The Rotation Measure and 3.5 Millimeter Polarization of Sagittarius A*
Open Access
- 17 July 2006
- journal article
- research article
- Published by IOP Publishing in The Astrophysical Journal
- Vol. 646 (2), L111-L114
- https://doi.org/10.1086/506932
Abstract
We report the detection of variable linear polarization from Sgr A* at a wavelength of 3.5 mm, the longest wavelength yet at which a detection has been made. The mean polarization is 2.1% ± 0.1% at a position angle of 16° ± 2° with rms scatters of 0.4% and 9° over the five epochs. We also detect polarization variability on a timescale of days. Combined with previous detections over the range 150-400 GHz (750-2000 μm), the average polarization position angles are all found to be consistent with a rotation measure of -(4.4 ± 0.3) × 105 rad m-2. This implies that the Faraday rotation occurs external to the polarized source at all wavelengths. This implies an accretion rate ~(0.2-4) × 10-8 M☉ yr-1 for the accretion density profiles expected of ADAF, jet, and CDAF models and assuming that the region at which electrons in the accretion flow become relativistic is within 10RS. The inferred accretion rate is inconsistent with ADAF/Bondi accretion. The stability of the mean polarization position angle between disparate polarization observations over the frequency range limits fluctuations in the accretion rate to less than 5%. The flat frequency dependence of the interday polarization position angle variations also makes them difficult to attribute to rotation-measure fluctuations and suggests that both the magnitude and position angle variations are intrinsic to the emission.This publication has 23 references indexed in Scilit:
- Radio linear and circular polarization from M 81*Astronomy & Astrophysics, 2006
- Variable Linear Polarization from Sagittarius A*: Evidence of a Hot Turbulent Accretion FlowThe Astrophysical Journal, 2004
- Detection of the Intrinsic Size of Sagittarius A* Through Closure Amplitude ImagingScience, 2004
- Interferometric Detection of Linear Polarization from Sagittarius A* at 230 GHzThe Astrophysical Journal, 2003
- BIMA Observations of Linear Polarization in Sagittarius A* at 112 GH[CLC]z[/CLC]The Astrophysical Journal, 2001
- Sagittarius A* Polarization: No Advection-dominated Accretion Flow, Low Accretion Rate, and Nonthermal Synchrotron EmissionThe Astrophysical Journal, 2000
- Detection of Polarized Millimeter and Submillimeter Emission from Sagittarius A*The Astrophysical Journal, 2000
- The Linear Polarization of Sagittarius A*. II. VLA and BIMA Polarimetry at 22, 43, and 86 GHzThe Astrophysical Journal, 1999
- The Linear Polarization of Sagittarius A*. I. VLA Spectropolarimetry at 4.8 and 8.4 GHzThe Astrophysical Journal, 1999
- The Simultaneous Spectrum of Sagittarius A* from 20 Centimeters to 1 Millimeter and the Nature of the Millimeter ExcessThe Astrophysical Journal, 1998