Download 3. Neutron Star X-ray Binaries

Magnetic Field Upper Limits
for Jet Formation
in X-ray binaries & AGNs
M. Kaufman Bernadó1,* & M. Massi1
1Max
Planck Institut für Radioastronomie, Bonn, Germany
*Humboldt Research Fellow
May 2008 - Ljubljana
INDEX
1. Introduction
2. Jet formation cycle A and B – Basic condition
3. Neutron Star X-ray Binaries
4. Black Hole X-ray Binaries and Supermassive Black Holes
5. Implications
6. Summary
INDEX
1. Introduction
2. Jet formation cycle A and B – Basic condition
1. Introduction
3. Neutron Star X-ray Binaries
4. Black Hole X-ray Binaries and Supermassive Black Holes
5. Implicactions
6. Summary
X-ray Binary
Binary
X-ray
System
System
Accretion Disk:
X-ray emission
Microquasar
Microquasars are defined as the XRB systems where
either high-resolution radio interferometric techniques
have shown the presence of collimated jets or a
flat/inverted radio spectrum has been observed
(indirect
Compact Object:
evidence of an expanding
continuous jet).
ACCRETOR
Companion Star:
Neutron Star or Black Hole
MASS
DONORobject, NS or BH, is still
The nature of the
compact
Low- ormicroquasars.
High-Mass
uncertain for several
Magnetic Field Upper Limits
for Jet Formation
Necessary initial condition:
a low magnetic field at the NS surface or at the
last stable orbit of the accretion disk of a BH.
Aim: to quantify this important parameter and therefore give an upper
limit for the magnetic field strength for which an ejection could happen
in a NS or BH XRB system, as well as to predict the corresponding
behaviour for Active Galactic Nuclei using standard scaling.
When will an accreting NS become a
microquasar and when, on the other hand,
an X-ray pulsar?
When will a BH XRB system be able to
evolve into a microquasar phase?
INDEX
1. Introduction
2. Jet formation cycle A and B
3. Neutron Star X-ray Binaries
condition
4. Black Basic
Hole X-ray Binaries
and Supermassive Black Holes
2. Jet formation cycle A and B – Basic condition
5. Implications
6. Summary
Initial Condition
for Jet Formation:
twisted B
PB < Pp

M
increase
Cycle A
Magnetic Lines
are compressed
PB
AMPLIFIED
The formation of a jet is based on
PB vs Pp
START
a competition process between
>P
the magnetic fieldPpressure,
PB, and the plasma pressure, Pp.
B
p
Because of the increasing
compression
of the magnetic field lines, the
Summarised
in a flowchart.
magnetic
will grow
and may
become
larger
than that
the gas
The strengthpressure
of the large-scale
poloidal
field must
be low
enough
the
pressure
on the surface
of theshow
accretion
disk,
whereofthe
density
is lower.
Numerical
that the
launch
a jet
involves
a
P dominates
Psimulations
(Blandford
1976).
p
B
weak large-scale poloidal magnetic field anchored in
Then,
the magnetic
field
i.e.
dynamically
dominant,
Only rapidly
under
that
condition,
< P“active”,
differentially
disk is
rotating
disksbecomes
orPBcompact
objects
(Meier
et rotating
al. 2001).
p, the
P
Ppbend
, and the
themagnetic
plasma has
to lines
followinthe
twisted magnetic
field lines,
able
field
a magnetic
spiral (Meier
et al.
B > to
creating
2001). two spinning-plasma flows.
PB > Pp
START
NO
B
YES
Twisted?
no JET
is formed
two spinning
plasma flows
a JET
is formed
QUIESCENT
The generation of jets and their presence in XRBs is coupled to the
M
evolution of a cycle that can be observed
in the X-ray states of this
BH: LOW/HARD
Neutron Star:
-----------kind of systems.
X-ray Pulsar
NS: IS / HB

increase

M
increase
Cycle B
new compression
of the
magnetic lines
We therefore complement the jet formation flowchart showing the
parallelism between the presence of a jet and the different X-ray
reconnection
states.
stored magnetic
energy released
untwisted
B
BH: HIGH/SOFT
------------NS: BS / FB
BH: VERY HIGH
----------NS: NB
The strong magnetic field cannot be twisted and is dynamically
dominant: the plasma is forced to move along the magnetic field lines
and converges onto the magnetic poles of the neutron star. There, it
releases its energy, creating two X-ray emitting caps (Psaltis 2004).
Alfvén Radius
Magnetic Field
Upper Limit
PB < Pp
JET FORMATION
The distance at which the magnetic
and plasma pressure balance each
other.
The Basic Condition
RA / RLSO = 1
BH Last Stable
Orbit
RA / R* = 1
NS Surface
Radius
INDEX
1. Introduction
2. Jet formation cycle A and B – Basic condition
3. Neutron
Star
X-ray
Binaries
3. Neutron Star X-ray Binaries
4. Black Hole X-ray Binary and Supermassive Black Holes
5. Implications
6. Summary

Using observed values of B and M for NS XRBs,
Classical X-ray Pulsars
ms X-ray Pulsars
Atoll-sources
Z-sources
Millisecond
Classical
(ms)
X-ray
Pulsars:
Pulsars:
Atoll
and ZX-ray
- Sources:
---rapidly
called spinning
“slow”
accretion-powered
period
1s or
more.
LMXBs
divided
in these two typespulsars,
depending
on ~their
timing
- -few
HMXB
detected
(fiveproperties
/ all
LMXB)
LMXB
and
spectral
- Z-type have larger mass accretion rates than Atoll-type
The intersection between the
function, RA/R*, and the basic
condition
plane,
RA/R*=1,
indicates the combination of the
magnetic field and the mass
accretion rate values for which
plasma pressure and magnetic
field pressure balance each other
at the surface of the star.
This ensures that the initial
condition for jet formation,
PB < Pp
is fulfilled over the whole
accretion disk.
Upper Limit for B
Z sources
108.2 G
Atoll Sources
107.7 G
107.5G
ms X-ray Pulsars
The association of a classical X-ray pulsar (B ~ 1012 G) with jets is
excluded even if they accrete at the Eddington critical rate.
Theses theoretical values are in complete agreement with the up to now existing
observational data:
Millisecond X-ray pulsar could switch to a microquasar phase during
We
thataccretion
Atoll-sources
potential sources
for generating
maximum
Thesee
magnetic
field rate.
strengthare
hasindeed
been determined
in a Z-source,
with
Classical X-ray pulsar: in agreement with the systematic search of
jets
and
in
fact
they
have
not
only
been
detected
in radio
(Fender
&
8 G,
For
their
average
B~10
the
basic
condition
would
only
be
fulfilled
In
fact,
in
the
millisecond
source
SAX
J1808.4-3658,
which
shows
hints
for
jets,
Scorpius
X-1,
from
magnetoacoustic
oscillations
in
kHz
QPO
radio emission in this kind of sources with so far negative result
Hendry
2000;
Rupen
et
al.
2005)
but more
recently
evidence
of jets in
7-8
a(Fender
radio
jet,
during
bright
states,
peak
values
of
for
a mass
accretion
rate
,
,
whereas
the
maximum
reaching
values
of
10
G
(Titarchuk
et
al.
2001).
Instead,
if
et al. 1997; Fender & Hendry 2000; Migliari & Fender 2006).
these
sources
has
been
etofal.magnitude
2006
andlower,
Russell
et al.
were
measured
and the
upper
limit(Migliari
of
theorder
magnetic
field strength
was found
observed
accretion
rate
isfound
nearly
one
2007).
to
be a few times 107 G .(Gilfanov et al. 1998).
INDEX
4. Black
Hole
X-ray
Binaries
2. Jet formation cycle A and B – Basic condition
&
3. Neutron Star X-ray Binaries
4. Black Hole X-ray Binaries and Supermassive Black Holes
Supermassive Black Holes
1. Introduction
5. Implications
6. Summary
Schwarzschild Stellar Mass BH
Kerr Stellar Mass BH
Upper Limit for B
with Eddington mass accretion rate
with
BHSchw
BHKerr
Stellar-Mass BHSchw
1.35 x 108 G
Stellar-Mass BHKerr
5 x 108 G
Straightforward dependency of the magnetic field strength with the mass
of the BH allowing us to establish its upper limit for the jet formation in
the case of supermassive BHs as well:
Schwarzschild and Kerr Supermassive BHs
Upper Limit for B
with Eddington mass accretion rate
Supermassive BHSchw
105.4 G
Supermassive BHKerr
105.9 G
SBHSchw
SBHKerr
Note: in the specific case of a supermassive Schwarzschild BH of
108
we get B < 104.3 G.
For a BH of the same mass Blandford & Payne (1982) established
B < 104 G at 10rg.
Scaling our value, which is relative to RLSO=6rg, to 10rg, we
get B < 104 G in complete agreement with the results of
Blandford & Payne (1982).
INDEX
1. Introduction
2. Jet formation cycle A and B – Basic condition
5. Implications
3. Neutron Star X-ray Binaries
4. Black Hole X-ray Binaries and Supermassive Black Holes
5. Implications
6. Summary
The analysis of the basic condition for jet formation has
two interesting possible implications:
Nature of the compact object in XRB systems
ms X-ray pulsars spin distribution
The nature of the compact object in XRB systems
& the magnetic field decay
Measurements of surface magnetic field strengths by cyclotron
resonance effects were carried out in a dozen of X-ray classical
pulsars show that B is tightly concentrated over:
(1 - 4) x 1012 G
(Makishima et al. 1999)
To achieve the basic conditions for forming a jet the field must decay to
B=107-8 G
The nature of the compact object in XRB systems
& the magnetic field decay
Analysis of pulsars data have indicated that B decays 4 orders of
magnitude by Ohmic dissipation in a timescale longer than 109 yr
(Konar & Bhattacharya 2001).
Therefore this kind of magnetic field decay process excludes the
possibility of a NS-HMXB evolving into a microquasar phase since
this decay is longer than the lifetime of the high-mass companion
star, 107 yr for
.
In this case then, the only possible accretor would be
a Black Hole.
The nature of the compact object in XRB systems
& the magnetic field decay
Faster decays of the magnetic field can occur with the
high-accretion-induced crust screening process.
(Zhang 1998)
Circinus X-1 is an XRB with a type I X-ray bursts NS. It has a
confirmed jet, so it is a microquasar.
 It is so young that its orbit has not yet had time to become circular
circularization time ~ 105 yr.
(Ransom et al. 2005)
 It has already reached B to fulfill the basic condition for jet formation.
In fact, Romani (1995) has deduced a characteristic timescale for the
initial field decay by screeing in the range of
104 yr < t < 106 yr.
The nature of the compact object in XRB systems
& the magnetic field decay
A decay in the B due only to Ohmic dissipation implies the presence
of a BH as the compact object in a microquasar-HMXB because of
the long timescales of this process.
Only in the case of high-accretion-induced crust screening process
the timescales can be as short as t ~ 105 yr and the issue of the nature
of the compact object remains open.
ms X-ray pulsars spin distribution
One of the major open issues concerning millisecond X-ray pulsars is the
absence of sub-millisecond X-ray pulsars. The spin distribution sharply
cuts off well before the strict upper limit on the NSs spin rate that is
given by the centrifugal breakup limit (0.3 ms depending on the NS
equation of state).
The physics setting that limit is unclear.
(Chakrabarty 2005)
Due to the possibility of jets in millisecond X-ray pulsars,
then the jet might be the suitable agent of angular momentum sink, as
in the bipolar outflows from young stellar objects.
The transport rate of angular momentum by the jet can be two thirds
or more of the estimated rate transported through the relevant portion
of the disk.
(Woitas et al. 2005)
INDEX
1. Introduction
2. Jet formation cycle A and B – Basic condition
6. Summary
3. Neutron Star X-ray Binaries
4. Black Hole X-ray Binaries and Supermassive Black Holes
5. Implications
6. Summary
 The
association of a classical
X-ray pulsar - B ~ 1012 G - with
jets is excluded.
Z sources
108.2 G
107.7 G
Atoll Sources
ms X-ray Pulsars
Stellar-Mass BHSchw
Stellar-Mass BHKerr
107.5G, and max.
1.35 x 108 G
5 x 108 G
Implications
 Compact
Supermassive BHSchw
105.4 G
Supermassive BHKerr
105.9 G

object nature vs. B decay
ms X-ray pulsars spin distribution
vs. presence of jets