1. X-ray Binaries in Nearby Galaxies Vicky Kalogera Northwestern University with Chris Belczynski (NU) Andreas Zezas and Pepi Fabbiano (CfA)

2. X-Ray Binaries in Nearby Galaxies Outline: Observations: Past and Present Questions and Puzzles Theoretical models of X-ray Binaries: What What can they tell us ? How How can we use them ? Population Synthesis Tutorial Results and Comparisons with Observations What's next...

3. X-Ray Binary Populations the Milky Way: first discovered in our Galaxy ~ 100 known 'low-mass' XRBs ( Roche-lobe overflow ) ~ 30 known 'high-mass' XRBs ( wind accretion ) long-standing problem with distance estimates: very hard to study the X-ray luminosity function and spatial distribution other properties, e.g., orbital period, donor masses known only for a few systems

4. X-Ray Binary Populations other galaxies: pre-Chandra... discovered in the LMC/SMC, M31, and another ~15 galaxies (all spirals), most of them with only a handful of point X-ray sources (< 10) > very limited spectral information due to low X-ray counts long-standing problems with low angular resolution and source confusion > XLF reliably constructed only for M31 and M101 'super-Eddington'tentatively > 'super-Eddington' sources were tentatively identified

5. X-Ray Binary Populations other galaxies: post-Chandra... more than ~100 galaxies observed galaxy types they cover a wide range of galaxy types star-formation histories and star-formation histories ~ 10-100 point sources in each: population studies become feasible known sample distance: great advantage for studies of X-ray luminosity functions and spatial distributions

6. The Antennae: ~ 80 point sources! courtesy Fabbiano,Zezas et al. Chandra ROSAT

7. X-Ray Binary Populations other galaxies: post-Chandra... [cont] typical sensitivity limits down to ~10 36 -10 37 erg/s spectral information useful for identification of point-source types: LMXBs, HMXBs, SNRs X-ray luminosity functions (XLF): power-lawsslopes correlating power-laws with slopes correlating with galaxy type

8. XLF slopes and galaxy types spiralsstarbursts from Kilgard et al. 2002 (astro-ph/0203190) ellipticals & bulges XLF shapes seem to correlate with SFR and age Older populations have steeper slopes, but is the correlation monotonic monotonic ? from Sarazin et al. 2001 XLF slope SFR

9. X-Ray Binary Populations other galaxies: post-Chandra... [ cont ] existence of Ultra-Luminous X-ray sources (ULXs): established, although not yet understood (formerly known as: super-Eddington sources) ? L X > 10 40 erg/s ===> M BH > 50 M o ? or beaming ? elliptical galaxies: high incidence of sources in globular clusters ? ( Sarazin et al. 2001; Kundu et al. 2002 )

10. XLF observations some of the puzzles: What determines the shape of XLFs ? Is it a result of a blend of XRB populations ? How does it evolve ? Are the reported breaks in XLFs real or due to incompleteness effects ? If they are real, are they caused by > different XRB populations ? ( Sarazin et al. 2000 ) > age effects ? ( Wu 2000; Kilgaard et al. 2002 ) > both ? (VK, Jenkins, Belczynski 2003)

11. Theoretical Modeling Current status: observationally-driven Chandra observations provide an excellent challenge and opportunity for progress in the study of global XRB population properties. Population Synthesis Calculations: necessary Basic Concept of Statistical Description: evolution of an ensemble of binary and single stars with focus on XRB formation and their evolution through the X-ray phase.

12. courtesy Sky & Telescope Feb 2003 issue How do X-ray binaries form ? primordial binary X-ray binary at Roche-lobe overflow Common Envelope: orbital contraction and mass loss NS or BH formation

13. 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

14. Population Synthesis with StarTrack Single-star models from Hurley et al. 2000 Tidal evolution of binaries included > important for wind-fed X-ray binaries tested with measured P orb contraction (e.g., LMC X-4; Levine et al. 2000) Mass transfer calculations ( M and L x ) > wind-fed: Bondi accretion > Roche-lobe overflow: M based on radial response of donor and Roche lobe to mass exchange and possible loss from the binary (tested against detailed mass-transfer calculations) > also included: Eddington-limited accretion ( testable) thermal-time scale mass transfer, transient behavior Belczynski et al. 2001,2003 ● ●

15. Example of Mass-Transfer Calculation time (yr) log[ M / (M o /yr) ] ● Comparison between a detailed caclulation with a full stellar evolution code (N. Ivanova) and the semi-analytic treatment implemented in StarTrack BH mass: 4.1M o donor mass: 2.5M o choice of masses from Beer & Podsiadlowski 2002 Results in very good agreement ( within 20-50%) semi-analytic calculation most appropriate for statistical modeling of large binary populations

16. NGC 1569 (post-)starburst galaxy at 2.2Mpc with well-constrained SF history: > 100Myr-long episode, probably ended 5-10Myr ago, Z ~ 0.25 Z o > older population with continuous SF for ~ 1.5Gyr, Z ~ 0.004 or 0.0004, but weaker in SFR than recent episode by factors of >10 Vallenari & Bomans 1996; Greggio et al. 1998; Aloisi et al. 2001; Martin et al. 2002 courtesy Schirmer, HST courtesy Martin, CXC,NOAO

17. log [ L x / (erg/s) ] log [ N( > L x )] Normalized Model XLFs non-monotonic behavior 10 Myr strong winds from most massive stars 50 Myr 100 Myr 150 Myr 200 Myr Roche-lobe overflow XRBs become important XLF dependence on age (cf. Grimm et al.; Wu; Kilgaard et al.)

18. log [ L x / (erg/s) ] log [ N( > L x )] all XRBs at ~100 Myr std model no BH kicks at birth Z = Z o stellar winds reduced by 4 Normalized Model XLFs XLF dependence on model parameters

19. Belczynski, VK, Zezas, Fabbiano 2003 NGC 1569 XLF modeling Hybrid of 2 populations:  underlying old  starburst young Old: 1.5 Gyr Young: 110 Myr SFR Y/O: 20 Old: 1.5 Gyr Young: 70 Myr SFR Y/O: 20 Old: 1.3 Gyr Young: 70 Myr SFR Y/O: 40

20. XLF slopes and breaks log [ L x / (erg/s) ] log [ N( > L x )] all XRBs Eddington-limited accretion no Eddington limit imposed Normalized XLFs Models match NGC1569 SF history Arons et al. 1992... Shaviv 1998... Begelman et al. 2001...

21. VK, Henninger, Ivanova, & King 2003 Observational Diagnostic for ULXs In young ( >100Myr ) stellar environments transient behavior is shown to be associated with accretion onto an IMBH IMBH or thermal - timescale mass transfer with anisotropic emission ?

22. Conclusions Current understanding of XRB formation and evolution produces XLF properties consistent with observations Model XLFs can be used to constrain star- formation properties, e.g., age and metallicity Shape of model XLFs appear robust against variations of most binary evolution parameters 'Broken' power-laws seem to be due to Eddington-limited accretion Transient behavior can distinguish between IM and stellar-mass BH

23. What's coming next... Choose a sample of galaxies with relatively well-understood star-formation histories and > indentify XRB models that best describe the XLF shape > use the results to 'calibrate' population models for different galaxy types (spirals, starburst, ellipticals) and derive constraints on the star-formation history of other galaxies Use the number of XRBs, to examine correlation with SFR and constrain binary evolution parameters that affect the absolute normalization of the XLF but not its shape

24. What's coming next... How are XLFs different if dynamical processes are important ? If IMBH form, how do they acquire binary companions that can initiate mass transfer ? (work with N. Ivanova & C. Belczynski)

25. ULX source in M82

26. NGC 1316 elliptical galaxy at XXXMpc with a recent merger: > short SF episode 1-3Gyr ago, Z ~ Z o > older population with and age of ~11.5Gyr Z ~ 0.29 courtesy Kim, Fabbiano CXC,DSS Goudfrooij et al. 2001 Trager et al. 2000

27. NGC 1316 log [ L x / (erg/s) ] log [ N( > L x )] data: ~55 sources ( Kim & Fabbiano 2002 ) all XRBs at 1Gyr Normalized XLFs Model matches NGC1316 SF history

28. Source Identification based on X-ray Colors Prestwich et al 2002 astro-ph/0206127

29. XLF observations: questions and puzzles Can the XLF properties (shapes, numbers) be used as star-formation indicators ? e.g., IMF, metallicity, star-formation rate, or age ? What is the origin of the ULXs ? Can we explain them as `normal' BH-XRBs or the hypothesis of intermediate-mass BH is necessary ? What is the role of XRB formation in globular clusters ? Do dynamically formed XRBs have different XLF characteristics ?

30. NGC 1569 log [ L x / (erg/s) ] log [ N( > L x )] data: 14 sources all XRBs at 110Myr NS XRBs wind-fed XRBs wind-fed NS XRBs Normalized XLFs Models match NGC1569 SF history