Ultraluminous Xray Sources ULXs and Intermediate Mass Black Holes IMBHs For Journal Club

1
Ultraluminous X-ray Sources (ULXs)
andIntermediate Mass Black Holes (IMBHs) (For
Journal Club)

• J. F. Wu
• Tsinghua Center for Astrophysics
• Department of Physics, Tsinghua University

2
Main References

• Miller M. C., Colbert E. J. M., 2004,
  International Journal of Modern Physics D, 13, 1,
  (astro-ph/0308402, final accepted version)
• Makishima K. et al., 2000, Astrophys. J., 535, 632

3
Contents

• I. Introduction
• II. Ultraluminous X-ray Sources
• III. Black Holes in Globular Clusters and as
  MACHOs
• IV. Formation Mechnisms for IMBHs
• V. Alternative Explanations of ULXs
• VI. Implications of IMBHs
• VII. Outlook

4
Introduction

• Description of Black Holes
• Kerr-Newman Metric
• No hair theorem three parameters to describe
  the black hole completely
• Mass M
• Angular Momentum a J/M
• Charge Q
• Only the first two are significant for real
  black holes Schwarzschild black hole
  (non-spinning) and Kerr black hole (spinning).

5
Introduction

• Two Distinct Populations of Black Holes

• Stellar-mass Black Holes in X-ray Binaries
• mass estimated from the careful radial
• velocity measurement of the companion
• Supermassive Black Holes in the
• Center of Galaxies
• tremendous mass in very small region
• e.g. M87

(Greiner et al., 2001)
(Orosz 2002)
(Tegmark 2002)
6
Introduction

• Intermediate Mass Black Holes (IMBHs)
• Suspicion
• IMBHs may form in the center of dense
  clusters
• Observations
• Ultraluminous X-ray Sources ( ULXs )
• an excess of dark mass in the cores
  of globulars

7
Ultraluminous X-ray Sources

• Preparation
• ISCO ( Innermost Stable Circular Orbit )
• Black hole with an accretion disk is usually
  an X-ray source. The inner edge of the accretion
  disk is near to the innermost stable circular
  orbit, which is 3 Rs for the Schwarzschild black
  holes while 0.5 4.5 Rs for the Kerr black holes.

8
Ultraluminous X-ray Sources

• Preparation
• Eddington luminosity
• Isotropic assumption for radiation
• Radiation force no greater than the gravity

9
Ultraluminous X-ray Sources

• Definitions
• Eddington luminosity limits the bolometric
  energy output of the object. The X-ray luminosity
  in 2 10 keV band will be a factor of a few 10
  times smaller. So
• The lower limit to the X-ray luminosity for a
  ULX is
• 1039.0 ergs s-1.
• The upper limit is not specified but for
  usually objects
• Lx lt 1040.5 ergs s-1.
• Ultraluminous is with respect to normal
  X-ray binaries. Another name for ULXs is
  Intermediate-luminosity X-ray Objects (IXOs),
  indicating their luminosities are intermediate
  between those of normal stellar-mass black hole
  X-ray binaries and AGNs.

10
Ultraluminous X-ray Sources

• Historical observations Einstein and ROSAT
• Einstein detected central X-ray Sources with
  luminosity gt 1039 ergs s-1, but cannot tell
  whether sources are single or multiple, or
  whether really coincide with the nuclei because
  of the bad angular resolution (1' ).

• ROSAT
• not coincident with the nucleus
• presented in every five nearby galaxies on
• average
• brightest ULXs Lx 9 1040 ergs s-1, implying
• mass gt 700 M?
• locations in galaxies
• spiral near but distinct from the
  dynamical center
• elliptical almost exclusively in the
  halos

11
Ultraluminous X-ray Sources

• X-ray Energy Spectra of ULXs
• Multicolor Disk (MCD) Blackbody Model each
  annulus of the accretion disk is assumed to
  radiate as a blackbody with a radius-dependent
  temperature
• the inferred temperature Tin of the
  innermost portion of the disk is related to the
  mass of the black hole

12
Ultraluminous X-ray Sources

• X-ray Energy Spectra of ULXs
• ASCA Spectral Modeling of ULXs
• Makishima et al., 2000, Astrophys. J., 535, 632
• usually with a ( soft ) MCD component for
  the disk emission, plus a (hard) power-law
  component for the presumedly Comptonized disk
  emission
• High Temperature Problem fitting kTin 1.1
  1.8 keV, while Galactic stellar mass BHXBs
  typically kTin 0.4 1 keV
• Solutions
• Stellar mass but beaming
• Modify thin disk model change ?2?, not
  effective
• Use slim disk model not effective
• Kerr black holes demand high inclination
  angle
• KEY ULXs are not well represented by a simple
  MCD disk model after all.
• e.g. CMCD for XMM-Newton Spectra 0.05 0.3 keV
  ( Wang et al. 2004)

13
Ultraluminous X-ray Sources

• X-ray Energy Spectra of ULXs
• XMM-Newton and Chandra Spectral Modeling of ULXs
• Often fit with a single model ( either MCD or
  power-law)
• Power-law with ? 5 super-soft
• Power-law with ? 2 may actually be
  background nuclei
• MCD model
• for spectra with MCD component
• no high temperature problem ( 0.1 keV)
• Fe K lines (6.4 -7.0 keV, M82) not
• favor of beaming mechanism but indirect
• evidence for IMBH
• Note nearly all the spectra of ULXs now
• are in spiral galaxies, for those in ellipticals
• may have harder spectra.

CMCD Fitting for NGC 1313 X-1, Tin 0.199 keV (
Wang et al., 2004)
14
Ultraluminous X-ray Sources

• ULXs and Host Galaxy Type
• Spiral Starburst Galaxies Antennae and
  Cartwheel
• ULXs are directly related to young star
  population
• ULXs may be a special type of HMXB with
  beamed X-ray
• emission
• Elliptical Galaxies
• elliptical galaxies with ULXs have a
  larger number per
• galaxy than do the spiral galaxies
  with ULXs
• HMXB scenario not for all ULXs
• Chandra Spectra show that ULXs in ellipticals
  are distinct from those in spirals.

15
Ultraluminous X-ray Sources

• X-ray Variability of ULXs
• Long-term ( months or longer ) variability of
  ULXs in many nearby spiral galaxies
• reject the system or group scenarios
• Variability with time scale less than a few week
• tempting to interpret as orbital periods
• Variability with short timescales ( second to
  minutes)
• the same level of fractional rms amplitude
  as variability on longer timescales, variability
  at the few percent level would be detectable out
  to the Nyquist frequency of observations of the
  brightest ULXs

16
Ultraluminous X-ray Sources

• X-ray Variability of ULXs
• QPOs one case of 54 mHz ( Strohmayer Mushotzky
  2003)
• disfavor of beaming scenario if the
  source is really a beamed stellar-mass black
  hole, the variability in the disk emission (which
  is nearly isotropic) would have to be of enormous
  amplitude to account
• for the observations
• Combined spectral and temporal analysis
• Powerful tool in diagnosing ULX emission
  processes
• normal BHXB soft spectra in high state, hard
  spectra in low state
• anomalous soft spectra in low state, hard
  spectra in high state
• ( Antennae) microquasars ?

17
Ultraluminous X-ray Sources

• Multiwavelength associations
• study the environment of ULXs ( companion,
  accretion disk and jets)
• Optical counterparts strong link between ULXs
  and star clusters
• spirals star-forming region, young
  cluster with O giants/supergiants
• HMXB scenario
• ellipticals globular clusters
• Radio counterparts just beginning
• Kaaret et al. (2003), NGC 5408 X-1
  relativistically beamed jet emission
  microblazar?

18
Black Holes in Globular Clusters and as MACHOs

• Observational Evidences for IMBHs in centers of
  globular clusters promising but not compelling
• Detailed modeling of properties of individual
  objects M/L
• Core rotation detecting
• IMBH in a binary system with a stellar
  mass black hole
• a massive black hole binary in the core
• X-ray Observations Bondi-Hoyle accretion onto
  the central black hole can produce emission in
  various bands, the most prominent perhaps being
  X-rays and radio.
• Microlensing detection

19
Formation Mechanisms for IMBHs

• Stellar mass limit
• not from core collapse recently
• Black holes in very early universe
• prior to Big Bang nucleosynthesis, lock
  matter in non-baryonic form
• horizon mass increase transition at
  uncomfortably low energies
• perturbation spectrum strongly peaked and
  finely tunned
• Population III Stars
• Conditions above 250 M? directly collapse
• large Jeans mass T3/2
• zero metallicity star little loss mass
  (insignificant winds, weak
• pulsations)
• Problems lack of observational constraints on
  Population III star
• Cooling mass cannot reach several
  hundred solar masses
• number of zero metallicity stars

20
Formation Mechanisms for IMBHs

• Growing in Dense Stellar Cluster
• Dynamics in stellar cluster
• more massive stars binaries tend to
  sink towards the core
• three body interactions one single and
  one tightened binaries (collision
• and merge)
• IMBHs captured and sink towards the core
  of young stellar cluster ( X-ray
• source)
• In globular clusters
• Merging of binaries kick outside the
  cluster
• Capture of a stellar mass black hole
  around the IMBHs
• Tightening if a BH/BH binary by a Kozai
  resonance
• In young clusters
• Multiple collision to a given ( central )
  object associations between ULXs
• and star formation region
• Questions and simulations promising

21
Alternate Explanations for ULXs

• Beaming
• the flux along the axis of symmetry can be
  enhanced by a factor of tens compared to the
  isotropic Eddington flux
• in spirals beamed sources involving
  HMXBs
• in ellipticals beamed sources involving
  LMXBs
• Advantages
• based on known source
• explain the associations of ULXs and star
  forming regions in spirals
• Challenges
• ULXs with no such rapid variability as
  stellar mass BHXBs ( e.g. Cyg X-1, 100 Hz )
• cannot explain the QPOs
• theoretical basis of relativistic outflow
  are not well established

22
Alternate Explanations for ULXs

• Super Eddington Emission
• Magnetic field
• B gt 1013G, suppress the Thomason Scattering
• neither black hole or accretion disk have
  no required magnetic field
• Supernovae
• enormous accretion rate for principal
  neutrino emission
• unimportant for normal accretion in X-ray
  Binaries
• Anistropy
• radiation causes accretion matter to clump
  which linked by weak magetic field ( simulation
  ), radiation moves from low density medium
• total luminosity lt 10 times Eddington
  limit, still need high mass

23
Alternate Explanations for ULXs

• Motivation for stellar mass models
• High temperature problem
• unwarranted, need careful examination on
  ULX spectra
• Luminosity function shows no evidence for a new
  component not compelling
• number of ULXs so small with huge error
  bar
• any change in source population would
  change the slope
• IMBH cant evolve in a binary orbit period
  excess a year
• capture companion in star cluster
• IMBH cant grow in clusters binary-single
  interaction prevent
• direct collision binary-binary
  interactions
• IMBH cant separate from clusters supernova
  kicks cant
• three body interaction kicks

24
Alternate Explanations for ULXs

• Motivation for stellar mass models
• No definitive observations exist for any
  single ULX, let alone the class of ULXs, that
  rule out intermediate-mass black holes, or
  beaming, or super-Eddington emission.
• the current disagreements exist because the
  crucial parameter the mass has not been
  measured observationally.
• one cannot make definitive statements about
  the entire class of ULXs, so it may be that some
  ULXs conform to each of the models proposed.

25
Implications of IMBHs

• Formation of SMBHs
• IMBHs sink to the center of galaxies seeds for
  SMBHs by gas accretion
• Coalescence of IMBHs angular momentum
  accretion
• Gravitational Radiation Sources
• Coalescence in stellar clusters
• Inspiral of stellar mass objects into IMBHs LISA
• Inspiral of IMBHs into SMBHs LISA
• Measuring spacetime near the rotating
  black holes

26
Outlook

• Radial velocity measurement mass
• Optical/UV/IR companion
• X-ray observations of ULXs energy spectra
• X-ray timing observations tens of milliseconds
• Multiwavelength observations of ULXs optical
  counterparts, broadband spectra, overall
  luminosity
• Kinematics of globular clusters detection of
  IMBH in center
• Tasks for three kinds of models more solid
  theoretical bases, accounting for observations
• Gravitational waves
• Debate on the nature of IMBHs will
  undoubtedly continue until rigorous measurements
  of the masses of IMBHs are possible. ( Radial
  velocity measurement or gravitational wave
  detection)

27
References

• References
• Greiner J., Cuby J. G. McCaughrean M. J., 2001,
  Nature, 414, 522
• Kaaret P., et al., 2003, Science, 299, 365
• Makishima K. et al., 2000, Astrophys. J., 535,
  632
• Miller M. C., Colbert E. J. M., 2004,
  International Journal of Modern Physics D, 13, 1,
  (astro-ph/0308402, final accepted version)
• Orosz J. A., 2002, astro-ph/0209041
• Strohmayer T. E., Mushotzky R. F., 2003,
  Astrophys. J., 586, L61
• Tegmark M., 2002, Science, 296, 1427
• Wang Q. D., et al., astro-ph/0403413

28
The End
Thanks for your attention!
Tsinghua Center for Astrophysics Physics
Department, Tsinghua University 100084
Beijing, P. R. China jfwu03_at_mails.tsinghua.edu.c
n ftp//166.111.16.2/incoming/study/journal_club/
Wujf_ULXs_IMBHs/