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).
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)