Date: Thursday, December 12, 2013
Time: 1:00 pm
Location: PHYS 401
Shedding New Light on Accreting Pulsars
Neutron stars are remnants of stellar evolution, the collapsed cores of massive stars. They are extremely dense and sustained against further gravitational collapse by neutron degeneracy pressure. Many have the strongest magnetic fields found in the universe. Accreting X-ray pulsars are rotating neutron stars which show regular flashes of X-ray emission powered by the accretion of material from a stellar companion onto the magnetic poles of the neutron star. The processes that take place at the poles involve strong gravitational fields, high temperatures and the most extreme magnetic fields. These are conditions that cannot take place naturally on Earth and cannot be reproduced in laboratories.
In recent years, considerable progress has been made regarding the development of physical models describing the accretion process onto the magnetic poles such that these new models can now be tested for the first time. These new models can now provide the first direct connection between physical parameters of the accretion process (magnetic field strength, plasma temperature, plasma density, mass accretion rate) and X-ray spectral shape. The standard empirical and new physical spectral models will be systematically applied to a sample of pulsars. Most of the chosen pulsars show a “cyclotron line”, a spectral feature that allows for a direct measurement of their magnetic fields. This detailed spectral analysis will be mainly based on observations from the Japanese X-ray satellite, Suzaku, due to its instruments’ high sensitivity, spectral resolution, and broad-band coverage. (The project will also include additional satellite data of a Symbiotic X-ray Binary, a member of a small, under-studied subclass of X-ray pulsars accreting from a dense stellar companion wind. Its study will involve modeling the spectrum as well as characterizing the variability and comparing the results with more common X-ray binaries.)
The goal of this project is provide the first steps towards a much needed improvement of our theories and observational analysis of magnetically dominated accretion, which can only be achieved by fitting the best physical models to the best available data.