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TOPIC: NGC 5408 X-1
Blobrana


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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 115.5±1.5 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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