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Optical and near-infrared polarimetry for V404 Cyg with 1.6m Pirka and 1.5m Kanata telescopes in Japan

ATel #7709; R. Itoh (Hiroshima Univ.), M. Watanabe, M. Imai (Hokkaido Univ.), T. Nakaoka, K. Takaki, K. Shiki, Y. T. Tanaka, M. Uemura, K. S. Kawabata (Hiroshima Univ.), on behalf of the OISTER collaboration
on 25 Jun 2015; 01:42 UT
Credential Certification: Yasuyuki T. Tanaka (tanaka@astro.isas.jaxa.jp)

Subjects: Infra-Red, Optical, Binary, Black Hole, Transient

Referred to by ATel #: 7721, 7722, 7734, 7740, 7959

We performed optical polarimetry for the recently-activated (e.g., ATel #7646) black hole X-ray binary V404 Cyg on 2015 June 17, 13:12 UT with the MSI (Watanabe et al., Proc. SPIE, 2012) on the 1.6m Pirka telescope. Preliminary analysis indicates that the R-band polarization degree was ~8%. We also performed optical and near-infrared polarimetry using the HONIR (Akitaya et al., Proc. SPIE, 2014) on the 1.5m Kanata telescope on 2015 June 21, 12:10 UT. We obtained a preliminary result of the polarization degree of ~8% in R-band and ~2% in Ks-band. The position angle of the polarization in each band was almost the same within a reliability of ~15 degrees.

Our R-band polarization is apparently consistent with previously-reported results (ATel #7674, #7678). The steep wavelength dependence of the polarization is similar to that of a highly reddened star having a smallest lambda_max, e.g., Cyg OB2 No. 12 (E(B-V)=3.31mag, P_max=9.9%, lambda_max=0.35um; Whittet et al. 1992, ApJ, 386, 562), suggesting that the polarization might still be an interstellar origin. If this is the case, the intrinsic polarization is small, especially in NIR band, which may disfavor a possible contribution of an optically-thin synchrotron emission component. Further observations and analyses are ongoing.

This work is supported by the Optical & Near-Infrared Astronomy Inter-University Cooperation Program, the MEXT of Japan.