Accreting Compact Objects in Nearby Galaxies Vicky Kalogera
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 -10 ke. V 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 M 101 ROSAT HRI detected sources (Wang et al. 1999) M 101 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: Science@NASA Image CXC Image Archive low-mass donor, ~1 Mo Roche-lobe overflow old, 108 -9 yr HMXB: HMXB high-mass donor, 5 -10 Mo 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, M 31, 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 M 31 and M 101 > '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 > mass. Our transfer modeling: synthesis code: stable driven by nuclear evolution or angular momentum loss Star. Track 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)x 1036 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 ≥ 5 x 1035 Is this all due to N 1569 erg/s. Supernova Kicks ? N 5253 < 1 XRB per cluster! M 82 50%
Theoretical XRB Distributions Sepinsky et al. 2005, Ap. JL Models: Population Syntheses of XRBs and Kinematic Orbit Evolution in Cluster Potential • cluster mass: ~5 x 104 Mo • LX > 5 x 1035 erg/s • average of 1, 000 cluster simulations • Significant age dependence • < 1 XRB per cluster 1 10 1000 Distance from Cluster Center [pc
HMXBs and SSCs XRB models without cluster dynamics appear in agreement with observations ü or M < 105 Mo and 10 -50 Myr more massive and ~50 Myr üSupernova kicks: eject XRBs @ D > 10 pc 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 M 81 Tennant et al. 2001 Characterizing XLFs: power-laws, slopes, breaks …
X-Ray Luminosity Functions M 81 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. 2 Mpc with well-constrained SF history: > ~100 Myr-long episode, probably ended 5 -10 Myr ago, Z ~ 0. 25 Zo > older population with continuous SF for ~ 1. 5 Gyr, 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, Ap. JL Hybrid of 2 populations: Ø underlying old Ø 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)x 1038 erg/s Below 5 x 1038 erg/s XLF slope: 0. 8+-0. 2 Kim & Fabbiano 2004; confirmed by Gilfanov 2004 Above 5 x 1038 erg/s XLF slope: 1. 8+-0. 6 Kim & Fabbiano 2004 XLF slope: 3. 9 -7. 3 Gilfanov 2004 Maximum Lx: 2 x 1039 erg/s
XLFs in Elliptical Galaxies Fabbiano et al. , Kim et al. 2006 2 x 1036 - 6 x 1038 erg/s 6 x 1036 - 5 x 1038 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 ~5 x 1038 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 > 5 x 1038 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 ~ 2 x 1039 erg/s implies max BH mass of 15 -20 Mo 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 Matches observed XLF slope below BREAK at ~5 x 1038 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 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 - 1000 Mo) § 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: > 10 Myr Blecha, Ivanova, VK, et al. 2005: NOT LIKELY IMBH binary: through exchanges with stellar binaries ULX phase duration: < 0. 1 Myr
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, 000 Mo IMBH for ANY orbital period Mass Transfer and LX calculation for isolated IMBH binaries with 5 -15 Mo MS donors No dynamical interactions and evolution included ULX phase duration per IMBH binary: >10 Myr 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 -500 Mo IMBH, 100 Myr old clusters, Trc < 30 Myr 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. 1 Myr
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 ( >100 Myr ) 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
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