INAF, Osservatorio Astronomico di Roma

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

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)

The lack of sub-ms pulsars

As we have seen, mass transfer in the progenitors of binary MSP should be able to spin up pulsars to periods well below the minimum observed,

1.56ms

This may mean that sub-ms pulsars are hidden in short Porb systems, or that many NS have collapsed to BH, or, most probably, that not enough matter is accreted. But we must find a mechanism more efficient than the “propeller” to get rid of matter in these low B systems, in which Rm~RNS

The radio-ejection When the radiation

pressure of the rotating magnetic dipole becomes large enough, it prevents accretion directly at the inner Lagrangian point! (Ruderman et al. 1989,

Burderi et al 2001)

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

reduced) to allow the radio pulsar switch on2) Ps short enough that Ppsr > Pmatter

Pulsar pressure:P psr ~Ps

-4r-2

Disc pressure:Pdisc ~ Lacc

(17/20)r-(21/8)

The equilibrium in the disk

Either the magnetic pressure acts, or the radio pulsar pressure, if the disk terminates outside the light cilinder

(dyn/cm2 ) valid for a Shakura-Sunayev accretion disk=viscosity n~1 f~1

radio-ejection Fluctuation of mass transfer: disc pressuregoes down, radio pulsar switches on

Accretion resumes. If matter enters at this point, P_disk>P_psrand accretion goes on

If the Roche lobe is out, P_disk<P_psrand the pulsar prevents accretion

Burderi et al. 2001,ApJL 560, L71

The critical Porb depends on a very high power of the spin

The radio-ejection is much more efficient than the “evaporation” proposed to destroy the binarycompanions: in fact, mass loss is driven by theAML losses and/or nuclear evolution and not by the pulsar energy

Binaries

in NGC 6397

Taylor et al. revealed in the PC field of the HST data possible binary objects, BY Dra and candidate He-WDs. The red dot is the companion of the MSP J1740-5340

The MSP J1740-5340 in NGC6397

Orbital period 32.5 hr Mass function 0.0026442

Spin period 3.65 ms M companion > 0.19 Mo

Period deriv. 16.87e-20 Pulsar power 1.4x1035 erg/s

Radio eclipse T=0.4 Porb R eclipse= a x sin(0.4 )

~4.4 1011cm

Radio freq. 1326 Mhz1454 Mhz

R2(Roche) 1.3 1011cm

Delays of pulses:

up to 0.8ms t_delay~-2 (free free abs.)

Ne~6.4e18cm-3 Mdot~10-10

D’Amico et al. 2001, ApJL 561, L89

The search for the optical

counterpart

Ferraro et al. 2001: search for variability at the MSP orbital period in the HST arrchive data, at the radio location

PSR J1740-5340: the optical component

The radio eclipses last for ~40% of the orbit: matter is flowing around the system, being present at a radius

larger than the secondary’s Roche lobe. The optical light modulation indicates a non spherical companion

1) Intrinsic wind from a MS star? Not expected (Lithium problem)

2) Bloated low mass companion, pulsar evaporated: energy requirements much too large

Burderi, D’Antona and Burgay 2002 ApJ 574, 325

Evolution of the system

The optical counterpartof the MSP J1740-5340 is NOT a He-WD as in most MSP, but it is a quasi-MS mass losing star! How is it possible that we SEE the radio MSP, even if only for 60% of the orbit?

Roche lobe overflow, inhibited by radio-ejection seems to remain the only possible model.

J1740-5340 is in a radio-ejection phase

If we take the system parameters, and we put them in this analytic expression, we find Pcrit=39hr,

While the system period is 32.5hr: in view of the steep dependence of Pcrit, especially on Ps, this coincidence seems compelling. And, it may be that J1740-5340 can be pushed again into accretion

A necessary ingredient: intermittent mass transfer

If the mass transfer is stationary, the radio pulsar can not become active, and the system can not enter in the radio ejection phase:

This is where we need the irradiation mostly

Artist view of

the system

PSR J1740-5340:an interactingcompanion to a MSP

Code ATON 1.1 by Mazzitelli 1989, D’Antona et al. 1989

Metallicity Helium content 0.0002 Y=0.23 Masses (Mo): 1.4 + 0.85 (close to end of core H

burning) Initial orbital period: 14.27 hr t~10GyrColor transformations: from Castelli et al. 19971) Conservative mass transfer: 2) Conservative until P=25hr, then mass loss from

system3) Systemic AML (Magnetic braking –Verbunt &

Zwaan with f_vz=1, 2, 0.3) and Gravitational radiation

4) Role of specific angular momentum losses5) Irradiation (following Tout et al, 1989;

D’Antona and Ergma 1993)6) We followed the NS spin evolution due to the

mass transfer and checked that at P=3.5ms we are in the condition of radio-ejection

Reproducing the optical

companion of PSR J1740-

5340

Open square: 22.5hr

Open triangle: 32.5hr

Blue: f_vz=1Green: f_vz=0.3

The initial orbital period is close to Pbif

We are accumulating evidence that in GCs many systems start their evolution close to thebifurcation period:

1) It is necessary for J1740-5340, to be able to reproduce its HR diagram location at the correct period of 32.5hr

2) It is convenient to explain the short orbital period systems, especially X1820-303 in NGC 6624 which has the shortest period of 11m

3) But this may be common also outside GCs: the two MSP in XTE J1751-306 and XTE J0929-314 have Porb~40m, compatible only with partially H-rich degenerate companions

Self-consiste

nt evolution

to He-WD

Red: f_vz=1Blue: f_vz=0.3Magenta:f_vz=2Black: irradiated

The internal helium profile

From the start ofmass transfer to the WD formationin the conservative case

Mass transfer is faster in the

irradiated case

This frozens the chemical evolution, as we see from thehydrogen profile

The irradiated case

Comparison between

the H- profiles

Consequences:•Much longer evolutionary times for the remnant of irradiated evolution

•In any case, very long H-burning times

AML during the radio-ejection phase

Until the systems transfer mass, it is appropriate to consider a conservative or quasi-conservative evolution. But as soon a s the radio-ejection begins, there is loss of AML associated to the loss of mass. How large is the specific AML? Numerical simulations in this case would help.

Remnant helium white dwarf mass

The final mass depends slightly on the mass loss rate (and then on the specific aml). It is very difficult that we may obtain a mass smaller than 0.2Mo.

This is also true if we consider irradiation.

Are the Taylor et

al. objects

He-WDs?The three most luminous stars: may be

The other objects have much larger radii than the minimum mass possible WD remnant of binary evolution

What is this

sequence of objects

at constant R~0.04 Rsun?

Are the He-wd

candidatequiescent CVs?

Townsley and Bildsten 2002 suggest that we are in the presence of accreting WDs in which Tc(core) is determined by compressional heating due to accretion

Mass transfer and AML

Conservativeevolution can bea good assumption only until the mass is accreted. In theradio-ejection phase the mass loss rate depends on the loss of angular momentum

Evolution of

orbital period

While conservative evolution or evolution with small specific aml leads to long orbital periods, during the radio-ejection phasethe period may increase only slightly, or even decreaseOrbital period (hr)

Log

Mdo

t