Time Lag in Intra-Day Variability of Sgr A* between the Light Curves at 90 and 102GHz

TL;DR

This study observed Sgr A* at 90 and 102GHz to detect potential time lags in intra-day variability, finding no lag and suggesting diverse plasma conditions or different emission origins at these frequencies.

Contribution

First simultaneous high-frequency observations of Sgr A* at 90 and 102GHz to investigate intra-day variability time lag.

Findings

No significant time lag detected between 90 and 102GHz.

Results imply diverse plasma properties or emission sources at these frequencies.

Supports the need for further high-frequency variability studies.

Abstract

We performed the observation of the flux densities of SgrA* at 90 and 102GHz in order to detect the time lag between these frequencies using the Nobeyama Millimeter Array, which was previously reported at lower frequencies. We detected a radio flare during the observation period on 6 April 2005 and calculated the z-transformed discrete correlation function between the light curves. The time lag between these frequencies was not detected. If the expanding plasma model which explains the time lag at lower frequencies is valid, the light curve at 90GHz would be delayed with respect to the one at 102GHz. This result suggests that the plasma blobs ejected near the Galactic Center black hole may be widely diverse especially in optical thickness. Another possibility is that the major portion of the flux above 100GHz does not originate from the blobs.