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Rotation of the optical polarization plane for the blazar OT 081

ATel #6396; G. Panopoulou (Univ. of Crete, Greece) on behalf of the RoboPol collaboration
on 15 Aug 2014; 23:52 UT
Credential Certification: Dmitriy Blinov (blinov@physics.uoc.gr)

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

Referred to by ATel #: 7872

Ongoing R-band polarimetric monitoring of the blazar OT81 (a.k.a. PKS 1749+096, RA: 17h51m32.8s, DEC: +09d39m01s, J2000) with the RoboPol instrument shows rotation of the polarization plane. From the beginning of the current observing season (late April) until July 26 the blazar showed rather smooth variability in polarization degree between ~4% and ~13% and position angle in the range 140 - 200 deg. Starting from July 26 polarization plane has been performing a monotonic rotation at a rate of 10 deg/day. The polarization degree has increased from ~4.5% to 25% during the rotation period. At the same time, the blazar is flaring in unpolarized flux. Relative photometry based on USNO-B1.0 catalog magnitudes (Monet et al., 2003, AJ, 125, 984-993) shows that the blazar reached R-band magnitude 15.7 on August 14. Preliminary analysis of the publicly available Fermi LAT data for the source 2FGL J1751.5+0938, which is positionally consistent with the blazar, shows a moderate increase of averaged photon flux (4.2+-1.3 x10^-8 ph cm^-2 s^-1, E>100MeV) during the rotation period compared to the value during the preceding period of RoboPol's monitoring this year (2.9+-0.7 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).