The Circular Polarization of Sagittarius A* at Submillimeter Wavelengths

Muñoz, Diego J.; Marrone, Daniel P.; Moran, J. M.; Rao, Ramprasad

doi:10.1088/0004-637x/745/2/115

Cited by 52 publications

(62 citation statements)

References 67 publications

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“…Several papers have suggested sign consistency at centimeter wavelengths in small numbers of sources or over short intervals [13,17,22] with perhaps the best established case the repeated measurements of Sgr A* over 20 years [24,25]. In our observations reduced to date, we have 39 sources with multi-epoch, three-sigma detections which span at least a year, and 35/39 of those are detected with the same sign as earlier epochs.…”

Section: Sign Consistencysupporting

confidence: 62%

“…Sources with circular polarization measurements above 0.5% may be more common at higher frequencies [20,21] which probe shorter length-scales in the jet, closer to the central engine. While circular polarization is clearly variable (e.g., [22,23]), there are indications that some sources may show a preferred sign of circular polarization at certain frequencies, e.g., [13,17,22], although this has only been well established for Sgr A* [24,25].…”

Section: Introductionmentioning

confidence: 99%

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Constraints on Particles and Fields from Full Stokes Observations of AGN

et al. 2018

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Combined polarization imaging of radio jets from Active Galactic Nuclei (AGN) in circular and linear polarization, also known as full Stokes imaging, has the potential to constrain both the magnetic field structure and particle properties of jets. Although only a small fraction of the emission when detected, typically less than a few tenths of a percent but up to as much as a couple of percent in the strongest resolved sources, circular polarization directly probes the magnetic field and particles within the jet itself and is not expected to be modified by external screens. A key to using full Stokes observations to constrain jet properties is obtaining a better understanding of the emission of circular polarization, including its variability and spectrum. We discuss what we have learned so far from parsec scale monitoring observations in the MOJAVE program and from multi-frequency observations of selected AGN.

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Section: Sign Consistencysupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Constraints on Particles and Fields from Full Stokes Observations of AGN

et al. 2018

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“…We will also consider closure phases and other similar diagnostics that are independent of visibility amplitudes and insensitive to single antenna phase errors (Doeleman et al 2001;Broderick et al 2011). CP, EVPA, and Faraday rotation can potentially probe the helical orientation of the jet magnetic field (Contopoulos et al 2009) or probe the degree of order of the disk magnetic field (Muñoz et al 2012). The hope is that EHT CP and EVPA observations at non-zero baselines at 230 GHz or higher frequencies will further constrain the disk, jet, and plasma properties in unique ways compared to thelinear polarization fraction.…”

Section: Future Workmentioning

confidence: 99%

Probing the Magnetic Field Structure in on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations

Gold

McKinney

Johnson

et al. 2017

ApJ

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Magnetic fields are believed to drive accretion and relativistic jets in black hole accretion systems, but the magnetic field structure that controls these phenomena remains uncertain. We perform general relativistic (GR) polarized radiative transfer of time-dependent three-dimensional GR magnetohydrodynamical simulations to model thermal synchrotron emission from the Galactic Center source SagittariusA * (SgrA * ). We compare our results to new polarimetry measurements by the Event Horizon Telescope (EHT) and show how polarization in the visibility (Fourier) domain distinguishes and constrains accretion flow models with different magnetic field structures. These include models with small-scale fields in disks driven by the magnetorotational instability as well as models with large-scale ordered fields in magnetically arrested disks. We also consider different electron temperature and jet mass-loading prescriptions that control the brightness of the disk, funnel-wall jet, and Blandford-Znajek-driven funnel jet. Our comparisons between the simulations and observations favor models with ordered magnetic fields near the black hole event horizon in SgrA * , though both disk-and jet-dominated emission can satisfactorily explain most of the current EHT data. We also discuss how the black hole shadow can be filled-in by jet emission or mimicked by the absence of funnel jet emission. We show that stronger model constraints should be possible with upcoming circular polarization and higher frequency (349 GHz) measurements.

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“…Circular polarization is present in Sgr A* from cm to submm wavelengths, a factor of more than 200 in wavelength (Bower et al 1999b;Sault & Macquart 1999;Bower et al 2002b;Muñoz et al 2012). The CP has constant handedness across all wavelengths and a magnitude < ∼ 1%.…”

Section: Introductionmentioning

confidence: 99%

ALMA Polarimetry of Sgr A*: Probing the Accretion Flow from the Event Horizon to the Bondi Radius

Bower¹,

Broderick

Dexter

et al. 2018

ApJ

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Millimeter polarimetry of Sgr A* probes the linearly polarized emission region on a scale of ∼ 10 Schwarzschild radii (R S ) as well as the dense, magnetized accretion flow on scales out to the Bondi radius (∼ 10 5 R S ) through Faraday rotation. We present here multi-epoch ALMA Band 6 (230 GHz) polarimetry of Sgr A*. The results confirm a mean rotation measure, RM ≈ −5 × 10 5 rad m −2 , consistent with measurements over the past 20 years and support an interpretation of the RM as originating from a radiatively inefficient accretion flow (RIAF) withṀ ≈ 10 −8 M y −1 . Variability is observed for the first time in the RM on time scales that range from hours to months. The long-term variations may be the result of changes in the line of sight properties in a turbulent accretion flow. Short-term variations in the apparent RM are not necessarily the result of Faraday rotation and may be the result of complex emission and propagatation effects close to the black hole, some of which have been predicted in numerical modeling. We also confirm the detection of circular polarization at a mean value of −1.1 ± 0.2%. It is variable in amplitude on time scales from hours to months but the handedness remains unchanged from that observed in past centimeter-and millimeter-wavelength detections. These results provide critical constraints for the analysis and interpretation of Event Horizon Telescope data of Sgr A*, M87, and similar sources.

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The Circular Polarization of Sagittarius A* at Submillimeter Wavelengths

Cited by 52 publications

References 67 publications

Constraints on Particles and Fields from Full Stokes Observations of AGN

Constraints on Particles and Fields from Full Stokes Observations of AGN

Probing the Magnetic Field Structure in on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations

ALMA Polarimetry of Sgr A*: Probing the Accretion Flow from the Event Horizon to the Bondi Radius

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