Stellar Systems Group

Meyer, L.; Do, T.; Ghez, A.; Morris, M. R.; Witzel, G.; Eckart, A.; Bélanger, G.; Schödel, R.
The Astrophysical Journal, Volume 688, Issue 1, pp. L17-L20.
11/2008

ABSTRACT

We present the longest, by a factor of 2, near-infrared light curve 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 light curve is used to address two outstanding problems. First, a putative quasi-periodicity of ~20 minutes 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 light curves from the two wavelength domains, the reported time lag of 20 minutes inferred using the Keck data of this common VLT/Keck night only is at odds with the lag of ~100 minutes reported earlier. With our long light curve, we find that (1) the simultaneous 1.3 mm observations are in fact consistent with a ~100 minute time lag, (2) the different methods of NIR photometry used by the VLT and Keck groups lead to consistent results, (3) the Lomb-Scargle periodogram of the whole NIR light curve is featureless and follows a power law with slope -1.6, and (4) scanning the light curve with a sliding window to look for a transient QPO phenomenon reveals for a certain part of the light curve a 25 minute peak in the periodogram. Using Monte Carlo simulations and taking the number of trials into account, we find it to be insignificant.