Testing for periodicities in near-IR light curves of Sgr A*

Details Testing for periodicities in near-IR light curves of Sgr A* Testing for periodicities in near-IR light curves of Sgr A*

Oct 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008jphcs.131a2003d&link_type=abstract

"Journal of Physics: Conference Series, Volume 131, Proceedings of "The Universe Under the Microscope - Astrophysics at High Ang

Astronomy and Astrophysics

Astrophysics

2

Scientific paper

We present the results of near-infrared (2 μm) monitoring of Sgr A*-IR with 1 minute time sampling using laser guide star adaptive optics (LGS AO) system at the Keck II telescope. Sgr A*-IR was observed continuously for up to three hours on each of seven nights, between 2006 May and 2007 August. Sgr A*-IR is detected at all times and is continuously variable. These observations allow us to investigate Nyquist sampled periods ranging from about 2 minutes to an hour. Of particular interest are periods of thicksim20 min, which corresponds to a quasi-periodic (QPO) signal claimed based upon previous near-infrared observations and interpreted as the orbit of a 'hot spot' at or near the last stable orbit of a spinning black hole. We investigate these claims by comparing periodograms of the light curves with models for red noise and find no significant deviations that would indicate QPO activity at any time scale probed in the study. We find that the variability of Sgr A* is consistent with a model based on correlated noise with a power spectrum having a frequency dependence of thicksim f-2.5, consistent with that observed in AGNs. Furthermore, the periodograms show power down to the minimum sampling time of 2 min, well below the period of the last stable orbit of a maximally spinning black hole, indicating that the Sgr A*-IR light curves observed in this study is unlikely to be from the Keplerian motion of a single 'hot spot' of orbiting plasma.

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