X-ray Binaries in Nearby Galaxies

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

2. X-Ray Binaries in Nearby Galaxies Outline: Observations: Past and Present Questions and Puzzles Theoretical models of X-ray Binaries: What can they tell us ? 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 ahandfulof point X-ray sources (< 10) > verylimited spectralinformation 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' sources were tentatively identified

5. X-Ray Binary Populations other galaxies: post-Chandra ... more than ~100 galaxies observed they cover a wide range of galaxy types 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! Chandra ROSAT courtesy Fabbiano,Zezas et al.

7. X-Ray Binary Populations other galaxies: post-Chandra ... [cont] typical sensitivity limits down to ~1036-1037erg/s spectral information useful for identification of point-source types: LMXBs, HMXBs, SNRs X-ray luminosity functions (XLF): power-laws with slopes correlating with galaxy type

8. XLF slopes and galaxy types spirals starbursts XLFshapesseemto correlatewithSFRand age Olderpopulations have steeperslopes, but is the correlation monotonic ? ellipticals & bulges from Kilgard et al. 2002 (astro-ph/0203190) XLF slope from Sarazin et al. 2001 SFR

9. X-Ray Binary Populations other galaxies: post-Chandra ... [cont] existence ofUltra-Luminous X-ray sources (ULXs): established, although not yet understood (formerly known as: super-Eddington sources) ? LX > 1040erg/s ===> MBH > 50 Mo ? 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: Whatdeterminestheshapeof XLFs ? Is it a result of a blend of XRB populations ? How does it evolve ? Are the reportedbreaksin XLFsreal ordue toincompletenesseffects ? 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. primordial binary How do X-ray binaries form ? Common Envelope: orbital contraction and mass loss NS or BH formation X-ray binary at Roche-lobe overflow courtesy Sky & Telescope Feb 2003 issue

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 withStarTrack Belczynski et al. 2001,2003 Single-star models from Hurley et al. 2000 Tidal evolution of binaries included > important for wind-fed X-ray binaries testedwith measured Porb contraction (e.g., LMC X-4; Levine et al. 2000) Mass transfer calculations ( M and Lx ) > 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 (testedagainst detailed mass-transfer calculations) >also included: Eddington-limited accretion (testable) thermal-time scale mass transfer, transient behavior ● ●

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

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 Zo >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 courtesy Schirmer, HST courtesy Martin, CXC,NOAO Vallenari & Bomans 1996; Greggio et al. 1998; Aloisi et al. 2001; Martin et al. 2002

17. XLF dependence on age (cf. Grimm et al.; Wu; Kilgaard et al.) 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 log [ N( > Lx )] log [ Lx / (erg/s) ]

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

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

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

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

22. Current understanding of XRB formation and evolution produces XLF properties consistent with observations Model XLFs can be used to constrainstar-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 Conclusions

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 andconstrain 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 dynamicalprocesses 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 ~ Zo >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 Normalized XLFs Model matches NGC1316 SF history data: ~55 sources (Kim & Fabbiano 2002) all XRBs at 1Gyr log [ N( > Lx )] log [ Lx / (erg/s) ]

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