PhD Stundent: David Cseh

• outreach page for this project, by David Cseh

Start Date: Jul 2009
End Date: Jun 2012
Responsible Advisor: Stéphane Corbel (CEA Saclay)
Co-Advisors: Rob Fender (Southampton), Luciano Burderi (Cagliari)

Ultraluminous X-ray  (ULX) sources are variable, off-nucleus X-ray sources in external galaxies with luminosities greatly exceeding those achievable by Galactic Black Holes (the remnants of massive stars), assuming  isotropic emission. The black hole masses required to produce such high luminosities are significantly above those expected from stellar black holes. Thus, assuming isotropic emission, the existence of ULXs would require a new class of "intermediate-mass'' black holes,  with masses as high as a few hundreds to thousands solar masses.

An important piece of information for our understanding of ULXs comes from the discovery of huge ionized bubble nebulae around a significant fraction of  unobscured ULXs in nearby galaxies, that allowed an independent measure of the (ionizing) X-ray luminosity. For some of these sources, we are also starting to observe associated radio nebulae. The nebulae tend to be quite large, with sizes ranging from 200 to 400 pc. These large nebulae could be interpreted as remnants of an extremely powerful supernova, which was more than 10 times more energetic than a normal supernova. Such ``hypernovae'' may also create Gamma-Ray Bursts, potentially linking ULXs with Gamma-Ray Bursts. An alternative interpretation of  the nebulae, which is supported by the recent detection of a radio counterpart, is that they are continuously energized by unseen jets produced by the ULX. The discovery of associated optical/radio nebulae with ULXs has therefore opened up a new window to uncover the nature of ULXs. Indeed, nebulae powered by  photo-ionization or jets provide a potential means to measure the total energy output  of a ULX in all directions. This capability could potentially enable us to finally answer the question if the X-rays from the ULX  are beamed along our line of sight.

In collaboration with University of Iowa (USA) and the University of Southampton (UK), the PhD student will work on radio and optical data  in order to characterize  the properties of radio nebulae associated with a few nearby ULXs.  By using these nebulae as a calorimeter, (s)he will be able to measure the total energy output of ULX independently. In addition, the student will also compare the properties of the ULX nebula with those of Galactic stellar mass black holes and particularly the microquasars. The researcher will make use of a large campaign of multi-wavelength observations, acquired with the various nodes of the ITN, that will help in characterizing both populations of black holes. If ULXs are indeed intermediate mass black holes, this project will help bridge the gap between stellar and supermassive black holes.

The project involves using the most sensitive observatories available to date, i.e., the VLA and ATCA for radio observations, the VLT (optical) and XMM-Newton and Chandra for X- ray observations. At the end of the PhD project, the researcher will have gained the expertise to reduce data at many wavelengths, which is now recognised as being of prime importance for the development of a future independent carrier at a time when many new major facilities are being built, such as LOFAR, ALMA, Simbol-X, JWST, etc...

An overview talk on the current state  of the project as presented at the Collaboration Meeting in September 2010 in Istanbul can be found here.

Related publications

5. Cseh, D., Grise, F., Corbel, S., and Kareet, P., 2010, Ultra-Luminous X-ray source NGC 5408 X-1 showing broad secondary component in line profiles, ApJ, submitted (ADS-Entry)
4. Frey, S., Paragi, Z., Gurvits, L. I., Cseh, D., and Gabanyi, K. E., 2010, High-resolution images of five radio quasars at early cosmological epochs, A&A, accepted (arXiv:1009.5023) (ADS-Entry)
3. Soria, R., Pakull, M. W., Broderick, J. W., Corbel, S., and Motch, C., 2010, Radio lobes and X-ray hotspots in the microquasar S26, MNRAS, 409, 541-551 (ADS-Entry)
2. Cseh, D., Kaaret, P., Corbel, S., Körding, E., Coriat, M., Tzioumis, A., and Lanzoni, B., 2010, Radio observations of NGC 6388: an upper limit on the mass of its central black hole, MNRAS, 406, 1049 (ADS-Entry)
1. Cseh, D., Frey, S., Paragi, Z., Gurvits, L. I., and Gabanyi, K. E., 2010, Radio interferometric observations of two core-dominated triple radio sources at z>3, A&A, 523, 34 (ADS-Entry)

1. Cseh, D., Lang, C., Corbel, S., Kaaret, P., and Grise, F., 2010, Large-scale radio nebula around the Ultra-Luminous X-ray Source IC 342 X-1, in: Romero, G. (ed.), Jets at all scales, Proc. IAU Symposium 275, in press (ADS-Entry)

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