INAF, Osservatorio Astronomico di Roma

1. Radio-ejection in an interacting binary MSP in a Globular Cluster F. D'Antona INAF, Osservatorio Astronomico di Roma XI Advanced School of Astrophysics, Brazil, 1-6 September 2002

2. 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)

3. 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 The lack of sub-ms pulsars 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

4. 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) The radio-ejection Pulsar pressure: Ppsr~Ps-4r-2 Disc pressure: Pdisc ~ Lacc(17/20)r-(21/8) • Requirement: • Mass transfer must stop (or be very much reduced) to allow the radio pulsar switch on • 2) Ps short enough that Ppsr > Pmatter

5. (dyn/cm2 ) valid for a Shakura-Sunayev accretion disk a =viscosity n~1 f~1 The equilibrium in the disk Either the magnetic pressure acts, or the radio pulsar pressure, if the disk terminates outside the light cilinder

6. Fluctuation of mass transfer: disc pressure goes down, radio pulsar switches on radio-ejection Accretion resumes. If matter enters at this point, P_disk>P_psr and accretion goes on If the Roche lobe is out, P_disk<P_psr and the pulsar prevents accretion Burderi et al. 2001, ApJL 560, L71

7. 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 binary companions: in fact, mass loss is driven by the AML losses and/or nuclear evolution and not by the pulsar energy

8. Binariesin 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

9. The MSP J1740-5340 in NGC6397

10. D’Amico et al. 2001, ApJL 561, L89

11. 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

12. Burderi, D’Antona and Burgay 2002 ApJ 574, 325 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 • Intrinsic wind from a MS star? Not expected (Lithium problem) • Bloated low mass companion, pulsar evaporated: energy requirements much too large

13. Evolution of the system The optical counterpart of 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?

14. J1740-5340 is in a radio-ejection phase Roche lobe overflow, inhibited by radio-ejection seems to remain the only possible model. 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

15. 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

16. Artist view of the system PSR J1740 -5340: an interacting companion to a MSP

17. Code ATON 1.1 by Mazzitelli 1989, D’Antona et al. 1989 • MetallicityHelium 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~10Gyr • Color transformations: from Castelli et al. 1997 • Conservative mass transfer: • Conservative until P=25hr, then mass loss from system • Systemic AML (Magnetic braking –Verbunt & Zwaan with f_vz=1, 2, 0.3) and Gravitational radiation • Role of specific angular momentum losses • Irradiation (following Tout et al, 1989; D’Antona and Ergma 1993) • 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

18. Reproducing the optical companion of PSR J1740-5340 Open square: 22.5hr Open triangle: 32.5hr Blue: f_vz=1 Green: f_vz=0.3

19. 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

20. Self-consistent evolution to He-WD Red: f_vz=1 Blue: f_vz=0.3 Magenta:f_vz=2 Black: irradiated

21. The internal helium profile From the start of mass transfer to the WD formation in the conservative case

22. Mass transfer is faster in the irradiated case This frozens the chemical evolution, as we see from the hydrogen profile

23. The irradiated case

24. Comparison between the H- profiles • Consequences: • Much longer evolutionary times for the remnant of irradiated evolution • In any case, very long H-burning times

25. 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.

26. 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.

27. 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

28. What is this sequence of objects at constant R~0.04 Rsun?

29. 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

30. Mass transfer and AML Conservative evolution can be a good assumption only until the mass is accreted. In the radio-ejection phase the mass loss rate depends on the loss of angular momentum

31. Evolution of orbital period While conservative evolution or evolution with small specific aml leads to long orbital periods, during the radio-ejection phase the period may increase only slightly, or even decrease Log Mdot Orbital period (hr)