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Accreting Compact Objects in Nearby Galaxies Vicky Kalogera @ Michigan State University, Nov 8, 2006 Chandra: a NASA ‘Great’ Observatory Launch: 1999 Energy range: 0.5-10keV Angular Resolution: ~ 0.5 arcsecond Chandra: the joys of high angular resolution • 51 point sources in 30 arcmin with ROSAT • 110 point sources in 8 arcmin with Chandra ACIS M101 ROSAT HRI detected sources (Wang et al. 1999) M101 Chandra detected Sources (Pence et al. 2001) X-Ray Binaries Point, variable on short time scale X-ray sources Neutron Stars or Black Holes Accreting from binary companions X-Ray Binaries LMXB LMXB: Science@NASA Image CXC Image Archive low-mass donor, ~1 Mo Roche-lobe overflow old, 108-9 yr HMXB: HMXB high-mass donor, 5-10Mo stellar wind accretion young, 106-7 yr X-Ray Binary Populations: pre-Chandra the Milky Way: first discovered in our Galaxy ~ 100 known 'low-mass' XRBs ~ 30 known 'high-mass' XRBs 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 X-Ray Binary Populations: pre-Chandra other galaxies: discovered in the LMC/SMC, M31, and another ~15 galaxies (all spirals) a handful of point X-ray sources (< 10) long-standing problems with low angular resolution and source confusion > XLF reliably constructed only for M31 and M101 > 'super-Eddington' sources were tentatively identified X-Ray Binary Populations: post-Chandra other galaxies: 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 Population 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. How do X-ray binaries form ? 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 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 > orbital evolution: e.g., tidal synchronization and circularization, mass loss, mass transfer population > massOur transfer modeling:synthesis code: stable driven by nuclear evolution or angular momentum loss StarTrack thermally unstable or dynamically unstable Belcynski et al. 2006 > compact object formation: masses and supernova kicks > X-ray phase: evolution of mass-transfer rate and X-ray luminosity In this talk … - some of the puzzles Are HMXBs connected to Super Star Clusters ? What determines the shape of X-Ray Luminosity Functions (XLF) ? What is the nature of Ultra-Luminous X-ray Sources (ULX) ? Super Star Clusters (SSCs) • Compact, young analog to globular clusters • Found frequently in starburst environments • Masses range from ~104 to ~106 Mo • Ages range from a few to tens of Myr Distribution of X-Ray point sources Kaaret et al. 2004 • Lx ≥ (0.5-3)x1036 erg/s < 1 XRB per cluster! Distribution of X-Ray point sources Kaaret et al. 2004 • XRBs closely associated with star clusters • Median distance ~30-100 pc • Lx ≥ 5x1035 Is this all due to erg/sSupernova Kicks ? N1569 50% N5253 < 1 XRB per cluster! M82 Theoretical XRB Distributions Sepinsky et al. 2005, ApJL Models: Population Syntheses of XRBs and Kinematic Orbit Evolution in Cluster Potential • cluster mass: ~5x104 Mo • LX > 5x1035 erg/s • average of 1,000 cluster simulations • Significant age dependence • < 1 XRB per cluster 1 10 100 1000 Distance from Cluster Center [pc] HMXBs and SSCs XRB models without cluster dynamics appear in agreement with observations or M < 105 Mo and 10-50Myr more massive and ~50Myr Supernova kicks: eject XRBs @ D > 10pc especially for M < 105 Mo Chandra X-Ray Binary Populations » Starbursts: dominated by recent/ongoing burst of star formation, and young HMXBs » Spirals: mix of ages and metallicities mix of LMXBs and HMXBs » Ellipticals: clean samples of LMXBs X-Ray Luminosity Functions M81 Tennant et al. 2001 Characterizing XLFs: power-laws, slopes, breaks … X-Ray Luminosity Functions M81 Old populations: flatter (slopes: -0.8 to -0.4) Young/Mixed populations: steeper (slopes: up to -1.0 or -1.5) Tennant et al. 2001 NGC 1569 courtesy Schirmer, HST courtesy Martin, CXC,NOAO (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 Vallenari & Bomans 1996; Greggio et al. 1998; Aloisi et al. 2001; Martin et al. 2002 NGC 1569 XLF modeling Old: 1.5 Gyr Young: 110 Myr SFR Y/O: 20 Belczynski, VK et al. 2004, ApJL Hybrid of 2 populations: underlying old starburst young Old: 1.5 Gyr Young: 70 Myr SFR Y/O: 20 Old: 1.3 Gyr Young: 70 Myr SFR Y/O: 40 XRBs in Starbursts 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 XLFs in Elliptical Galaxies Summary of observations (5+-1.6)x1038erg/s Below 5x1038erg/s XLF slope: 0.8+-0.2 Kim & Fabbiano 2004; confirmed by Gilfanov 2004 Above 5x1038erg/s XLF slope: 1.8+-0.6 Kim & Fabbiano 2004 XLF slope: 3.9-7.3 Gilfanov 2004 Maximum Lx: 2x1039 erg/s XLFs in Elliptical Galaxies Fabbiano et al., Kim et al. 2006 2x1036 - 6x1038 erg/s 6x1036 - 5x1038 erg/s XLF slope: 0.9 +- 0.1 XLFs in Elliptical Galaxies Fragos, VK, et al. Accreting NS dominate over BH accretors XLF - DCtr=1% XLF - DCtr=10% No transients Donors of Persistent LMXBs: MS very low-mass, degenerate He WD Red Giant model XLF slope: 0.9 XLFs in Elliptical Galaxies Fragos, VK, et al. Accreting NS dominate over BH accretors XLF - DCtr=1% XLF - DCtr=10% No transients Donors of Persistent LMXBs: MS very low-mass, degenerate He WD Red Giant model XLF slope: 0.9 LMXB origin in Ellipticals: Clusters and/or Field ? Bildsten & Deloye 2004: NS Ultra-Compact Binaries from Clusters Analytical models of Ultra-Compacts Matches observed XLF slope below BREAK at ~5x1038 erg/s Persistent sources LMXB origin in Ellipticals: Clusters and/or Field ? Bildsten & Deloye 2004: NS Ultra-Compact Binaries from Clusters Juett 2005:Ellipticals’ Field Must Contribute Irwin 2005: Ellipticals’ Field Must Contribute based on how population properties scale with the frequency of clusters per unit galaxy mass LMXB origin in Ellipticals: Clusters and/or Field ? Bildsten & Deloye 2004: NS Ultra-Compact Binaries from Clusters Juett 2005:Ellipticals’ Field Must Contribute Irwin 2005: Ellipticals’ Field Must Contribute Ivanova & VK 2005: Brightest sources Field BH LMXBs Sources with Lx > 5x1038 erg/s too bright for NS accretor BH LMXBs not expected in GCs, (VK, King, & Rasio 2004) but are expected in the Field as BH transients If Loutburst ~ Ledd : XLF slope above BREAK is a footprint of BH mass spectrum Current Lmax ~ 2x1039 erg/s implies max BH mass of 15-20Mo consistent with stellar evolution LMXB origin in Ellipticals: Clusters and/or Field ? Bildsten & Deloye 2004: NS Ultra-Compact Binaries from Clusters Juett 2005:Ellipticals’ Field Must Contribute Irwin 2005: Ellipticals’ Field Must Contribute Ivanova & VK 2005: Brightest sources are Field BH LMXBs Fragos, VK, Belczynski, et al. 2006:NS Ultra-Compacts from Field Matches observed XLF slope below BREAK at ~5x1038 erg/s Persistent sources LMXB origin in Ellipticals: Clusters and/or Field ? Bildsten & Deloye 2004: NS Ultra-Compact Binaries from Clusters Juett 2005:Ellipticals’ Field Must Contribute Irwin 2005: Ellipticals’ Field Must Contribute Ivanova & VK 2005: Brightest sources are Field BH LMXBs Fragos, VK, Belczynski, et al. 2006:NS Ultra-Compacts from Field NS Ultra-Compacts dominate Ellipticals’ LMXBs Field and Cluster Ultra-Compacts: same properties Cluster and Field XLFs very similar, as observed Consistent answer appears to be: Both Clusters & Field Ultra-Luminous X-ray Sources Single sources with LX > 1039 erg/s Associated with young populations and star clusters What is their origin? Intermediate-Mass Black Holes? (50 - 1000Mo) Anisotropic/Beamed XRB emission ? Do accreting IMBH in clusters form observable ULXs ? Hopman, Portegies Zwart, Alexander 2004: YES IMBH binary: through tidal capture (TC) of MS companions ULX phase duration: > 10Myr Blecha, Ivanova, VK, et al. 2005: NOT LIKELY IMBH binary: through exchanges with stellar binaries ULX phase duration: < 0.1Myr Do accreting IMBH in clusters form observable ULXs ? Hopman, Portegies Zwart, Alexander 2004: YES through TC Most optimistic assumptions for TC survival of MS stars: “hot squeezars” and ETC x Porb ~ LEdd Analytical estimate of TC rate for 1,000Mo IMBH for ANY orbital period Mass Transfer and LX calculation for isolated IMBH binaries with 5-15Mo MS donors No dynamical interactions and evolution included ULX phase duration per IMBH binary: >10Myr Fraction of Clusters with IMBH-MS ULX: 30-50% Do accreting IMBH in clusters form observable ULXs ? Blecha, Ivanova, Kalogera, et al. 2005: NOT LIKELY Cluster core simulations with full binary evolution and dynamical interactions: TC, exchanges, disruptions, collisions (N. Ivanova’s talk from Monday’s morning session) 100-500Mo IMBH, 100Myr old clusters, Trc < 30Myr Time fraction with IMBH binary: > 50% Time fraction with Mass-Transfer: ~1-3% MS donors dominate by time; Post-MS donors dominate by number Fraction of Mass-Transfer time as a ULX: ~2% Average ULX phase duration per cluster: <0.1Myr Observational Diagnostic for ULXs VK, Henninger, Ivanova, & King 2003 IMBH or thermal-timescale mass transfer with anisotropic emission ? Minimum accretor mass for transients In young ( >100Myr ) stellar environments transient behavior is shown to be associated with accretion onto an IMBH What to Expect in the Future ? Systematic modeling of galaxy samples: dependence on SFR, galaxy mass, age, metallicity spirals and mixed populations, bulges and disks Bigger source samples: probing the rare brightest sources, questions of BH formation, ULXs Long-term time monitoring: identification of X-ray transients and clues to ULX nature