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

2. 2Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 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 2

3. 3Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 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 r m = f r co f~0.4 3

4. 4Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 Propeller accretion Inner disk rotates faster than magneto sphere and plasma is funnelled to the surface by B-field 4 AccretionPropeller Magnetos phere rotates faster than accretion flow and matter can be centrifugal ly ejected.

5. 5Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 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. 5 Illarionov & Sunyaev (1975); Lovelace, Romanova and Bisnovatyi-Kogan (1999)

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

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

8. 8Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 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 –α v =0.1-0.3, α d =0.1 Turbulent MRI-driven disks. Cylindrical coordinates –Viscosity is determined by MRI. –Diffusivity is free parameter 8 Utsyugova et al. (2006) Lii et al. (2014)

9. 9Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 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 9 Romanova et al. (2008) Kuulkarni & Romanova (2008) Spruit et al. (1995); Lubow & Spruit (1993); Kaisig, Tajima, Lovelace (1992) g eff = g – Ω 2 r

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

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

12. 12Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 Propeller Conical winds dominate the outwards mass outflow Strong magnetic tower produces a more collimated Pointing dominated jet. Accretion continues on episodic fashion 12 r m > r co

13. 13Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 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 13 Slow rotatorFast rotator propeller Romanova et al. (2005)

14. 14Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 Transport Matter cannot escape system efficiently in weak propeller Simulation parameters have influence on efficiency 14 Utsyugova et al. (2006)

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

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

17. 17Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 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* 17 Always a fraction is accreted

18. 18Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 Dependencies Strong.......................... Weak 18 r m /r co =2.5r m /r co =1.5r m /r co =1.1 Diffusivity quenches bursts of accretion because of diffusive penetration through the boundary. Lii et al. (2014)

19. 19Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 Poynting jet A magnetic tower is formed and produces a collimated jet 19

20. 20Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 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. 20 Papitto+ (2013)

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

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

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

24. 24Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 Always pulsed 24

25. 25Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 Two accretion states 25 Higher state Lower state TWO log- normal distributions 2 x10 36 erg/s10 35 erg/s time Bins = 1 s

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

27. 27Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 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 27

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

29. 29Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 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 ! 29

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

31. 31Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 MHD modelling Semi- periodic Flaring α d =0.1 Not what we observe in IGR J18245 31 ms

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

33. 33Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 Higher diffusivity α d =0.1 With higher viscosity flaring is less regular It is what we observe in IGR J18245 33 ms

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

35. 35Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 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 (r m /r co ~2-3), M wind >M star ; weak propeller (r m /r co ~1), M star >M wind 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? 35

36. 36Propeller and Variability IGR J18245-2452 - C. FerrignoEWASS 26.06.2015 Far prospectives Discovery of important transients relies on quick data transmission and prompt analysis. INTEGRAL is unique for faint hard transients (<~20 mCrab) in crowded regions of the sky. A monitoring facility and telescopes with high throughput are a winning combination to study X-ray sources. New project like LOFT, combining wide field monitor and large detectors will boost our knowledge on these systems. 36 –LOFT is one of the four M3 mission candidates selected by ESA in 2011 to compete for a launch opportunity in ~2020.Payload: Large Area Detector (LAD) Area ~12 m 2 - 200 eV spectral resolution in 2-80 keV bandWide Field Monitor (WFM) 2 sr FOV - arcmim localization - 2- 80 keV band -80 cm 2 area