Conference Program | Physics at the Magnetospheric Boundary

Invited talks are in bold.

25 June 2013

09:00-09:55	Welcome (registration) and coffee
09:55-10:00	Introductory remarks

	SESSION 1 (Chair: R. Staubert)
10.00-10:45	Theory of disk accretion (D. Lai) Disk accretion onto magnetic stars occurs in a variety of systems, including accreting neutron stars (with both high and low magnetic fields), white dwarfs, and protostars. I will review some of the key physical processes in magnetosphere-disk interactions, highlighting the theoretical uncertainties. I will also discuss some applications to the observations of accreting neutron star systems, as well as possible connections to protostellar disks and (exo)planetary systems.
10.45-11:05	Disk accretion onto a magnetized star (Y. Istomin) The problem of interaction of the rotating magnetic field, frozen to a star, with a thin well conducting accretion disk is solved exactly. It is shown that a disk pushes the magnetic field lines towards a star, compressing the stellar dipole magnetic field. At the point of corotation, where the Keplerian rotation frequency coincides with the frequency of the stellar rotation, the loop of the electric current appears. The electric currents flow in the magnetosphere only along two particular magnetic surfaces, which connect the corotation region and the inner edge of a disk with the stellar surface. It is shown that the closed current surface encloses the magnetosphere. Rotation of a disk is stopped at some distance from the stellar surface, which is 0.55 of the corotation radius. Accretion from a disk spins up the stellar rotation. The angular momentum transferred to the star is determined.
11.05-11:25	Dead discs, unstable discs and the stars they surround (C. D'Angelo) Strong stellar magnetic fields significantly alter the behaviour of surrounding accretion discs. Recent work has demonstrated that at low accretion rates a large amount of mass can remain confined in the disc, contrary to the standard assumption that the magnetic field will expel the disc in an outflow (the "propeller regime"). These "dead discs" often become unstable, causing cycles of accretion onto the central star. I will present the main predictions of this model, and argue that it provides a good explanation for the peculiar behaviour seen in some accreting sources with strong magnetic fields. I will focus in particular on three accreting millisecond X-ray pulsars: SAX J1808.4-3658, NGC 6440 X-2 and IGR J00291+5934. These sources all show low-frequency quasi-periodic oscillations consistent with a variable accretion rate, as well as unusual outburst patterns that suggest gas is confined in the inner disc regions during quiescence.
11.25-11:45	Swinging between rotation and accretion power in a binary millisecond pulsar (A. Papitto) The very fast spin periods measured in radio millisecond pulsars are thought to be the outcome of an earlier X-ray bright phase, during which the neutron star accretes matter and angular momentum from a low mass companion star in a binary system. This evolutionary scenario has been supported by the detection of X-ray millisecond pulsations from several accreting neutron stars in the past fifteen years, as well as by the indirect evidence for the presence of a disk in the past around a millisecond radio pulsar now powered by rotation. However, a transition between a rotation-powered and an accretion-powered state was never observed. Here we present the detection of millisecond X-ray pulsations from an accreting neutron star which showed multiple accretion event in the past few years, and was already known as a radio millisecond pulsar. This source proves that in the context of the evolutionary link between millisecond pulsars fueled either by rotation or by mass accretion, these states may alternate over a time scale of a few years in a cyclic fashion. We also discuss the puzzling variations observed in the X-ray light curve, and the peculiar properties of the X-ray pulse profile, in terms of the propeller inhibition of mass accretion down to the neutron star surface.
11.45-12:05	A possible link between kHz QPOs and the magnetospheric boundary (M.H. Erkut) The quasi-periodic oscillations (QPOs) observed with a 200-1300 Hz frequency range in the X-ray power spectra of low mass X-ray binaries (LMXBs) might be considered as one of the observational clues to the physics at the innermost regions of accretion disks around neutron stars. In a neutron star LMXB, the magnetospheric boundary is likely to be close to the surface of the neutron star because of its presumably weak magnetic dipole field. The kHz QPOs can therefore be interpreted as the modulation of X-ray emission with smallest timescales associated with the dynamics of accreting disk matter at the magnetospheric boundary. As a result of magnetosphere-disk interaction we expect the rotational dynamics of the disk matter in the boundary region to be characterized by either sub-Keplerian or super-Keplerian flow depending on the fastness of the neutron star. We summarize our current understanding of the kHz QPO frequency correlations in terms of the oscillatory modes amplified in the magnetic boundary region and discuss the future prospects related to the possible link between kHz QPOs and the rotational dynamics at the magnetospheric boundary.
12.05-12:20	discussion
12.20-12.30	Posters Advertisements (P7, P13, P14, P22)

12:30-14.00	lunch break

	SESSION 2 (Chair: J. Bouvier)
14:00-14.45	Theory of accretion onto young stellar objects (R. Pudritz) The interaction of the magnetospheres of forming stars with their surrounding protostellar disks is a central problem in the theory of star formation. The observations show clear evidence for magetospheric accretion. However, a key aspect of this issue is to identify how the associated angular momentum of accreting material is dealt with. The coupling of accretion with some mechanism of angular momentum removal from accreting gas is crucial since otherwise young stars would quickly reach break-up spin rates, which is not observed. We will review the observational, theoretical, and more recently, computational advances in the field and show how these impact our ideas about early stellar evolution.
14.45-15.05	The evolution of the star-disk interaction for newborn solar-like stars (S. Gregory) Magnetic mapping studies using the technique of Zeeman-Doppler imaging have now revealed that low mass accreting T Tauri stars can host a variety of multipolar magnetic field topologies. Fully convective stars, above approximately half a solar mass at an age of a few Myr, host axisymmetric large scale magnetic fields with kilo-Gauss dipole components, while stars which have developed a partially convective interior with a radiative core host more complex magnetic fields. The most intriguingly result, in terms of the rotational evolution of the star, is that the dipole component (that which is most important in terms of controlling the disk truncation radius and therefore the balance of torques in the star-disk system) appears to drop by an order of magnitude with the development of a radiative core. For accreting T Tauri stars of solar mass and above a radiative core develops in 2.5 Myr or less, within the typical timescale for disk dispersal. I will demonstrate that, for any reasonable assumption of how the mass accretion rate declines with age, the observed drop in the stellar dipole component as a star develops a radiative cores leads to a period of stellar spin-up. I will explore the evidence for this scenario within star-forming regions of differing average age.
15.05-15.25	Accretion shock stability on a dynamically heated YSO atmosphere with radiative transfer (L. DE SA) The aim of the project ANR STARSHOCK is to understand the dynamics and the radiative properties of accretion columns, linking the inner circumstellar disk to the photosphere of Young Stellar Objects. Theory and simulations predict Quasi-Periodic Oscillations of a shock in the magnetically driven accretion funnel. X-ray observations however do not show evidence of the expected periodicity. We investigate here, in a first attempt, a mechanism to suppress this periodicity using both radiative transfer and a basic model of a dynamically heated stellar atmosphere with the 1D RHD code ASTROLABE. The use of a dynamical atmospheric heating slightly perturbs these oscillations, whereas they can be totally suppressed by an efficient coupling between gas and radiation, which allows the shock to go deeper in the chromosphere. 2D and 3D MHD simulations suggest other possible scenarii, taking into account the influence of the magnetic field on the dynamics of the column. These results are post-processed using the radiative transfer codes SYNSPEC (1D) and IRIS (3D). Comparison between outcoming spectra and observations will help us to constrain our models and better understand the underlying physics of accretion shocks. This work is supported by french ANR, under grant 08-BLAN-0263-07
15.25-15.45	2D/3D numerical modeling of YSO accretion shocks and their observational relevance (T. Matsakos) The dynamics of YSO accretion shocks is determined by radiative processes as well as the strength and structure of the magnetic field. A quasi-periodic emission signature is theoretically expected to be observed, but observations do not confirm any such pattern. In this work, we assume a uniform background field, in the regime of optically thin energy losses, and we study the multi-dimensional shock evolution in the presence of perturbations, such as either clumps in the stream or an acoustic energy flux flowing at the base of the chromosphere. We perform 2D/3D MHD simulations using the PLUTO code, modeling locally the impact of the infalling gas on the chromosphere. We find that the structure and dynamics of the post-shock region is strongly dependent on the plasma-beta value (thermal over magnetic pressure) but not on the type of the perturbations applied. We show that different values for the plasma-beta give different and distinguishable emission signatures, relevant for observations. In particular, a strong magnetic field effectively confines the plasma inside its flux tubes and leads to the formation of quasi-independent fibrils. The fibrils may oscillate out of phase and hence the sum of their contributions in the emission results in a smooth overall profile. On the contrary, a weak magnetic field is not found to have any significant effect on the shocked plasma and the turbulent hot slab that forms is found to retain its periodic signature. The work is supported by French ANR, under grant 08-BLAN-0263-07.

15.45-16.15	coffee break

16:15-16.35	Observable Signatures of Classical T Tauri Stars Accreting in an Unstable Regime (R. Kurosawa) Variable nature of Classical T Tauri stars (CTTSs) are known to exists in different time-scales. However, CTTSs accreting through the Rayleigh-Taylor instability, which occurs at the interface between an accretion disc and a stellar magnetosphere, could exhibit unique observable signatures in their variability patterns. The instability causes gas to accrete in a several temporarily formed accretion streams which appear in random locations, and produce stochastic photometric and line variability. In this study, the results of global 3-D MHD simulations of matter flows, in both stable and unstable regimes, are used to predict the variability behavior of hydrogen line profiles and light curves associated with those two distinctive accretion flow patterns. In the stable regime, some hydrogen lines show a redshifted absorption component only during a fraction of a stellar rotation period, and its occurrence is periodic. This is caused by an ordered accretion funnel stream which passes across the line of sight to an observer only once per stellar rotation period. On the other hand, in the unstable regime, the redshifted absorption component is present rather persistently during a whole stellar rotation cycle, and its strength varies non-periodically. This is caused by a several accreting streams, which are formed randomly, passing across the line of sight to an observer during one stellar rotation. This results in the quasi-stationarity appearance of the redshifted absorption despite the strongly unstable nature of the accretion since at least one of the accretion stream is almost always in the line of sight to an observer. In the unstable regime, multiple hot spots formed on the surface of the star, produce the stochastic light curve with several peaks per rotation period. In the stable regime, two stable hot spots produce a smooth and periodic light curve that shows only one or two peaks per stellar rotation. This study suggests a CTTS that shows a stochastic light curve and a stochastic line variability, with a rather persistent redshifted absorption component, is possibly accreting in the unstable accretion regime caused by the Rayleigh-Taylor instability.
16:35-16.55	discussion
16.55-17.00	Posters Advertisements (P01,P15)

	SESSION 3 (Chair: C. Hellier)
17:00-17.40	Theory of accretion onto white dwarfs (D. Wickramasinghe) The Intermediate Polars and the AM Herculis type variables are close interacting binary systems where mass transfer occurs from a late type star onto a rotating magnetic white dwarf. Depending on the binary parameters and the magnetic field strength of the white dwarf accretion can occur via a variety of modes. These range from direct accretion onto an asynchronous magnetic white dwarf, indirect accretion via a truncated accretion disc onto a asynchronous magnetic white dwarf, to direct accretion onto a synchronously rotating magnetic white dwarf. Mode switching driven by changes in the mass transfer rate has also been documented. We summarise the properties of these systems and review the theory of magnetospheric accretion onto magnetic white dwarfs.
17:40-18.00	Features of the mass transfer in magnetic CVs with fast-rotating white dwarfs (P. Isakova) The flow structure in a typical CV was investigated taking into account the effects of strong magnetic field and fast rotation of the accretor. We modeled the AE Aqr system as the representative observational object that has the rotation period is about 1000 times shorter than the orbital period of the binary system. Observations show that in spite of fast rotation some part of the stream from the inner Lagrangian point comes into the Roche lobe region. We analyzed the possible mechanisms preventing material to outflow from the system. Among these mechanisms are the ambipolar diffusion, the pressure of electromagnetic waves and the relativistic lag of magnetic field lines. Our analysis has shown that the degree of ionization is high enough in the inner Lagrangian point of the considered system so the ambipolar diffusion is not effective. For the AE Aqr system the inner Lagrangian point is located inside the light cylinder, but the light radius is smaller than the orbit separation. Hence, the pressure of electromagnetic waves caused by the white dwarf rotation also can not stop material. The only effective mechanism allowing to the stream comes inside the Roche lobe is connected with the effect of relativistic lag of rotating magnetic field. In our simulations the relativistic lag effect was taken into account approximately assuming that angular velocity of magnetic field lines falls with the distance from the white dwarf. Both ballistic calculations and 3D MHD simulations show the formation of fairly stable ring-like structures around the accretor in the AE Aqr system caused by presence of this mechanism. The gradual accumulation of material in the ring leads to increase of the pressure gradient, and, as a result, to the transforming of the original ring into the disk.
18.00-18.15	discussion
18.15-18.20	Posters Advertisements (P12)

26 June 2013

	SESSION 4 (Chair: J. Wilms)
09.00-09:45	Theory of wind accretion (N. Shakura) A review of wind accretion in high-mass X-ray binaries is presented. We focus attention to different regimes of quasi-spherical accretion onto the neutron star: the supersonic (Bondi) accretion, which takes place when the captured matter cools down rapidly and falls supersonically toward NS magnetospghere, and subsonic (settling) accretion which occurs when plasma remains hot until it meets the magnetospheric boundary. Two regimes of accretion are separated by an X-ray luminosity of about 4 x 10**36 erg/s. In the subsonic case, which sets in at low luminosities, a hot quasi-spherical shell must be formed around the magnetosphere, and the actual accretion rate onto NS is determined by ability of the plasma to enter the magnetosphere due to Rayleigh-Taylor instability. We calculate the rate of plasma entry the magnetopshere and the angular momentum transfer in the shell due to turbulent viscosity appearing in the convective differentially rotating shell. We discuss how observations of spin-up/spin-down of slowly rotating X-ray pulsars with moderate X-ray luminosities can be used to estimate the neutron star magnetic field and other parameters of the model.
09.45-10.05	Do we see accreting magnetars in X-ray pulsars? (K. Postnov) The strong magnetic field of accreting neutron stars (10^14 G) cannot be probed by spectroscopic observations but can be indirectly estimated from spin-up/spin-down measurement in X-ray pulsars. The existing observations of slowly rotating X-ray pulsars will be discussed. It will be shown that magnetic fields of neutron stars derived from these observations (or lower limits in some cases) fall within the standard 10^12-10^13 G range. Claims about the evidence for accreting magnetars will be critically discussed in the light of recent progress in understanding of accretion onto slowly rotating neutron stars in the subsonic regime.
10.05-10:25	A multi-model approach to X-ray pulsars: Connecting spectral and timing models to pin down the intrinsic emission characteristics of magnetized, accreting neutron stars (G. Schonherr) The emission characteristics of X-ray pulsars are governed by magnetospheric accretion within the Alfven radius, leading to a direct coupling of accretion coulumn properties and the interactions at the magnetosphere. The complexity of the physical processes governing the formation of radiation within the accreted, strongly magnetized plasma has led to the development of sophisticated theoretical modelling efforts over the last decade, dedicated to either the formation of the broad band continuum, the formation of cyclotron resonance scattering features (CRSFs) or the formation of pulse profiles. While these individual approaches are powerful in themselves, they quickly touch their limits when aiming at a quantitative comparison to observational data: Too many fundamental parameters, describing the formation of the accretion columns and the system’s overall geometry are unconstrained and different models are often based on quite different fundamental assumptions, while everything is intertwined in the observed, highly phase-dependent spectra and pulse profiles. To name just one example: the (phase variable) line width of the CRSFs is highly dependent on temperature, the existence of B-field gradients (geometry) and observation angle, parameters which in turn drive the continuum radiation and are driven by the overall two-pole geometry for the light bending model respectively. This renders a parallel assessment of all available spectral and timing information by a compatible across-models-approach indispensable. In a collaboration of theoreticians and observers, we have been working on a model unification project over the last years, bringing together theoretical calculations of the Comptonized continuum, Monte Carlo simulations and Radiation Transfer calculations of CRSFs as well as a GR light bending model for ray tracing of the incident emission pattern from both magnetic poles. The ultimate goal is to implement a unified fitting model for phase-resolved spectral and timing data analysis. We present the current status of this project and discuss constraints for, as well as new questions about, the physical parameters of the system, arising from the cross-correlation of our individual models. We acknowledge the International Space Science Institute, Bern, for hosting two very fruitful international team meetings about ”The physics of the accretion column of X-ray pulsars” in 2011/2012 to start this collaborative effort.

10.25-10.55	coffee break

10.55-11:15	Magnetic field structure in accretion columns on HMXB and the effect on CRSF (D. Mukherjee) In accreting neutron star binaries, matter is channelled by the magnetic fields from the accretion disc to the poles of neutron stars forming an accretion mound. We model such mounds by numerically solving the Grad-Shafranov (GS) equation for axisymmetric static MHD equilibria. From our solutions we infer local distortion of field lines due to the weight of accreted matter. Variation in mass loading at the accretion disc will alter the shape of the accretion mound which will also affect the local field distortion. From simulations of cyclotron resonance scattering features (CRSF) from HMXBs, we conclude that local field distortion will greatly affect the shape and nature of the CRSF. From phase resolved spectral analysis one can infer the local field structure and hence the nature of mass loading of field lines at the accretion disc. We also study the stability of such mounds by performing MHD simulations using the PLUTO MHD code. We find that pressure and gravity driven instabilities depend on the total mass accreted and the nature of mass loading of the field lines. The effects of the instabilities on the CRSF spectra and on timing features from such systems have been explored.
11.15-11:35	A reflection model for the cyclotron lines in the spectra of X-ray pulsars (A. Mushtukov) Cyclotron resonance scattering features observed in the spectra of some X-ray pulsars show a significant changes of the line energy with the pulsar luminosity. At high luminosities, these variations are often associated with the onset and growth of the accretion column, which is believed to be the origin of the observed emission and of the cyclotron lines. However, this scenario inevitably implies large gradient of the magnetic field strength within the line-forming region, which makes the formation of the observed line-like features problematic. Moreover, the observed variation of the cyclotron line energy is much smaller than could be anticipated for the corresponding luminosity changes. We argue here that a more physically realistic situation is that the cyclotron line forms when the radiation emitted by the accretion column is reflected from the neutron star atmosphere, where the gradient of the magnetic field strength is significantly smaller. We develop the reflection model and apply it to explain the observed variations of the cyclotron line energy in a bright X-ray pulsar V~0332+53 over a wide range of luminosities.
11.35-11:55	Accretion in supergiant High Mass X-ray Binaries (A. Manousakis) Supergiant High Mass X-ray Binary systems (sgHMXBs) consist of a massive, late type, star and a neutron star. The massive stars exhibits strong, radiatively driven, stellar winds. Wind accretion onto compact object triggers X-ray emission, which alters the stellar wind significantly. Hydrodynamic simulation has been used to study the neutron star - stellar wind interaction it two sgHMXBs: i) A heavily obscured sgHMXB (IGR J17252-3616) discovered by INTEGRAL. To account for observable quantities (i.e., absorbing column density) we have to assume a very slow wind terminal velocity of about 500 km/s and a rather massive neutron star. If confirmed in other obscured systems, this could provide a completely new stellar wind diagnostics. ii) A classical sgHMXB (Vela X-1) has been studied in depth to understand the origin of the off-states observed in this system. Among many models used to account for this observed behavior (clumpy wind, gating mechanism) we propose that self-organized criticality of the accretion stream is the likely reason for the observed behavior. In conclusion, the neutron star, in these two examples, acts very efficiently as a probe to study stellar winds.
11.55-12.10	discussion
12.10-12.20	Posters Advertisements (P04, P02, P06, P05)

12:20-13.40	lunch break

	SESSION 5 (Chair: K. Postnov)
13.40-14.25	Numerical modelling of magnetospheric accretion, ejection and plasma-field interactions (M. Romanova) I will discuss the results of axisymmetric and global 3D MHD simulations of magnetospheric accretion and outflows. 3D simulations show that magnetized stars may accrete in a stable regime, where matter accretes to the star in ordered funnel streams, or in an unstable regime, where matter penetrates through the magnetosphere in several unstable tongues due to the magnetic Rayleigh-Taylor instability. The boundary between the stable and unstable regimes depends on a number of factors, which will be discussed. A rotating magnetized star excites bending and density waves in the surrounding accretion disk, including a warp near the magnetosphere. These waves may be responsible for different types of periodic and quasi-periodic variability. Waves which form in the inner parts of the disk may influence the rotation of the funnel streams and the unstable tongues, thus affecting the motion of the hot spots on the surface of the star and associated variability. Differential rotation between the inner disk and the magnetosphere leads to inflation of the field lines and to outflows from the disk-magnetosphere boundary. Outflows are stronger during episodes of enhanced accretion, where the disk compresses the magnetosphere, and a magnetically-driven outflow is launched from the disk-magnetosphere boundary. If a star accretes in the "propeller regime", the outflows have two components: matter-dominated wind and a magnetically-dominated axial jet. Both accretion and outflows in the propeller regime are strongly non-stationary and occur in flares, which may be episodic or quasi-periodic. Results of the simulations are applicable to stars of different types, from young stars to compact stars.
14.25-14.45	MHD simulations of magnetized stars in the propeller regime of accretion (P. Lii) Accreting magnetized stars may be in the propeller regime of disc accretion in which the angular velocity of the stellar magnetosphere exceeds that of the inner disc. In these systems, the stellar magnetosphere acts as a centrifugal barrier and inhibits matter accretion onto the rapidly rotating star. Instead, the matter accreting through the disc accumulates at the disc-magnetosphere interface where it picks up angular momentum and is ejected from the system as a wide-angled outflow which gradually collimates at larger distances from the star. If the ejection rate is lower than the accretion rate, the matter will accumulate at the boundary faster than it can be ejected; in this case, accretion onto the star proceeds through an episodic accretion instability in which the episodes of matter accumulation are followed by a brief episode of simultaneous ejection and accretion of matter onto the star. In addition to the matter dominated wind component, the propeller outflow also exhibits a well-collimated, magnetically-dominated Poynting jet which transports energy and angular momentum away from the star. The propeller mechanism may explain some of the weakly-collimated jets and winds observed around some T Tauri stars as well as the episodic variability present in their lightcurves. It may also explain some of the flaring variability observed in cataclysmic variables, millisecond pulsars and other magnetized stars.
14.45-15.05	3D MHD Simulations of Waves Excited in an Accretion Disc by a Rotating Magnetized Star (R. Lovelace) We report results of the first global 3D MHD simulations of warp and density waves in accretion discs excited by a rotating star with a misaligned dipole magnetic field (Romanova et al. 2013). A wide range of cases are considered. We find for example that if the star's magnetosphere corotates approximately with the inner disc, then a strong one-arm bending wave (a warp) forms. The warp corotates with the star and has a maximum amplitude ($\|\Delta z\|/r \sim 0.35$) between the corotation radius and the radius of the vertical resonance. If magnetosphere rotates more slowly than the inner disc, then a bending wave is excited at the disc-magnetosphere boundary, but it does not form large-scale warp. In this case the angular rotation of the disc ($\Omega(r)$) has a maximum as a function of $r$ so that there is an inner region where $d\Omega/dr >0$. In this region we observe radially trapped density waves in approximate agreement with the theoretical prediction of a Rossby wave instability (Lovelace, Turner, and Romanova 2009).
15.05-15.25	Role of local absorption on the X-ray emission from MHD accretion shocks in classical T Tauri stars (R. Bonito) Accretion processes onto classical T Tauri stars (CTTSs) are believed to generate shocks at the stellar surface due to the impact of supersonic downflowing plasma. Although current models of accretion streams provide a plausible global picture of this process, several aspects are still unclear. For example, the observed X-ray luminosity in accretion shocks is, in general, well below the predicted value. A possible explanation discussed in the literature is in terms of significant absorption of the emission due to the thick surrounding medium. Here we consider a 2D MHD model describing an accretion stream propagating through the atmosphere of a CTTS and impacting onto its chromosphere. The model includes all the relevant physics, namely the gravity, the thermal conduction, and the radiative cooling, and a realistic description of the unperturbed stellar atmosphere (from the chromosphere to the corona). From the model results, we synthesize the X-ray emission emerging from the hot slab produced by the accretion shock, exploring different configurations and strengths of the stellar magnetic field and different density profiles of the accretion stream (accounting also for non uniform streams). The synthesis includes the local absorption by the thick surrounding medium and the Doppler shift of lines due to the component of plasma velocity along the line-of-sight. We explore the effects of absorption on the emerging X-ray spectrum, considering different inclinations of the accretion stream with respect to the observer. We also investigate the detectability of line shift due to Doppler effect under different physical conditions. Finally we compare our results with the observations.
15.25-15.45	Modulating magnetar emission by magneto-elastic oscillations (M. Gabler) Our numerical simulations show that axisymmetric, torsional, magneto-elastic oscillations of magnetars including a superfluid core can explain the whole range of observed quasi-periodic oscillations (QPOs) in the giant flares of soft gamma-ray repeaters. There exist constant phase, magneto-elastic QPOs at both low (f500 Hz), in full agreement with observations. The range of magnetic field strengths necessary to match the observed QPO frequencies agrees with the spin-down estimates. These results strongly suggest that neutrons in magnetar cores are superfluid. These oscillations of the magnetar can modulate the electro-magnetic emission by resonant cyclotron scattering (RCS). The QPOs couple to the magnetosphere through the magnetic field. We present a new code to calculate the RCS in the magnetoshpere of magnetars. It includes: i) a consistent calculation of the magnetic field; ii) a Monte-Carlo approach for the relativistic radiation transport of the photons that is employing the QED-corrected cross sections for the RCS; iii) a consistent calculation of the momentum distribution of the currents in the magnetosphere induced by the twisted magnetic field.
15.45-16.05	discussion
16.05-16-10	Posters Advertisements (P16, P17, P19, P20)

18.00	Social Event & dinner

27 June 2013

	SESSION 6 (Chair: M. Romanova)
09.00-09.45	Magnetospheric ejection (C. Zanni) Different classes of outflows can be associated with the magnetospheric activity of accreting stellar-type objects like TTauri protostars or X-Ray pulsars. Stellar winds are accelerated along the open field lines anchored into the stellar surface; another type of ejection can arise from the region of interaction of the closed magnetosphere with the surrounding accretion disk (magnetospheric ejections, conical winds); disk-winds (extended or X-winds) can be launched along the open magnetic surfaces threading the accretion disk. Primarily using numerical models, I will present the main dynamical properties of the different outflows, with a particular focus on protostellar systems. On one hand, I will try to understand if these ejection phenomena can account for the origin of the jets often observed in these systems. On the other hand, I will evaluate the impact of these outflows on the angular momentum evolution of the central star.
09.45-10.05	Three dimensional simulations of MHD disk winds to 90 AU scale from the protostar (J. Staff) We present the results of four, large scale, three dimensional magneto-hydrodynamics simulations with different initial magnetic field configuration of protostellar jets. The jets are followed from the source out to 90 AU, a scale that covers several pixels of HST images of nearby protostellar jets. The jets are launched by the magnetocentrifugal mechanism, and one of the goals for these simulations is to look for clues to rotation that observers can track through observations of forbidden lines. We have therefore created synthetic emission line maps of the simulated jets, to better compare with observations and possibly allow for the determination of the magnetic field structure on the disk around observed low mass proto-stars.
10:05-10:25	Magnetic field and angular momentum evolution models (F. Gallet) The magnetic field in young stellar object is undoubtedly the most important component when one dealing with the angular momentum evolution. It controls this latter one from the pre-main sequence (PMS), during the so-called disk locking phase where the stars magnetically interact with their surrounding disk, to the main-sequence (MS) through powerful stellar winds that remove angular momentum from the stellar surface. We present new models for the rotational evolution of solar-like stars between 1~Myr and 10~Gyr with the aim to reproduce the distributions of rotational periods observed for star forming regions and young open clusters within this age range. The models include a new wind braking law based on recent numerical simulations of magnetized stellar winds and specific dynamo and mass-loss prescriptions are adopted to tie angular momentum loss to angular velocity. The model additionally allow for decoupling between the radiative core and the convective envelope as soon as the former develops and the star/disk interaction process is explored by using several ongoing scenarios in order to reproduce the apparent small angular velocities undergone by stellar surfaces during the disk accretion phase. We have developed rotational evolution models for slow, median and fast rotators along with numerous physical star/disk interaction prescriptions including the Magnetospheric Ejection and the Accretion Powered Stellar Winds scenarios. The models appear to fail at reproducing the rotational behaviour of solar-type stars unless by using a more intense dipolar magnetic field component, of about 1 kG, during the disk accretion phase. This presentation aims at highlighting the impact of the magnetic field on the processes involved into the angular momentum removal from the PMS to the MS, and to add more constraints on the magnetic field observations and simulations.
10.25-10.45	discussion

10.45-11.25	coffee break

	SESSION 7 (Chair: M. Audard)
11.25-12:10	Observational clues to the physics at the magnetosphere in young stellar objects (S. Alencar) We will discuss, through observational examples, how the description of a low-mass star static and axisymmetric magnetosphere from the early 90s has evolved to a very dynamical multipolar region that takes into account non-steady accretion and time-dependent star-disk interactions.
12.10-12:30	Analysis of Star-Disk Interaction in Young Stellar Systems (N. N. J. Fonseca) We present the study of star-disk interaction in the classical T Tauri star V354 Mon, a member of the young stellar cluster NGC 2264. As part of an international campaign of observation of NGC 2264 organized from December 2011 to February 2012, high resolution photometric and spectroscopic data of this object were obtained simultaneously with the Chandra, CoRoT and Spitzer satellites, and ground-based telescopes, as CFHT and VLT/FLAMES at ESO. The optical and infrared light curves of V354 Mon show periodic brightness minima that vary in depth and width every rotational cycle. We found evidence that the H/alpha emission line profile changes according to the period of photometric variations, indicating that the same phenomenon causes both modulations. Such a correlation between emission line variability and light curve modulation was also identified in a previous observational campaign on the same object, where we concluded that material non-uniformly distributed in the inner part of the disk is the main cause of the photometric modulation. This assumption is supported by the fact that the system is seen at high inclination. It is believed that this distortion of the inner part of the disk results from the dynamical interaction between the stellar magnetosphere, inclined with respect to the rotation axis, and the circumstellar disk, as also observed in the classical T Tauri star AA Tau, and predicted by magnetohydrodynamic numerical simulations. A model of occultation by circumstellar material was applied to the photometric data in order to determine the parameters of the obscuring material during both observational campaigns, thus providing an investigation of its stability on a timescale of a few years. We also studied V422 Mon, a classical T Tauri star with photometric variations similar to those of V354 Mon at optical wavelengths, but with a distinct behavior in the infrared. The mechanism that produces such a difference is investigated, testing the predictions of magnetospheric accretion models.

12.30-14.00	lunch break

14.00-14:20	Observational Tests of Magnetospheric Accretion Models in Young Stars (C. Johns-Krull) Magnetically controlled accretion of disk material onto the surface of Classical T Tauri stars is the dominant paradigm in our understanding of how these young stars interact with their surrounding disks. These stars provide a powerful test of magnetically controlled accretion models since all of the relevant parameters, including the magnetic field strength and geometry, are in principle measureable. Both the strength and the field geometry are key for understanding how these stars interact with their disks. This talk will focus on recent advances in magnetic field measurements on a large number of T Tauri stars, as well as very recent studies of the accretion rates onto a sample of young stars in NGC 2264 with known rotation periods. We discuss how these observations provide critical tests of magnetospheric accretion models which predict a rotational equilibrium is reached. We find good support for the model predictions once the complex geometry of the stellar magnetic field is taken into account. We will also explore how the observations of the accretion properties of the 2264 cluster stars can be used to test emerging ideas on how magnetic fields on young stars are generated and organized as a function of their internal structure (i.e. the presence of a radiative core). We do not find support for the hypothesis that large changes in the magentic field geometry occur when a radiative core appears in these young stars.
14.20-14.40	Dynamic young stars and their disks: a temporal view (A. M. Cody) Variability is a signature feature of young stars. Among the well known light curve phenomena are periodic variations attributed to surface spots and irregular changes associated with accretion or circumstellar disk material. While decades of photometric monitoring have provided a framework for classifying young star variability, we still know surprisingly little about its underlying mechanisms and connections to the surrounding disks. In the past few years, dedicated photometric monitoring campaigns from the ground and space have revolutionized our view of young stars in the time domain. We present a selection of optical and infrared time series from several recent campaigns, highlighting the Coordinated Synoptic Investigation of NGC 2264 ("CSI 2264")-- a joint 30-day effort with the Spitzer, CoRoT, and MOST telescopes. The extraordinary photometric precision, high cadence, and long time baseline of these observations is now enabling correlation of variability properties at very different wavelengths, corresponding to locations from the stellar surface to the inner 0.1 AU of the disk. We present some results of the CSI 2264 program, including new classes of optical/infrared behavior, as well as light curves that defy explanation. Further efforts to tie observed variability features to physical models will provide insights into the inner disk environment at a time when planet formation may be underway..
14.40-15.00	Emission line diagnostics for accretion and outflows in young brown dwarfs (B. Stelzer) We present broad-band (350-2500nm) mid-resolution X-Shooter/VLT spectra of three accreting young stellar objects with spectral types between M5 and M8, i.e. near or within the brown dwarf regime. The spectra were obtained in the framework of the Italian X-Shooter GTO Survey of nearby galactic star forming regions (Alcala et al. 2011). These observations enable a detailed characterization of young (sub)stellar objects, including an accurate assessment of their fundamental parameters, kinematics, rotation, and magnetic activity. In particular, they provide a rich database of accretion diagnostics from the Brackett gamma and Paschen beta lines in the near-IR to the Balmer jump in the UV including the full optical band with the Balmer series and He 5876 and the Ca Infrared Triplet. Finally, outflows can be traced through forbidden line emission. In this contribution we focus on three of the most interesting targets from our survey: 1) For FUTauA we constrain the possible influence of excess luminosity from accretion and of stellar activity on its position in the HR diagram where FUTauA appears over-luminous with respect to the predictions of pre-main sequence evolutionary models. Moreover, we discuss the possibility of X-ray emission produced in the accretion shock of FUTauA on the basis of a Chandra observation. 2) TWA-27 (alias 2M1207-39) is the most well-studied among the brown dwarfs in the nearby 10Myr old TWHya association. It has a disk from which it is accreting, an outflow and a planetary companion. An almost two dex variation of the accretion rate has been inferred in the past based on the Halpha emission from different epochs. Here we measure accretion in TWA-27 using our new calibrations between line and continuum luminosity. 3) Par-Lup3-4 has an edge-on disk and a known jet which has been imaged in optical forbidden lines. Our repeated X-Shooter spectroscopy aims at studying the accretion and outflow variability and the relation of the mass accretion and mass outflow rates.
15.00-15.20	Magnetic fields of Herbig Ae/Be stars (S. Hubrig) We report on the status of our spectropolarimetric studies of Herbig Ae/Be stars carried out during the last years. The magnetic field geometries of these stars, investigated with spectropolarimetric time series, can likely be described by centred dipoles with polar magnetic field strengths of several hundred Gauss. A number of Herbig Ae/Be stars with detected magnetic fields have recently been observed with X-shooter in the visible and near-IR, as well as with the high-resolution near-IR spectrograph CRIRES. These observations are of great importance to understand the relation between the magnetic field topology and the physics of accretion flow and accretion disk gas emission.
15.20-15.40	discussion
15.35-15.45	Posters Advertisements (P11, P10, P18, P21)

15.45-16.10	coffee break

	SESSION 8 (Chair: M. Falanga)
16.10-16.55	Observational clues to the physics at the magnetosphere in white dwarf (C. Hellier)
16.55-17:15	V2487 Oph 1998: a post nova in an intermediate polar (M. Hernanz) V2487 Oph (Nova Oph 1998) was a classical nova that exploded in 1998. XMM-Newton observation performed between 2 and 9 years after the explosion showed emission related to restablished accretion, and indicative of a magnetic white dwarf. The spectrum looks like that of a cataclysmic variable of the intermediate polar type. Anyway, we don't have yet a definitive confirmation of the intermediate polar character, through determination of spin and orbital periods. Although it is not the first nova exploding a magnetic white dwarf, it is always challenging to reach explosive conditions when a standard accretion disk can't be formed, because of the magnetic field. In addition, V2487 Oph has been the first nova where a detection of X-rays - in the host binary system - has been reported prior to its eruption, in 1990 with the ROSAT satellite. V2487 Oph has been also detected in hard X-rays with INTEGRAL/IBIS. Last but not least, V2487 Oph has been identified as a recurrent nova in 2008, since a prior eruption in 1900 has been reported through analysis of Harvard photographic plates. Therefore, it is expected to host a massive white dwarf and be a candidate of type Ia supernova explosion. In a recent study of the progenitors of galactic novae, it has been emphasized that V2487 Oph is an important and interesting object, "intermediate" between the "standard" classical novae and other historical and well-known recurrent novae with shorter recurrence periods. It could be that in the end there's a continuous distribution of recurrence periods, instead of the common understanding up to now that "classical" and "recurrent" novae were quite appart (with recurrence periods of more than 1e4 years and less than 100 years - approximately - respectively). We will present the results of our campaign of 4 observations with XMM-Newton, as well as some optical observations. The consequences for the understanding of such a puzzling object will be discussed.
17.15-17.35	The perculiar binary system AE Aquarii from its characteristic multi-wavelength emission (B. Oruru) The multi-wavelength properties of the novalike variable system AE Aquarii are discussed in terms of the interaction between the accretion inflow from a late-type main sequence star and the magnetosphere of a fast rotating white dwarf. This matter-field interaction results into an efficient magnetospheric propeller process and particle acceleration. The spin-down of the white dwarf at a period rate of 5.64*10^-14 s s^-1, and the observed non-thermal checkbox, x-ray and (possibly) VHE and TeV gamma-ray emission may suggest that AE Aquarii can be placed in the category of spin-powered pulsars. This paper will discuss some recent theoretical studies and data analysis of AE Aquarii.
17.35-17.55	Phased Resolved X-ray Spectroscopy of EX Hya and FO Aqr (Y. Pekon) Intermediate Polars (IPs) are a subclass of Cataclysmic Variables (CVs) where a white dwarf with magnetic field strength of about 1-10 MG accretes material from a main sequence companion through a truncated disc. In this talk we will present orbital and spin phase-resolved X-ray spectroscopy of EX Hya and orbital phase-resolved X-ray spectroscopy of FO Aqr. We utilize XMM-Newton archive data of these objects for analysis. We investigate the change of the source spectrum over the spin and orbital periods. This analysis enhances our understanding about the accretion structure in these systems, temperature and composition of the X-ray emitting region together with the structure of the outer accretion disc and absorption in the system.
17.55-18.15	discussion
18.15-18-20	Posters Advertisements (P23)

28 June 2013

	SESSION 9 (Chair: I. Kreykenbohm)
09.00-09.45	Observational clues to the physics at the magnetosphere in neutron stars (J. Wilms)
09:45-10:05	Accretion geometry in the persistent Be/X-ray binary RX J0440.9+4431 (C. Ferrigno) The persistent Be/X-ray binary RX J0440.9+4431 has flared in 2010 and 2011 and it has been followed by various X-ray facilities (Swift, RXTE, XMM-Newton, and INTEGRAL). We have studied the source properties as function of its X-ray luminosity to investigate the transition from normal to flaring activity. The source spectrum can always be described by a bulk motion Comptonization model of black-body seed photons attenuated by a moderate photoelectric absorption. At the highest luminosity, we have measured a curvature of the spectrum, which we attribute to a significant contribution of the radiation pressure in the accretion process. This allows us to estimate that the transition from a bulk-motion dominated flow to a radiatively dominated one happens at a luminosity of ~2e36 erg/s. The luminosity dependency of the size of the black body emission region is found to be proportional to L_X^ (0.39+/-0.02). This suggests that either matter accreting onto the neutron star hosted in RX J0440.9+4431 penetrates through closed magnetic field lines at the border of the compact object magnetosphere, or the neutron star magnetic field has a more complicated structure close to its surface with respect to a simple dipole.
10:05-10:25	The stable accretion mechanism of GRO J1008-57 (M. Kuhnel) Based on all available RXTE-, Swift-, and Suzaku-data of type I outbursts we show that the spectral shape of the transient high mass X-ray binary GRO J1008-57 is defined by only one parameter: the X-ray flux. This, in combination with the well-known type I outburst behaviour of this source, allows for predictions of spectral as well as timing properties. We compare these results with data collected during an unusual type II ''giant'' outburst of the source in 2012 November. To the authors knowledge, there are no further transient X-ray binaries known, where the spectrum and outburst times -- during phases of activity -- can be as well predicted as for GRO J1008-57. We discuss possible origins for this remarkable result and the role of the claimed strong magnetic field of the neutron star of around 7e12 G.
10:25-10:45	The magnetic fields of neutron stars in BeXB in the SMC (H. Klus) Using archival data taken with the Rossi X-ray Timing Explorer (RXTE) we have determined the spin period, X-ray luminosity and rate of change of spin period for over 50 neutron stars in high mass X-ray binaries (HMXB) in the Small Magellanic Cloud (SMC). Using this information, plus the orbital period of each star which we took from a variety of sources, we have determined their magnetic field using six different methods, three for accretion with the formation of a disc and three without. All methods showed a strong positive correlation between magnetic field and spin period. In addition, all methods but the Shakura (2011) method for accretion without a disc give magnetic fields over the quantum critical value for all stars with a period over about 80 seconds. The pros and cons of these different accretion models will be reviewed and the consequence for the magnetic field in these neutron stars presented.

10.45-11.15	coffee break

11:15-11:35	Volatile wind accretion in X-ray pulsars and the Supergiant Fast X-ray transients (V. Doroshenko) We review the properties of several wind accreting X-ray pulsars with emphasis on so-called "off-states", when the observed flux sharply drops by orders of magnitude for several pulse cycles. Since the pulsed flux does not cease completely, we argue that the flux drop is due to partial magnetospheric inhibition of the accretion. We also find, that if the source remains off sufficiently long, the intervals between "off"-states may appear as flares similar to those observed in Supergiant Fast X-ray transients. Magnetospheric inhibition scenario has been proposed before to explain the flaring activity of the Supergiant Fast X-ray transients, and similar phenomenology observed in ordinary pulsars strongly supports this scenario providing potential link between the two classes.
11:35-11:55	Buried and re-emerging magnetic field of the neutron star in Her X-1 (D. Klochkov) We present a study of the long-term evolution of the cyclotron line energy in the accreting pulsar Her X-1. Our collection of the line measurements covers the entire 35-years history of observations of the source - the longest and the most complete records among all cyclotron line sources. It is generally accepted that the energy of the cyclotron feature reflects the strength of the magnetic field at the place of the line formation. If interpreted as a long-term evolution of the surface magnetic field of the star driven by accumulation of accreted matter, the presented variability implies substantial variations in the radius of the pulsar's magnetosphere ("stopping radius"). We demonstrate that such a variability naturally explains the historical "inactive" states observed in the binary before 1960s. Such states must be caused by the pulsar switching to the "propeller" regime. The magnetic field evolution also explains the observed long-term decrease of the neutron star spin period which would otherwise have remained close to its equilibrium value. We, thus, present a self-consistent picture where the long-term evolution of an accreting binary pulsar is governed by the evolving surface magnetic field of the neutron star.
11:55-12:15	Discovery of decaHz flaring in SAX J1808.4-3658 (P. Bult) We report on the discovery of strong decaHz flaring in the early decay of two out of five outbursts of the accreting millisecond X-ray pulsar SAX J1808.4-3658. The decaHz flaring switches on and, after ~ 3 days, off again, on a time scale of 1-2 hours. When the flaring is present, the total 0.1-10 Hz variability has a fractional rms amplitude of 20 to 30 percent, well in excess of the 8 to 12 percent rms broad-band noise usually seen in power spectra of SAX J1808 in this frequency range. Coherent 401 Hz pulsations are seen throughout the observations in which the decaHz flaring is detected. We find that the absolute amplitude of the pulsations varies with the flux modulation of the decaHz flaring, indicating that the flaring is caused by an accretion rate modulation already present in the accretion flow prior to matter entering the accretion funnel. We suggest that the decaHz flaring is the result of the Spruit-Taam instability (Spruit & Taam 1993). This instability arises when the inner accretion disk approaches co-rotation. The rotation of the stellar magnetosphere then acts as a propeller, suppressing accretion onto the neutron star. A matter reservoir forms in the inner accretion disk, which episodically empties onto the neutron star, causing flares at a decaHz timescale. A similar explanation was proposed earlier for 1 Hz flaring occurring late in three of five outbursts, mutually exclusive with the decaHz flaring. The 1 Hz flaring was observed at luminosities a factor 5 to 10 below where we see the decaHz flaring. That a different branch of the Spruit-Taam instability could also act at the much higher luminosity levels of the decaHz flaring had recently been predicted by D'Angelo & Spruit (2010, 2012). We discuss these findings in the context of the parameters of the Spruit-Taam-d'Angelo model of the instability. If confirmed, after millisecond pulsations, 1 Hz and decaHz flaring would be another diagnostic of the presence of a magnetosphere in accreting low-magnetic field neutron stars.
12.15-12.35	discussion
12.30-12.40	Posters Advertisements (P03, P09, P08)

12:40-14.00	lunch break

	SESSION 10 (Chair: P. Kretschmar)
14.00-14.30	Future perspectives in theory and observations: young stellar objects (J. Bouvier)
14.30-15.00	Future perspectives in theory and observations: compact objects (L. Stella)
15.00-15.10	Final discussion and concluding remarks

Posters

Posters will be advertised during the conference through a presentation of 1 slide for about 1 min.

All posters will be displayed during the entire conference in the coffee break hall.

P01	3D Grey Radiative Properties of Accretion Shocks in Young Stellar Objects (L. Ibgui) Magnetospheric accretion is the reference scenario adopted for the Classical T Tauri stars (CTTS). Within a few stellar radii, the accretion shock disk dynamics is controlled by the stellar magnetic field: the ionized disk is truncated, the matter falls onto the stellar surface along magnetic funnels and impacts onto the stellar surface at free-fall speed, which results in the formation of radiative shocks. Current models have investigated the structure and dynamics of these shocks through 1D RHD or 2D MHD simulations. Using the 3D radiative transfer code IRIS coupled with grey opacities, we post-process a 3D accretion column built from a 2D axisymmetric MHD simulation performed with PLUTO, a Godunov-type code for astrophysical plasmas. The primary goal is to assess the possibility of a radiative feedback on the dynamics of an accretion shock, by comparing the radiative moments to the thermal and magnetic quantities. Moreover, we evaluate the spatial and angular distribution of the radiation that emerges from the stream. The work is supported by French ANR, under grant 08-BLAN-0263-07.
P02	Latest Results of pulse phase resolved spectroscopy of CRSFs in accretion powered pulsars & their implications (C. Maitra) We have performed Pulse Phase Resolved Spectroscopy of the Cyclotron Resonance Scattering Features (CRSF) of some bright accretion powered X-ray pulsars like 1A 1118-61, Vela X-1, A0535+26, XTE J1946+274, 4U 1907+09 and GX 301-2 using Suzaku observations with long exposures. We have performed the study using different spectral models for the continuum and have obtained similar patterns of variations of the CRSF in all the cases, thus demonstrating the robustness of our results. CRSFs which are found in 19 accretion powered pulsars till date provide us one of the surest estimates of the magnetic field strength of the neutron star. Pulse phase resolved spectroscopy of these CRSFs can in addition provide us with a wealth of information on the emission geometry,the beaming pattern of the radiation, and the magnetic field structure of the neutron star as we probe it at different viewing angles. Correlated study of these variations with the pulse profiles at different energy bands can provide estimates of the viewing angle parameters of the neutron star. Further, better constraints on the viewing angle parameters and the magnetic field structure would be useful to obtain meaningful estimates of the X-ray polarization expected from these sources.
P03	Pulse-phase resolved analysis of the Be/X-ray binary GX 304-1 observed with INTEGRAL during an outburst (C. Malacaria) We present timing and spectral properties of the periodic High Mass X-ray Binary (HMXB) GX 304-1 during its outburst in January-February 2012, observed with INTEGRAL. The pulse profile and the spectral parameters exhibit significant variation during the evolution of the outburst, as a consequence of the change in luminosity and hence in the accretion rate. A positive correlation between the cyclotron line energy and the flux is found. This is in agreement with the most recent models of accretion in accreting X-ray pulsars, which distinguish between two different accretion regimes, separated by a critical X-ray luminosity, that in turn depends on the magnetic field strength. Also, the spectral photon index anti-correlates with the flux. The pulse profile does vary strongly throughout the outburst. The energy of the cyclotron absorption line does not change significantly with pulse phase. The photon index and the cutoff energy show some variation with phase, but no clear correlation with flux is observed. The Swift/BAT and the GBM data are shown to highlight the peculiarity and evolution of the outbursts shape in the last year. Two (probably three) double-peaked outbursts appear in the recent Swift/BAT light curve, with increasing peak flux (reaching luminosities typical of giant outbursts) and followed by a very weak outburst observed last.
P04	A new simulation for modeling cyclotron lines (F.-W. Schwarm) X-ray binary systems consisting of a mass donating optical star and a highly magnetized neutron star, under the right circumstances, show quantum mechanically absorption features in the observed spectra called cyclotron resonant scattering features (CRSFs). The strong magnetic field forces the accreted matter to form an accretion column populated by seed photons generated by various continuum processes such as cyclotron, and blackbody radiation. The photons within the column interact with infalling electrons moving with relativistic velocities towards the hot spot on the neutron star's surface. Photons interacting with an electron may excite it to a higher Landau level thereby being absorbed or scattered into another spectral regime. This way cyclotron resonant absorption features are formed providing insight to the physics of the line forming part of such an accretion column. We developed a simulation able to model CRSFs using Monte-Carlo Methods. This simulation not only allows for the calculation of Green's tables which can be used to imprint CRSFs to X-ray continuua rapidly enough to allow for a feasible fitting process. The simulation also extends the number of variable parameters of previous works and introduces the possibility to simulate parameter gradients by splitting the column into smaller slices each with its own set of parameter values. We present simulated spectra for some CRSF candidates together with the observed spectrum and interpret similarities and differences. The not very well constrained range of parameters makes it difficult to disentangle geometric, general relativistic effects, and CRSFs raising the importance of an unified model including all these effects. The simulation presented here will be used by our collaboration for the CRSF part.
P05	XMM-Newton look at 1A 0535+262 in quiescence (V. Doroshenko) We report on a XMM-Newton observation of the transient Be X-ray binary source 1A 0535+262 taken during quiescence. The source was significantly detected and a detailed spectral and timing analysis was performed. The phenomenological behavior in quiescence appears to be similar to the one at higher fluxes. We therefore discuss the origin of the X-ray emission during quiescence, and based on the observed aperiodic variability and spin evolution of the source, conclude that similarly to outbursts, the accretion in quiescence likely proceeds from an accretion disk around the neutron star.
P06	Timing and spectral properties of the X-ray pulsar 4U\,0115+63: pulse period history and cyclotron absorption line energy (P. Boldin) Results of observations of the Be/X-ray transient pulsar 4U\,0115+63 since it's discovery and to the present days ($\sim40$ yr) are reviewed. These results were acquired from an analysis of data more than dozen of observatories and telescopes. The overall light curve of the source and history of its pulsation frequency are presented. Both of them include results of recent observations with the INTEGRAL observatory, obtained during outbursts in 2004, 2008 and 2011. INTEGRAL observations during the 2011 outburst allowed us to reconstruct the source spectra for a dynamic range of luminosities $10^{37} - 7 \times 10^{37}$s erg/sec. Based on these data, it was shown that apart from the cyclotron resonance scattering feature (CSRF) at $\approx 11$~keV there are four higher harmonics in the source spectrum at $\approx 24, 35.6, 48.8, 60.7$~keV. We performed also a detailed analysis of the 4U\,0115+63 spectra in the 4-28 keV energy band using all available data obtained by the RXTE observatory during bright outbursts in 1995-2011. It was confirmed that a previously found anticorrelation between the CSRF's centroid energy and the source luminosity can disappear for some modifications of the continuum model. Thus, an evolution of the CSRF's energy with the luminosity for the X-ray pulsar 4U\,0115+63 is still an open topic. To answer to this question a physically corrected spectrum model for X-ray pulsars is required.
P07	The reflection component in NS LMXBs (A. D'Ai) Broad iron emission lines have been observed in many low-mass X-ray binaries hosting both neutron stars and black-holes with high statistics and good spectral resolution by the Epic-PN onboard of XMM-Newton. There is growing evidence that these lines are formed by reflection of corona/boundary layer emission in the accretion disk and broadened by a combination of dynamical and relativistic effects. In my contribution, I will review the observational aspects of this field, focusing on interplay between continuum formation and reflected component, the importance of the spectral shape of the boundary layer, and the presence of a magnetospheric boundary.
P08	Pulse-to-pulse variations in accreting X-ray pulsars (P. Kretschmar) In most accreting X-ray pulsars, the periodic signal is very clear and easily shows up as soon as data covering sufficient pulse periods (a few ten) are available. The mean pulse profile is often quite typical for a given source and with minor variations repeated and recognisable across observations done years or even decades apart. At the time scale of individual pulses, significant pulse-to-pulse variations are commonly observed. While at low energies some of these variations might be explained by absorption, in the hard X-rays they will reflect changes in the intrinsic emission. Interestingly, the amount of these variations appears to be quite different between otherwise similar sources. While in some sources the individual pulses can be clearly discerned in their lightcurves, in other sources the short-term lightcurve appears almost chaotic, while still producing a stable profile when folded with the pulse period. We investigate this behaviour for a sample of well-known representative sources, accreting in different ways and search for connections to other source properties.
P09	RXTE and Swift Observations of SWIFT J1729.9-3437 (A. Baykal) We analyze Swift and RXTE observations of SWIFT J1729.9-3437 after its outburst from 2010 July 20 to 2010 August 12. We connect pulse arrival times in phase. Phase connected pulse arrival times indicated that the source is spinning up. The residuals of the pulse arrival times after removing spin up trend suggests that the sources may have orbital period 15.3 days and a mass function 1.3 solar mass. These residuals can also be explained by a torque noise strength seen by accretion powered X-ray pulsars. We also find that double peak to single peak pulse shape changes in the source. Pulse phase, X-ray spectra shows that photon index varies with pulse phase.
P10	The high energy view of DG Tau (C. Schneider) The DG Tau jet is one of the best-studied protostellar jets and contains plasma with temperatures ranging over three orders of magnitude within the innermost 50 AU of the jet. The brightness of the jet and the favorable viewing geometry allow us to trace the jet emission very close to the star. We present HST FUV data tracing plasma with temperatures between 1e3 and 1e5 K. The hot plasma (T~1e5 K) is almost co-spatial with the X-ray emitting plasma of the jet (T~1e6 K) while the cooler plasma is spatially disjunct from the hot plasma. These data rule out a simple hot stellar wind as the origin of the hot, X-ray emitting plasma and suggest local heating by internal shocks or magnetic reconnection events.
P11	The Herbig Ae SB2 system HD 104237 (S. Hubrig) The Herbig Ae/Be star HD 104237 was intensively studied during the last years using multi-wavelength observations, in particular due to the possible presence of a magnetic field announced more than 15 years ago by Donati et al. (1997). In their work the authors reported on the probable detection of a weak magnetic field of the order of 50 G. Imaging observations by Grady et al. (2004) suggested that the disk of HD104237 is seen nearly face-on. The star is a primary in an SB2 system with an orbital period of 19.86 d (Böhm et al. (2004). A recent study of chemical abundances in both components is presented by Cowley et al. (2013). Abundances are derived for 25 elements in the primary, and 17 elements in the secondary. Apart from lithium and zirconium, abundances do not depart significantly from solar. Our new magnetic field measurement, Bz=63 G, using very high spectral resolution (R=110,000) HARPS polarimetric spectra is the first confirmation of the presence of a magnetic field in this star.
P12	Long term variability of low mass X-ray binaries with late type giant companions (E. Filippova) In this work we propose a physical mechanism for generation of noise in mass accretion rate in low mass X-ray binaries (LMXB) with giant stars at large time scales. With 3D simulations we show that highly probable accretion from the stellar wind in such systems results in variability of mass accretion rate with characteristic time scale related to the orbital period even with zero eccentricity of the binary. Our estimates show that observational appearance of the stellar wind is quite similar to one of accretion disk corona. This mechanism can be used to explain observed peculiarities of PDS of mass accretion rate variation of LMXB with long orbital period (Gilfanov, Arefiev, 2005).
P13	Suzaku studies of 4U 1822: an LMXB involving a strongly magnetized neutron star (M. Sasano) Low-mass X-ray binaries (LMXBs), X-ray emitting binaries with low-mass primaries, are believed to generally involve neutron stars with weak magnetic field strengths. However, three LMXBs, Her X-1, 4U 1626-67 and GX 1+4, are exceptional. Magnetic field strengths of Her X-1 and 4U 1626-67 have been precisely measured with cyclotron resonance scattering features (CRSFs) as a few times 10^12 G. That of GX 1+4 is also considered to be very high, as judged from its very hard spectrum extending to >100 keV (though no CSRF have been detected yet). In the present study, we focus on the LMXB 4U 1822-37. This source exhibits dips synchronized with its orbital period of 5.7 hr, and was reported to show shallow pulsations with a prior of 0.7 s, but its magnetic field strength remained uncertain. We hence analyzed the Suzaku public data of 4U 1822-37. Comparing its 1-50 keV Suzaku spectrum with those of other accreting neutron stars, we argue that 4U 1822-37 in fact has a strong magnetic field, several times 10^12 G. This is evidenced by clear Fe-K lines, and a very hard continuum with a prominent break above ~20 keV. Thus, 4U 1822-37 may be regarded as a precious additional example of the LMXBs involving strongly magnetized neutron stars.
P14	Evolution of the accretion geometry through an outburst decay phase of the NS-LMXB Aquila X-1 (S. Sakurai) Low-Mass X-ray Binaries hosting neutron stars (NS) are known to reside either in the soft or the hard spectral states. The soft-state studies from 1980's have revealed its accretion geometry (e.g. Mitsuda+1984); the matter accretes onto an equatorial zone of the NS, through a standard disk of which the inner radius is comparable to or somewhat larger than the NS radius (~10 km). The X-ray spectrum in this case consists of a ``disk blackbody" emission from the standard disk, and a blackbody component from the NS surface. To understand accretion geometry in the hard state, we investigated Suzaku broad-band spectra of Aquila X-1, taken on seven occasions in the decaying phase of an outburst in 2007. The source luminosity decreased meantime by ~3 orders of magnitude from ~10^37 erg/s to ~10^34 erg/s. The first spectrum with 0.8-100 keV luminosity (L) of ~10^37 erg/s exhibited characteristics typical of the soft state, and were consistent with previous studies. The next three (2nd to 4th) data sets exhibited the typical hard-state spectra, which were detected over 0.7-100 keV with a luminosity of ~10^36 erg/s. They were successfully reproduced by a disk blackbody of an inner radius of ~20 km, and a strongly-Comptonized blackbody (BB) of which the seed photon radius is ~10 km. Therefore, the standard disk is inferred to be truncated at ~20 km, and the accreting matter within this radius becomes hot coronal flows which accrete onto the NS nearly spherically (Sakurai+2012).
P15	Interactions between exoplanets and the stellar winds of young stars (A. Vidotto) The topology of stellar magnetic field is important not only for the investigation of magnetospheric accretion, but also responsible in shaping the large-scale structure of stellar winds, which are crucial for regulating the rotation evolution of stars. Because stellar winds of young stars are believed to have enhanced mass-loss rates compared to those of cool, main-sequence stars, the interaction of winds with newborn exoplanets might affect the early evolution of planetary systems. This interaction can also give rise to observational signatures which could be used as a way to detect young planets, while simultaneously probing for the presence of their still elusive magnetic fields. In this poster, we compile results from Vidotto et al (2009,2010), where we have investigated the interaction of stellar winds of young stars with hypothetical planets. For that, we modeled the stellar winds by means of 3D numerical magnetohydrodynamic simulations. Although these models adopt si mplified topologies of the stellar magnetic field (dipolar fields that are misaligned with the rotation axis of the star), we showed that asymmetric field topologies can lead to an enhancement of the stellar wind power, resulting not only in an enhancement of angular momentum losses, but also intensifying and rotationally modulating the wind interactions with exoplanets.
P16	Boundary between stable and unstable regimes of accretion (A. Blinova) 3D MHD simulations show that magnetized stars can accrete in the stable regime, where matter accretes to the star in ordered funnel streams, or in the unstable regime, where matter penetrates through the magnetosphere in several unstable tongues due to the magnetic Rayleigh-Taylor instability. The boundary between stable and unstable regimes depends on a number of factors, which will be discussed in the poster. We performed multiple simulation runs with the goal of investigating the boundary between stable and unstable regimes of accretion and its dependence on the stellar period, grid resolution, and viscosity in the disk, and on the tilt of the dipole magnetosphere. Simulations were performed using a ``cubed sphere” code with high grid resolution (244 grid points in the azimuthal direction), which is twice as high as that used in our earlier study. We chose a very low viscosity value, with alpha-parameter alpha=0.02 in the majority of the cases. We observed from the sim ulations that the boundary strongly depends on the ratio between the magnetospheric radius r_m (where the magnetic pressure in the magnetosphere matches the matter pressure in the disk) and corotation radius r_cor (where Keplerian velocity in the disk equals to the angular velocity of the star). For a small misalignment angle of the dipole field, Theta=5 degrees, accretion is stable if r_m/r_cor > 0.74, and is unstable otherwise. In cases of a larger misalignment angle of the dipole, Theta=20 degrees (and high grid resolution), the instability occurs at slightly smaller r_m/r_cor values, with r_m/r_cor=0.72. Overall, new simulations at higher grid resolution show that instability occurs more easily than in our earlier simulations with a courser grid.
P17	Oscillations of the boundary layer and high-frequency QPOs (A. Blinova) We observed persistent high-frequency oscillations of the boundary layer near an accreting, weakly-magnetized star. The tilted dipole magnetic field is not strong enough to open a gap between the star and the disk. Instead, it forms a highly-wrapped azimuthal field near the surface of the star, which slows down accretion, while a small tilt of the field excites oscillations of the boundary layer with a frequency close to the Keplerian frequency near the surface of the star. This mechanism may be responsible for the high frequency oscillations in accreting neutron stars, white dwarfs and Classical T Tauri stars.
P18	The magnetosphere of the close accreting pre-main sequence binary V4046 Sgr (S. Gregory) The close short-period classical T Tauri binary system V4046 Sgr is accreting from a large and massive circumbinary disk. In 2011, de Val-Borro et al. presented simulations of V4046 Sgr that suggest that accretion streams from the circumbinary disk form local small circumstellar disks around each component of the system. Their simulations do not include magnetic fields, and as de Val-Borro et al. point out, it is not clear if the inclusion of the stellar magnetospheres will inhibit the formation of local disks. To address this issue we present the first models of the magnetosphere of an accreting PMS binary, V4046 Sgr. The 3D field topology is obtained via field extrapolation from magnetic maps derived from Zeeman-Doppler imaging, using a new code. This is part of a coordinated large multi-wavelength, near-simultaneous, observing campaign involving, in particular, spectropolarimetric and high-resolution X-ray observations covering roughly 2.5 system rotations.
P19	The NuSTAR ULX program (M. Bachetti) The bright X-ray emission from ULX binaries greatly exceeds the Eddington luminosity for a spherically accreting stellar-mass compact object, and understanding why this is so is one of the biggest mysteries in high energy astrophysics. The origin of these luminosities may be related to the existence of a (poorly explained) regime of super-Eddington accretion onto a stellar mass black hole (BH), or even more intriguing, the presence of black holes more massive than standard stellar remnants. Attempts to model the 0.3 – 10 keV spectra in order to understand the accretion mechanisms have been plagued by degeneracies resulting from the limited bandpass. The spectrum above 10 keV is also very poorly studied as a result of the limited sensitivity of non-focusing hard X-ray instruments. We present the results of the first large program of broadband ULX observations with Chandra, Suzaku, XMM-Newton and NuSTAR, yielding high-quality spectra and timing measurements from 0.3–30 keV in 6 ULXs, providing powerful information for understanding the accretion modes and nature of the central BHs.
P20	A NuSTAR view on GS 0834-430 (M. Bachetti) GS 0834-430 is a 12.3 s accretion-powered X-ray pulsar that was discovered by Granat/WATCH in 1990. After a period of several years where quasi-regular outbursts were observed having average cadence of ∼110 days, GS 0834-430 became dormant for 19 years. In 2012 June INTEGRAL detected GS 0834-430 in an outburst state typical of those seen previously. On 2012 July 11, the NuSTAR high energy X-ray telescope observed GS 0834-430 for a total integration time of 31.0 ksec. In this poster we present the results of the spectral and timing analysis of this observation.
P21	Episodic accretion: interactions between the accretion disk and the stellar magnetosphere (M. Audard) In the recent years, several young accreting stars have displayed outbursts that have been monitored through photometry and spectroscopy, from X-rays to checkbox. Such outbursts are thought to be due to increases in mass accretion rates either due to thermal instabilities in the disk or the perturbation by nearby companions. The outbursts provoke significant interactions between the accretion material and the stellar magnetosphere. I propose to present results of recent studies of outbursting sources, focussing on the physics at the magnetospheric boundary.
P22	The neutron star low mass X-ray binary Cen X-4: learning from quiescent variability (F. Bernardini) The physics of accretion during quiescence in low-mass X-ray binaries (LMXBs) is poorly understood, yet there are signs that accretion must be happening. Several LMXBs show variability during quiescence. This is particularly striking in the nearby neutron star Cen X-4, the best target for quiescent studies. Cen X-4 is seen to be variable on timescale from hundreds of seconds to years, suggesting that accretion is still occurring even at very low X-ray luminosities. We performed daily monitoring of Cen X-4 with Swift for 2 months in 2012 following the optical, UV and X-ray fluxes. We found clear evidence that the X-ray, UV and optical emission are correlated on timescales down to less than 110 s. The X-ray spectrum is well fitted by a neutron star atmosphere (kT=60-80 eV) made by pure hydrogen and a power law (with spectral index 1.4-2.0). Both components are varying in tandem with the X-ray flux, each contributing of about 50% of the total X-ray flux. We conclude that the X-rays are generated by matter accreting down to the NS surface overtaking the centrifugal barrier of the rotating magnetosphere. Moreover, based on the short timescale of the correlation, we also unambiguously demonstrate that the UV emission can not be due to thermal emission from the stream impact point, and neither to thermal or reprocessed emission from a standard optically thick and geometrically thin disk, but must be produced by reprocessing from the companion star. We also found the accretion disk in quiescence to be UV faint, being its contribution to the whole UV flux less than 2%.
P23	New Observations of Accretion Phenomena in Magnetic Cataclysmic Variables (D. Buckley) We present an overview of the ongoing observational, theoretical and modelling work on magnetically controlled accretion phenomena in magnetic cataclysmic variables. With SAAO's high speed polarimeter, HIPPO, we have discovered polarized Quasi-Periodic Oscillations, on a timescale of several minutes. We have investigated various scenarios in which such QPOs can be created, all of them requiring some interaction between the ballistic accretion flow and the magnetic field of the accreting white dwarf. With high speed photometry, including observations with SALT, we are investigating the nature of high frequency QPOs (~sub-few seconds) from the accretion shocks in mCVs. We also present some high speed photometric observations revealing the magnetic accretion spots on the accreting White Dwarfs. Developments in the use of Doppler tomography is also presented. Our new "inside-out" methodology gives an alternative way of calculating Doppler tomograms that can better emphasize the ballistic and magnetically confined accretion flows and curtains.