Proprietà Osservative delle Binarie X Contenenti Stelle di Neutroni

1. Proprietà Osservative delle Binarie X Contenenti Stelle di Neutroni Tiziana Di Salvo Dipartimento di Scienze Fisiche ed Astronomiche, Università di Palermo Via Archirafi 36- 90123 Palermo Italy

2. X-ray Binaries Classification • High Mass X-ray Binaries: Young objects with a high mass companion star (> 10 Msun) and (usually) High magnetic field (about 1012 Gauss) neutron stars Cyclotron lines

3. X-ray Binaries Classification • High magnetic field neutron stars in X-ray binaries • Black Hole Candidates in X-ray binaries

4. X-ray Binaries Classification • High magnetic field neutron stars in X-ray binaries • Black Hole Candidates in X-ray binaries • Low magnetic field neutron • stars in X-ray binaries: • temporal and spectral • analysis

5. Caratteristiche generali dell’accrescimento • Energia liberata: • Luminosità: • Valore massimo dato dalla luminosità di Eddington • Efficienza: • Valore tipico per una NS: • Valore tipico per la fusione nucleare:

6. Caratteristiche generali Range tipico di emissione • Modalità di accrescimento: • Accrescimento tramite venti stellari.(Binarie X di alta massa) • Accrescimento tramite tracimazione dal lobo di Roche.(Binarie X di bassa massa) Emissione X e γ

7. Mass Transfer in LMXBs: Roche Lobe Overflow Potenziale di Roche

8. X-ray pulsars

9. PL a~1 BB Ecyc Fe Lines Wien Hump Dal Fiume et al. 1998

10. Meszaros, 1992 Cyclotron lines

11. Coburn et al. 2002 Meszaros 1992 Orlandini & Dal Fiume 2001 Santangelo et al. 2003

12. There are however some “extraordinary” observations…. Multiple Harmonics? BeppoSAX has discovered or has evidence of multiple harmonics in some of the sources, therefore establishing the presence of second harmonic as a rather common feature! CEN X-3 4U1907 4U1626-67 (?) VELA X-1 (?)

13. Similar asymmetric variations of the cyclotron line energy (up to 8 keV) were observed in Cen X-3 (Burderi et al. 2000). These variations of the cyclotron line energy could be explained by assuming an offset (~ 0.1 RNS) of the dipolar magnetic field with respect to the neutron star center. Offsets are also suggested by an analysis of pulse profiles (Leahy 1991). The case of X0115+63 The EW of harmonics were found to be larger than the fundamental Deep 2nd harmonic E1cyc@ 12.74 E2cyc@ 24.16 keV E3cyc@ 35.74 E4cyc@ 49.5 keV E5cyc@ 60. keV Santangelo et al. 1999

14. Low Mass X-ray Binaries Close X-ray binaries: Companion star: M < 1 MSUN Compact object: NS with B < 1010 G Accretion disk

15. Low Mass X-ray Binaries • Close X-ray binaries: • Rich time variability, such as twin QPOs at kHz frequencies (from 400 to 1300 Hz, increasing with increasing mass accretion rate);kHz QPOs are thought to reflect Keplerian frequencies at the inner accretion disk. Companion star: M < 1 MSUN Compact object: NS with B < 1010 G Accretion disk

16. kHz QPOs Possibly related to Keplerian frequencies at the inner edge of the disk. Sco X-1 Two peaks are usually present, whose frequency increses when the mass accretion rate increases, with almost constant separation. The peak separation is almost equal to the NS spin frequency (if known from pulsations or burst oscillations) 4U 1608

17. Low Mass X-ray Binaries • Close X-ray binaries: • Rich time variability, such as twin QPOs at kHz frequencies (from 400 to 1300 Hz, increasing with increasing mass accretion rate);kHz QPOs are thought to reflect Keplerian frequencies at the inner accretion disk. • Type-I X-ray bursts, with nearly coherent oscillations in the range300-600 Hz(probably theNS spinfrequency). • Some aretransient, with quiescent luminosities of 1032-1033 erg/s and outburst luminosities of 1036-1038 erg/s. Companion star: M < 1 MSUN Compact object: NS with B < 1010 G Accretion disk

18. . Measuring P and P The energy lost in electromagnetic radiation and relativistic particle beam comes from the rotational energy of the pulsar, which slows down. Radio Pulsars . allows to derive m: B ~ 108 Gauss for MSPs

19. The “classical” recycling scenario Low mass X-ray Binaries B ~ 108 – 109 G Low mass companion (M ~ 1 Msun) Progenitors (Pspin >> 1ms) Accretion of mass from the companion causes spin-up Millisecond radio Pulsars B ~ 108 – 109 G Low mass companion (M ~ 0.1 Msun) End products (Pspin ~ 1ms)

21. Confirmed by 7 (transient) LMXBs which show X-ray millisecond coherent pulsations Known accreting millisecond pulsars (in order of increasing spin period): IGR J00291+5934: Ps=1.7ms, Porb=2.5hr(Galloway et al. 2005) XTE J1751-306:Ps=2.3ms, Porb=42m (Markwardt et al. 2002) SAX J1808.4-3658:Ps=2.5ms, Porb=2hr (Wijnands & van der Klis 1998) HETE J1900.1-2455: Ps=2.7ms, Porb=1.4hr(Kaaret et al. 2005) XTE J1814-338:Ps=3.2ms, Porb=4hr (Markwardt et al. 2003) XTE J1807-294:Ps=5.2ms, Porb=40m (Markwardt et al. 2003) XTE J0929-314:Ps=5.4ms, Porb=43.6m (Galloway et al. 2002)

22. Rossi X-ray Timing Explorer RXTE carries 5 Proportional Counter Units, which constitues the Proportional Counter Array (PCA), with a large effective area of about 6000 cm2 and very good time resolution (up to 1 msec), working in the X-ray range (2-60 keV)

23. Spin Frequencies of AMSPs All the spin frequencies are in the rather narrow range between 200 and 600 Hz. (From Wijnands, 2005)

24. Light Curves of AMSPs (X-ray Outburst of 2002) All the 7 known accreting MSPs are transients, showing X-ray outbursts lasting a few tens of days. Typical light curves are from Wijnands (2005)

25. Disc Pressure proportional to M Magnetic Pressure Proportional to B2 Disc – Magnetic Field Interaction . Rm = 10 B84/7 dotM-8-2/7 m1/7 km

26. Accretion conditions (Illarionov & Sunyaev 1975) Rco = 15 P–32/3 m1/3 km RLC = 47.7 P–3 km Accretion regime R(m) < R(cor) < R(lc) Pulsar spin-up • accretion of matter onto NS (magnetic poles) • energy release L = dotM G M/R* • Accretion of angular momentum dL/dt = l dotM where l = (G M Rm)1/2 is the specific angular momentum at Rm

27. 2 The accreting matter transfers its specific angular momentum (the Keplerian AM at the accretion radius) to the neutron star: L=(GMRacc)1/2 Pulsars spin up The process goes on until the pulsar reaches the keplerian velocity at Racc (equilibrium period); Pmin when Racc = Rns Pmin << 1 ms for most EoS The conservation of AM tells us how much mass is necessary to reach Pmin starting from a non-rotating NS. Simulations give ~0.3Msun (e.g. Lavagetto et al. 2004) During the LMXB phase ~1 Msun is lost by the companion

28. . M Propeller phase Propeller regime R(cor) < R(m) < R(lc) • centrifugal barrier closes (B-field drag stronger than gravity) • matter accumulates or is ejected from Rm • accretion onto Rm: lower gravitational energy released • energy releaseL =eGM(dM/dt)/R*,e= R*/2 Rm

29. . M Rotating magnetic dipole phase Radio Pulsar regime Rm > RLC • no accretion, radio pulsar • emission • disk matter swept away • by pulsar wind and pressure • Energy release given by the • Larmor formula: • L = 2 R6/3c3 B2 (2 p / P)4

30. Timing Technique • Correct time for orbital motion delays:t tarr – xsin 2/PORB (tarr –T*)wherex = a sini/c is the projected semimajor axis in light-s and T* is the time of ascending node passage. • Compute phase delays of the pulses ( -> folding pulse profiles) with respect to constant frequency • Main overall delays caused by spin period correction (linear term) and spin period derivative (quadratic term)

31. Accretion Torque modelling Bolometric luminosity L is observed to vary with time during an outburst. Assume it to be a good tracer of dotM:L= (GM/R)dotMwith 1, G gravitational constant, M and R neutron star mass and radius Matter accretes through a Keplerian disk truncated at magnetospheric radiusRm dotM-. In standard disk accretion  =2/7 Matter transfers to the neutron star its specific angular momentum l = (GM Rm)1/2at Rm, causing a torque= l  dotM. Possible threading of the accretion disk by the pulsar magnetic field is modelled here as in Rappaport et al. (2004), which gives the total accretion torque: t = dotM l– m2 / 9 Rco3

32. IGR J00291: the fastest accreting MSP Porb = 2.5 h ns = 600 Hz 8 0 dotn = 8.5(1.1) x 10-13Hz/s (c2/dof = 106/77) (Burderi et al. 2007, ApJ; Falanga et al. 2005, A&A)

33. Conclusions: Spin-up in IGR J00291 IGR J00291+5934 shows a strong spin-up:ndot = 1.2 x 10-12 Hz/s,which indicates a mass accretion rate ofdotM = 7  10-9 Myr-1. Comparing the bolometric luminosity of the source as derived from the X-ray spectrum with the mass accretion rate of the source as derived from the timing, we find a good agreement if we place the source at a quite large distance between7 and 10 kpc.

34. Spin down in the case of XTE J0929-314 Porb = 44 min ns = 185 Hz Spin down in XTE J0929, the slowest among accreting MSPs. During the only outburst of this source observed by RXTE. Measured spin-down rate: dotn= -5.5 10-14 Hz/s Estimated magnetic field: B = 5 x 108 Gauss (Di Salvo et al. 2007)

35. Results for 6 of the 7 known LMXBs which show X-ray millisecond coherent pulsations Results for accreting millisecond pulsars (in order of increasing spin period): IGR J00291+5934: Ps=1.7ms, Porb=2.5hrSPIN UP XTE J1751-306:Ps=2.3ms, Porb=42m SPIN UP SAX J1808.4-3658:Ps=2.5ms, Porb=2hr SPIN UP (SPIN DOWN) HETE J1900.1-2455: Ps=2.7ms, Porb=1.4hr ?? XTE J1814-338:Ps=3.2ms, Porb=4hr SPIN DOWN XTE J1807-294:Ps=5.2ms, Porb=40m SPIN UP XTE J0929-314:Ps=5.4ms, Porb=43.6m SPIN DOWN These exclude GR as a limiting spin period mechanism

36. Spettri dei Black Holes Candidates in X-ray Binaries Stati hard o low • Sono fittati da: • Legge di potenza • G = 1.4 – 1.9 • alle alte energie, con cutoff a circa 100 KeV. • Corpo nero alle basse energie (circa 0.1 keV) • Luminosità < 0.1 LEDD.

37. Spettri dei BHXB Stati soft o high • Sono fittati da: • Corpo nero alle basse energie (temp. kT circa 0.5-1KeV) dominante rispetto alla legge di potenza. • Legge di potenza: • G = 2 – 3 • alle alte energie senza evidenza di cutoff fino a energie dell’ordine di circa 511KeV • Luminosità > 0.2-0.3LEDD.

38. Spettri dei BHXB Stati molto alti Stati high o soft Stati intermedi Stati low o hard Stati di quiescenza

39. Schema della regione di emissione Fe K-shell Line and Reflection Cygnus X-1: BeppoSAX Broad Band (0.1 – 200 keV) Spectrum Di Salvo et al. (2001) HPGSPC MECS MECS

40. Spettri dei BHXB: Componente di riflessione Compton • Componente di riflessione è dovuta all’incidenza della componente hard di Comptonizzazione sul disco di accrescimento. • Energia dei fotoni incidenti inferiore a circa 15 KeV: predomina il fotoassorbimento righe di emissione e bordi di assorbimento (sprattutto relativi al Fe). • Energia dei fotoni incidenti maggiore di 15KeV: predomina la riflessione Compton larga “gobba” tra circa 10 e 50 KeV.

41. Fe K-shell Line and Reflection Important information can be obtained from the iron line profile. Doppler and relativistic effects due to the keplerian motion in the disk modify the profile (double peak, Doppler boositng, Gravitational redshift). From high resolution spectra we can obtain info on the inner disk radius and inclination of the disk. HPGSPC Iron line profile E E0

42. Self consistent models of Compton reflection and associated iron line narrow Reflection from ionized matter Reflection from Neutral matter smeared

43. High resolution spectroscopy of massive BHs: MCG-6-30-15 XMM observation of the iron line region in MCG-6-30-15 taken in 2001. The red wing extends to less than 4 keV, indicating an inner radius of less than 6 G M / C2. Spinning black hole? (a > 0.93) Fabian et al. 2002)

44. Spettri di LMXB contenenti NS • Forti analogie con gli spettri di BHXBs:presenza di stati hard e soft. • Differenza nella temperatura della nube comptonizzante. Raffreddamento extra dovuto alla superficie della NS.

45. Neutron star low mass x-ray binaries classification Atoll sources: Lx ~ 0.01-0.1 L(Edd) type I X-ray bursts some transients Z-sources: Lx ~ 0.1-1.0 L(Edd) all persistent -Late type mass donor (usually K-M star) or white dwarf - Accreting NS primary: fast spinning (2-3 ms), weakly magnetic - Characteristic phenomena: type I X-ray bursts, fast (> 100 Hz) quasi periodic oscillations in the X-ray flux - Useful classification: Z-sources, Atoll sources

46. Atoll sources: energy spectra - Soft component (few keV) (blackbody or disk-blackbody model) - Power law with exponential cutoff (5-20 keV): Thermal Comptonization. - Soft and hard states: in the hard state the cutoff shifts to higher energies (up to > 200 keV) - Iron emission (fluorescence) line at ~6.4 keV - Evidence for a reflection component

47. X-ray energy spectra of Z sources up to ~20 keV X-ray energy spectra up to ~20 keV Two components needed (at least): - Eastern model (Mitsuda et al. 1984): multitemperature-blackbody + blackbody spectra (disk emission with kT = a R-3/4, and NS surface comptonized emission) - Western model (White et al. 1986): blackbody + Comptonized blackbody spectra (NS or disk emission, and disk emission modified by Comptonization in a hotter region).

48. Fe K-shell Line in Neutron Star Low Mass X-ray binaries Chandra observation of the LMXB/atoll source 4U 1705-44 (Di Salvo et al. 2005, ApJ Letters) TE Mode 25 ks CC Mode 5 ks

49. Fe K-shell Line in NS LMXBs TE Mode 25 ks • Soft Comptonization model for the X-ray continuum plus 3 narrow lines and a broad Fe line: • E1 = 1.476 keV, s1 = 17 eV • (ID: Mg XII Ly-a, 1.473 keV) • E2 = 2.03 keV, s2 = 28 eV • (ID: Si XIV Ly-a, 2.006 keV) • E3 = 2.64 keV, s3 = 40 eV • (ID: S XVI Ly-a, 2.6223 keV) • E_Fe = 6.54 keV, sFe = 0.51 keV • EW = 170 eV

50. Fe K-shell Line in Neutron Star Low Mass X-ray binaries • Fitting the iron line profile with a disk (relativistic) line we find: • E_Fe = 6.40 keV • Rin = 7-11 Rg (15-23 km) • Inclination = 55 – 84 deg • Alternatively, Compton broadening in the external parts of the Comptonizing corona (s = 0.5 implies • t = 1.4 for kT = 2 keV) TE Mode 25 ks Hints of a double-peaked line profile