A 600 Minute Near-Infrared Light Curve of Sagittarius A*

We present the longest, by a factor of two, near-infrared lightcurve from Sgr A * – the supermassive black hole in the Galactic center. Achieved by combining Keck and VLT data from one common night, which fortuitously had simultaneous Chandra and SMA data, this lightcurve is used to address two outstanding problems. First, a putative quasi-periodicity of ∼20min reported by groups using ESO’s VLT is not confirmed by Keck observations. Second, while the infrared and mm-regimes are thought to be related based on reported time lags between lightcurves from the two wavelength domains, the reported time lag of 20min inferred using the Keck data of this common VLT/Keck night only is at odds with the lag of ∼ 100min reported earlier. With our long lightcurve, we find that (i) the simultaneous 1.3 millimeter observations are in fact consistent with a ∼ 100min time lag, (ii) the different methods of NIR photometry used by the VLT and Keck groups lead to consistent results, (iii) the Lomb-Scargle periodogram of the whole NIR lightcurve is featureless and follows a power-law with slope-1.6, and (iv) scanning the lightcurve with a sliding window to look 1 Supported by a fellowship within the Postdoc-Program of the German Academic Exchange Service (DAAD). – 2 – for a transient QPO phenomenon reveals for a certain part of the lightcurve a 25min peak in the periodogram. Using Monte Carlo simulations and taking the number of trials into account, we find it to be insignificant. Subject headings: black hole physics, Galaxy: center 1.