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

Ignacio Negueruela Universidad de Alicante

GranadaMay 2008

José Miguel TorrejónUniversidad de Alicante & M.I.T.

Silvia Martínez-Núñez Universidad de Alicante

Pablo Reig University of Crete

David M. Smith UCSC

Pere Blay Universidad de Valencia

Marc Ribó Universitat de Barcelona

GranadaMay 2008

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Accretion from the wind of a supergiantAccretion from the wind of a supergiant

Roche-lobe overflow

Roche-lobe overflow

High Mass X-ray binaries

Be/X-ray binariesBe/X-ray binaries

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 )

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 from LX < 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)

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Log (orbital period in days)

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Wind accretorsWind accretors

High Mass X-ray binaries

Supergiant X-ray binaries

Object Pulse Counterpart PeriodTypical LX

(erg s-1)

2S 0114+65 10000 s B1 Iab 11.6 d ~ 1036

Vela X-1 283 s B0.5 Iab 8.9 d ~ 1036

1E 1145.1-6141

297s B2 Iae 14.4 d ~ 1036

GX 301-02 698 s B1 Ia+ 41.5 d ~ 1037

4U 1538-52 529 s B0 I 3.7 d ~ 1036

OAO 1657-415 38 s B I 10.4 d ~ 1036

4U 1700-37 NO O6.5 Iaf+ 3.4 d ~ 1036

4U 1907+09 440 s O8 I 8.4 d ~ 1036

Cyg X-1 BH O9.7 Iab 5.6 d ~ 1037

Vela X-1: Short term flaring Long term variability by a

factor of 4

Supergiant X-ray binaries

Flare from 4U 1907+09Fritz et al. 2006 (A&A 458, 885)

Ribó et al. 2006 (A&A, 449, 687)

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.

A working definition of SFXTs

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)

INTEGRAL long-term lightcurve of XTE J1739-302

From Blay et al. (2008, A&A, soon)See poster by S. Martínez-Núñez

Activity from XTE J1739-302 during GC monitoring

September 2006

March 2007

August 2007

From Blay et al. (2008, A&A, soon)

Activity from XTE J1739-302 during GC monitoring

September 2006

March 2007

Detection limit

LX > 1034 erg s-1

See poster by S. Martínez-Núñez

IGR J17544-2619

250 ksec Suzaku exposure on IGR J17544-2619 (PI Smith)

Quiescence 1x1033 ergs-1Quiescence 1x1033 ergs-1

Outburst 1.2x1036 ergs-1Outburst 1.2x1036 ergs-1

Wind accretors as seen by INTEGRAL

Persistent SGXBsIrregularly flaring SFXTs (defined as variability factor >100 by Walter & Zurita Heras (2007, A&A 476, 335)XTE J1739-302, IGR 08408-4503SAX J1818.6-1703IGR J16479-4514Intermediate systems (smaller variability)

AX 1845.0-0433XTE J1743-363Regular outbursters IGR J00370+6122, IGR J11215-5952

Parameters of SFXTs

Optical counterpart to AX 1845.0-0433 (VLT+FORS1)

IGR J16465-4507 B0.5 Ib

Radiative winds as accretion fodder

Heavy ions have large Thompson cross sections

The law 0.8 – 1.2

r

Rvrv *

w 1)(

*w

*w

3at 7.0)(

2at 5.0)(

Rrvrv

Rrvrv

Review: Kudritzki & Puls 2000, ARA&A, 38, 613

)(

)()(4 4

rel

w2X rv

rrvGMM

X

XX R

MGML

2rel

Xacc

2~

v

GMr

Where are the low luminosity SGXBs?

1s km1000 v 1s km2000

v

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)()(4 4

rel

w2X rv

rrvGMM

The source of the instability

Images stolen from Stan Owocki

Development of instability

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Height (R* )

Velocity

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smooth wind

Images stolen from Stan Owocki

Owocki & Rybicki 1984, ApJ, 284, 337cf. Feldmeier et al. 1997, A&A, 322, 878

Wind clumping Clumping factor Size and geometry of clumps Shells or blobs Optically thin?

1D simulations Runacres & Owocki 2002, A&A, 381, 10152D simulations Dessart & Owocki 2003, A&A, 406, L1Porous 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

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

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 observationsTaking L0 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

2rel

Xacc

2~

v

GMr

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??

Supergiant fast X-ray transients

The neutron star is in a region where

*5.2 Ra

*4Rafor relatively frequent outbursts.

Such systems may eventually evolve into SGXBs.

But we still probably require

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

Regular outbursterNeutron stars in systems with wide eccentric orbits spend most of the time in regions where they cannot accrete.

Porb=15.7 d, BN0.5 II-III Porb=165 d, B0.7 Ia

IGR J00370+6122

IGR J11215-5952

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

IGR J11215-5952

ESO 2.2m + FEROS Dec 2006 to

Feb 2007

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. 2008 arXiv:0805.1849)

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).

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.