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TOPIC: NGC 5408 X-1


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NGC 5408 X-1
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Title: Confirming the 115.5-day periodicity in the X-ray light curve of ULX NGC 5408 X-1
Authors: Xu Han, Tao An, Jun-Yi Wang, Ji-Ming Lin, Ming-Jie Xie, Hai-Guang Xu, Xiao-Yu Hong, Sandor Frey

The Swift/XRT light curve of the ultraluminous X-ray (ULX) source NGC 5408 X-1 was re-analysed with two new numerical approaches, Weighted Wavelet Z-transform (WWZ) and CLEANest, that are different from previous studies. Both techniques detected a prominent periodicity with a time scale of 115.51.5 days, in excellent agreement with the detection of the same periodicity first reported by Strohmayer (2009). Monte Carlo simulation was employed to test the statistical confidence of the 115.5-day periodicity, yielding a statistical significance of > 99.98% (or >3.8\sigma). The robust detection of the 115.5-day quasi-periodic oscillations (QPOs), if it is due to the orbital motion of the binary, would infer a mass of a few thousand solar masses for the central black hole, implying an intermediate-mass black hole in NGC 5408 X-1.

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Swift XMM-Newton Satellites Tune Into a Middleweight Black Hole
Astronomers at NASA's Goddard Space Flight Centre in Greenbelt, Md., find that an X-ray source in galaxy NGC 5408 represents one of the best cases for a middleweight black hole to date.

"Astronomers have been studying NGC 5408 X-1 for a long time because it is one of the best candidates for an intermediate-mass black hole. These new results probe what is happening close to the black hole and add strong evidence that it is unusually massive" - Philip Kaaret at the University of Iowa, who has studied the object at radio wavelengths but is unaffiliated with the study.

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