Rotation of the optical polarization plane for the blazar OT 081

ATel #7872; D. Blinov (Univ. of Crete/St. Petersburg Univ.), E. N. Einoder (Caltech), K. Kokolakis, I. Liodakis, E. Makrydopoulou, G. V. Panopoulou (Univ. of Crete) on behalf of the RoboPol collaboration
on 3 Aug 2015; 22:24 UT
Credential Certification: Dmitriy Blinov (blinov@physics.uoc.gr)

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Ongoing R-band polarimetric monitoring of the blazar OT 081 (a.k.a. PKS 1749+096, RA: 17h51m32.8s, DEC: +09d39m01s, J2000) with the RoboPol instrument shows a rotation of the polarization plane. From the beginning of the current observing season May 9, 2015 until July 10 the blazar showed rather random variations of the polarization angle in the range between -350 and -300 degrees and polarization degree between ~8% and ~16%. Starting from July 10 the polarization plane has been performing a rotation with average rate 9.5 deg/day. The ongoing rotation is in the same direction (clockwise) and has a similar rotation rate as the one we reported last year ATel #6396 for this blazar. The polarization degree has slightly dropped during the rotation, and is varying between ~2% and 12%. At the same time, we don't see any clear increase in the total flux from the blazar. Preliminary analysis of the publicly available Fermi LAT data for the source 3FGL J1751.5+0939, which is positionally consistent with the blazar, gives an upper limit on the average photon flux (E>100MeV) 4.9x10^-8 ph cm^-2 s^-1 during the rotation period, while the average photon flux reported in 3FGL catalog is (5.3+/-0.58)x10^-8 ph cm^-2 s^-1. Multiwavelength observations of the blazar are encouraged.

The RoboPol program aims to understand 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).