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NEWS FROM GALACTIC XRBs

NEWS FROM GALACTIC XRBs. •. „Cloudy” weather in SgXRBs. •. The mystery of the missing population of Be/BH XRBs. •. Spins of compact objects in XRBs. „CLOUDY” WEATHER IN SgXRBs. „Clumpy” winds in SgXRBs. •. Cyg X-3 SFXTs. •. Cyg X-3 (Szostek & Zdziarski, 2008).

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NEWS FROM GALACTIC XRBs

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  1. NEWS FROM GALACTIC XRBs • „Cloudy” weather in SgXRBs • The mystery of the missing population of Be/BH XRBs • Spins of compact objects in XRBs

  2. „CLOUDY” WEATHER IN SgXRBs „Clumpy” winds in SgXRBs • Cyg X-3 SFXTs •

  3. Cyg X-3(Szostek & Zdziarski, 2008) Analysing X-ray spectra from Beppo SAX authors found that strong wind from WR component must be very „clumpy”. The shapes of the spectra imply that it consist of two phases: ● hot tenuous plasma carrying most of the wind mass ● cool dense clumps (filling factor < 0.01)

  4. SFXTs (Negueruela et al., 2008) Authors analyse the variability of SgXRBs ( wind fed systems) Classical SgXRBs are persistent systems New cathegory of SFXTs show very rapid variability They display outbursts with a rise time scale of tens of minutes lasting a few hours

  5. Two sources (XTE J1739-3020 & IGR J17544-2619) increased their X-ray luminosity by a factor > 100 in a few minutes ! Such increase cannot be explained by an orbital motion through a smooth medium MEDIUM IS NOT SMOOTH ! Clumpy winds will help Clumpy wind model of Oskinova et al. (2007)

  6. vw (r) = v∞ (1- R*/r)β raccr≈ 2 G Mx/vrel2 vrel2 = vw2 + vorb2 Ncl = 4πΔt/L03 L0 - porosity length Δt = Δr/vwΔt ≈ 2raccr/vw when r↑thenraccr↓and vw↑ Ncl↓↓

  7. Number of clumps in a ring of width 2 raccr and height 2 raccr

  8. The change of the slope of Ncl(r) at r ~ 2 R* is very abrupt It defines two regimes of accretion: The inner regime, where NS almost always „sees” a clump ( clasical SgXRBs) The outer regime, where NS very rarely „sees” a clump ( SFXTs)

  9. The Mystery of the Missing Population of Be+Black Hole X-Ray Binaries At present, 117 Be/NS binaries are known in the Galaxy and the Magellanic Clouds, but not a single Be/BH binary was found so far 117 : 0 !!! In all XRBs the ratio of NSs to BHs is 4:1

  10. Short tutorial on Be XRBs • These systems composed of a Be star and a compact object form the most numerous class ofXRBs in our Galaxy • At present, 117systems of that type are known in the Galaxy and theMagellanic Clouds • In all systems (discovered so far), the compact object is a NS.

  11. Be+NS system consists of a NS orbiting a Betype star on a rather wide (orbital periods in the range of ~10 to ~ 300 days), frequently eccentric, orbit. NShas astrong magnetic field and, in vast majority of cases, is observedas anX-ray pulsar(with the spin periods in the range of34ms to~ 6000 s). The Be component is deep inside its Roche lobe. This is a distinct property of Be XRBs. In all other types of XRBs, the optical component always fills or almost fills its Roche lobe (even if the accreted matter is supplied by the winds).

  12. X-ray emission from Be XRBs X-Ray emission (with a few exceptions) has distinctly transient nature with rather short active phases (a flaring behaviour). There are two types of flares, which are classified as Type I outbursts (smaller and regularly repeating) and Type II outbursts (larger and irregular). Type I bursts are observed in systems with highly eccentric orbits. They occur close to periastron passages of NS. They are repeating at intervals ~Porb. Type II bursts may occur at any orbital phase. They are correlated with the disruption of the exretion disc around Be star (as observed in Hα line). They repeat on time scale ~years.

  13. Type I burst trec~ Porb

  14. Type II burst trec~ years

  15. At present, 117 Be/NS binaries are known in the Galaxy and the Magellanic Clouds (which is almost a half of the total number of the known NS binaries), but not a single Be/BH binary was found so far (although 58 BH candidate systems are known). This disparity (117 Be/NS type systems out of 252 known NS XRBsvs. not a single Be/BH type system among 58 known BH XRBs) calledthe attention of the researchers already for some time.

  16. In particular, Zhang etal. (2004) noted that, according to stellar population synthesiscalculations by Podsiadlowski et al. (2003), BH binaries areformed predominantly with relatively short orbital periods(Porb < 10days). If this is the case, then, accordingto Zhang et al., the excretion disc truncation mechanism(Artymowicz & Lubow, 1994) might be so efficient, that theaccretion rate is very low and the system remains dormant (andtherefore invisible) for almost all the time. One should note,however, that Podsiadlowski et al.considered, essentially, BHsystems with Roche lobe filling secondaries, which definitely isnot the case of Be XRBs. Therefore, their results are not relevantfor the case of Be/BH XRBs.

  17. Stellar population synthesis (SPS) calculations Sądowski, Ziółkowski, Belczyński & Bulik carried out calculations using the STAR TRACK code (Belczynski, Kalogera& Bulik, 2002; Belczynski et al., 2008). „State of art” SPS code (Vicki Kalogera)

  18. Definition of a Be star (for the purpose of SPS calculations) The primary property of Be stars distinguishing them from other B stars is rapid rotation. All other properties (in particular, the presence of an excretion disc, which permits the efficient accretion on the compact companion) are the consequences of the fast rotation. It is not clear how Be stars achieved their fast rotation (although different hypothesis like rapid rotation at birth or spin-up due to binary mass transfer are advanced – see e.g. McSwain & Gies, 2005). The fraction of Be stars among all B stars is similar for single stars and for those in binary systems (one quarter to one third).

  19. For simplicity, we assumed that one quarter of all B stars are always Be stars and that these stars are always efficient mass donors, independently of the size of the binary orbit (as is, in fact, observed in Be/NS XRBs).

  20. The preliminary results of our calculations, showing the expected ratio of the number of Be/NS binaries to the number of Be/BH binaries are shown in Fig. 1. Fig. 1 clearly shows that the expected numbers of Be/NS and Be/BH binaries should be roughly comparable. The estimated masses of observed Be stars cover the range from~ 2.3MSUN(Lejeune & Schaerer, 2001) to~ 25 MSUN(McSwain & Gies, 2005). Independently of the value of the minimum mass assumed for a Be star, it is obvious that, according to our calculations, Be/NS systems should not outnumber Be/BH systems by more than a factor of about 2.5. What is the cause of so dramatic discrepancy ? The answer is shown in Fig. 2

  21. NS BH BH NS MBe,min = 3 MSUN MBe,min = 8 MSUN

  22. According to our calculations, the distributionof the orbital periods is completely different for Be/NS and Be/BHsystems. Within the orbital period range where Be XRBs are found(~ 10 to ~ 300 days), Be systems are formedpredominantly with a NS component. The ratio of the expectednumber of Be/NS systems to the expected number of Be/BH systemsis, for this orbital period range, larger than 50. The systemswith a BH component are formedpredominantly with much longerorbital periods. Suchsystems are very difficult to detect, bothdue to very long orbital periods and due to, probably, very lowluminosities (the accretion at such large orbital separations mustbe very inefficient). CAUTION: there might be also other factors !

  23. CAUTION: there might be also other factors ! Anotherpossible factor may be related to the previous evolution of a Bestar. If, indeed, a B star must be a member of a binary system andundergo a mass transfer in order to become a Be star, then one canimagine that the systems composed of a Be star and a relativelyless massive companion (which collapses to a NS) remain bound,while those composed of a Be star and a relatively more massivecompanion (which collapses to a BH) are disrupted in the processof a supernova explosion.

  24. SPINS of COMPACT OBJECTS in XRBs • BHs a*€ (< 0.26, > 0.98) • NSs Pspin € (0.89 ms, 104 s)

  25. SPINS of BHs • Spins of accreting BHs could be deduced from: • X-ray spectra (continua) • 2. X-ray spectra (lines) • 3. kHz QPOs

  26. Specific angular momentum for circular orbits

  27. X-RAY SPECTRA Zhang et al. (1997): GRO J1655-40a*= 0.93 GRS 1915+105a*≈ 1.0 Gierliński et al. (2001):GRO J1655-40a*= 0.68 ÷ 0.88 McClintock et al. (2006):LMC X-3 a* < 0.26 GRO J1655-40a*= 0.65 ÷ 0.80 4U 1543-47a*= 0.70 ÷ 0.85 GRS 1915+105a* > 0.98

  28. SPECTRAL LINES MODELING THE SHAPE OF Fe Kα LINE Miller et al. (2004): GX339-4 a*≥ 0.8 ÷ 0.9 Miller et al. (2005): GRO J1655-40a* > 0.9 XTE J1550-564a* > 0.9 Miller et al. (2002): XTE J1650-500a*≈ 1.0

  29. Miller (2004)

  30. NEW ERA OF PRECISION Reis et al. (2008) determined the spin of BH in GX 339-4 (from RXTE & XMM): rin = 2.02+0.02-0.06rg at very high state rin = 2.04+0.07-0.02 rg at low/hard state a* = 0.935 ± 0.02 at 90 % confidence(!) Miller et al. (2008) did this from Suzaku & XMM: a* = 0.93 ± 0.05

  31. GX 339-4

  32. kHz QPOs Name νQPO [Hz] MBH [MSUN] GRO J1655-40 300± 23 6.3 ± 0.5 450 ± 20 XTE J1550-564 184± 26 10.5 ± 1.0 272± 20 H 1743-322 166 ± 8 240 ± 3 GRS 1915+105 41 ± 114 ± 4.4 67 ± 5 113 164 ± 2 4U1630-472184 ±5 XTE J1859+226193 ±49 ±1 XTE J1650-500 2505 ±2

  33. a ≈ 0.7 ÷ 0.99 a*≈ 0.7 ÷ 0.99

  34. BHs SPINS(summary) (1)GRS 1915+105 has a rotation close to nearly maximal spin ( a* >0.98) (2)several other systems (GRO J1655-40, 4U 1543-47, XTEJ1550-564, XTE J1650-500 and GX 339-4 have largespins (a* ≥ 0.65) (3)not all accreting black holes havelarge spins (robust result a* < 0.26 for LMC X-3)

  35. ●almost all BHs for which there is a reliableestimate of high spin (with the sole exception of 4U 1543-47) are microquasars ●perhaps, it is so, that all microquasar BHs havehigh spins, while other accreting BHs might or might not have highspins.

  36. SPINS of NSs • Spins of accreting NSs could be deduced from: • X-ray pulses 2. kHz QPOs (especially during the tails of X-ray bursts)

  37. Spins determined from X-ray pulses They are, at present, in the range: 1.67 msIGR J100291+5934 to 10 008 s2S 0114+650 (135 X-ray pulsars known so far (among them 9 millisecond pulsars)

  38. Spins determined from kHz QPOs There are two types of kHz QPOs: • burst QPOs νB = νSPIN • pair QPOs ΔνPAIR = νSPINorΔνPAIR = 0.5νSPIN

  39. Burst QPOs reflect the true spin frequency This is known from three sources which display simultaneously X-ray pulses: XTE J1814-338 νSPIN = 314 Hz SAX J1808.4-3658 νSPIN = 401 Hz Aql X-1 νSPIN = 550 Hz Spin periods from burst QPOs are known for 13 (14) other bursters. These spin periods are in the range 1.62 to 10.5 ms New discovery: XTE J1739-285 PSPIN = 0.89 ms (Kaaret et al., 2007)

  40. Pair QPOs are less obvious to interpret XTE J1807-294ΔνPAIR ≈ 200 Hz (= νSPIN) SAX J1808.4-3658ΔνPAIR ≈ 200 Hz (= 0.5 νSPIN) Aql X-1 ΔνPAIR ≈ 275 Hz (= 0.5 νSPIN) fast rotators (νSPIN≥ 400 Hz) seem to have ΔνPAIR ≈0.5 νSPIN, while slow rotators (νSPIN <400 Hz) have ΔνPAIR≈νSPIN (sample of 7 sources) 13 additional spin determinations Parametric epicyclic resonance theory (Abramowicz & Kluzniak, since 2001) seems to be able to explain this behaviour

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