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

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

• Ignacio Negueruela
• Universidad de Alicante

Granada May 2008
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• José Miguel Torrejón
• Universidad de Alicante M.I.T.

Silvia Martínez-Núñez Universidad de Alicante
David M. Smith UCSC
Pere Blay Universidad de Valencia
Marc Ribó Universitat de Barcelona
Pablo Reig University of Crete
Granada May 2008
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High Mass X-ray binaries
Be/X-ray binaries
Accretion from the wind of a supergiant
Roche-lobe overflow
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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 )

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Supergiant Fast X-ray Transients

• Very short (only a few hours) outbursts with
  complex structure (Sguera et al. 2005, AA 444,
  221 2006, ApJ 646, 452)
• X-ray spectra are hard and look typical of
  neutron stars in HMXBs (González-Riestra et al.
  2004, AA 420, 589 Smith et al. 2006)
• Several examples of sudden rises from LX lt 1033
  erg s-1 to LX?? 1036 erg s-1 in minutes (int
  Zand 2005, AA 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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High Mass X-ray binaries
Wind accretors
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Supergiant X-ray binaries
Object Pulse Counterpart Period Typical LX (erg s-1)
2S 011465 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 190709 440 s O8 I 8.4 d 1036
Cyg X-1 BH O9.7 Iab 5.6 d 1037
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Supergiant X-ray binaries

• Vela X-1
• Short term flaring
• Long term variability by a factor of 4

Ribó et al. 2006 (AA, 449, 687)
Flare from 4U 190709Fritz et al. 2006 (AA 458,
885)
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A working definition of SFXTs

• Walter Zurita Heras (2007, AA 476, 335)
  attempt to define SFXTs with quantitative
  criteria
• Count rate contrast gt 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, arXiv0805.1808) carry out
  monitoring with Swift.
• Occasionally, they are at LX lt 1033 erg s-1
• Most of the time, they seem to emit at LX ? 1034
  erg s-1 (perhaps depending on source)

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INTEGRAL long-term lightcurve of XTE J1739-302
See poster by S. Martínez-Núñez
From Blay et al. (2008, AA, soon)
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Activity from XTE J1739-302 during GC monitoring
September 2006
March 2007
From Blay et al. (2008, AA, soon)
August 2007
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Activity from XTE J1739-302 during GC monitoring
September 2006
March 2007
Detection limit LX gt 1034 erg s-1
See poster by S. Martínez-Núñez
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IGR J17544-2619
Outburst 1.2x1036 ergs-1
Quiescence 1x1033 ergs-1
250 ksec Suzaku exposure on IGR J17544-2619 (PI
Smith)
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Wind accretors as seen by INTEGRAL

• Persistent SGXBs
• Irregularly flaring SFXTs (defined as variability
  factor gt100 by Walter Zurita Heras (2007, AA
  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 J003706122, IGR J11215-5952

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Parameters of SFXTs
IGR J16465-4507 B0.5 Ib
Optical counterpart to AX 1845.0-0433 (VLTFORS1)
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Radiative winds as accretion fodder
Heavy ions have large Thompson cross sections
Review Kudritzki Puls 2000, ARAA, 38, 613
The ? law ? ? 0.8 1.2
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Where are the low luminosity SGXBs?
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The source of the instability
Images stolen from Stan Owocki
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Development of instability
smooth wind
Owocki Rybicki 1984, ApJ, 284, 337 cf.
Feldmeier et al. 1997, AA, 322, 878
Images stolen from Stan Owocki
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Wind clumping

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

1D simulations Runacres Owocki 2002, AA, 381,
1015 2D simulations Dessart Owocki 2003, AA,
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,
AA 430, L41 Bouret et al. 2005, AA, 438,
301 Puls et al. 2006, AA, 454, 625
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Wind clumping

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

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(No Transcript)
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Porous winds

• We have used the porous wind model by Oskinova
  et al. (2007, AA 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
  10 R.

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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
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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??

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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.
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Eccentric SFXT
Eccentricity results in systems that may show
(quasi-)periodic changes in their behaviour
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Regular outburster
Neutron stars in systems with wide eccentric
orbits spend most of the time in regions where
they cannot accrete.
Porb15.7 d, BN0.5 II-III Porb165 d, B0.7 Ia
IGR J003706122
IGR J11215-5952
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Alternatives the disk model

• Proposed by Sidoli et al. (2007, AA 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

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IGR J11215-5952

• ESO 2.2m FEROS
• Dec 2006 to Feb 2007

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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 arXiv0805.1849)

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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).

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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.