AAS Kalogera

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Science-Technology

Published on August 29, 2007

Author: GenX

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Understanding LMXBs in Elliptical Galaxies:  Understanding LMXBs in Elliptical Galaxies Vicky Kalogera Slide2:  Low-Mass X-Ray Binaries Accretors: NS or BH RLOF Donors: MS, RG, WD/degenerate low-mass: andlt; 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) Slide3:  courtesy Sky andamp; Telescope Feb 2003 issue How do Low-Mass X-ray binaries form in galactic fields ? primordial binary Common Envelope: orbital contraction and mass loss NS or BH formation X-ray binary at Roche Lobe overflow LMXB Population Modeling:  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:  Population Synthesis Elements Star formation conditions: andgt; time and duration, metallicity, IMF, binary properties Slide6:  Population Synthesis Elements Star formation conditions: andgt; time and duration, metallicity, IMF, binary properties Modeling of single and binary evolution andgt; mass, radius, core mass, wind mass loss andgt; orbital evolution: e.g., tidal synchronization and circularization, mass loss, mass transfer andgt; mass transfer modeling: stable driven by nuclear evolution or angular momentum loss thermally unstable or dynamically unstable andgt; compact object formation: masses and supernova kicks andgt; X-ray phase: evolution of mass-transfer rate and X-ray luminosity Slide7:  Population Synthesis Elements Star formation conditions: andgt; time and duration, metallicity, IMF, binary properties Modeling of single and binary evolution andgt; mass, radius, core mass, wind mass loss andgt; orbital evolution: e.g., tidal synchronization and circularization, mass loss, mass transfer andgt; mass transfer modeling: stable driven by nuclear evolution or angular momentum loss thermally unstable or dynamically unstable andgt; compact object formation: masses and supernova kicks andgt; X-ray phase: evolution of mass-transfer rate and X-ray luminosity Slide8:  Population Synthesis Elements Star formation conditions: andgt; time and duration, metallicity, IMF, binary properties Modeling of single and binary evolution andgt; mass, radius, core mass, wind mass loss andgt; orbital evolution: e.g., tidal synchronization and circularization, mass loss, mass transfer andgt; mass transfer modeling: stable driven by nuclear evolution or angular momentum loss thermally unstable or dynamically unstable andgt; compact object formation: masses and supernova kicks andgt; X-ray phase: evolution of mass-transfer rate and X-ray luminosity Slide9:  Population Synthesis Elements Star formation conditions: andgt; time and duration, metallicity, IMF, binary properties Modeling of single and binary evolution andgt; mass, radius, core mass, wind mass loss andgt; orbital evolution: e.g., tidal synchronization and circularization, mass loss, mass transfer andgt; mass transfer modeling: stable driven by nuclear evolution or angular momentum loss thermally unstable or dynamically unstable andgt; compact object formation: masses and supernova kicks andgt; X-ray phase: evolution of mass-transfer rate and X-ray luminosity Slide10:  Population Synthesis Elements Star formation conditions: andgt; time and duration, metallicity, IMF, binary properties Modeling of single and binary evolution andgt; mass, radius, core mass, wind mass loss andgt; orbital evolution: e.g., tidal synchronization and circularization, mass loss, mass transfer andgt; mass transfer modeling: stable driven by nuclear evolution or angular momentum loss thermally unstable or dynamically unstable andgt; compact object formation: masses and supernova kicks andgt; X-ray phase: evolution of mass-transfer rate and X-ray luminosity Slide11:  Population Synthesis Elements Star formation conditions: andgt; time and duration, metallicity, IMF, binary properties Modeling of single and binary evolution andgt; mass, radius, core mass, wind mass loss andgt; orbital evolution: e.g., tidal synchronization and circularization, mass loss, mass transfer andgt; mass transfer modeling: stable driven by nuclear evolution or angular momentum loss thermally unstable or dynamically unstable andgt; compact object formation: masses and supernova kicks andgt; 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 Slide12:  XLFs in Elliptical Galaxies (3-4)x1036 - (5-6)x1038 erg/s XLF slope: 0.9 +- 0.1 Fabbiano et al., Kim et al. 2006 Slide13:  Field LMXB models for NGC 3379 and NGC4278 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% Fragos, VK, Belczynski, et al. 2007 See poster by Fragos et al. (#155.01) Slide14:  Field LMXB models for NGC 3379 and NGC4278 best-fit XLF slope: 0.9 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 Slide15:  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 Slide16:  Field LMXB models for NGC 3379 and NGC 4278 Dominant LMXB Donor Types: andlt; ~5x1036 erg/s transient LMXBs with MS donors 5x1036 - 2x1037 persistent LMXBs with RG donors andgt; ~2x1037 transient LMXBs with RG donors (not just transient RG as in Piro andamp; Bildsten 2002) Slide17:  Field LMXB models for NGC 3379 and NGC 4278 LMXBs contributing to the observed XLF: LX andgt; 5x1036 erg/s Slide18:  Field LMXB models for NGC 3379 and NGC 4278 Short andamp; 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 Slide19:  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% Slide20:  LMXBs in Globular Clusters Bildsten andamp; 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 Slide21:  LMXBs Above the 'Break' ... Ivanova andamp; Kalogera 2006: BH transients in outburst RG or MS donors XLF slope possible tracer of BH mass spectrum ... @ (4-5)x1038 erg/s (i.e., NS Eddington limit for He) King 2002: BH transients in outburst wide orbits, RG donors 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) Slide22:  LMXBs in Elliptical Galaxies 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 andamp; persistent) GC ultra-compact NS-LMXBs (persistent) Current Conclusions – Open Issues Q: Points to contributions from both field and clusters, but how can different LMXB types give similar XLF slope andamp;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? Slide23:  LMXBs in Elliptical Galaxies 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 Current Conclusions – Open Issues Even in the field LXMB formation rate is sustained over long timescales after an early phase of enhanced formation

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