“New Views on Accreting X-ray Pulsars, a brief review of recent results”

1. “New Views on Accreting X-ray Pulsars,a brief review of recent results” Andrea Santangelo (…and the Magnet Collaboration) Institut für Astronomie und Astrophysik Kepler Center for Astro and Particle Physics Karls-Eberhard-Universität Tübingen MAXI International Symposium

2. Magnet Collaboration … A. Santangelo, D. Klochkov, V. Doroshenko, D. Müller, R. Doroshenko, R. Staubert, M. Sasaki (IAAT), J. Wilms, L. Barragán, T. Dauser, I. Kreykenbohm, J. Schmid, F. Schwarm (ECAP), G. Schönherr (AIP), I. Caballero (Saclay), C. Ferrigno, N. Mowlawi (ISDC), P. Kretschmar (ESAC), V. McBride (Soton), U. Kraus (Uni Hildesheim), O. Nishimura (Nagano), K. Postnov, N. Shakura (SAI), K. Pottschmidt (CRESST/UMBC/GSFC), R. Rothschild, S. Suchy (UCSD), L. Sidoli (INAF Milano) … Partial list …

3. Liu et al. A&A, 2000, 2005 X-ray Binaries with a NS: Pulsars? Most of them are in HMXRB A few LMXRB (Her X-1, 4U1626-67, GX1+4) Mass Transfer from the Normal to the compact star Seminar at RIKEN Courtesy of Scientific American

4. Accretion Roche Lobe Overflow Wind Accretion Lubov & Shu, 1975 Davidson & Ostriker, 1973

5. SG/X-ray Binaries Wind Accretion Bozzo+, 2008 SFXT Interaction between the inflow wind matter and the NS magnetosphere: different regimes at different luminosities Kreykenbhom, 2004

6. Interaction disk/wind magnetosphere Details of matter transfer are not understood

7. In the Boundary Layer disk is not longer keplerian Ghosh & Lamb, 1978, 79 rH rA At the Boundary Layer disk is disrupted. The plasma is forced to follow the field lines and matter is funnelled in accretion column onto the Neutron Star Magnetic Poles Kuster, 2003

8. What is the Corotation Radius ? At the Corotation Radius the angular velocity of the magnetosphere equals the keplerian velocity of the Disk. rH

9. Not so simple: Open Field lines Lovelace et al. 1995

10. Outflows and conical winds MHD simulations Romanova et al., 2009

11. Do we have evidence of these outflows?

12. Continuous Monitoring of Pulse Period, Pdot, Lx P Based on Swift/BAT data . Her X-1 P Klochkov +, 2009 Time

13. Strong Spin-down episodes Outflow episodes!

14. Other evidence: decay of Porb Klochkov +, 2008; Staubert+, 2009 A decay of the Orbital Period has been measured It cannot be reconciled with a conservative scenario Matter is ejected! In strong spin-down episodes the spin-down power is used to expel matter from the inner disk radius Ji et al., 2009 (Chandra)

15. Surprises from wind/magnetosphere interactions?

16. The strange case of an old friendGX 301-2 Doroshenko+, 2010 Why is GX 301-2 so slow? Seminar at RIKEN

17. Torque Balance The Spin frequency of the source is determined by accelerating and braking torques Davies +, 1979 Accelerating Torque depends on accretion rate, wind velocity through kw Decelerating Torques Davidson & Ostriker, 1973 Turbolent Viscosity Ilarionov & Kompaneets, 1990 Compton Heated Outflows

18. Assuming equilibrium… kw~0.25-1

19. CGRO-BATSE Seminar at RIKEN Doroshenko et al., 2009

20. Seminar at RIKEN

21. GX 301-2 a hidden “magnetar”? Not an unique case…

22. Doroshenko 2010a, (submitted) Vela X-1 (Ps ~283.5 s)_ Kreykenbohm+, 2008, Inoue+ 1984 Other evidence from: QPOs, Noise Power Spectrum Flux drops dramatically OFF states (Suzaku obs.) Propeller regime due to wind density fluctuations of clumpy winds? Gogus+, 2010 in GX 301-2

23. Peculiar hard emission at lower luminosity (Doroshenko +, 2010b, in prep.) The source still pulsates OFF state Pulse profile changes at hard energies Accretion though at much lower luminosity is there! We possibly observe the inhibition of the column at lower luminosities: radiation comes from the polar cap In “the gated accretion” scenario of Bozzo+ (2008), we might see here the transition to KH Instab.

24. Emission from the accretion column

25. Basko & Sunyaev, 1976 Accretion Columns Kuster, 2003 Solid Column Hallow Cylinder

26. Transition between two accretion regime depending on the luminosity: Eddington vs. Sub-Eddington Right) High accretion rate: shock is formed, plasma is decelerated to subsonic speed and heated. The Plasma then sinks to the NS surface. Emitted photons can only escape perpendicularly to the column forming a wide Fan beam. Left) Lower accretion rateNo shock is formed, plasma is decelerated onto the neutron star surface by Coulomb collisons; photons are generated by Bremsstrahlung and Compton Cooling. They can escape along the accretion column, generating a pencil beam Seminar at RIKEN Kretschmar, 1996 Harding, 1994

27. Cyclotron Lines Electrons in the magnetosphere plasma move helicodally along the B field lines: their motion perpendicularly to the B field is quantized in the Landau levels For B<< Bcr Equispaced

28. Cyclotron lines as absorption lines Mean free path is short, quasi instantaneous re-capturing of the photon Electron is excited to the n Landau level Lifetime is short De-excitation to ground state via single or multiple photon emission Seminar at RIKEN

29. Can we probe these two regimes Using Cyclotron lines… + GX 304-1 ~54 keV P13 Wilms+, 2010

30. Do cyclotron lines trace the B field of the Neutron Star? • Do cyclotron lines trace the B field of the NS? • How the energy of the line is related to the luminosity ? Do we observe a change of regime around 1037 ergs/sec ? Anticorrelation ? Correlation ?

31. Mihara+ 2007, Nakajima 2008

32. Caballero et al., 2007, 2009 • A0535+26 Correlation or Anti-correlation? • Tsygankov et al., 2006; 2010 Mowlavi et al., 2006 • V0332+53, Outburst 2005 • Anti-correlation is clearly observed • Staubert et al., 2007 • Her X-1, 5 years of data • Correlation is clearly observed; sub-Eddington!

33. New Studies using pulse to pulse variability…

34. Pulse to pulse variability…(Klochkov+, P23) light curve V0332+53 repeated pulse profile PCA cts/s/PCU (~3-30 keV) Time in days

35. Strong spectral variability pulse flux bins PCA cts/s/PCU (~3-30 keV) Time in days

36. Klochkov+ 2010 (in prep.) Example: X0115+63 Spectral variability with the single pulse amplitude With increasing pulse amplitude, the power-law becomes steeper, the cyclotron line shifts towards lower energies

37. Dependence of spectral parameters on pulse height: summary “negative pulsars” “positive pulsars” We found two types of spectral dependencies on the single pulse flux. We interpret them as an indication of two distinct accretion regimes (poster by D. Klochkov et al.)

38. Again instabilities…

39. A0535+26 (2005 Outburst) Caballero + 2007, 2008 Seminar at RIKEN

40. Seminar at RIKEN

41. Seminar at RIKEN

42. A question remains… is the cyclotron line tracing the B field of the NS (in systems like GX 301-2 and Vela X-1)?

43. Doroshenko et al., 2009 Solution of the contradiction? The Cyclotron lines traces the field of the production site and this could be located at the top of the column Basko & Sunyaev,1976  high columns can be predicted

44. Formation of the spectra is very complex…

45. E-a E<Ecut POHEI (E) = E-aexp(-(E-Ecut)/Ef)) E>Ecut The continuum? White+, 1983 Tanaka, 1986 Mihara+, 1995 Approximates thermal comptonization  Sunyaev and Titarchuk, 1980 Segreto, 2001

46. Becker & Wolff, 2005a,b and 2007 Physical Models (high luminosity) • Accretion mound produces soft X-rays via bremsstrahlung • X-rays are up-scattered via bulk motion comptonization and diffuse through the walls of the columns • Cyclotron emission occurs together with bbody emission from a thermal mound Limited to COLUMN! A Radiative shock dominates the formation of the emitted continuum

47. Ferrigno et al., 2009: Model in XSPEC! A quantitative attempt: 4U 0115+634 Thermal and bulk Comptonization of Cyclotron emission. Cyclotron emission is concentrated around the peak. Thermal comptonization is almost constant Thermal Comptonization of 0.5 keV BB Gaussian to correct the rough modelling

48. Ferrigno et al., 2009 4U 0115+634 Emission Geometry Beamed High Energy emission from the column (Fan beam) Low Energy Diffused Halo producing a fan component Analysis is being extended to other sources like 4U1907+67, Cen X-3, …(Ferrigno et al. 2010) Magnetic field of Cyclotron emission and of absorption line forming region are different!

49. Light Bending and Geometry Kraus, 2003, 2010; Sasaki 2010; Caballero 2010

50. Kraus et al., 2010 Beam Pattern: three components Reprocessed radiation in the accretion stream Column component Low Energy Diffuse Halo Component • Isotropic column emission • Beamed emission Emission components?