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

Shogo Nishiyama(1,2), Motohide Tamura(3), Hirofumi Hatano(4), Tetsuya Nagata(1), Tomoyuki Kudo(3), Miki Ishii(5), Rainer Schödel(6), and Andreas Eckart(7,8)

(1) Department of Astronomy, Kyoto University, Kyoto, 606-8502 Japan
(2) Research Fellow of the Japan Society for the Promotion of Science (JSPS)
(3) National Astronomical Observatory of Japan, Mitaka, Tokyo, 181-8588 Japan
(4) Department of Astrophysics, Nagoya University, Nagoya, 464-8602 Japan
(5) Subaru Telescope, National Astronomical Observatory of Japan, 650 North A`ohoku Place, Hilo, HI 96720
(6) Instituto de Astrofísica de Andalucía (IAA)-CSIC, Camino Bajo de Huétor 50, E-18008 Granada, Spain
(7) I.Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
(8) Max Planck Institute für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Paper: ApJ, accepted


EPrint Server: 0907.5466


We have performed near-infrared monitoring observations of Sgr A*, the Galactic center radio source associated with a super-massive black hole, with the near-infrared camera CIAO and the 36-element AO 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 percent, 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).

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