We present a summary of our ongoing efforts to study one of the brightest ultraluminous X-ray source, NGC 1313 X-2. Despite a large coverage in the X-rays, much of the information we have about the source and its environment comes from optical wavelenghts. Here, we report on the properties of the stellar environment, and the differences in the optical counterpart between our two observing epoch...

We report the results of an analysis of two XMM-Newton EPIC-pn spectra of the bright ultraluminous X-ray source M81 X-9 (Holmberg IX X-1) obtained in snapshot observations. Soft thermal emission is clearly revealed in spectra dominated by hard power-law components. Depending on the model used, M81 X-9 was observed at a luminosity of LX 1⁄4 1:0 1:6 ð Þ ; 10 ergs s 1 (0.3–10.0 keV). The variabili...

Hong-Ya Xu,1 Liang Huang,2 Danhong Huang,3,4 and Ying-Cheng Lai1,5,* 1School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, USA 2School of Physical Science and Technology, and Key Laboratory for Magnetism and Magnetic Materials of MOE, Lanzhou University, Lanzhou, Gansu 730000, China 3Air Force Research Laboratory, Space Vehicles Directorate, Kir...

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