Near-infrared Polarimetry of flares from Sgr A* with Subaru/CIAO

Abstract

We have performed near-infrared monitoring observations of Sgr A*, the Galactic center radio source associated with a supermassive black hole, with the near-infrared camera CIAO and the 36-element adaptive optics system on the Subaru telescope. We observed three flares in the Ks band (2.15micron) during 220 min monitoring on 2008 May 28, and confirmed the flare emission is highly polarized, supporting the synchrotron radiation nature of the near-infrared emission. Clear variations in the degree and position angle of polarization were also detected: an increase of the degree of polarization of about 20 %, and a swing of the position angle of about 60 - 70 degrees in the declining phase of the flares. The correlation between the flux and the degree of polarization can be well explained by the flare emission coming from hotspot(s) orbiting Sgr A*. Comparison with calculations in the literature gives a constraint to the inclination angle i of the orbit of the hotspot around Sgr A*, as 45 < i < 90 degrees (close to edge-on).

14 pages, 4 figures, Accepted for publication in ApJ Letters. For higher resolution, see http://www.kusastro.kyoto-u.ac.jp/~shogo/paper/ApJ/SgrAS08/09NishiyamaSgrASNIRPol.pdf

References in corpus (16)

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• Near-infrared polarimetry setting constraints on the orbiting spot model for Sgr A* flares
• Polarized NIR and X-ray Flares from SgrA*
• K-band polarimetry of an Sgr A* flare with a clear sub-flare structure
• A 600 minute near-infrared lightcurve of Sagittarius A*
• On the orientation of the Sagittarius A* system
• General Relativistic Flux Modulations from Disk Instabilities in Sagittarius A*
• Linearly and Circularly Polarized Emission in Sagittarius A*
• An evolving hot spot orbiting around Sgr A*
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Cited by in corpus (9)

• The Galactic Center Massive Black Hole and Nuclear Star Cluster
• 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
• 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*
• Dynamo activities driven by magneto-rotational instability and Parker instability in galactic gaseous disk
• A Plasmoid Model for the Sgr A* Flares Observed with GRAVITY and Chandra
• Bright X-ray flares from Sgr A*
• Flare emission from Sagittarius A*
• Polarimetric Imaging of Sgr A* in its Flaring State