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Sylvain CHATY (Université Paris 7 / Service d’Astrophysique, France) ESO - 28 novembre 2006

The most obscured high energy sources. Or how infrared observations allow to reveal mysteries of the most obscured X-ray sources of our Galaxy…. Sylvain CHATY (Université Paris 7 / Service d’Astrophysique, France) ESO - 28 novembre 2006. Plan. The INTEGRAL observatory

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Sylvain CHATY (Université Paris 7 / Service d’Astrophysique, France) ESO - 28 novembre 2006

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  1. The most obscured high energy sources Or how infrared observations allow to reveal mysteries of the most obscured X-ray sources of our Galaxy… Sylvain CHATY (Université Paris 7 / Service d’Astrophysique, France) ESO - 28 novembre 2006

  2. Plan • The INTEGRAL observatory • Discovery of new sources in our Galaxy • How to understand their nature? • Multi-wavelength optical/NIR/MIR observations: • Obscured X-ray sources: the archetype IGR J16318-4848 • Supergiant Fast X-ray Transients: the archetype IGR J17544-2619 • Results and discussion on new INTEGRAL sources • Conclusions and perspectives S. Chaty - ESO - 28/11/2006

  3. Plan • The INTEGRAL observatory • Discovery of new sources in our Galaxy • How to understand their nature? • Multi-wavelength optical/NIR/MIR observations: • Obscured X-ray sources: the archetype IGR J16318-4848 • Supergiant Fast X-ray Transients: the archetype IGR J17544-2619 • Results and discussion on new INTEGRAL sources • Conclusions and perspectives S. Chaty - ESO - 28/11/2006

  4. The INTEGRAL observatory INTEGRAL satellite: 2 keV – few MeV Launched on 17 October 2002 by PROTON rocket on excentric orbit S. Chaty - ESO - 28/11/2006

  5. INTEGRAL observatory • 4 instruments • 2 coded mask telescopes: imager IBIS and spectro-imager SPI: 10keV-4MeV • Resolution 12’, fov 19° • 1 coded mask X telescope JEM-X: 2-100keV • 1 optical telescope: OMC S. Chaty - ESO - 28/11/2006

  6. Multi-wavelength observations • Ground and space… • Multi-wavelength observations (radio, infrared and X/grays S. Chaty - ESO - 28/11/2006

  7. Plan • The INTEGRAL observatory • Discovery of new sources in our Galaxy • How to understand their nature? • Multi-wavelength optical/NIR/MIR observations: • Obscured X-ray sources: the archetype IGR J16318-4848 • Supergiant Fast X-ray Transients: the archetype IGR J17544-2619 • Results and discussion on new INTEGRAL sources • Conclusions and perspectives S. Chaty - ESO - 28/11/2006

  8. The Milky Way, our Galaxy (seen from inside) S. Chaty - ESO - 28/11/2006

  9. The Milky Way, our Galaxy (seen from outside) Side view Face-on S. Chaty - ESO - 28/11/2006

  10. The Milky Way, our Galaxy S. Chaty - ESO - 28/11/2006

  11. Discovery of a new type of sources in the sky Observations of the Milky Way: • Mystery of the X-ray background • IBIS resolved it in many point sources • (>200: Bird et al. 2006) • Still present at higher energies New sources towards the Norma arm of the Galaxy, previously unknown… And this Norma arm is full of star formation regions! Zoom on the center G-rays (INTEGRAL/ISGRI) IR (COBE) S. Chaty - ESO - 28/11/2006 Lebrun et al. 2004 Tomsick et al. 2004

  12. Plan • The INTEGRAL observatory • Discovery of new sources in our Galaxy • How to understand their nature? • Multi-wavelength optical/NIR/MIR observations: • Obscured X-ray sources: the archetype IGR J16318-4848 • Supergiant Fast X-ray Transients: the archetype IGR J17544-2619 • Results and discussion on new INTEGRAL sources • Conclusions and perspectives S. Chaty - ESO - 28/11/2006

  13. Unidentified INTEGRAL sources • Among IGR sources: • ~1/10: already known faint ASCA sources (Sugizaki) • A few already known RXTE sources • ~1/10: certainly AGNs (Bassani et al.) • 25% of INTEGRAL sources have a likely ROSAT counterpart • 50% of the sources detected by par INTEGRAL! (Stephen et al) S. Chaty - ESO - 28/11/2006

  14. X-RAY BINARIES X-ray binary: binary system containing a compact object (neutron star or stellar-mass black hole) accreting matter from the companion star. Accreted matter carries angular momentum and on its way to the compact object usually forms an accretion disk, responsible for the X-ray emission. 280 X-ray binaries are known (Liu et al. 2000, 2001). High Mass X-ray Binaries (HMXBs). Optical companion with spectral type O or B. Mass transfer via decretion disk (Be stars) or via strong wind or Roche-lobe overflow (OB SG). 131 known HMXBs. Low Mass X-ray Binaries (LMXBs). Optical companion with spectral type later than B. Mass transfer via Roche-lobe overflow. 149 known LMXBs. S. Chaty - ESO - 28/11/2006

  15. Galactic distribution 131 • A fair fraction of new INTEGRAL sources should be High Mass X-ray Binaries (HMXBs) • Over-density of INTEGRAL sources in the region tangent to the Norma arm (5–8kpc) 149 New : -0.9 HMXB : -0.6 HMXB+new: -0.6 HMXB (XTE): -0.6±0.1 Walter et al. 2006 S. Chaty - ESO - 28/11/2006

  16. Discovery of a new type of sources • How to identify all these new INTEGRAL sources? • To observe in X/g rays is not enough: • ISGRI localisation not enough to identify the counterpart • To observe in optical is difficult: • Sources mainly in the plane (centre) of the Galaxy: too much absorption (interstellar dust and gas) => Observe in INFRARED S. Chaty - ESO - 28/11/2006

  17. ESO observations • Programme of study of new high energy binary sources • Identification of counterparts, nature of system, compact object, companion star, distance, accretion type… • characterize presence, temperature, composition of dust • Photometry/Spectroscopy on 15 INTEGRAL sources • 3 domains: • Optical EMMI (400-800 nm): La Silla (3.5m-NTT) • Near-infrared SOFI (1-2.5 mm): La Silla (3.5m-NTT) • Mid-Infrared VISIR (5-20mm): Paranal (8m-VLT/UT3) • 2 modes of observations (European Southern Observatory): • « Target of Opportunity mode»: ~16h/semester to observe new binary systems • « Visitor mode »: 3 nights 07/2004, 1 night 06/2005, 2 nights 06/2006 S. Chaty - ESO - 28/11/2006

  18. Plan • The INTEGRAL observatory • Discovery of new sources in our Galaxy • How to understand their nature? • Multi-wavelength optical/NIR/MIR observations: • Obscured X-ray sources: the archetype IGR J16318-4848 • Supergiant Fast X-ray Transients: the archetype IGR J17544-2619 • Results and discussion on new INTEGRAL sources • Conclusions and perspectives S. Chaty - ESO - 28/11/2006

  19. Plan • The INTEGRAL observatory • Discovery of new sources in our Galaxy • How to understand their nature? • Multi-wavelength optical/NIR/MIR observations: • Obscured X-ray sources: the archetype IGR J16318-4848 • Supergiant Fast X-ray Transients: the archetype IGR J17544-2619 • Results and discussion on new INTEGRAL sources • Conclusions and perspectives S. Chaty - ESO - 28/11/2006

  20. The Obscured INTEGRAL source IGR J16318-4848: • From INTEGRAL high energy … • …to Optical/MIR observations. • (Chaty & Rahoui, 2006; Chaty & Filliatre, Ap&SS, 2005; Filliatre & Chaty, ApJ, 2004) S. Chaty - ESO - 28/11/2006

  21. Discovery of IGR J16318-4848 by INTEGRAL • 1st source discovered by INTEGRAL (IBIS/ISGRI) on 29 January 2003 • Position: • (l,b)~(336°, 0.5°) • RA=16h31.8m, DEC=-48°48’ • Localisation accuracy: 2’ with INTEGRAL (Moon: 30’!) • Non-absorbed Flux: • 15-40 keV Flux: 50-100 mCrab (Courvoisier et al. 2003) • L5kpc = 1-20 1036 erg/s INTEGRAL/ISGRI (15-40 keV) Norma arm region image (Walter et al. 2003) S. Chaty - ESO - 28/11/2006

  22. ToO observations with XMM-Newton • XMM observations (28ks ToO on 10/02/2003): 4”localisation • Comptonised spectrum: • Nh=1.84+/-0.06x1024 cm-2 • kT = 9±0.5 keV • Photon index ~ 2 • Strong photoelectric absorption: • Fe absorption edge at 7.1keV • Fe K, K, Ni K Fluorescence lines • Variability: • RXTE: no oscillation detected • variable flux (factor 20) • 10 hours between each flare • Sometimes 2-3 days of inactivity • Nh-flux correlation? • Variations of lines and continuum on temporal scale of 1000s: size of emitting region < 3 x 1013 cm (Walter et al. 2003) • X-ray properties ~ CI Cam, Vela X1, GX 301-2 EPIC PN, EPIC MOS2 and ISGRI spectra (Matt & Guainazzi 2003; Walter et al. 2003) S. Chaty - ESO - 28/11/2006

  23. Discovery of the optical/NIR counterpart • photometric observations on 23-25/02/2003 • Discovery of the R, I, Z counterpart • Comparison with USNO B1.0 plate R band: only one of the two sources varied in the XMM EPIC 4” uncertainty circle. • Confirmation of NIR counterpart proposed by Walter et al. 2003 by an improved astrometry B>25.4+/-1; V>21.1+/-0.1 R=17.72+/-0.12; I=16.05+/-0.54 J=10.33+/-0.14; H=8.33+/-0.10 Ks=7.20+/-0.05 IGR J16318-4848 Target of Opportunity S. Chaty - ESO - 28/11/2006

  24. Absorption in optical/NIR • B, V, R, I, J, H, K magnitudes of candidate and 4 neighbours • IGR source exhibits unusual 17.4magabsorption • stronger than absorption along line of sight objects (11.4mag), • but 100 x lower than X-rays!!! • Material absorbing in X-rays must be concentrated near the compact object S. Chaty - ESO - 28/11/2006

  25. NIR spectroscopy: 0.95-2.5 mm Unusual spectrum very rich in many strong emission lines • Strong H (Br, Pa, Pf) and HeI (P-Cyg): emanate from dense, ionised wind • He II: highly excited region in vicinity of compact object • [FeII]: indication of shock heated material • FeII => densities > 105-106 cm-3 • NaI: cool/dense regions shielded from stellar and compact object radiation • Lines originate from different media (various densities, temperature) • Highly complex, stratified circumstellar environment + enveloppe, wind… • => luminous post main sequence star: most likely an uncl/sgB[e] star: High-mass X-ray binary system,similar to CI Cam S. Chaty - ESO - 28/11/2006

  26. Spectral Energy Distribution • Fit parameters: L ~ 106 d26kpcLSun T = 20 250 K M = 30 MSun High L, T and M: • Supergiant star • Distance = 6kpc • Av = 17.5 mag r/D=5x10-10 • Unusual absorption: cocon of dust? Hertzprung-Russel Diagram S. Chaty - ESO - 28/11/2006

  27. Color-magnitude diagramme Position computed for 2 different absorptions (11.8 and 17.4 mag) and for distances between 1 and 8 kpc Parameter space indicate a hot supergiant between 1 and 6 kpc Absorption <17.4mag Compatible with OB type supergiants S. Chaty - ESO - 28/11/2006

  28. IGR J16318-4848 Optical -> mid-infrared SED Spitzer • Unusual absorption: • cocoon of dust? • Model: • Companion star: sgB[e], T=23500 K, R=20.4 Rsun = 15 106 km • Dust component: T=900K, R=12 R* = 1ua • Av=17.6, D=1.2 kpc • Result: Fit 2/dof=89.4/99 • Need for extra (e.g. dust) component. Extension of this dust component seems to suggest that it is enshrouding the whole binary system. ESO/NTT VLT/VISIR S. Chaty - ESO - 28/11/2006

  29. Nature of the compact object Correlation in LHS black hole systems between X-ray/radio flux densities: 50-100 mCrab X-ray flux => 10 mJy radio flux Radio ATCA observation on 2003 Feb 9: no detection up to 0.1 mJy associated with low/hard X-ray emission => compact object is a neutron star Gallo et al. 2004 But correlation not always verified… S. Chaty - ESO - 28/11/2006

  30. Nature of IGR J16318-4848 • High Mass X-ray Binary system: • neutron star + early-type supergiant B[e] star • the 2nd HMXB with sgB[e] after CI Cam • Distance 1 to 6 kpc • Absorption: • in X-rays 2 orders of magnitude > IR • in opt/IR 2 orders of magnitude > line of sight • System surrounded by dense and absorbing dusty circumstellar material/enveloppe, + cold and hot stellar wind components • Because they are obscured, the « Norma arm » sources can only be studied in high-energy and infrared domains. S. Chaty - ESO - 28/11/2006

  31. Plan • The INTEGRAL observatory • Discovery of new sources in our Galaxy • How to understand their nature? • Multi-wavelength optical/NIR/MIR observations: • Obscured X-ray sources: the archetype IGR J16318-4848 • Supergiant Fast X-ray Transients: the archetype IGR J17544-2619 • Results and discussion on new INTEGRAL sources • Conclusions and perspectives S. Chaty - ESO - 28/11/2006

  32. The SFXT (Supergiant Fast X-ray Transient) source IGR J17544-2619… • From INTEGRAL high energy … • …to Optical/MIR observations. • (Chaty & Rahoui 2006, proc. INTEGRAL; Pellizza, Chaty, Negueruela, 2006, A&A) S. Chaty - ESO - 28/11/2006

  33. IGR J17544-2619 Recurrent transient X-ray source discovered by INTEGRAL (09/2003) near the Galactic center (Sunyaev et al. 2003, ATel 190) Negueruela, Smith, Reig, Chaty, Torrejon, 2005 Bursts last ~hours, long quiescence periods, no radio emission reported (Gonzalez-Riestra et al. 2004, A&A 420, 589) Very hard X-ray spectrum, Nh~2 1022, another highly absorbed galactic XB? (Gonzalez-Riestra et al. 2004, A&A 420, 589) Similar to other IGR sources (J16318-4848, J16320-4851, J16358-4726) (Chaty 2004, Gonzalez-Riestra et al. 2004, A&A 420, 589; Smith 2005, ATEL 338) A new kind of XBs? Important to establish their nature Optical/NIR Target of Opportunity observations 1 day after discovery! S. Chaty - ESO - 28/11/2006

  34. 2’ J-band image 5.5’x5.5’ INTEGRAL: 2’ error radius ROSAT: 23” error radius XMM: 4” error radius Image Ks IGR J17544-2619 optical/NIR counterpart Ks-band image XMM: 4” error radius 1RXS J175428: ROSAT source not connected with IGR J17544 IGR J17544-2619 (Pellizza, Chaty, Negueruela, 2006, A&A) Chandra: 0.4’’ S. Chaty - ESO - 28/11/2006

  35. IGR J17544-2619 optical/NIR counterpart 1 bright candidate (B) identified in USNO & 2MASS 3 very faint candidates (F1-3): foreground dwarf stars? 1 extended object (E) high-z galaxy? S. Chaty - ESO - 28/11/2006

  36. Candidate B spectrum Blue supergiant O9 Ib (25-28 M, T~32000K) High-mass X-ray binary Existence of a stellar wind: 265 ± 20 km/s (unusually mild for O stars, cf. 400 km/s in IGR J16318-4848: Filliatre & Chaty 2004, ApJ 616, 469) S. Chaty - ESO - 28/11/2006

  37. IGR J17544-2619 Optical -> mid-infrared SED ESO/NTT • Model: • Companion star: O9Ib, T=30500K, R=21.9 Rsun • Av=5.9, D=3.9kpc • Fit result: 2/dof=84/48 • no need for extra (e.g. dust) component Presence of dust? Spitzer VLT/VISIR S. Chaty - ESO - 28/11/2006

  38. Nature of IGR J17544-2619 • HMXB with companion of 25-28 Msupergiant O9Ib • Presence of mild stellar wind • Compact object: likely Neutron Star (in’t zand 2005) • Distance: 3-4 kpc • Faint intrinsic absorption (1022cm-2), Long Poutburst=165d • Detection of flux variations during quiescence • Archetype of “SFXTs”: Supergiant Fast X-ray transients: • O/B supergiant companions, • Compact object = BH or NS, • faint quiescent emission, outbursts lasting only hours. S. Chaty - ESO - 28/11/2006

  39. Plan • The INTEGRAL observatory • Discovery of new sources in our Galaxy • How to understand their nature? • Multi-wavelength optical/NIR/MIR observations: • Obscured X-ray sources: the archetype IGR J16318-4848 • Supergiant Fast X-ray Transients: the archetype IGR J17544-2619 • Results and discussion on new INTEGRAL sources • Conclusions and perspectives S. Chaty - ESO - 28/11/2006

  40. Results • IGR J16318-4848 and IGR J17544-2619 exhibit common characteristics: • High Mass X-ray Binaries with O/B companion • Compact object: neutron star or black hole • X-ray transients • No radio emission • But they also exhibit differences: • High intrinsic absorption around the compact object / the binary system • A new population of sources revealed by INTEGRAL. • Because some are obscured, these sources can only be studied at high-energies and IR. S. Chaty - ESO - 28/11/2006

  41. Characteristics of the studied INTEGRAL sources Zurita 2006 adapted S. Chaty - ESO - 28/11/2006

  42. Results of 2004 NTT-SOFI/EMMI and 2005/2006 Paranal UT3-VISIR observations 9 sources detected in MIR out of 14 = 2/3: MIR (stellar) emission seems usual around these sources, but the case of IGR J16318-4848 remains exceptional! S. Chaty - ESO - 28/11/2006

  43. The systems • 30% of sources detected by INTEGRAL/IBIS were not known. • 80% of Norma sources are X-ray pulsars, high spin periods • Spectra typical of neutron stars • No radio emission • 85% of sources are highly absorbed (X-ray observations):column density NH>1023 cm-2 • X-ray absorption >> IR => absorbing matter local to neutron star • NH variation on short periods? => link with accretion column/geometry? • A big fraction of these sources are close to the galactic plane |b|< 1° • They are HMXBs, some identified with OB types (Opt/NIR observations) S. Chaty - ESO - 28/11/2006

  44. Nature of systems: Corbet Diagramme Underfilled Roche lobe Supergiants • 80% of Norma sources are X-ray pulsars • High spin periods • Star Porb=10d, M=20Msol, a=50Rsol < Rdust (Rdust=240RSunfor IGR J16318) • HMXBs Pspin vs Porb: • Be Binaries • supergiant Roche lobe overflow systems • super-giant wind accretors S. Chaty - ESO - 28/11/2006

  45. So, what are these sources?Different geometries, different possible scenarii • A new population of sources of our Galaxy revealed by INTEGRAL • ~15 sources with same characteristics: not by chance! • 80% are neutron stars orbiting around super-giant stars (hot, massive, luminous): • Presence of a cocoon of dense and absorbing dust concentrated: • 1) Either around the compact object: SFXTs (~IGR J17544): • Wide orbit, neutron star penetrates inside the atmosphere/envelope of companion star, causing outbursts? • 2) Or enshrouding the whole system: obscured sources (~IGR J16318) : • neutron star orbits within a dense equatorial wind • density 1011–12 cm–3 • Disc thickness 1012–13 cm (10-100 RSun) • Disc radius 1013–14 cm (1-10 a.u.) • The answer will be given by orbital periods of these sources… • High and persistent column density => special wind configuration • Many such sources => geometry favours accretion S. Chaty - ESO - 28/11/2006

  46. Plan • The INTEGRAL observatory • Discovery of new sources in our Galaxy • How to understand their nature? • Multi-wavelength optical/NIR/MIR observations: • Obscured X-ray sources: the archetype IGR J16318-4848 • Supergiant Fast X-ray Transients: the archetype IGR J17544-2619 • Results and discussion on new INTEGRAL sources • Conclusions and perspectives S. Chaty - ESO - 28/11/2006

  47. Conclusions • Obscured sources and SFXTs share similar properties: • High Mass X-ray Binaries with O/B supergiant secondaries • But they are not the same! • Intrinsic absorption around the compact object / whole system • Extension of the absorbing material (dust…) • X-ray transient/persistent (due to geometry?) • INTEGRAL doubled the population of massive binaries with supergiant in our Galaxy, and revealed a class of highly absorbed binaries. • This new population will constrain the geometry and evolution of X-ray binaries: • dominant population born with two very massive components? • Primary progenitors of NS/NS or NS/BH mergers: • Link with short/hard gamma-ray bursts? • Good candidates of gravitational waves emitters? S. Chaty - ESO - 28/11/2006

  48. And then? • Still many questions: • What is the geometry of these systems (size of orbit, orbital period…)? • No radio emission: does geometry or dust prevent jet formation? • And also, where does this dust come from? • How were they formed? • Link with region of stellar formation of Norma arm? • How will they evolve? (neutron star decelerated?) • Does this circumstellar environment result from binarity or stellar evolution? • These sources will allow to better understand birth, evolution and geometry of HMXB with supergiants. • To answer to these questions: new observing campaigns foreseen or pending, in high energies and NIR/MIR, during and inbetween flares Multi-wavelength study necessary to reveal the nature of these sources... S. Chaty - ESO - 28/11/2006

  49. Se acabo… gracias! • El universo es tremendamente creativo, lo que nos obliga a abrirnos a lo desconocido… (Alberto Ludwig Urquieta, 1926) Naturaleza Azul, Francisco Brugnoli S. Chaty - ESO - 28/11/2006

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