The aperiodic variability of the Ultraluminous X-ray source in NGC 5408
  Ultra-Luminous X-ray sources are accreting black holes that might represent strong evidence of the Intermediate Mass Black Holes (IMBH), proposed to exist by theoretical studies but with no firm detection (as a class) so far. We analyze the best X-ray timing and spectral data from the ULX in NGC 5408 provided by XMM-Newton. The main goal is to study the broad-band noise variability of the source. We found an anti-correlation of the fractional root-mean square variability versus the intensity of the source, similar to black-hole binaries during hard states. 
M. D. Caballero-Garcia (1), S. E. Motta (1), T. M. Belloni (1) and A.   Wolter (2) ((1) INAF-OAB, Merate, (2) INAF-OAB, Brera)
astro-ph.HE astro-ph.CO