 10Gyr to present
Short-lived LMXBs (e.g., persistent ultra-compacts)
follow the LMXB formation rate pattern
and NOT the star formation of the galaxy
Field LMXB models for NGC 3379 and NGC 4278
Model Normalization depends on:
assumed total galaxy mass (3x1010 Mo)
assumed binary fraction
(50%)
Total Galaxy Mass depends on:
total stellar light
assumed mass-to-light ratio (uncertain by ~2)
NGC 3379: 1-3 x 1010 Mo (uncertain by ~3)
NGC 4278: same (within 25%) total stellar light
Models favored based on XLF slope naturally
give normalization consistent with observations:
NGC 3379: within ~3
NGC 4278: within 15%
LMXBs in Globular Clusters
Bildsten & Deloye 2002:
NS with WD donors
in ultra-compact binaries ( ~10 min orbital periods)
persistent, short-lived (1-10Myr),
continually formed through dynamical interactions
XLF slope (~ 0.8) and normalization
consistent with observations (within uncertainties)
up to ~5x1038 erg/s
LMXBs Above the 'Break' ...
... @ (4-5)x1038 erg/s
(i.e., NS Eddington limit for He)
Sarazin et al. 2001:
LMXBs with BH accretors
King 2002:
BH transients in outburst
wide orbits, RG donors
Ivanova & Kalogera 2006:
BH transients in outburst
RG or MS donors
XLF slope possible tracer
of BH mass spectrum
Bright XRBs in GCs ??
Kalogera et al. 2004:
1-2 BH LMXBs per cluster
BUT low detection probability
(transients)
LMXBs in Elliptical Galaxies
Current Conclusions – Open Issues
Slope and Normalization of XLF in ~5x1036 – 5x1038 erg/s
can be explained by both:
Field NS-LMXBs with low-mass MS and RG donors (transient & persistent)
GC ultra-compact NS-LMXBs (persistent)
Q: Points to contributions from both field and clusters, but
how can different LMXB types give similar XLF slope &normalization?
Bright-end XLF could be due to transient BH-LMXBs in outburst
Field and GC XLFs similar, but note: small-N sample
Q: Given BH evolution in GCs and transient nature,
are there too many bright point sources in GCs ?
Q: Could bright sources in GCs be due to superposition ?
Q: Could all bright sources be simply super-Eddington NS-LMXBs (by x10!) ?
Where are the BH-LMXBs, similar to transients in the Milky Way?
LMXBs in Elliptical Galaxies
Current Conclusions – Open Issues
Models of Field NS-LMXBs are favored with:
Transient DC ~15%
Outburst Lx connected to long-term mass transfer rate and DC:
empty disk mass accumulated during quiescence
Moderate CE efficiencies
Shape changes at ~1x1037 erg/s could be connected to outburst Lx and DC
Even in the field LXMB formation rate is sustained over long timescales
after an early phase of enhanced formation