Wednesday Colloquium


"Magnetic relaxation and turbulence in pulsar wind nebulae"

Jonathan Zrake (Columbia University)

Pulsar wind nebulae (PWNe) are energized by the electromagnetic spin-down power of a rapidly rotating neutron star. Their emission is primarily synchrotron, produced by relativistic electrons radiating in a sub-equipartition magnetic field. The processes by which a pulsar wind, which is born in a strongly magnetized state, eventually shares its energy with electrons, has been a long-standing question in the theory of pulsars and their nebulae (sometimes referred to as the sigma-problem). I will discuss how dissipation in PWNe may be understood in terms of a process known as magnetic relaxation, and give an overview in general physics terms of recent advances in this topic. MHD simulations reveal the process is generally turbulent, and that magnetic field structures tend to organize themselves spatially, even when the field lacks net magnetic helicity. I will discuss how this process helps to explain the magnetization level of the Crab's synchrotron nebula.


"Evolution and pulsations of massive stars with the effects of rotation and mixing processes"

Jakub Ostrowski (Uniwersytet Wrocławski)

Massive stars are often fast rotators and they are subject to various mixing processes. Both stellar rotation and mixing are not perfectly understood and their proper implementation into stellar evolution codes is complex. However, they play a central role in modern stellar modelling due to their overwhelming influence on stellar structure and theoretical oscillation spectra. Moreover, rotation and mixing are two closely related subjects. Presence of differential rotation leads to emergence of many instabilities. They contribute to transport of chemical elements and angular momentum in the stellar interiors. During my lecture I plan to assess how rotation and mixing processes are implemented in a modern evolution code - MESA and discuss their influence on massive stellar models, which I have calculated. My aim is to demonstrate how sophisticated rotating models have provided us with a way to constrain various stellar parameters of HD 163899 - the prototype of Slowly Pulsating B-type supergiants.


"Nova Scorpii 1437 A.D. - now a cataclysmic variable"

Joanna Mikołajewska (NCAC, Warsaw)

I will present and discuss a recovery of the binary underlying the classical nova of 11 March 1437 recorded by Korean royal astronomers whose age is independently confirmed by proper motion-dating.


"Back to the future: highlights of the observing campaign of the large scale jets of XTE J1550-564"

Giulia Migliori (Université Paris Diderot)

The large-scale decelerating jets of the XTE J1550-564 represent an unique laboratory to investigate the physics of microquasars’ jets and their interaction with the interstellar medium In this talk, I will present the results of the multi-frequency campaign of observations which probed the inner structure of the western jet in 2001-2003. The complex, evolving morphology of the jet in X-rays, the detection of polarized radio emission and the chromatic decay of the broad-band emission give indications on how the particles are accelerated and energy is dissipated at large distances from the black hole. I will discuss our findings in relation to the radiative and dynamical models proposed for this system, and examine the similarities with other microquasars’ jets, such as H 1743-322. Finally, I will briefly illustrate how the incoming facilities will significantly improve our powers of observations of this class of transient objects.