Gabriele Schnherr

-----------------------------------
PhD Student
Tuebingen (Germany) / ESAC (Spain)
gschoen@astro.uni-tuebingen.de
-----------------------------------

At present, I am working on my PhD project 'Strong magnetic fields
of accreting neutron stars' in high-energy astrophysics. Part of
this work is carried out at ESAC.

I first came to ESAC during a five months traineeship (ESAC Trainee
Programme) in 2004. I then worked with Marcus Kirsch and the XMM
Newton team. At that time I studied XMM Newton EPIC pn data of the
Crab and performed phase and spatially resolved spectroscopy of the
Crab pulsar and nebula. Also some calibration issues concerning the
Burst and Small Window modes of the XMM Newton EPIC pn camera have
been assessed.

In 2005 I started my PhD project in the field of accreting X-ray
pulsars at the University of Tuebingen (Germany) in collaboration
with ESAC and the University of Warwick (UK). At ESAC, I mainly
work with Peter Kretschmar from the INTEGRAL team.

My project focuses on cyclotron resonance scattering features
('cyclotron lines'/CRSF) in accreting neutron stars. Cyclotron
lines appear as absorption features in the spectra of highly
magnetized X-ray pulsars. The line positions are directly linked to
the strength of the magnetic field. The study of cyclotron lines is
up to today the only method to DIRECTLY determine the magnetic
field strength of a neutron star. 

Using Monte Carlo simulations, I study in detail the line profiles
of synthetic spectra, linking line parameters to physical
parameters of the assumed model setting. In this way the influence
of e.g. the geometry of the accretion region, its optical depth,
the viewing angle of the observer or variations of the neutron star
magnetic field can be assessed.

Having also developed a local XSPEC convolution model for modelling
cyclotron lines in observational data, we can now directy compare
our theoretic predictions to spectra of real sources. At present,
no other such physical XSPEC model for fitting CRSF in X-ray pulsar
spectra is available. So far, fits are usually done with
phenomenological models, which imply information loss concerning
the physical processes relevant for neutron star accretion. Our
approach should be a first step to change this situation.