Submillimeter and radio variability of Sagittarius A*

A statistical analysis^⋆

¹ I. Physikalisches Institut der Universität zu Köln (PH1), Zülpicher Straße 77, 50937, Köln, Germany
e-mail: subroweit@ph1.uni-koeln.de
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³ Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
⁴ Dep. of Physics and Astronomy, University of California Los Angeles (UCLA), 465 Portola Plaza, Los Angeles, CA 90095, USA

Received: 16 March 2016
Accepted: 25 January 2017

Abstract

We report on a statistical analysis of the 345 GHz submillimeter (submm) and 100 GHz radio flux density distribution of Sagittarius A* (Sgr A*). The submm data set consists of 345 GHz data obtained from different Large Apex Bolometer Camera (LABOCA) campaigns between 2008 and 2014, and additional literature data from 2004 to 2009 at comparable wavelengths. The radio observations were carried out with the Australia Telescope Compact Array (ATCA) between 2010 and 2014. We used a combined maximum likelihood estimator (MLE) and Kolmogorov-Smirnov (KS) statistics method to test for a possible power-law distribution in the high flux density excursions (flares) at both wavebands. We find that both flux density distributions can be described by a shifted power-law of the form p(x) ∝ (x − s)^{− α} with α ~ 4 (submm: α = 4.0 ± 1.7; radio: α = 4.7 ± 0.8). The same power-law index was previously found for the near-infrared (NIR) flux density distribution. These results may strengthen our preferred flare emission model: a combined synchrotron self-Compton (SSC) and adiabatically expanding self-absorbed synchrotron blob model where the flaring activity across all wavebands stem from the same source components and the variable emission can be described by a single state red noise process. Within the framework of the expanding blob model the similarity of the radio and the submm flux density distribution may also narrow down possible initial synchrotron turnover frequencies ν₀ to be mainly around 350 GHz and possible expansion velocities v_exp to be predominantly around 0.01 c.