TY - JOUR
T1 - Flaring activity of sagittarius A* at 43 and 22 GHz
T2 - Evidence for expanding hot plasma
AU - Yusef-Zadeh, F.
AU - Roberts, D.
AU - Wardle, M.
AU - Heinke, C. O.
AU - Bower, G. C.
N1 - Copyright:
Copyright 2015 Elsevier B.V., All rights reserved.
PY - 2006/10/10
Y1 - 2006/10/10
N2 - 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-α, 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.
AB - 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-α, 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.
KW - Galaxy: center
KW - Techniques: interferometric
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U2 - 10.1086/506375
DO - 10.1086/506375
M3 - Article
AN - SCOPUS:34248188650
VL - 650
SP - 189
EP - 194
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1 I
ER -