The source X-9 was discovered with the Einstein Observatory in the field of M81 , and is located in the dwarf galaxy Holmberg IX .
X-9 has a 0.2-4.0 keV luminosity of \sim 5.5 \times 10 ^ { 39 } ergs s ^ { -1 } , if it is at the same distance as Holmberg IX ( 3.4 Mpc ) .
This luminosity is above the Eddington luminosity of a 1 M _ { \odot } compact accreting object .
Past hypotheses on the nature of this Super-Eddington source included a SNR or supershell , an accreting compact object and a background QSO .
To shed light on the nature of this source , we have obtained and analyzed archival data , including the Einstein data , 23 ROSAT observations , Beppo-SAX and ASCA pointings .
Our analysis reveals that most of the emission of X-9 arises from a point-like highly-variable source , and that lower luminosity extended emission may be associated with it .
The spectrum of this source changes between low and high intensity states , in a way reminiscent of the spectra of galactic Black Hole candidates .
Our result strongly suggest that X-9 is not a background QSO , but a bonafide ‘ Super-Eddington ’ source in Ho IX , a dwarf companion of M81 .