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Kink instabilities in jets from rotating magnetic fields
R. Moll, H. C. Spruit, M. Obergaulinger
We have performed 2.5D and 3D simulations of conical jets driven by the rotation of an ordered, large-scale magnetic field in a stratified atmosphere. The simulations cover about t…
Soft X-ray components in the hard state of accreting black holes
Caroline D'Angelo, Dimitrios Giannios, Cornelis Dullemond +1
Recent observations of two black hole candidates (GX 339-4 and J1753.5-0127) in the low-hard state (L_X/L_Edd ~ 0.003-0.05) suggest the presence of a cool accretion disk very close…
Rapid optical and X-ray timing observations of GX 339-4: flux correlations at the onset of a low/hard state
P. Gandhi, K. Makishima, M. Durant +6
We present the discovery of optical/X-ray flux correlations on rapid timescales in the low/hard state of the Galactic black hole GX 339-4. The source had recently emerged from outb…
Theory of magnetically powered jets
H. C. Spruit
The magnetic theory for the production of jets by accreting objects is reviewed with emphasis on outstanding problem areas. An effort is made to show the connections behind the occ…
Origin of neutron star magnetic fields
H. C. Spruit
Possible origins of the magnetic fields of neutron stars include inheritance from the main sequence progenitor and dynamo action at some stage of evolution of progenitor. Inheritan…
Spectral and timing properties of a dissipative GRB photosphere
Dimitrios Giannios, Henk C. Spruit
We explore the observational appearance of the photosphere of an ultrarelativistic flow with internal dissipation of energy as predicted by the magnetic reconnection model. Previou…
Magnetostatic penumbra models with field-free gaps
G. B. Scharmer, H. C. Spruit
We present numerical 2D magnetostatic models for sunspot penumbrae consisting of radially aligned field-free gaps in a potential magnetic field, as proposed by Spruit and Scharmer…
Magnetic instability in a differentially rotating star
H. C. Spruit
Instabilities in magnetic fields wound up by differential rotation as reviewed in Spruit (1999) are discussed with some detail and new developments added. In stellar models which i…
The role of kink instability in Poynting-flux dominated jets
Dimitrios Giannios, Henk C. Spruit
The role of kink instability in magnetically driven jets is explored through numerical one-dimensional steady relativistic MHD calculations. The instability is shown to have enough…
Evolution of the magnetic field in magnetars
J. Braithwaite, H. C. Spruit
We use numerical MHD to look at the stability of a possible poloidal field in neutron stars (Flowers & Ruderman 1977), and follow its unstable evolution, which leads to the complet…
A differential rotation driven dynamo in a stably stratified star
J. Braithwaite, H. C. Spruit
We present numerical simulations of a self-sustaining magnetic field in a differentially rotating non-convective stellar interior. A weak initial field is wound up by the different…
Fine structure, magnetic field and heating of sunspot penumbrae
H. C. Spruit, G. B. Scharmer
We interpret penumbral filaments as due to convection in field-free, radially aligned gaps just below the visible surface of the penumbra, intruding into a nearly potential field a…
Magnetic flux captured by an accretion disk
Dmitri A. Uzdensky, H. C. Spruit
We suggest a possible mechanism of efficient transport of the large-scale external magnetic flux inward through a turbulent accretion disk. The outward drift by turbulent diffusion…
A fossil origin for the magnetic fields of A-stars and white dwarfs
J. Braithwaite, H. C. Spruit
Some main-sequence stars of spectral type A are observed to have a strong (300-30000 G), static, large-scale magnetic field, of a chiefly dipolar shape -- the `Ap stars' (for examp…
Evaporation of ion-irradiated disks
C. P. Dullemond, H. C. Spruit
We calculate the evaporation of a cool accretion disk around a black hole due to the ion-bombardment by an ion supported accretion flow (here ISAF, or optically thin ADAF). As firs…
Presupernova Evolution of Differentially Rotating Massive Stars Including Magnetic Fields
A. Heger, S. E. Woosley, H. C. Spruit
As a massive star evolves through multiple stages of nuclear burning on its way to becoming a supernova, a complex, differentially rotating structure is set up. Angular momentum is…
Search for fast correlated X-ray and optical variability in Cir X-1 and XTE J1746-321
H. C. Spruit, H. Steinle, G. Kanbach
Coordinated observations X-ray+optical observations of two southern X-ray binaries, the black hole candidate XTE J1746-321 and the neutron star accreter Cir X-1 (a `microquasar') a…
Local Axisymmetric Diffusive Stability of Weakly-Magnetized, Differentially-Rotating, Stratified Fluids
Kristen Menou, Steven A. Balbus, Henk C. Spruit
We study the local stability of stratified, differentially-rotating fluids to axisymmetric perturbations in the presence of a weak magnetic field and of finite resistivity, viscosi…
Excess mid-IR emission in Cataclysmic Variables
G. Dubus, R. Campbell, B. Kern +2
We present a search for excess mid-IR emission due to circumbinary material in the orbital plane of cataclysmic variables (CVs). Our motivation stems from the fact that the strong…
Accretion Onto Fast X-Ray Pulsars
S. A. Rappaport, J. M. Fregeau, H. Spruit
The recent emergence of a new class of accretion-powered, transient, millisecond X-ray pulsars presents some difficulties for the conventional picture of accretion onto rapidly rot…
The optical and X-ray flickering of XTE J1118+480
J. Malzac, T. Belloni, H. C. Spruit +1
We use both time-domain and Fourier techniques to study the correlated optical and X-rays variability in the black hole X-ray nova XTE J1118+480. Its X-ray timing properties, such…
Origin of the torsional oscillation pattern of solar rotation
H. C. Spruit
A model is presented that explains the `torsional oscillation' pattern of deviations in the solar rotation rate as a geostrophic flow. The flow is driven by temperature variations…
Efficient acceleration and radiation in Poynting flux powered GRB outflows
G. Drenkhahn, H. C. Spruit
We investigate the effects of magnetic energy release by local magnetic dissipation processes in Poynting flux-powered GRBs. For typical GRB parameters (energy and baryon loading)…
The Structure and Evolution of Circumbinary Disks in Cataclysmic Variable Systems
G. Dubus, R. E. Taam, H. C. Spruit
We investigate the structure and evolution of a geometrically thin viscous Keplerian circumbinary (CB) disk, using detailed models of their radiative/convective vertical structure.…