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Rotation of the optical polarization plane for the blazar 4C +38.41

ATel #9331; G. V. Panopoulou, G. M. Maragkakis, K. Xexakis (Univ. of Crete, Greece) on behalf of the RoboPol collaboration
on 6 Aug 2016; 12:53 UT
Credential Certification: Dmitriy Blinov (blinov@physics.uoc.gr)

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

We report on the ongoing rotation of the optical polarization angle (R-band) seen in the monitored blazar 4C +38.41 (RA=16:35:15.5, DEC=38:08:05, J2000) as recorded within the framework of the RoboPol program. Starting from July, 27 the polarization plane has been performing a monotonic rotation at a rate of 11 deg/day. The total amplitude of the rotation is ~100 deg (clockwise) so far. The polarization degree has decreased from 10% to 4% during the rotation period. At the same time, the blazar is increasing its optical total flux. Relative photometry based on PTF catalog magnitudes (Ofek et al., 2012, PASP, 124, 854) shows that it reached R=17m on August 5. Preliminary analysis of the publicly available Fermi LAT data for the source 3FGL J1635.2+3809, which is associated with the blazar, shows no increase in the gamma-ray emission. Averaged gamma-ray photon flux (E>100MeV) during the rotation period (0.8+/-0.3)x10^-7 ph cm^-2 s^-1 is lower than the average flux reported in 3FGL catalog (2.7+/-0.1)x10^-7 ph cm^-2 s^-1.
Multifrequency observations of the blazar are strongly encouraged.

The RoboPol programme 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).