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Ongoing rotation of the optical polarization plane for the blazar S4 1749+70

ATel #6351; I. Liodakis (Univ. of Crete, Greece) on behalf of the RoboPol collaboration
on 29 Jul 2014; 00:32 UT
Credential Certification: Dmitriy Blinov (blinov@physics.uoc.gr)

Subjects: Optical, Gamma Ray, AGN, Black Hole, Blazar

We report the ongoing rotation of the optical polarization plane seen in the blazar S4 1749+70 (RA= 17:48:32.8, DEC=+70:05:50.7, J2000). Observations were performed within the framework of the RoboPol program. The rotation of the polarization angle began after May 27, 2014. Its magnitude as of July 27, 2014 was ~170 degrees, clockwise. The polarization degree was varying between 12% and 4% on course of the rotation and the R band magnitude 14.8 estimated using USNO-B1.0 catalog magnitudes (Monet et al., 2003, AJ, 125, 984) shows that the blazar is in the brightest state as observed by RoboPol. It is approximately one magnitude brighter comparing to R=15.83 reported by (Urry et al., 2000, ApJ, 532, 816). There is a slight increase in the gamma-ray emission according to the available Fermi LAT data for the source 2FGL J1748+7005. The average gamma-ray photon flux (E>100MeV) during the rotation period is (3.47+-0.86)x10^-8 ph cm^-2 s^-1, whereas the 2FGL value corresponding to the source is (2.49+-0.58)x10^-8 ph cm^-2 s^-1.
Multiwavelength observations of the blazar are encouraged.

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).