High resolution X-ray spectroscopy of Active Galactic Nuclei
Prof. Graziella Branduardi-Raymont
High resolution X-ray
spectroscopy is one of MSSL's astrophysics group well established lines of
research, focussing on the study of Active Galactic
Nuclei (AGN), and the ionised gas (the 'warm absorber') that lies in our line
of sight to the central engine. The detailed analysis of
the absorption features imprinted by the gas on the nuclear X-ray continuum, as
well as of the emission lines generated in the gas,
is a powerful diagnostic of the physical conditions of the environment
surrounding the nuclear black hole, of the dynamics of the
gas, its chemical composition and ionisation state. The gas is generally observed
to be outflowing from the innermost regions of
the AGN; the outflow rates are often comparable to, or even larger than, those
of the matter accreting onto the black hole, and leading
to the AGN powerful X-ray emission. This suggests that both outflow and
accretion play a major role in the evolution of the black
hole mass and of the AGN as a whole. The feedback mechanism associated with
this may regulate star formation in the host galaxy, and
may determine the known relationship between the mass of the black hole and
that of the surrounding spheroid. The research student is
expected to become very familiar with AGN science and learn the techniques employed
in the analysis of high-resolution X-ray
spectra, with the aim to contribute to and to further our investigations in the
topics outlined above. The student will employ
archive as well as guest observer data obtained with the XMM-Newton Reflection
Grating Spectrometer (RGS), which MSSL
contributed to build. The knowledge acquired in building, testing and
calibrating the instrument has translated into a deep
understanding and interest in the exploitation of the data returned by the
spectrometer. This combination of knowledge and observational
expertise in high resolution X-ray spectroscopy is unique among UK astronomy
groups, and puts us in a strong position for exploiting
high-resolution data from the non-dispersive X-ray spectrometers of the future.
RGS spectrum of
the Seyfert 1 galaxy NGC3516,fitted using the 'slab' absorption model. Some of the strongest absorption
features are labelled (from Mehdipour et al. 2010, A&A, 514,100 - Missagh
Mehdipour is a current MSSL PhD student).
Artist's impression of the core of the Narrow Line Seyfert 1 galaxy Arakelian 564 showing the limits (set by the RGS data) on the locations of the broad emission, narrow emission and absorption line regions (from Smith et al. 2008, A&A, 490, 103 – Rebecca Smith was a PhD student at MSSL who received her doctorate in 2009).
References
Mehdipour, M., Branduardi-Raymont, G. et al. Multiwavelength campaign on Mrk 509. IV. Optical-UV-X-ray variability and the nature of the soft X-ray excess, Astronomy and Astrophysics, Volume 534, 39 (2011)
Mehdipour, M., Branduardi-Raymont, G. and Page, M. The X-ray warm absorber and nuclear obscuration in the Seyfert 1.8 galaxy ESO 113-G010, Astronomy and Astrophysics, Volume 542, 30 (2012)
