Understanding the Radio Variability of Sgr A*

Abstract

We determine the characteristics of the 7mm to 20cm wavelength radio variability in Sgr A* on time scales from days to three decades. The amplitude of the intensity modulation is between 30 and 39% at all wavelengths. Analysis of uniformly sampled data with proper accounting of the sampling errors associated with the lightcurves shows that Sgr A* exhibits no 57- or 106-day quasi-periodic oscillations, contrary to previous claims. The cause of the variability is investigated by examining a number of plausible scintillation models, enabling those variations which could be attributed to interstellar scintillation to be isolated from those that must be intrinsic to the source. Thin-screen scattering models do not account for the variability amplitude on most time scales. However, models in which the scattering region is extended out to a radius of 50-500pc from the Galactic Center account well for the broad characteristics of the variability on >4-day time scales. The ~ 10% variability on <4-day time scales at 0.7-3cm appears to be intrinsic to the source. The degree of scintillation variability expected at millimeter wavelengths depends sensitively on the intrinsic source size; the variations, if due to scintillation, would require an intrinsic source size smaller than that expected.

arXiv commentAp.J. accepted, high-resolution version at http://www.aoc.nrao.edu/~jmacquar/SgrA.pdf

References in corpus (20)

• The Proper Motion of Sgr A*: II. The Mass of Sgr A*
• Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic Centre
• A Jet-ADAF model for Sgr A*
• Spectral Models of Advection-Dominated Accretion Flows with Winds
• The Proper Motion of SgrA*: I. First VLBA Results
• Detection of the Intrinsic Size of Sagittarius A* through Closure Amplitude Imaging (includes Online Supporting Material)
• First Simultaneous NIR/X-ray Detection of a Flare from SgrA*
• Extreme scattering events and Galactic dark matter
• PKS 0405--385: the smallest radio quasar?
• Intrinsic Size OF Sgr A*: 72 Schwarzschild Radii
• Variability of Sagittarius A* - Flares at 1 Millimeter
• Hyperstrong Radio-Wave Scattering in the Galactic Center. II. A Likelihood Analysis of Free Electrons in the Galactic Center
• Proper Motion of the Compact, Nonthermal Radio Source in the Galactic Center, Sagittarius a*
• The Spectrum and Variability of Circular Polarization in Sagittarius A* from 1.4 to 15 GHz
• Interstellar Scintillation of the Polarized Flux Density in Quasar, PKS 0405-385
• Intra-day Variability of Sagittarius A* at 3 Millimeters
• Radio Variability of Sagittarius A* - A 106 Day Cycle
• The Variability of Sagittarius A* at Centimeter Wavelengths
• Interstellar Scintillation od Pulsar B0809+74
• A Radio Outburst Nearly Coincident with the Large X-ray Flare from Sgr A* on 2002-10-03

Cited by in corpus (29)

• The Galactic Center Massive Black Hole and Nuclear Star Cluster
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• Flaring Activity of Sgr A* at 43 and 22 GHz: Evidence for Expanding Hot Plasma
• A Multi-Wavelength Study of Sgr A*: The Role of Near-IR Flares in Production of X-ray, Soft $\gamma$-ray and Sub-millimeter Emission
• Radio and Millimeter Monitoring of Sgr A*: Spectrum, Variability, and Constraints on the G2 Encounter
• Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity
• Prospects for testing the nature of Sgr A*'s NIR flares on the basis of current VLT- and future VLTI-observations
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• A High-Frequency Search for Pulsars Within the Central Parsec of SgrA*
• Galactic Center Research: Manifestations of the Central Black Hole
• Jet-lag in Sgr A*: What size and timing measurements tell us about the central black hole in the Milky Way
• The Proper Motion of the Galactic Center Pulsar Relative to Sagittarius A*
• Dynamically important magnetic fields near the event horizon of Sgr A*
• The Intrinsic Two-Dimensional Size of Sagittarius A*
• ALMA Observations of the Terahertz Spectrum of Sagittarius A*
• Radio Synchrotron Emission from a Bow Shock around the Gas Cloud G2 Heading toward the Galactic Center
• Rapid Intrinsic Variability of Sgr A* at Radio Wavelengths
• Time Variations in the Flux Density of Sgr A* at 230 GHz Detected with ALMA
• A Black Hole Mass-Variability Time Scale Correlation at Submillimeter Wavelengths
• Simultaneous Monitoring of X-ray and Radio Variability in Sagittarius A*
• Multi-Epoch VERA Observations of Sagittarius A*: I. Images and Structural Variability
• Detection of a 20 minute time lag observed from Sgr A* between 8 and 10 GHz with the VLA
• Detecting Stars at the Galactic Centre via Synchrotron Emission
• Very Large Array multi-band monitoring observations of M 31*
• New Evidence for a Flux-independent Spectral Index of Sgr A* in the Near-infrared
• The Core-shift of Sagittarius A* as a Discriminant between Disk and Jet Emission Models with millimeter-VLBI
• SgrA* emission at 7mm: variability and periodicity
• Flaring Activity of Sgr A*: Expanding Hot Blobs