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Understanding LMXBs in Elliptical Galaxies

Vicky Kalogera . Understanding LMXBs in Elliptical Galaxies. CXC Image Archive. Low-Mass X-Ray Binaries. Accretors: NS or BH RLOF Donors: MS, RG, WD/degenerate low-mass: < 1M o Binary Periods: minutes to ~10 days Ages: old, ~ 0.1 - 10 Gyr Persistent X-rays:

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Understanding LMXBs in Elliptical Galaxies

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  1. Vicky Kalogera Understanding LMXBs in Elliptical Galaxies

  2. CXC Image Archive Low-Mass X-Ray Binaries Accretors: NS or BH RLOF Donors: MS, RG, WD/degenerate low-mass: < 1Mo Binary Periods: minutes to ~10 days Ages: old, ~ 0.1 - 10 Gyr Persistent X-rays: ~10 Myr - ~1 Gyr LMXBs form in both galactic fields (isolated binaries) globulars (dynamical interactions)

  3. primordial binary How do Low-Mass X-ray binaries form in galactic fields ? Common Envelope: orbital contraction and mass loss NS or BH formation X-ray binary at Roche Lobe overflow courtesy Sky & Telescope Feb 2003 issue

  4. 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).

  5. Population Synthesis Elements Star formation conditions: >time and duration, metallicity, IMF, binary properties

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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 Our population synthesis code: StarTrack Belcynski et al. 2006 including (simple) cluster dynamics: Ivanova et al. 2005

  12. 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

  13. 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: 50% Initial Mass Fn: power-law index -2.7 (Scalo/Kroupa) also -2.35 (Salpeter) CE efficiency: 50% also: 100% See poster by Fragos et al. (#155.01)

  14. Field LMXB models for NGC 3379 and NGC4278 NS accretors dominate over BHs Transients in outburst more numerous than Persistent sources XLF shape depends on transient Duty Cycle: Lout=min (LX/DC, 2LEDD) i.e., empty disk mass accumulated during quiescence DC ~ 15-20% favored best-fit XLF slope: 0.9

  15. 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

  16. 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)

  17. Field LMXB models for NGC 3379 and NGC 4278 LMXBs contributing to the observed XLF: LX > 5x1036 erg/s

  18. 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

  19. 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%

  20. 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

  21. LMXBs Above the 'Break' ... ... @ (4-5)x1038 erg/s (i.e., NS Eddington limit for He) Sarazin et al. 2001: LMXBs with BH accretors Bright XRBs in GCs ?? Kalogera et al. 2004: 1-2 BH LMXBs per cluster BUT low detection probability (transients) 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

  22. 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?

  23. 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

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