Flaring activity of sagittarius A* at 43 and 22 GHz

Evidence for expanding hot plasma

F. Yusef-Zadeh*, D. Roberts, M. Wardle, C. O. Heinke, G. C. Bower

*Corresponding author for this work

Research output: Contribution to journalArticle

119 Citations (Scopus)

Abstract

We have carried out Very Large Array (VLA) continuum observations to study the variability of Sgr A* at 43 GHz (λ = 7 mm) and 22 GHz (λ = 13mm). Alow level offlare activity has been detected with a duration of ∼2hr at these frequencies, showing the peak flare emission at 43 GHz leading the 22 GHz peak flare by ∼20-40 minutes. The overall characteristics of the flare emission are interpreted in terms of the plasmon model of van der Laan by considering the ejection and adiabatic expansion of a uniform, spherical plasma blob due to flare activity. The observed peak of the flare emission with a spectral index, v, of α = 1.6 is consistent with the prediction that the peak emission shifts toward lower frequencies in an adiabatically expanding self-absorbed source. We present the expected synchrotron light curves for an expanding blob, as well as the peak frequency emission, as a function of the energy spectral index constrained by the available flaring measurements in near-IR, submillimeter, millimeter, and radio wavelengths. We note that the blob model is consistent with the available measurements; however, we cannot rule out the jet of Sgr A*. If expanding material leaves the gravitational potential of Sgr A*, the total mass-loss rate of nonthermal and thermal particles is estimated to be ≤2 × 10-8 M yr-1. We discuss the implication of the mass-loss rate, since this value matches closely the estimated accretion rate based on polarization measurements.

Original languageEnglish
Pages (from-to)189-194
Number of pages6
JournalAstrophysical Journal
Volume650
Issue number1 I
DOIs
Publication statusPublished - 10 Oct 2006

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