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X-ray pulsars through the eyes of INTEGRAL

This presentation outlines the new findings in the study of X-ray pulsars using the INTEGRAL satellite. It discusses the hard X-ray spectra of pulsars, the dependence of cyclotron line energy on luminosity, and the pulse profiles dependence on luminosity and energy band.

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X-ray pulsars through the eyes of INTEGRAL

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  1. X-ray pulsarsthrough the eyes of INTEGRAL A.Lutovinov, S.Tsygankov (IKI) & the discussion with J.Poutanen, M.Revnivtsev and V.Suleimanov Funasdalen 2008

  2. OUTLINE (What is a new in hard X-rays)I. Hard X-ray spectra of X-ray pulsars II. Cyclotron line energy dependence on the X-ray pulsars luminosity III. Pulse profiles dependence on the luminosity and energy bandIV. Pulse fraction dependence on the luminosity and energy band

  3. Name Type P Porb Companion INTEGRAL totally observed more than 70 X-ray pulsars during 5 years of the operation, discovered several new pulsars. 38 of them were detected at the high significance level, that gave a possibility to reconstruct their spectra

  4. B=5.3x1012 Гс B=3x1012 G B=3.1x1012G B=1.4x1012G B=2.6x1012G Filippova, Tsygankov, Lutovinov, Sunyaev (2005)

  5. Range of luminosities ~2х1037 – ~5х1038 erg/s (d~7 kpc), Pspin ~ 4.375 s, Porb ~ 34.25 d V0332+53 High state α = -0.09+/-0.01 Ecut = 9.15+/-0.03 кэВ Ecyc1 = 26.21+/-0.15 кэВ Ecyc2 = 50.66+/-0.3 кэВ Ecyc3 = 73.8+/-1.8 кэВ Ecyc1/Ecyc2/Ecyc3= 1/1.93/2.82 Tsygankov, Lutovinov, Churazov, Sunyaev (2006)

  6. The cyclotron line energy dependence on the source luminosity Ecyc≈-0.1L37+29.0 keV B=((1+z)/11.6)xEcycx1012 G=3x1012 G

  7. 1) L<L* - no shock 2) L>L* - shock L*~1037 erg/s Shock height above the neutron star surface: - accretion rate (1039 erg/s) Accretion stream structure (Basko, Sunyaev, 1976) In an approaching of the dipole magnetic field ΔEcycl ~ 25% corresponds to a ΔR~ 7.5%, thus “effective” height of the cyclotron feature formation is l~750 m. Accretion column structure (Lyubarskyi, Sunyaev, 1982) H ~ few km

  8. Maximal luminosity range ~1х1037 – ~2х1038 erg/s (d~7 kpc) X-ray outbursts of 4U 0115+63 Spectral parameters α = 0.09+/-0.01 Ecut = 8.9+/-0.1 keV Ecyc1 = 11.16+/-0.03 keV Ecyc2 = 21.2+/-0.1 keV Ecyc3 = 34.6+/-0.2 keV Ecyc4 = 44.9+/-0.3 keV Ecyc1/Ecyc2/Ecyc3/Ecyc4= 1/1.9/3.1/4.0 Ecyc3 Ecyc1 Ecyc4 Ecyc2 Tsygankov, Lutovinov, Churazov, Sunyaev (2007)

  9. The cyclotron line energy dependence on the source luminosity Lx~5x1037 erg/s Sharp shift of the cyclotron energy occurs at the same luminosity – the fundamental property of pulsar (?)

  10. A0535+26 KS1947+300 Disk accretion (Ghosh,Lamb 1978): Tsygankov, Lutovinov (2008) Tsygankov, Lutovinov (2005)

  11. 2.6х1038 erg/s 1.8х1038 erg/s 8.2х1037 erg/s 6х1037 erg/s Luminosity and energy dependence of pulse profiles (V0332+53 example)

  12. Evolution of pulse profiles near the main cyclotron line harmonic 6х1037erg/s 2.6х1038erg/s Ecycl

  13. 6х1037erg/s 2.6х1038erg/s 3D- and 2D-pulse profile variations Tsygankov, Lutovinov, Churazov, Sunyaev (2006)

  14. Her X-1 Vela X-1 There is catalog of hard pulse profiles of 10 bright X-ray pulsars, their dependences on the energy, luminosity, orbital phases, etc. Soon on the web!

  15. Toy model Rotation axis is inclined in a such way that the accretion column at one of the poles is seen over its entire height, but only the upper part emitting softer photons is seen in the second column. Should be taking into account also a light bending, possible reflection from the neutron star surface and plasma on the Alfven surface, beam function dependence from the energy, etc. See e.g. poster Annala & Poutanen

  16. Pulse fraction dependence on the luminosity and energy band Timing analysis of the INTEGRAL/IBIS data of X-ray pulsars in narrow energy bands. Only bright sources (flux in the 20-50 keV range >100 mCrab): Name Ecyc 4U 0115+63 ~11, 21, 34, 45 keV V 0332+53 ~28, 55 keV A 0535+262 ~45, 100 keV Hercules X-1 ~38 keV Vela X-1 ~22, 56 keV GX 301-2 ~50 keV GX 1+4 - Cen X-3 ~31 keV OAO 1657-415 ~78 keV (not detected with INTEGRAL) EXO 2030+375 -

  17. Pulse fraction dependence on the energy Also for millisecond pulsars (Falanga 2007)

  18. - spectrum of the Nebula (non-pulsed) - spectrum of the pulsar (pulsed) Segreto et al. (2005) Crab for Crab-like spectrum The increasing of the pulse fraction is a steeper than we expect from our simple suggestion.

  19. X-ray pulsars The situation is more complicated: Typical X-ray pulsars spectrum; corresponds to Presence of cyclotron lines; PF dependence on the luminosity Different mechanisms of the emission;

  20. PF vs I(E)-1 A(E) - non-universal and different for different X-ray pulsars

  21. Preliminary ideas The rise of the amplitude in the exponential tail: Temperature grows towards deeper layers At higher inclinations - cooler outer layers At lower inclinations – hotter deeper layers are visible The intensity in the Wien tail will be strongly modulated The rise of the amplitude in the cyclotron line: A strong dependence of the opacity on the angle with the magnetic field can give a large modulation.

  22. Summary • Mostly accurate results of the spectral and timing analysis of several dozens X-ray pulsars in hard X-rays at the moment • The evolution of the cyclotron energy with the source luminosity was studied in detail for the first time. It was shown that for V0332+53 and A535+26 this dependence is linear, but for 4U0115+63 is more complicated • Strong dependence of the pulse fraction on the energy and source luminosity is revealed and study in detail • The prominent feature in the dependence of the pulse fraction on energy band was revealed near the cyclotron frequency for several bright sources • There are preliminary ideas how to explain above, but may be something else?...

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