INAF, Osservatorio Astronomico di Roma

XI Advanced School of Astrophysics, Brazil, 1-6 September 2002

* Low mass X ray binaries and millisecond pulsars GCs

* The case of PSR J1740-5340 and the helium remnant WDs

* Low mass X ray binaries and millisecond pulsars GCs

* The case of PSR J1740-5340 and the helium remnant WDs

Summary

King, Cool & Piotto HST data

The global HR

diagram of

NGC6397

The global HR

diagram of

NGC6397

1) White dwarfs are today’s stellar remnants in GC (M evolving ~ 0.8Mo

2) What about the remnants of the more massive stars? We have already seen that inermediate masses influence the chemistry of the GCs through selfpollution from their low v winds: these stars too (M<6Mo) evolve into (more massive) WDs

3) More massive stars have evolved into supernovae in the first phases of life of the clusters: but we see their remnant neutron stars population through the huge millisecond pulsar population and the (few) low mass Xray binaries

1) White dwarfs are today’s stellar remnants in GC (M evolving ~ 0.8Mo

2) What about the remnants of the more massive stars? We have already seen that inermediate masses influence the chemistry of the GCs through selfpollution from their low v winds: these stars too (M<6Mo) evolve into (more massive) WDs

3) More massive stars have evolved into supernovae in the first phases of life of the clusters: but we see their remnant neutron stars population through the huge millisecond pulsar population and the (few) low mass Xray binaries

The other stellar remnants in GCs

Binaries containing neutron stars

Millisecond radioPulsars

Low mass companion

B ~ 108 – 10

9 G

Low mass X-raybinary

Low mass companion

B ~ 108 – 10

9 G

X-ray binaries with known Porb in GCs

a Deutsch, Margon, & Anderson 2000. c Ilovaisky et al. 1993. d in’t Zand et al. 2000.

e Sansom et al. 1993. f Homer et al. 1996. g van der Klis et al. 1993. h Stella et al. 1987.

Three are ultracompact!

X-ray imaging of the core of 47 Tuc (Chandra)

Grindlay et al. 2001 Science

70Ks exposure with resolution <1”: 108 faint (Lx=1030-33 erg s-1 X-ray sources located in the central 2’x2.5’, >half with Lx<1030.5

All the 15 MSPs are identified.The authors suggest: 50% are MSPs 30% accreting WDs 15% MS binaries in flare outbursts 2-3 quiescent LMXBs with NS

The Pulsar population

from D.R. Lorimer 2001

The millisecond Pulsar population

1) ~1400 radio pulsars known

2) ~100 have at least one of the properties: * very short pulse period (~77 have P<12ms) * relatively weak magnetic field (~46 have B<1010G) * are found in binaries (~66) * are located in a globular cluster (~50)3) One major class of binary radio-pulsar in the disk have low

mass companions (0.1 –0.4 Mo) and nearly circular orbit. Porb goes from a fraction of day to 103 days4) Most of the wide systems thus seem to have low mass helium

white dwarfs companion, remnant of mass transfer starting when the secondary star is a subgiant or a giant with a helium core.

1) ~1400 radio pulsars known

2) ~100 have at least one of the properties: * very short pulse period (~77 have P<12ms) * relatively weak magnetic field (~46 have B<1010G) * are found in binaries (~66) * are located in a globular cluster (~50)3) One major class of binary radio-pulsar in the disk have low

mass companions (0.1 –0.4 Mo) and nearly circular orbit. Porb goes from a fraction of day to 103 days4) Most of the wide systems thus seem to have low mass helium

white dwarfs companion, remnant of mass transfer starting when the secondary star is a subgiant or a giant with a helium core.

List of MSPs in GCs

MSPs in Globular Clusters

MSPs in Globular Clusters

Total Number 53 (Sept. 2001)

47 Tuc 20

NGC 6752 5

M15 8

Terzan 2 2

Not all in binaries

Spin periods From 2.1ms to 1s

Orbital periods From 0.07 to 256 days

Why so many MSPs in Globular Clusters?

Why so many MSPs in Globular Clusters?

In the field of the Galaxy, it is necessary that :1)the primordial binary in which the NS is

formed survives the SN explosion;2) The binary parameters allow, later on, a

phase of mass transfer which spins the pulsar up to ms periods

In the field of the Galaxy, it is necessary that :1)the primordial binary in which the NS is

formed survives the SN explosion;2) The binary parameters allow, later on, a

phase of mass transfer which spins the pulsar up to ms periods

GCs are the best place to produce binary systems containing a NS even a long time after

the NS independent formation

GCs are the best place to produce binary systems containing a NS even a long time after

the NS independent formation

(Why so many neutron stars in Globular Clusters?)

(Why so many neutron stars in Globular Clusters?)

(In the following we will not discuss a key problem: the embarassing presence of so many NSs in GCs. In fact, in the Galactic disk, <v>~200Km/s (implying some “kick” velocity at the SN event). Being vesc~25Km/s typically from Gcs, a low fraction of NS should be retained in the clusters. For this reasons some invoke an AIC scenario for the NS formation)

(In the following we will not discuss a key problem: the embarassing presence of so many NSs in GCs. In fact, in the Galactic disk, <v>~200Km/s (implying some “kick” velocity at the SN event). Being vesc~25Km/s typically from Gcs, a low fraction of NS should be retained in the clusters. For this reasons some invoke an AIC scenario for the NS formation)

Mechanisms for binary formation

Mechanisms for binary formation

Bound system of two stars formed from an unbound configuration: a sink of orbital energy is required:

Bound system of two stars formed from an unbound configuration: a sink of orbital energy is required:

1) Collision involving three stars; one takes up the excess energy and escapes (very small probability);

2) Exchange interaction of a NS with an existing binary: the NS replaces one of the components;

3) Tidal capture: deformation of a normal star by close passage of a compact star takes away kinetic energy of the orbit, then dissipated through oscillations and heating of the envelope. If Ek exceeds the total positive energy of the initial orbit, a bound system is formed.

1) Collision involving three stars; one takes up the excess energy and escapes (very small probability);

2) Exchange interaction of a NS with an existing binary: the NS replaces one of the components;

3) Tidal capture: deformation of a normal star by close passage of a compact star takes away kinetic energy of the orbit, then dissipated through oscillations and heating of the envelope. If Ek exceeds the total positive energy of the initial orbit, a bound system is formed.

Which mechanism dominates?

Which mechanism dominates?

Exchange encounters: i) Direct exchangeii) Resonance encounter in which a temporary

triple is formed, followed by the ejection of the third component (more frequent than i). For equal masses M

bin ~ nNS nbin M a/v inf (v inf =vel. at large separation)

Tidal captures: (require d<3R) bin ~ nNS n (m+M) 3R/v inf (cross section is favoured for exchange

encounters -a versus 3R-, but nbin<<n)

Exchange encounters: i) Direct exchangeii) Resonance encounter in which a temporary

triple is formed, followed by the ejection of the third component (more frequent than i). For equal masses M

bin ~ nNS nbin M a/v inf (v inf =vel. at large separation)

Tidal captures: (require d<3R) bin ~ nNS n (m+M) 3R/v inf (cross section is favoured for exchange

encounters -a versus 3R-, but nbin<<n)

Tidal capture

Tidal capture

1) MS of RG companion (relatively distant encounters)

2) Binaries with WD companions, from direct collision with RGs

1) MS of RG companion (relatively distant encounters)

2) Binaries with WD companions, from direct collision with RGs

1) Mass transfer will begin soon, leading either to larger or to shorter Porb, depending on the nuclear evolution of the acquired companion. The system becomes a LMXB

2) GR - AML can bring the system into contact at very short (minutes) Porb. Mass transfer increases P leading to a system like the 11m binary in NGC 6624 (But also another channel..)

1) Mass transfer will begin soon, leading either to larger or to shorter Porb, depending on the nuclear evolution of the acquired companion. The system becomes a LMXB

2) GR - AML can bring the system into contact at very short (minutes) Porb. Mass transfer increases P leading to a system like the 11m binary in NGC 6624 (But also another channel..)

Recycling model for

MSPs

Recycling model for

MSPs

Old Neutron stars spun up by accretion from a

companion

Old Neutron stars spun up by accretion from a

companion

1)LMXB phase preceding the MSP stage; 2) mass transfer stops3) the radio MSP emerges

Orbital evolution:

* P initial>P bifurcation: nuclear evolution drives mass exchange: MS RG RLO NS spun up

Porb increases He WD + MSP

** Pinitial<P bifurcation: systemic AML drives mass exchange during MS Porb decreases when

MSP appears, the strong MSP radiation evaporates the companion (!) single MSP

1)LMXB phase preceding the MSP stage; 2) mass transfer stops3) the radio MSP emerges

Orbital evolution:

* P initial>P bifurcation: nuclear evolution drives mass exchange: MS RG RLO NS spun up

Porb increases He WD + MSP

** Pinitial<P bifurcation: systemic AML drives mass exchange during MS Porb decreases when

MSP appears, the strong MSP radiation evaporates the companion (!) single MSP

Bifurcation period

Bifurcation period

The evolutionary meaning of the bifurcation is:has the secondaryenough time to grow a helium core? In that case, it will evolve towards large orbits

The bifurcation period from 100 binary sequences

The bifurcation period from 100 binary sequences

Podsiadlowski, Rappaport& Pfhal 2002

Again about the

bifurcation period in GCs

Again about the

bifurcation period in GCs

The known binary periods of LMXBs in GCs, ranging from 17hr to 11min ….

The known binary periods of LMXBs in GCs, ranging from 17hr to 11min ….

seem all in favour of tidal capture which leads naturally to periods 13 –17hr. These values are below or very close to Pbif , so that the systems will evolve towards shorter Porb

seem all in favour of tidal capture which leads naturally to periods 13 –17hr. These values are below or very close to Pbif , so that the systems will evolve towards shorter Porb

In addition, partial hydrogen burning in the core of the secondary, may lead to very short Porb (with the secondary transformed into a degenerate white dwarf having a hydrogen-helium intermediate composition, see Ergma and Fedorova 1998, Podsiadlowski et al. 2002, and the following lesson)

In addition, partial hydrogen burning in the core of the secondary, may lead to very short Porb (with the secondary transformed into a degenerate white dwarf having a hydrogen-helium intermediate composition, see Ergma and Fedorova 1998, Podsiadlowski et al. 2002, and the following lesson)

The “normal” MSP

companions

The “normal” MSP

companions

Most binary MSPs have long orbital periods and

mass function identifying the companions as low mass

helium white dwarfs

Most binary MSPs have long orbital periods and

mass function identifying the companions as low mass

helium white dwarfs

*Porb’s are compatible with the evolution with mass transfer from a subgiant or giant, which finally leaves a helium WD remnant of mass 0.45 >~ M/Msun>~0.2 *if we notice that the radius is determined mainly by the core mass Mc, and put R=R 2,R a relation (Porb,Mc,M2) is obtained* Pfin is then obtained by assuming Mc=M2 (at which stage Mdot stops)

*Porb’s are compatible with the evolution with mass transfer from a subgiant or giant, which finally leaves a helium WD remnant of mass 0.45 >~ M/Msun>~0.2 *if we notice that the radius is determined mainly by the core mass Mc, and put R=R 2,R a relation (Porb,Mc,M2) is obtained* Pfin is then obtained by assuming Mc=M2 (at which stage Mdot stops)

Is the recycling model reasonable?

Is the recycling model reasonable?

As we have seen, the majority of binary MSP have long Porb and He-WD companions, as predicted by evolution at Pinitial>P bifurcation . (Caveat: in Gcs the LMXBs with known Porb are all at short Porb, and GC MSPs have Porb<2.6days -apart from two at hundreds of days- It is possible that in GCs the long period binaries have been broken by further encounters)The answer is YES! The recycling model makes sense

As we have seen, the majority of binary MSP have long Porb and He-WD companions, as predicted by evolution at Pinitial>P bifurcation . (Caveat: in Gcs the LMXBs with known Porb are all at short Porb, and GC MSPs have Porb<2.6days -apart from two at hundreds of days- It is possible that in GCs the long period binaries have been broken by further encounters)The answer is YES! The recycling model makes sense

Proposed solutions:1) Mass transfer very large in LMXBs;

2)Accretion and spin up inhibited by propeller

Proposed solutions:1) Mass transfer very large in LMXBs;

2)Accretion and spin up inhibited by propeller

But: 1)Birthrates of LMXBs << MSPs;

2)why we do not find MSP modulation in many LMXBs?

3)Where are the submilllisecond pulsars?

But: 1)Birthrates of LMXBs << MSPs;

2)why we do not find MSP modulation in many LMXBs?

3)Where are the submilllisecond pulsars?

Open Problems

Open Problems

The problem of the

birthrates

The problem of the

birthrates

Birthrate of LMXBs ~1/10 – 1/100

than birthrate of MSPs

Birthrate of LMXBs ~1/10 – 1/100

than birthrate of MSPs

*this is found both in the disk (Kulkarni and Narayan 1988) and in the GCs (Fruchter and Goss 1990);*observationally exhacerbated by the fact that the radio MSP population is not complete, the LMXBs are all known

*this is found both in the disk (Kulkarni and Narayan 1988) and in the GCs (Fruchter and Goss 1990);*observationally exhacerbated by the fact that the radio MSP population is not complete, the LMXBs are all known

The result depends mainly on taking ~ 109yr as lifetime of the LMXB phase

IRRADIATION by the X ray emission enhances the mass transfer and may be at least part of the solution

IRRADIATION by the X ray emission enhances the mass transfer and may be at least part of the solution

The lack of X-ray MSPs

The lack of X-ray MSPs

There are now only 3 LMXBs (transients) which show X-ray

millisecond modulation

There are now only 3 LMXBs (transients) which show X-ray

millisecond modulation

SAX J1808.4-3658: Ps=2.5ms Porb=2hr (Wijnands & van derl Klis 1998)

XTE J1751-306: Ps=2.3ms Porb=42m (Markwardt et al.2002)

XTE J0929-314 Ps=5.4ms, Porb=43.6m (Galloway et al. 2002)

SAX J1808.4-3658: Ps=2.5ms Porb=2hr (Wijnands & van derl Klis 1998)

XTE J1751-306: Ps=2.3ms Porb=42m (Markwardt et al.2002)

XTE J0929-314 Ps=5.4ms, Porb=43.6m (Galloway et al. 2002)

The “standard” LMXB phase is, after all, NOT the main acceleration phase of the MSP?

Again this may be linked to the evolutionary timescale of LMXBs

Again this may be linked to the evolutionary timescale of LMXBs

The lack of sub-ms pulsars

The lack of sub-ms pulsars

In the standard LMXBs evolution, enough mass may

be accreted to lead to Ps<1ms

In the standard LMXBs evolution, enough mass may

be accreted to lead to Ps<1ms

•Either conservative mass transfer leads often to accretion induced collapse of the NS to Black Hole (for mass MNS<~2Msun for a “soft” EOS, to MNS>~3Msun for the stiffest EOS) (Cook Shapiro Teukolski );•Or –in short Porb systems- the detection of the radio pulsar is hampered by the strong orbital Doppler modulation of the radio signal•Or not enough matter is accreted (see later)

•Either conservative mass transfer leads often to accretion induced collapse of the NS to Black Hole (for mass MNS<~2Msun for a “soft” EOS, to MNS>~3Msun for the stiffest EOS) (Cook Shapiro Teukolski );•Or –in short Porb systems- the detection of the radio pulsar is hampered by the strong orbital Doppler modulation of the radio signal•Or not enough matter is accreted (see later)

The propeller does not

work!

The propeller does not

work!

When Rm>Rcorotation, the matter can not be accreted (Illarionov and Sunayev 1975)

When Rm>Rcorotation, the matter can not be accreted (Illarionov and Sunayev 1975) Consequence:

We need to expel matter far away from

the NS surface!

Consequence:We need to expel

matter far away from the NS surface!

1)But in these systems Rm~RNS, so there is a huge energy requirements to eject matter

2) Even with ad hoc tuning, the maximum efficiency of a propeller is <50%

1)But in these systems Rm~RNS, so there is a huge energy requirements to eject matter

2) Even with ad hoc tuning, the maximum efficiency of a propeller is <50%

The radio-ejection

The radio-ejection

When the radiation pressure of the rotating magnetic dipole becomes large enough, it prevents accretion directly at the inner Lagrangian point!

When the radiation pressure of the rotating magnetic dipole becomes large enough, it prevents accretion directly at the inner Lagrangian point!

Requiremnt:1) Mass transfer must stop (or be very much

reduced) to allow the radio pulsar switch on2) Ps short enough that P psr > P matter

Requiremnt:1) Mass transfer must stop (or be very much

reduced) to allow the radio pulsar switch on2) Ps short enough that P psr > P matter

(Burderi et al. 2001) (Burderi et al. 2001)

The first MSP in an interacting binary: J1740-

5340

The first MSP in an interacting binary: J1740-

5340

and in a globular cluster!

is observed during the radio-ejection phase?(Burderi D’Antona &

Burgay 2002)

is observed during the radio-ejection phase?(Burderi D’Antona &

Burgay 2002)