Wind accretion in supergiant X-ray binaries A coherent picture within the porous wind framework

1. Wind accretion in supergiant X-ray binariesA coherent picture within the porous wind framework Ignacio Negueruela Universidad de Alicante Granada May 2008

2. David M. Smith UCSC Silvia Martínez-Núñez Universidad de Alicante Pere Blay Universidad de Valencia Marc Ribó Universitat de Barcelona José Miguel Torrejón Universidad de Alicante & M.I.T. Pablo Reig University of Crete Granada May 2008

3. High Mass X-ray binaries Be/X-ray binaries Accretion from the wind of a supergiant Roche-lobe overflow

4. New “classes” of HMXBs found by INTEGRAL • IGR J16318-4848 and a few other very absorbed sources. • Most sources likely to be similar to old classes but more obscured. • A group of flaring sources with very short outbursts and supergiant companions (Smith et al. 2006, ApJ 638, 974; Negueruela et al. 2006, ESA-SP 604 (1), 165 )

5. Supergiant Fast X-ray Transients • Very short (only a few hours) outbursts with complex structure (Sguera et al. 2005, A&A 444, 221; 2006, ApJ 646, 452) • X-ray spectra are hard and look typical of neutron stars in HMXBs (González-Riestra et al. 2004, A&A 420, 589; Smith et al. 2006) • Several examples of sudden rises fromLX < 1033 erg s-1 to LX 1036 erg s-1 in minutes (in’t Zand 2005, A&A 441, L1; Bamba et al. 2001, PASJ 52, 1179; Sakano et al. 2002, ApJS 138, 19) Lightcurve from XTE J1739-302 during an outburst observed by INTEGRAL on 2003 March 22nd (Sguera et al. 2005)

6. High Mass X-ray binaries Wind accretors

7. Supergiant X-ray binaries

8. Supergiant X-ray binaries Vela X-1: • Short term flaring • Long term variability by a factor of 4 Ribó et al. 2006 (A&A, 449, 687) Flare from 4U 1907+09Fritz et al. 2006 (A&A 458, 885)

9. A working definition of SFXTs Walter & Zurita Heras (2007, A&A 476, 335)attempt to define SFXTs with quantitative criteria: • Count rate contrast > 100 in INTEGRAL passbands • Outbursts last for hours. Typical (average) duration is 3ks for the strong flares and 4h for the whole outburst. What do they do when not detected by INTEGRAL? Sidoli et al. (2008,arXiv:0805.1808) carry out monitoring with Swift. • Occasionally, they are at LX < 1033 erg s-1 • Most of the time, they seem to emit at LX 1034 erg s-1(perhaps depending on source)

10. INTEGRAL long-term lightcurve ofXTE J1739-302 See poster by S. Martínez-Núñez From Blay et al. (2008, A&A, soon)

11. Activity fromXTE J1739-302 during GC monitoring September 2006 March 2007 From Blay et al. (2008, A&A, soon) August 2007

12. Activity fromXTE J1739-302 during GC monitoring September 2006 March 2007 Detection limit LX > 1034 erg s-1 See poster by S. Martínez-Núñez

13. IGR J17544-2619 Outburst 1.2x1036 ergs-1 Quiescence 1x1033 ergs-1 250 ksec Suzaku exposure on IGR J17544-2619 (PI Smith)

14. Wind accretors as seen by INTEGRAL • Persistent SGXBs • Irregularly flaring SFXTs (defined as variability factor >100 by Walter & Zurita Heras (2007, A&A 476, 335) XTE J1739-302, IGR 08408-4503 SAX J1818.6-1703 IGR J16479-4514 • Intermediate systems (smaller variability) AX 1845.0-0433 XTE J1743-363 • Regular outbursters IGR J00370+6122, IGR J11215-5952

15. Parameters of SFXTs IGR J16465-4507 B0.5Ib Optical counterpart to AX 1845.0-0433 (VLT+FORS1)

16. Radiative winds as accretion fodder Heavy ions have large Thompson cross sections Review: Kudritzki & Puls 2000, ARA&A, 38, 613 The  law   0.8 – 1.2

17. Where are the low luminosity SGXBs?

18. The source of the instability Images stolen from Stan Owocki

19. Velocity Density Development of instability smooth wind Owocki & Rybicki 1984, ApJ, 284, 337 cf. Feldmeier et al. 1997, A&A, 322, 878 Images stolen from Stan Owocki

20. Wind clumping • Clumping factor • Size and geometry of clumps • Shells or blobs • Optically thin? 1D simulations Runacres & Owocki 2002, A&A, 381, 1015 2D simulations Dessart & Owocki 2003, A&A, 406, L1 Porous winds Owocki et al. 2004, ApJ, 616, 525 Oskinova et al. 2006, MNRAS, 372, 313 Constraints from spectra Prinja et al. 2005, A&A 430, L41 Bouret et al. 2005, A&A, 438, 301 Puls et al. 2006, A&A, 454, 625

21. Wind clumping • If winds are clumped, • Is the smooth wind approximation completely invalid? • Why does it sort of work for SGXBs?

23. Porous winds • We have used the “porous wind” model by Oskinova et al. (2007, A&A 476, 1331) • Results do not depend strongly on model used • Clumpiness parameterised by a single factor L0, which must take values L0 0.2 - 0.5 to fit optical and UV observations Taking L0 0.2 , we have a few 103 clumps out to 10R*.

24. The porous wind as “seen” by the neutron star Number of clumps that will be inside the accretion radius of the neutron star in one orbit

25. Classical supergiant systems • The neutron star is always inside the region where it sees most of the wind • Circularised orbits help it not to get outside • Note that SGXBs with an O-type supergiant do not evolve into SGXBs with B1-2 companions. They go TZO??

26. Supergiant fast X-ray transients The neutron star is in a region where But we still probably require for relatively frequent outbursts. Such systems may eventually evolve into SGXBs.

27. Eccentric SFXT Eccentricity results in systems that may show (quasi-)periodic changes in their behaviour

28. Regular outburster Neutron stars in systems with wide eccentric orbits spend most of the time in regions where they cannot accrete. Porb=15.7 d, BN0.5II-III Porb=165 d, B0.7Ia IGR J00370+6122 IGR J11215-5952

29. Alternatives: the disk “model” Proposed by Sidoli et al. (2007, A&A 476, 1307) based on properties of IGR J11215-5952 • Based on an object which is not an SFXT • Has no physical motivation • Requires huge disks around OB supergiants that should have observational signatures • Requires SFXT outbursts to happen at regular outbursts against observations • Is incompatible with observed lightcurves

30. IGR J11215-5952 • ESO 2.2m + FEROS • Dec 2006 to Feb 2007

31. Alternatives: centrifugal inhibition First proposed by Grebenev and Sunyaev (2007, AstL 33, 149) requires the neutron stars to be spinning close to their equilibrium period. • There is no reason to expect normal neutron stars with B1012 G to be rotating at their equilibrium period. • May make sense if B can have a wide range of values • In this case, SFXTs should host magnetars (Bozzo et al. 2008arXiv:0805.1849)

32. Wind accretors: a coherent picture • Warning: wind clumping is a working hypothesis. Physical parameters of clumps are unconstrained. • However, the scenario presented is independent of clumping details. • Values favoured are compatible with those derived from optical and UV observations of wind lines (e.g., Oskinova et al. 2007). • Calculations in good agreement with independent estimates by Walter & Zurita-Heras (2007).

33. Wind accretors: a coherent picture • The scenario presented provides a coherent framework where all wind accretors fit. Peculiarities can be explained as due to particularities within the framework. • It provides an explanation for both the outbursts and the quiescence of SFXTs. • In addition, it explains at once some puzzling properties of SGXBs. • However, it does not exclude that other mechanisms are also at work.