Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 436, Issue 4, Pages 3262-3270Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stt1807
Keywords
accretion; accretion discs; black hole physics; X-rays: galaxies; X-rays: general
Categories
Funding
- INAF
- ASI-INAF [I/009/10/]
- INAF [PRIN-2011-1]
- ASI/INAF [I/009/10/0]
- European Community [ITN 215212]
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Ultra-Luminous X-ray sources (ULXs) are thought to be accreting black holes (BHs) that might host intermediate-mass black holes (IMBH), proposed to exist by theoretical studies, even though a firm detection (as a class) is still missing. The brightest ULX in M82 (M82 X-1) is probably one of the best candidates to host an IMBH. In this work, we analysed the data of the recent release of observations obtained from M82 X-1 taken by XMM-Newton. We performed a study of the timing and spectral properties of the source. We report on the detection of approximate to(46 +/- 2) mHz quasi-periodic oscillations (QPOs) in the power density spectra of two observations. A comparison of the frequency of these high-frequency QPOs with previous detections supports the 1:2:3 frequency distribution as suggested in other studies. We discuss the implications if the approximate to(46 +/- 2) mHz QPO detected in M82 X-1 is the fundamental harmonic, in analogy with the high-frequency QPOs observed in BH binaries. For one of the observations, we have detected for the first time a QPO at 8 mHz (albeit at a low significance), which coincides with a hardening of the spectrum. We suggest that the QPO is a millihertz QPO originating from the close-by transient ULX M82 X-2, with analogies to the low-frequency QPOs observed in BH binaries.
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