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Propeller and Variability IGR J18245-2452 - C. Ferrigno

Numerical simulations of propeller accretion regime and the variability of IGR J18245-2452 Carlo Ferrigno University of Geneva Marina Romanova Cornell University. EWASS 26.06.2015. Propeller and Variability IGR J18245-2452 - C. Ferrigno. 1. General view.

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Propeller and Variability IGR J18245-2452 - C. Ferrigno

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  1. Numerical simulations of propeller accretion regime and the variability of IGR J18245-2452 Carlo Ferrigno University of Geneva Marina Romanova Cornell University EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 1

  2. General view • Matter of the disk is stopped by the magnetic pressure • Accretion and outflows depend on amount of matter accretion rate • Diffusivity at the disk-magnetosphere boundary EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 2

  3. Terminology • Corotation radius: radius at which the magnetic field rotates at the local Keplerian speed • Alfven radius: distance from a non- rotating star where the free-fall of a quasi-spherical accretion flow is stopped. • Magnetospheric radius: radius at which magnetic pressure overcomes the ram pressure and flow is trapped by magnetic field in discs rm = f rcof~0.4 EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 3

  4. Propeller accretion • Inner disk rotates faster than magnetosphere and plasma is funnelled to the surface by B-field Accretion Propeller • Magnetosphere rotates faster than accretion flow and matter can be centrifugally ejected. EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 4

  5. Theory • Study of the effective Alfven radius, which flickers in and out the corotation radius • Matter and angular momentum flow due to coupling of magnetic field and plasma • Transitions from propeller to accretion may be stochastic or chaotic in nature, with triggering due to small variations in the accretion flow or in the magnetic field configuration. Illarionov & Sunyaev (1975); Lovelace, Romanova and Bisnovatyi-Kogan (1999) EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 5

  6. The MHD problem • Reference frame corotating with the star • Solving for 8 variables: B field (3), plasma speed (3), density, energy density Viscosity Stress tensor No shocks Ideal Diffusivity γ=5/3 Adiabatic e.g., Utsyugova (2006) EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 6

  7. Scalable simulations • Adimensional variables. • Scalable to objects with small magnetosphere EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 7

  8. Set-up of propeller simulations • Gudonov type MHD code: 2.5D simulations of propeller • Laminar α- disks. Spherical coordinates, 2.5D • also top-bottom symmetry • αv=0.1-0.3, αd=0.1 • Turbulent MRI-driven disks. Cylindrical coordinates • Viscosity is determined by MRI. • Diffusivity is free parameter Utsyugova et al. (2006) Lii et al. (2014) EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 8

  9. Accretion excursus • α-disk model. 3-D simulations to study the Reyleigh-Taylor instabilities. • Heavy matter pervades the light medium across magnetic field line and produces accretion tongues (low viscosity 0.02) • Reduction of significance of coherent pulsations geff = g – Ω2r Romanova et al. (2008) Kuulkarni & Romanova (2008) Spruit et al. (1995); Lubow & Spruit (1993); Kaisig, Tajima, Lovelace (1992) EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 9

  10. Stable/Unstable accretion • High accretion rate, unstable accretion. • Inclination stabilizes. Blinova et al. (2013) EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 10

  11. Dependencies • Hollow column or crescent shape • Dependency on accretion rate is less steep than standard theory (1/5 < 2/7) Kuulkarni & Romanova (2013) EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 11

  12. Propeller • Conical winds dominate the outwards mass outflow • Strong magnetic tower produces a more collimated Pointing dominated jet. • Accretion continues on episodic fashion rm > rco EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 12

  13. Slow and fast rotators • Outflows are present in both cases together with accretion in funnels. • In propeller, there is a fast axial jet, which does not form in conical wind only regime Slow rotator Fast rotator propeller Romanova et al. (2005) EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 13

  14. Cyclic accretion • Matter accumulates and then is accreted in cyclic fashion • Contemporary ejections of material Lii et al. (2014) EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 15

  15. Episodic accretion cycle • Observed sporadically in outburst of AMSP, but at different time scale and duty cycle • Lower diffusivity may reconcile the observations. SAX J1808, Patruno et al. 2009; NGC 6440 X-2 Patruno & D’Angelo 2013 D’Angelo & Spruit 2010; EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 16

  16. Strong propeller outflow • one-sided outflow half-opening angle: ~20-40°, with continued collimation further out • time averaged ejection efficiency: 50-90% depending on Ω* • Always a fraction is accreted EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 17

  17. Dependencies • Strong .......................... Weak rm/rco=2.5 rm/rco=1.5 rm/rco=1.1 Lii et al. (2014) • Diffusivity quenches bursts of accretion because of diffusive penetration through the boundary. EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 18

  18. IGR J18245/M 28I • In the globular cluster M 28: it is at 5.5 kpc. • In 2013: one bright accretion driven outburst. Coherent pulsation. Strong spectral and timing variability. • Intermediate accretion events: X-ray & optical brightening. Mode switch variability. • Faint radio pulsar with irregularly eclipses due to outflows. Papitto+ (2013) EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 20

  19. IGR J18245/M 28I in accretion phase • Only a fewdays after the last X-ray detection ! Papitto+ (2013) EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 21

  20. XMM-Newton light curve time Bins >= 200 s • Very interesting variability, unique among AMSP. • Episodes of enhanced hardness at low flux • No orbital dependency. Hard 3.5-10 keV Soft 0.5-3.5 keV Ferrigno + (2014) EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 22

  21. Two branches time Bins >= 200 s • Blue: higher flux, limited Hardness variation • Magenta: lower flux, swings of hardness, what are they? EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 23

  22. Always pulsed EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 24

  23. Light curve - Blue state • Strong second-scale variability. • red points are bins of 200 s EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 26

  24. Wavelets • Try to understand if there are particular time scales in the variability of this source. • Try to check when they appear, if they appear. • Use a wavelet power spectrum: • continuous wavelet transform • Morlet wavelet with index 6 investigating time scales from 2dt for 8 octaves EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 27

  25. Wavelet investigation • Stripe with period at ~20 s. 20 s EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 28

  26. Zoomed wavelet • There seems to be a typical time scale around 20 s • Short peaks are highlighted, but do not represent a true periodicity. • Wavelet are sensitive to shot noise ! EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 29

  27. A faster variability sec. scale ~2 s scale EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 30

  28. MHD modelling • Semi-periodic Flaring αd=0.1 • Not what we observe in IGR J18245 ms EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 31

  29. Wavelet • A clear periodicity is detected at ~60 s and peaks are highlighted by shorter term power. ms EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 32

  30. Higher diffusivity • αd=0.1 • With higher viscosity flaring is less regular • It is what we observe in IGR J18245 ms EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 33

  31. Wavelet 2 • No clear periodicity. • Short-time variability at strong peaks • Longer term variability at ~250 s (windowing problems). • Irregular. ms EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 34

  32. Conclusions • Numerical simulations are a unique tool to study accreting system behavior in terms of realistic physical conditions for various scales of objects • MRI simulations evidence that in propeller regime both accretion and outflows are present both in weak and strong propeller. Strong propeller (rm/rco~2-3), Mwind>Mstar ; weak propeller (rm/rco~1), Mstar>Mwind • High magnetic diffusivity plays an important role in smoothing spikes. Observed variability might provide a mean to narrow down the parameter space. • Wavelet is a powerful tool to investigate the intermittent quasi-periodic signal in light curve. Work in progress to identify possible quasi periodic behavior. • IGR J18245 has a pronounced variability never observed in aMSP: peculiar of transitional pulsars? EWASS 26.06.2015 Propeller and Variability IGR J18245-2452 - C. Ferrigno 35

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