Ultraluminous X-ray Sources

1
Ultraluminous X-ray Sources Andrew
King, University of Leicester
Penn State 22.5.04
² Lx(apparent) gt 1039 erg s-1 LEdd(10 M) ²
do ULXs contain intermediatemass black holes,
M 102 104 M (IMBH) ?
2
major constraint ULX star formation
connection, e.g. Antennae
3
Using IMBH to make ULXs in star-forming
galaxies 1. If IMBH are
primordial (Pop III), new star clusters must
light up accretion -- unclear how a
primordial IMBH acquires a companion star
4
IMBH formation in dense star clusters? either
2. merge stars, tmerge ltlt tMS and
build up large M (Gurkan et al. 2003 Portegies
Zwart et al., 2004) problem mass loss in
merger? or 3. merge black holes ? IMBH (Miller
Hamilton, 2002) problem GR reaction
merged BH lost from cluster with low M
5
in all 3 cases, any ULX is formed in a cluster
² most ULXs are observed near but outside
clusters -- must eject (with companion
star?) ² make at most 1 ULX per cluster, i.e.
gt 105 M needed to make each ULX
6
could ULXs instead be an unusual phase of X-ray
binary evolution?
(King et al., 2001)
7
(Grimm, Gilfanov Sunyaev, 2003)
no break at 1039 erg s-1 most ULXs are HMXBs
8
likely candidates 2 types (1)
highmass Xray binaries
thermaltimescale mass transfer
rate Mdot(tr) Mdonor/tKH 10-4 - 10-3 M
yr-1 nuclear-timescale mass transfer rates
comparable black hole mass can grow
significantly
9
star formation MS evolution of massive stars, lt
108 yr high-mass X-ray binary (wind-fed) 104,
5 yr star fills Roche lobe, very high Mdot,
ULX phase, 103, 4 yr ULX phase reached
in lt 108 yr after SF
10
highmass Xray binaries
² present in star-forming regions ² found near
but outside clusters SNe kicks ²
thermaltimescale phase is like SS433 viewed
from the side
11
(2) bright, long-lived soft X-ray transient
outbursts
(SXTs)
low-mass donor
black hole with unstable accretion disc (cool
edges)
² present in both ellipticals and spirals ² long
outbursts like GRS 1915105 (on since 1992)
12
How does an Xray binary appear so luminous?
² LEdd 4.4 1039 erg s-1 (20 M BH,
hydrogen-depleted accretion) two ways of
increasing this (1) ² GRS 1915105 has L gt 6
1039 erg s-1 with BH mass 14M, i.e. gt 3
LEdd ² with mild anisotropy apparent luminosity
can reach 4 1040 erg s-1
13
luminosity (2) ²
extremely high mass transfer rates Mdot (tr)
103 104 Mdot(Edd) ² outer disc unaware of
this until radius REdd where
GMMdot(tr) /REdd Ledd_
14
² then total disc luminosity is Ldisc
Ledd1 ln(Mdot(tr)/Mdot(Edd)
10LEdd
15
² thus expect L 1 4 1040 erg s-1 for
20M BH with hyper-Eddington accretion ²
characteristic blackbody radius R 109 cm ² cf
ultrasoft components in ULXs e.g. NGC 1313
(Miller et al 2003 if instead R is
assumed to relate to BH size, get M 103 M)
16

• Outflows from ULXs
• ² Mdot gtgt Mdot(Edd), so most mass expelled
• ² optically thick outflow with
• Mdot(out)v LEdd/c
• ² outflow momentum sweeps up ISM
• nebula

17
Eout h M2c2 1052 erg hypernova
energy ² ULX nebulae larger than SNR ²
supermassive BH analogue ? M-s relation for
galaxies
18
Gao et al., 2003
19
star formation ring began expanding
t 3 108 yr ago, but takes lt 107
yr to pass any radius ULXs live
tlife lt 107 yr, so number of dead ones
inside ring is N gt
(n/bd)(t/tlife) gt 300/bd where b is
anisotropy and d is duty cycle (both lt1)
(King, 2004)
20
² mass transfer lifetime M2/L of ULX
lt 107 yr ² companion stars MS
lifetime lt 107 yr, otherwise ULXs form after
ring has passed ² consistent with 3000
superEddington HMXBs with M2 gt 15M ² but
IMBH binaries transient (small disc) so duty
cycle d ltlt 1 ² requires gt 3 104 IMBH, and thus
gt 1010M in clusters, most mass not accreted
21
² population properties of
ULXs in star-forming galaxies similar to
HMXBs, but incompatible with IMBH ²
luminosities suggest HMXBs in super-Eddington
phase ² outflows ? nebulae most ULXs are
HMXBs or SXTs
22
² exception? M82 ULX L gt 1041 erg s-1
too high for stellar-mass BH ?
other sources possible too, but may be
superpositions (check variability)
23
² number of such hyperluminous Xray sources
(HLXs) is very small at most one per few
galaxies ² Occams razor try existing BH models
stellarmass binaries or galactic nuclei ²
not stellarmass galactic nuclei?
(King Dehnen, 2004)
24
² hierarchical merging every large galaxy has
10 100 satellites
² most orbits miss host, but occasional
collisions
25
² if colliding satellite retains central BH
and star cluster, tides trigger accretion,
just like AGN
² satellite can have BH mass gt 104 M
² accretion time ltlt orbital timescale HLX
activity only close to galaxy plane
² passage of satellite stimulates star
formation HLX accompanied by stellarmass ULXs
26
Summary
² most ULXs are stellarmass XRBs rather than
IMBHs (L lt 1041 erg s-1 )
² high L from large accretion rate,
superEddington accretion or anisotropic
emission
² HLXs (L gt 1041 erg s-1 ) may be captured
satellite galaxy nuclei
² ULX star formation and HLX galaxy
formation links