The Variability of Polarized Radiation from Sgr A*

Abstract

Sgr A* is variable at radio and submillimeter wavelengths on hourly time scales showing time delays between the peaks of flare emission as well as linearly polarized emission at millimeter and sub-mm wavelengths. To determine the polarization characteristics of this variable source at radio frequencies, we present VLA observations of Sgr A* and report the detection of polarized emission at a level of 0.77\pm0.01% and 0.2\pm0.01% at 43 and 22 GHz, respectively. The change in the time averaged polarization angle between 22 and 43 GHz corresponds to a RM of -2.5\pm0.6 x10^3 rad m{-2} with no phase wrapping (or \sim 5x10^4 rad m^2 with 2πphase wrap). We also note a rise and fall time scale of 1.5 -- 2 hours in the total polarized intensity. The light curves of the degree of linearly polarized emission suggests a a correlation with the variability of the total intensity at 43 GHz. The available polarization data at radio and sub-mm wavelengths suggest that the rotation measure decreases with decreasing frequency. This frequency dependence, and observed changes in polarization angle during flare events, may be caused by the reduction in rotation measure associated with the expansion of synchrotron-emitting blobs.

11 pages, 3 figures, ApJL (in press)

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• An X-ray, IR, and Submillimeter Flare of Sagittarius A*
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• Millimeter Flares and VLBI Visibilities from Relativistic Simulations of Magnetized Accretion onto the Galactic Center Black Hole
• Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity
• Variability Timescale and Spectral Index of Sgr A* in the Near Infrared: Approximate Bayesian Computation Analysis of the Variability of the Closest Supermassive Black Hole
• Simultaneous Multi-Wavelength Observations of Sgr A* during 2007 April 1-11
• Source-intrinsic near-infrared properties of Sgr A*: Total intensity measurements
• Simultaneous NIR/sub-mm observation of flare emission from SgrA*
• A hidden friend for the galactic center black hole, Sgr A*
• Near infrared flares of Sagittarius A*: Importance of near infrared polarimetry
• Concurrent X-ray, near-infrared, sub-millimeter, and GeV gamma-ray observations of Sgr A*
• The instrumental polarization of the Nasmyth focus polarimetric differential imager NAOS/CONICA (NACO) at the VLT - Implications for time-resolved polarimetric measurements of Sgr A*
• Polarized light from Sgr A* in the near-infrared $K_s$-band
• The Circular Polarization of Sagittarius A* at Submillimeter Wavelengths
• Simultaneous X-ray and Infrared Observations of Sagittarius A*'s Variability
• The extreme luminosity states of Sagittarius A*
• Polarized Emission of Sagittarius A*
• Positron Effects on Polarized Images and Spectra from Jet and Accretion Flow Models of M87* and Sgr A*
• Radio$-\gamma -$ray response in blazars as a signature of adiabatic blob expansion
• Near-infrared polarimetry as a tool for testing properties of accreting super-massive black holes
• Linearly and Circularly Polarized Emission in Sagittarius A*
• Multi-wavelength Variability of Sagittarius A* in July 2019
• Polarized signatures of adiabatically expanding hotspots in Sgr A*'s accretion flow