Transcript M sun

What are the essential ingredients
of ultraluminous X-ray sources?
Roberto Soria (CfA & MSSL)
Some ULX collaborators: M Cropper, C Copperwheat (MSSL),
R Fender (Southampton), Z Kuncic, C Hung (Sydney), D Swartz (MSFC),
A Goncalves (Paris-M), M Pakull, F Grise’ (Strasbourg), R. Mushotzky (GSFC)
What we’d like to know about ULXs
1) Mass
No direct (kinematic) mass determination yet.
Two or three candidates perhaps feasible now.
2) How to gain a factor of ~ 50 in apparent Lx
with respect to stellar-mass BHs
Beamed (microblazars?)
Higher BH mass (IMBHs?)
Not beamed
Super-Eddington luminosity
Searching for common features
in the ULX population
“Soft-excess” in their X-ray spectra?
Signature of a cool disk?
higher BH mass?
Holmberg II X-1 (Lx ~ 2E40 erg/s)
“soft excess”
kT ~ 0.15 keV
Holmberg II X-1 (Lx ~ 2E40 erg/s)
Searching for common features
in the ULX population
“Soft-excess” in their X-ray spectra?
Signature of a cool disk?
higher BH mass?
Most bright ULXs (Lx ~ 1E40 erg/s) have it (Stobbart et al 06)
A few do not, pure power-law spectrum (Winter et al 06)
Evidence of IMBHs, M ~ 1000 Msun ?
“Soft-excess” interpretation is still unclear
See also poster by Soria, Goncalves & Kuncic
Cool disk emission
Smeared absorption lines
in fast, ionized outflow
Holmberg II X-1 (Lx ~ 2E40 erg/s)
Holmberg II X-1 (Lx ~ 2E40 erg/s)
Injected spectrum (power-law)
Emerging spectra with absorption
from ionized, fast-moving outflow
(v ~ 0.1 c, nH ~ 3E22)
Models by Goncalves et al.
References:
Gierlinski & Done (2004)
Crummy et al (2006)
Goncalves & Soria (2006)
“Soft-excess” interpretation is still unclear
See also poster by Soria, Goncalves & Kuncic
Standard disk around IMBH
Cool disk emission
Non-standard disk
Smeared absorption lines
in fast, ionized outflow
More generally: absorption + re-emission + reflection
Essential feature of X-ray spectra:
Dominated by non-thermal emission
Disk radiates only ~ 10-20% of output accretion power
Most power is efficiently transferred
from disk to upscattering medium (jet/corona)
Disk should be cooler than a standard SS disk
for a given BH mass
Chilled disk
Cooler than standard disk
because power is drained
from disk into jet+wind+corona
see also Z. Kuncic’s talk
Chilled disk
Cooler than standard disk
because power is drained
from disk into jet+wind+corona
see also Z. Kuncic’s talk
(Soria & Kuncic, in prep.)
Searching for common features
in the ULX population
Jets, outflows?
Radio cores: not detectable yet (< 0.1 mJy)
Resolved jets: not detectable yet
Radio lobes: likely detection in a few sources
Energy in lobes >~ 1E52 erg
Size ~ 50-70 pc
Typical fluxes ~ 0.1-0.2 mJy at 5 GHz
Radio lobes of a ULX
in NGC 5408
(Soria, Fender et al 2006)
Subaru B + ATCA 5 GHz
CFHT Ha + ATCA 5 GHz
Searching for common features
in the ULX population
Jets, outflows?
Radio cores: not detectable yet (< 0.1 mJy)
Resolved jets: not detectable yet
Radio lobes: likely detection in a few sources
Optical nebulae: observed in many bright ULXs
sizes ~ 50-400 pc
X-ray photoionized or collisionally ionized?
HST/ACS
Optical nebulae
Jet lobes?
NGC 1313 X-2
(Pakull, Grise & Motch 2006)
ULX
30 pc
Star
Hot spot?
(hot ring?)
MF16 “SNR” + ULX, in NGC 6946
(Swartz et al 2006, in prep)
= 80 pc
Searching for common features
in the ULX population
Jets, outflows?
Likely to be essential ingredient
but more evidence needed
Searching for common features
in the ULX population
Young host environment?
Not essential for fainter ULXs (Lx <~ 3E39 erg/s)
Essential for brighter ULXs (Lx >~ 1E40 erg/s)
Only found in spiral & irregular galaxies
“Young” = less than 50 Myr
Donor = OB star transferring gas on its nuclear timescale
Searching for common features
in the ULX population
Starburst environment?
Some ULXs are in starburst galaxies
(eg, Cartwheel, Antennae, Mice)
Some are in very quiet corners
of nuclear starburst or starforming galaxies
(eg, NGC 7714, M83, M99)
Some are in tidal dwarfs with little star formation
(eg, Ho II, Ho IX)
NOT AN ESSENTIAL INGREDIENT
but some association
Searching for common features
in the ULX population
Super star-clusters?
Suggested as site of IMBH formation
via O-star coalescence (Portegies Zwart et al; Rasio et al)
But inconsistent with ULX observations
(except for M82 X-1)
Most ULXs found in OB associations or
open clusters, with masses <~ a few 1000 Msun
NOT AN ESSENTIAL INGREDIENT
Searching for common features
in the ULX population
Colliding or tidally interacting systems?
Galaxy-galaxy collisions
(eg, ULXs in Antennae, Mice, Cartwheel, NGC 4485/90, NGC 7714/15)
Satellite dwarf – galaxy collisions
(eg ULX in NGC 4559)
HI cloud – disk collisions
(eg ULX in M99)
Tidal dwarfs and tails
(eg ULXs in Ho II, Ho IX)
Searching for common features
in the ULX population
Colliding or tidally interacting systems?
Essential or very important ingredient
The Antennae
NGC 4559
Examples of ULXs
formed in colliding events
M99
(Soria & Wong 2006)
XMM EPIC image (0.2-12 keV)
HI contours over R image
LX ~ 2 1040 erg/s
(see poster by Soria & Wong)
High-velocity cloud collision with M99 gas disk
Only a coincidence?
Searching for common features
in the ULX population
Low-metallicity environment?
Mounting evidence but no systematic study yet
(eg, ULXs in Cartwheel, Ho II, NGC 4559, NGC 5408, 1 Zw 18)
More massive BH remnants
from
. expected
metal-poor O stars (Mwind ~ Z0.5-0.8)
Probably a very important ingredient
My (biased) conclusions:
I: NATURE OF (MOST) ULXs
Simplest model still consistent with the data:
BH masses ~ 30 – 100 Msun
(upper limit of stellar processes)
Age of the accreting systems < 50 Myr
(OB donor)
II: (SPECULATIVE) FORMATION PROCESS
Triggered star formation
(eg, ram p from cloud/galaxy collisions)
Dynamical collapse of molecular clumps
(as opposed to turbulent fragmentation)
Fast gas accretion and protostellar mergers
in a dense protocluster core
(clump mass ~ a few 1000 Msun, much smaller than a super cluster)
Massive stellar progenitor, Mstar ~ 200 Msun
if metal abundance is low
BH with a mass ~ 50-100 Msun
Externally-triggered dynamical collapse
of a molecular clump in the Milky Way
Total mass ~ 1700 Msun Infall rate ~ 10-3 Msun/yr
Infall timescale ~ 1.7 105 yr
CMM3 has 40 Msun, still accreting & merging
35 Msun
15 Msun 40 Msun
Peretto et al. (2006)
Very massive stars from clustered
star formation exist in the Milky Way & LMC:
Pistol star: initial mass ~ 200 Msun
(but too metal rich to collapse into a BH)
R145 in 30 Dor: M sin3i = (140 +/- 37) Msun
III. POWER BUDGET
Accretion rate up to ~ 10 times Eddington
Luminosity near or a few times Eddington
Disk radiates only < 20% of the output power
Disks are cooler than standard SS
Kin. power available for outflows and jets
Can BHs have steady jets when accreting
at or above Eddington?
ULXs could be test cases for QSO super-Edd
accretion and feedback models at high redshift
A finis si’.
Mersi’ che i l’eve scota’.
Black hole masses in ULXs
Optical counterparts too faint for direct
mass-function determinations
X-ray Luminosity function cuts off at ~ 3 x 1040 erg/s
Eddington limit suggests M ~ 30 - 200 Msun
Higher masses (~ 103 Msun) speculated from
X-ray timing and spectral studies
BH mass from X-ray spectral models
Galactic X-ray binaries generally show:
power-law component + thermal disk component
Flatter (G ~ 1.5) when LX <~ 0.01 LEdd
Steeper (G ~ 2.5) when LX ~ LEdd
4
2
4
2
LX ~ Tin R ~ Tin M
-4
Lmax ~ LEdd ~ M ~ Tin
X-ray spectrum of NGC4559 X7 (XMM)
Power-law (G ~ 2.3)
Tbb ~ 0.12 keV
X-ray spectrum of NGC4559 X7 (XMM)
G ~ 2.0
Disk kTin ~ 0.13 keV
Disk kTin ~ 1.9 keV
kTphot ~ 0.27 keV
LX (erg/s)
1042
1041
1000 Msun
Lx = LEdd
Hot-disk model
1040
1039
IMBH model
15 Msun
GBHs
1038
5 Msun
0.1
0.2
1
Tin
2
(keV)
IMBH model
Miller, Fabian & Miller (2004)
Feng & Kaaret (2005)
kTin ~ 0.12 – 0.15 keV
M >~ 1000 Msun
LX ~ 0.05 – 0.2 LEdd
Hot-disk model
kTin ~ 1.5 – 2.5 keV
M <~ 10 Msun
LX ~ 10 LEdd
Stobbart, Roberts & Wilms (2006)
PROBLEMS:
IMBH model
kTin ~ 0.12 – 0.15 keV
M >~ 1000 Msun
LX ~ 0.05 – 0.2 LEdd
Hot-disk model
kTin ~ 1.5 – 2.5 keV
M <~ 10 Msun
LX ~ 10 LEdd
similar to NLSy1
requires exotic
formation processes
why do they
never reach LEdd?
PROBLEMS:
IMBH model
kTin ~ 0.12 – 0.15 keV
M >~ 1000 Msun
LX ~ 0.05 – 0.2 LEdd
similar to NLSy1
requires exotic
formation processes
why do they
never reach LEdd?
Hot-disk model
kTin ~ 1.5 – 2.5 keV
M <~ 10 Msun
LX ~ 10 LEdd
ad hoc (esp. ~ 10 keV)
standard SS disk should
not survive at 10 LEdd !
Alternative model: broad absorption
G ~ 2.8
Summary I
Unwise to estimate BH masses from X-ray spectra
“Soft excess” may be due to absorption
New spectral state? (for ULXs and NLSy1?)
Steep pl + absorption
in fast, dense outflow
Very high (steep pl)
High/soft (disk)
Low/hard (flat pl)
.
M
ULX radio counterparts: proof of IMBHs?
“fundamental plane” of BH activity
(Merloni, Heinz & DiMatteo 2004; Fender et al 2004)
Few ULXs have a radio counterpart
M82 (Kording et al 2005)
Holmberg II (Miller, Mushotzky & Neff 2005)
NGC 5408 (Kaaret et al 2003; Soria, Fender et al 2006)
NGC 7424 (Soria, Kuncic et al 2006)
NGC 6946 (Swartz et al 2006, in prep)
NGC 5408 (zoomed in)
Coincidence between:
X-ray (~1E40 erg/s)
Radio (~ 0.3 mJy at 5 GHz)
Ha (~1E36 erg/s)
Comparison with X-ray and radio luminosities of Galactic BHs
However:
Steep radio spectrum (thin synchrotron)
Same value in 2000 and 2004
Marginally resolved (radius ~ 30 pc)
More likely radio emission from lobes, not core
Core = X-rays, flat radio spectrum (if present)
Traces the instantaneous accretion state
Lobes = steep radio spectrum
Trace the integrated jet power over ~ 0.1 Myr
Radio lobes or supernova remnant?
Not easy to distinguish or disentangle the two
(eg, SS433 has SNR + jet lobes)
Leptonic jet model in NGC 5408:
E ~ 3 1051 erg
PJ ~ 7 1038 erg/s over 1.5 105 yr
Expansion velocity ~ 80 km/s
A SN model (= 99% relativistic protons)
would require E ~ 3 1052 erg
(A hypernova, perhaps?)
NGC 7424 (d ~ 12 Mpc)
(Soria, Kuncic, Broderick & Ryder 2006)
ULX-2
State transition
low/hard
high/soft
5 1038
7 1039 erg/s
(with thermal plasma)
Age = 8 +/- 2 Myr
Point-like (< 60 pc) radio source
Index ~ - 0.6 (thin synchrotron)
LR ~ 3 x Cas A
Radio lobe or young SNR?
(Soria et al 2006b)
Summary II
We are starting to find ULX radio counterparts
Radio lobes (FR2 microquasars?) or SNR?
Many ULX radio lobes may have been misclassified
as SNRs if the central X-ray source is off
Ratio of ULX radio lobes / “fossil” radio lobes
may give us clues on the X-ray duty cycle
Radio/ULX associations useful to determine
power budget = radiative vs mechanical output
(also important for estimating feedback from early quasars)
Part III:
speculations on ULX formation
IMBH formation in a young super-star-cluster?
Dynamical friction
106 Msun cluster
Mass segregation
Runaway core-collapse
1000 Msun BH
Stellar collisions/mergers in the core
Short-lived, very massive star (~1000 Msun)
Hypernova or direct collapse into IMBH
Numerical simulations by Portegies Zwart et al
and by Gurkan, Rasio et al.
Problem:
most ULXs are not in super-star-clusters
Near OB stars but not inside a bound cluster
Have their parent clusters dispersed?
Tidal disruption: always too slow (>~ 50 Myr)
SN disruption: perhaps….but there are no signs
of the dispersed super clusters
Were they ejected?
Inconsistent with IMBH, would require low BH mass
(eg, Zezas et al 2002; Belczynski et al 2005)
106 Msun super star clusters
with 1000 Msun BHs
Rarely found
Probably not needed
We only need M ~ 30 -- 200 Msun
Suggestion:
IMBHs formed in smaller proto-clusters,
not super clusters
(Soria 2005)
Ionized gas
protostars
Neutral gas
t ~ 0.5 Myr
protocluster
(eg, Kroupa & Boily, 2002-2004; Geyer & Burkert 2001)
sh < 10 km/s
M ~ 103.5 -- 105 Msun
Ideal conditions for
forming progenitor “star” with M ~ 100 -- 300 Msun
dispersing the protocluster (binding energy <~ 1052 erg)
Combination of accretion (large-scale gas inflow)
+ coalescence in the protocluster core?
Dense proto-clusters ideal for coalescence
Stellar captures and mergers are favoured
by proto-stellar disks / envelopes
Collision cross section enhanced
at low velocity dispersion (gravitational focussing)
Collision rates & maximum BH mass
enhanced at high density
Merging BHs: most difficult
Merging O stars: somewhat easier
Merging protostars, molecular cores: easiest
Two regimes for coalescence + IMBH formation?
M <~ 105 Msun
sh < 10 km/s
M >~105.5 Msun
tcc <~ 0.5 Myr
tcc <~ 3 Myr
sh >~ 10 km/s
IMBH formation
in unbound proto-cluster
IMBH formation
in bound cluster
ULX in a sparse OB assoc
(size >~ 100 pc)
with expanding gas nebula
ULX in a cluster
(size <~ 3 pc)
Additional advantage
of the proto-cluster scenario
Same physical process that creates massive
[O + O] binaries, progenitors of BH HMXBs
ULXs = high-luminosity end of HMXBs
up to ~ 100-200 Msun
Protoclusters
near the Cone nebula
(Peretto, Andre’ & Belloche 2006)
Near-IR contours + 1.2mm continuum
Peretto, Andre’ & Belloche (2006)
Two necessary ingredients for a massive BH:
1
Supersonic global inflows in protoclusters
(as opposed to random turbulent motion)
An external trigger may cause
compression and dynamical collapse
2
Small mass loss from progenitor star
before SN core-collapse
Low metal abundance (~ 0.1 solar)
reduces mass loss in stellar winds
Importance of low metal abundance
Heger et al (2003)
Galaxy collisions, cloud-disk collisions
Triggered star formation
Denser protoclusters,
dynamical collapse,
high-mass stars
ULXs, upper end
of HMXB distribution
(often) starbursts,
large number of
HMXBs
Observational evidence for ULXs in SSCs?
ULX in a young super-star-cluster in M82
Lx varying from ~ 1039 to 1041 erg/s
Mbh ~ 1000 Msun
Mcl ~ 4 105 Msun
Portegies Zwart et al, Nature, 2004
Near clusters but not in one
ULX in the starburst dwarf NGC 5408
with Lx ~ 1040 erg/s
Near B stars but not in a cluster
Kaaret et al 2003
Soria et al 2004
Near OB stars but not in a super-star-cluster
ULX in the dwarf galaxy NGC 5204
Liu et al 2004
Not in super-star-clusters
ULX in the starburst dwarf NGC5408
with Lx ~ 1040 erg/s
Two ULXs in NGC4559 with Lx ~ 1 – 4 1040 erg/s
NGC4559 X-10: near OB stars, no super cluster
A few B stars
but no big clusters
Cropper et al 2005
Soria et al 2005
Antennae: lots of ULXs, displaced from clusters
ULXs are displaced from SSCs by ~ 100 – 300 pc
Zezas, Fabbiano et al 2002
Massive proto-stellar mergers
Explosive expulsion of gas
proto-cluster disruption
Binding energy of the gas in a 105 Msun cluster
~ a few 1050 -- 1051 erg
Single SN releases ~ 1051 erg
Merger of 100 + 100 Msun stars
releases ~ 1051 erg
(Bally & Zinnecker 2005)
Not in clusters
4 ULXs in the colliding galaxies NGC 7714 / 7715
with Lx ~ 2 – 8 1040 erg/s
2 are in clusters, 2 are not
Smith et al 2005, AJ, 129, 1350
NGC4559 X-7: near OB stars, no super cluster
A few B stars
but no SSCs
Soria et al 2005