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A Multi-Epoch Timing and Spectral Study of the Ultraluminous X-Ray NGC 5408 X-1 with XMM-Newton
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External Online Source: doi:10.1088/0004-637X/753/2/139
Author and Affiliation:
Dheeraj, Pasham(Maryland Univ., Dept. of Astronomy, College Park, MD, United States);
Strohmayer, Tod E.(NASA Goddard Space Flight Center, Greenbelt, MD, United States)
Abstract: We present results of new XMM-Newton observations of the ultraluminous X-ray source (ULX) NGC 5408 X-1, one of the few ULXs to show quasi-periodic oscillations (QPOs). We detect QPOs in each of four new (approximately equal to 100 ks) pointings, expanding the range of frequencies observed from 10 to 40 mHz. We compare our results with the timing and spectral correlations seen in stellar-mass black hole systems, and find that the qualitative nature of the timing and spectral behavior of NGC 5408 X-1 is similar to systems in the steep power-law state exhibiting Type-C QPOs. However, in order for this analogy to quantitatively hold we must only be seeing the so-called saturated portion of the QPO frequency-photon index (or disk flux) relation. Assuming this to be the case, we place a lower limit on the mass of NGC 5408 X-1 of greater than or equal to 800 solar mass. Alternatively, the QPO frequency is largely independent of the spectral parameters, in which case a close analogy with the Type-C QPOs in stellar system is problematic. Measurement of the source's timing properties over a wider range of energy spectral index is needed to definitively resolve this ambiguity. We searched all the available data for both a broad Fe emission line as well as high-frequency QPO analogs (0.1- 1 Hz), but detected neither. We place upper limits on the equivalent width of any Fe emission feature in the 6-7 keV band and of the amplitude (rms) of a high-frequency QPO analog of approximately equal to 10 eV and approximately equal to 4%, respectively.
Publication Date: Jun 22, 2012
Document ID:
20130009063
(Acquired Feb 07, 2013)
Subject Category: ASTRONOMY
Report/Patent Number: GSFC-E-DAA-TN6677
Document Type: Journal Article
Publication Information: The Astrophysical Journal; Volume 753; no. 2; 139
Financial Sponsor: NASA Goddard Space Flight Center; Greenbelt, MD, United States
Organization Source: NASA Goddard Space Flight Center; Greenbelt, MD, United States
Description: 16p; In English; Original contains black and white illustrations
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: No Copyright
NASA Terms: LUMINOSITY; X RAY SOURCES; ACCRETION DISKS; XMM-NEWTON TELESCOPE; SPECTRAL CORRELATION; TIME MEASUREMENT; BLACK HOLES (ASTRONOMY); OSCILLATIONS; ENERGY SPECTRA; STELLAR MASS
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