Optical polarization of V404 Cyg

ATel #7674; G. Panopoulou (Univ. of Crete), P. Reig (Univ. of Crete/FORTH), D. Blinov (Univ. of Crete/St. Petersburg Univ.) on behalf of the RoboPol collaboration
on 20 Jun 2015; 15:12 UT
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Credential Certification: Dmitriy Blinov (blinov@physics.uoc.gr)

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We report on the optical polarimetry follow-up of the black hole X-ray binary V404 Cyg (GCN #17929, #17931, #17933, #17940; ATel #7646, #7647, #7650, #7658, #7659, #7661, #7662, #7663, #7665, #7666, #7667, #7669, #7671) performed with RoboPol. Our measurements on Jun 18, 2015 (22:49 UT) and Jun 19 (21:42 UT and 00:45 UT) show that the R-band emission of the source is polarized with P=7.7+-0.1% (not corrected for interstellar polarization). All three measurements are consistent, within errors. Additional polarimetry of nearby stars is required for interstellar polarization correction.

The RoboPol program aims at understanding the AGN physics through optical linear polarization monitoring of a large sample of gamma-ray loud blazars as well as a comparison sample of gamma-ray quiet ones. It utilizes a novel-design 4-channel optical polarimeter mounted at the 1.3-m Skinakas telescope in Crete. It is a collaboration between the University of Crete (Greece), Max-Planck-Institut fur Radioastronomie (Germany), California Institute of Technology (USA), Nicolaus Copernicus University (Poland) and the Inter-University Centre for Astronomy and Astrophysics (India).