X-ray observations of the radio-loud narrow-line Seyfert 1 J1548+3511.

A major open question in astrophysics concerns the formation of highly collimated beams of matter and electromagnetic radiation, so-called relativistic jets, emerging from active galactic nuclei (AGN) in the center of certain galaxies. It is not known how, or why, these jets are formed nor how they maintain their collimated state for such large distances. For long it has been thought that jets can only be hosted in large, elliptical galaxies, though quiterecently AGNs have been discovered that contradict these beliefs. These objects are called radio-loud narrow-line Seyfert 1 galaxies (RLNLSy1). In this thesis an AGN belonging to this class is analysed. Utilising an X-ray spectral fitting package (XSPEC), data from two separate observations obtained from the X-ray Multi-Mirror Mission observatory (XMM-Newton) of the radio-loud narrow-line Seyfert 1 galaxy SDSS J154817.92+351128.0 are fitted through the use of different models and analysed in the energy region of 0.3 keV to 10 keV. The purpose is to disentangle the emission from the light-emitting accretion disk surrounding the central supermassive black hole(SMBH) and the emission from a possible jet, as well as to determine their properties. The results indicate a strong presence of a jet while still maintaining a visible spectrum from the accretion disk. No sign of the Fe line, usually seen in radio-quiet NLSy1s, can be detected, even though the data is not of sufficientquality to exclude the possibility of detection. Furthermore, considerable amounts of enhanced emission below 2 keV is observed, a so-called soft excess. The soft excess could be explained by inverse comptonisation of the light emitted from the disk and/or reflections in the disk. Our results confirm the presence of powerful relativistic jets emerging from J1548+3511. The wider implications of jet formation are further discussed