Accreting Compact Objects in Nearby Galaxies Vicky Michigan State University, Nov 8, 2006

Chandra: a NASA ‘Great’ Observatory Launch: 1999 Energy range: keV Angular Resolution: ~ 0.5 arcsecond

Chandra: the joys of high angular resolution M101 ROSAT HRI detected sources (Wang et al. 1999) 51 point sources in 30 arcmin with ROSAT M101 Chandra detected Sources (Pence et al. 2001) 110 point sources in 8 arcmin with Chandra ACIS

X-Ray Binaries Point, variable on short time scale X-ray sources Neutron Stars or Black Holes Accreting from binary companions

X-Ray Binaries CXC Image Archive LMXB LMXB: low-mass donor, ~1 M o Roche-lobe overflow old, yr HMXB Image HMXB: high-mass donor, 5-10M o stellar wind accretion young, 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'tentatively > '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 ~ 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.

courtesy Sky & Telescope Feb 2003 issue How do X-ray binaries form ? primordial binary Common Envelope: orbital contraction and mass loss NS or BH formation 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 > 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 Our population synthesis code: StarTrack Belcynski et al. 2006

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 ~10 4 to ~10 6 M o Ages range from a few to tens of Myr

Kaaret et al L x ≥ (0.5-3)x10 36 erg/s Distribution of X-Ray point sources < 1 XRB per cluster!

Kaaret et al L x ≥ 5x10 35 erg/s Distribution of X-Ray point sources XRBs closely associated with star clusters Median distance ~ pc < 1 XRB per cluster! M82 N5253 N % Is this all due to Supernova Kicks ?

Theoretical XRB Distributions cluster mass: ~5x10 4 M o L X > 5x10 35 erg/s average of 1,000 cluster simulations Significant age dependence < 1 XRB per cluster Models: Population Syntheses of XRBs and Kinematic Orbit Evolution in Cluster Potential Sepinsky et al. 2005, ApJL   Distance from Cluster Center [pc]

HMXBs and SSCs XRB models without cluster dynamics appear in agreement with observations M < 10 5 M o and 10-50Myr or more massive and ~50Myr Supernova kicks: eject D > 10pc especially for M < 10 5 M o

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 Characterizing XLFs: power-laws, slopes, breaks …

X-Ray Luminosity Functions M81 Tennant et al Old populations: flatter (slopes: -0.8 to -0.4) Young/Mixed populations: steeper (slopes: up to -1.0 or -1.5)

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 ~ or , 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 courtesy Schirmer, HST courtesy Martin, CXC,NOAO

Belczynski, VK et al. 2004, ApJL 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

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 (5+-1.6)x10 38 erg/s Below 5x10 38 erg/s XLF slope: Above 5x10 38 erg/s XLF slope: Kim & Fabbiano 2004; confirmed by Gilfanov 2004 Kim & Fabbiano 2004 XLF slope: Gilfanov 2004 Maximum L x : 2x10 39 erg/s Summary of observations

XLFs in Elliptical Galaxies 2x x10 38 erg/s 6x x10 38 erg/s XLF slope: Fabbiano et al., Kim et al. 2006

XLFs in Elliptical Galaxies model XLF slope: 0.9 XLF - DC tr =1% XLF - DC tr =10% No transients Donors of Persistent LMXBs: MS Accreting NS dominate over BH accretors very low-mass, degenerate He WD Red Giant Fragos, VK, et al.

XLFs in Elliptical Galaxies model XLF slope: 0.9 XLF - DC tr =1% XLF - DC tr =10% No transients Donors of Persistent LMXBs: MS Accreting NS dominate over BH accretors very low-mass, degenerate He WD Red Giant Fragos, VK, et al.

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 ~5x10 38 erg/s Persistent sources

LMXB origin in Ellipticals: Clusters and/or Field ? Irwin 2005:Ellipticals’ Field Must Contribute Bildsten & Deloye 2004:NS Ultra-Compact Binaries from Clusters Juett 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 ? Irwin 2005:Ellipticals’ Field Must Contribute Bildsten & Deloye 2004:NS Ultra-Compact Binaries from Clusters Juett 2005:Ellipticals’ Field Must Contribute Ivanova & VK 2005: Brightest sources Field BH LMXBs Sources with L x > 5x10 38 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 L outburst ~ L edd : XLF slope above BREAK is a footprint of BH mass spectrum Current L max ~ 2x10 39 erg/s implies max BH mass of 15-20M o consistent with stellar evolution

LMXB origin in Ellipticals: Clusters and/or Field ? Irwin 2005:Ellipticals’ Field Must Contribute Bildsten & Deloye 2004:NS Ultra-Compact Binaries from Clusters Juett 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 ~5x10 38 erg/s Persistent sources

LMXB origin in Ellipticals: Clusters and/or Field ? Irwin 2005:Ellipticals’ Field Must Contribute Bildsten & Deloye 2004:NS Ultra-Compact Binaries from Clusters Juett 2005:Ellipticals’ Field Must Contribute Ivanova & VK 2005: Brightest sources are Field BH LMXBs Consistent answer appears to be: Both Clusters & Field 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

Ultra-Luminous X-ray Sources  Single sources with L X > erg/s  Associated with young populations and star clusters  What is their origin?  Intermediate-Mass Black Holes? ( M o )  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 E TC x P orb ~ L Edd Analytical estimate of TC rate for 1,000M o IMBH for ANY orbital period Mass Transfer and L X calculation for isolated IMBH binaries with 5-15M o 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) M o IMBH, 100Myr old clusters, T rc < 30Myr Average ULX phase duration per cluster: <0.1Myr 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%

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 ? Minimum accretor mass for transients

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 Long-term time monitoring: identification of X-ray transients and clues to ULX nature Bigger source samples: probing the rare brightest sources, questions of BH formation, ULXs