Wind accretion in supergiant Xray binaries A coherent

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

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

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

New “classes” of HMXBs found by INTEGRAL n n n IGR J 16318 -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, Ap. J 638, 974; Negueruela et al. 2006, ESA-SP 604 (1), 165 )

Supergiant Fast X-ray Transients n n n Very short (only a few hours) outbursts with complex structure (Sguera et al. 2005, A&A 444, 221; 2006, Ap. J 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 from LX < 1033 erg s-1 to LX 1036 erg s-1 in minutes (in’t Zand 2005, A&A 441, L 1; Bamba et al. 2001, PASJ 52, 1179; Sakano et al. 2002, Ap. JS 138, 19) Lightcurve from XTE J 1739 -302 during an outburst observed by INTEGRAL on 2003 March 22 nd (Sguera et al. 2005)

High Mass X-ray binaries Wind accretors

Supergiant X-ray binaries Object Pulse Counterpart Period Typical LX (erg s-1) 2 S 0114+65 10000 s B 1 Iab 11. 6 d ~ 1036 Vela X-1 283 s B 0. 5 Iab 8. 9 d ~ 1036 1 E 1145. 1 -6141 297 s B 2 Iae 14. 4 d ~ 1036 GX 301 -02 698 s B 1 Ia+ 41. 5 d ~ 1037 4 U 1538 -52 529 s B 0 I 3. 7 d ~ 1036 OAO 1657 -415 38 s BI 10. 4 d ~ 1036 4 U 1700 -37 NO O 6. 5 Iaf+ 3. 4 d ~ 1036 4 U 1907+09 440 s O 8 I 8. 4 d ~ 1036 Cyg X-1 BH O 9. 7 Iab 5. 6 d ~ 1037

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

A working definition of SFXTs Walter & Zurita Heras (2007, A&A 476, 335) attempt to define SFXTs with quantitative criteria: n Count rate contrast > 100 in INTEGRAL passbands n Outbursts last for hours. Typical (average) duration is 3 ks for the strong flares and 4 h for the whole outburst. What do they do when not detected by INTEGRAL? Sidoli et al. (2008, ar. Xiv: 0805. 1808) carry out monitoring with Swift. n Occasionally, they are at LX < 1033 erg s-1 n Most of the time, they seem to emit at LX 1034 erg s-1 (perhaps depending on source)

INTEGRAL long-term lightcurve of XTE J 1739 -302 From Blay et al. (2008, A&A, soon) See poster by S. Martínez-Núñez

Activity from XTE J 1739 -302 during GC monitoring September 2006 March 2007 From Blay et al. (2008, A&A, soon) August 2007

Activity from XTE J 1739 -302 during GC monitoring September 2006 March 2007 Detection limit LX > 1034 erg s-1 See poster by S. Martínez-Núñez

IGR J 17544 -2619 Outburst 1. 2 x 1036 ergs-1 Quiescence 1 x 1033 ergs-1 250 ksec Suzaku exposure on IGR J 17544 -2619 (PI Smith)

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 J 1739 -302, IGR 08408 -4503 SAX J 1818. 6 -1703 IGR J 16479 -4514 Intermediate systems (smaller variability) AX 1845. 0 -0433 XTE J 1743 -363 Regular outbursters IGR J 00370+6122, IGR J 11215 -5952

Parameters of SFXTs IGR J 16465 -4507 B 0. 5 Ib Optical counterpart to AX 1845. 0 -0433 (VLT+FORS 1)

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

Where are the low luminosity SGXBs?

The source of the instability Images stolen from Stan Owocki

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

Wind clumping Clumping factor Size and geometry of clumps Shells or blobs Optically thin? 1 D simulations Runacres & Owocki 2002, A&A, 381, 1015 2 D simulations Dessart & Owocki 2003, A&A, 406, L 1 Porous winds Owocki et al. 2004, Ap. J, 616, 525 Oskinova et al. 2006, MNRAS, 372, 313 Constraints from spectra Prinja et al. 2005, A&A 430, L 41 Bouret et al. 2005, A&A, 438, 301 Puls et al. 2006, A&A, 454, 625

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

Porous winds n We have used the “porous wind” model by Oskinova et al. (2007, A&A 476, 1331) n n Results do not depend strongly on model used Clumpiness parameterised by a single factor L 0, which must take values L 0 0. 2 0. 5 to fit optical and UV observations Taking L 0 0. 2 , we have a few 103 clumps out to 10 R*.

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

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 B 1 -2 companions. They go TZO? ?

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.

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

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, BN 0. 5 II-III IGR J 00370+6122 Porb=165 d, B 0. 7 Ia IGR J 11215 -5952

Alternatives: the disk “model” Proposed by Sidoli et al. (2007, A&A 476, 1307) based on properties of IGR J 11215 -5952 n Based on an object which is not an SFXT n Has no physical motivation n Requires huge disks around OB supergiants that should have observational signatures n Requires SFXT outbursts to happen at regular outbursts against observations n Is incompatible with observed lightcurves

IGR J 11215 -5952 n n ESO 2. 2 m + FEROS Dec 2006 to Feb 2007

Alternatives: centrifugal inhibition First proposed by Grebenev and Sunyaev (2007, Ast. L 33, 149) requires the neutron stars to be spinning close to their equilibrium period. n There is no reason to expect normal neutron stars with B 1012 G to be rotating at their equilibrium period. n May make sense if B can have a wide range of values n In this case, SFXTs should host magnetars (Bozzo et al. 2008 ar. Xiv: 0805. 1849)

Wind accretors: a coherent picture n n 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).

Wind accretors: a coherent picture n n 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.