Volume 550, February 2013
|Number of page(s)||13|
|Published online||18 January 2013|
An XMM-Newton search for X-ray sources in the Fornax dwarf galaxy
1 Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, CP 193, 73100 Lecce, Italy
2 INFN, Sez. di Lecce, via Per Arnesano, CP 193, 73100 Lecce, Italy
Received: 2 August 2012
Accepted: 23 November 2012
We report the results of a deep archive XMM-Newton observation of the Fornax spheroidal galaxy that we analyzed with the aim of fully characterizing the X-ray source population (in most of the cases likely to be background active galactic nuclei) detected towards the target. A cross correlation with the available databases allowed us to find a source that may be associated with a variable star belonging to the galaxy. We also searched for X-ray sources in the vicinity of the Fornax globular clusters GC 3 and GC 4 and found two sources probably associated with the respective clusters. The deep X-ray observation was also suitable for the search of the intermediate-mass black hole (of mass ≃ 104 M⊙) expected to be hosted in the center of the galaxy. In the case of Fornax, this search is extremely difficult since the galaxy centroid of gravity is poorly constrained because of the large asymmetry observed in the optical surface brightness. Since we cannot firmly establish the existence of an X-ray counterpart of the putative black hole, we put constraints only on the accretion parameters. In particular, we found that the corresponding upper limit on the accretion efficiency, with respect to the Eddington luminosity, is as low as a few 10-5.
Key words: X-rays: individuals: Fornax dSph / black hole physics
© ESO, 2013
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