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New UBVRI polarimetry of OJ 287

ATel #8806; S. Muneer, C. S. Stalin (Indian Institute of Astrophysics, Bengaluru, India), A. K. Venkataramana, R. Baskar (Vainu Bappu Observatory, IIA, Kavalur, India)
on 12 Mar 2016; 17:20 UT
Credential Certification: S. Muneer (muneers@iiap.res.in)

Subjects: Optical, AGN, Blazar

Further to our photo-polarimetric observations of the BL Lac object OJ 287 (z= 0.306) (ATel #8697), we report here new measurements of linear polarization of the object in UBVRI bands, and in integrated light in V-I spectral region (denoted as R' band) obtained during 8-11 March, 2016. The object has been monitored photometrically by several observers (ATel #8705, #8768, #8777, #8778) after the discovery of a strong outburst during November-December 2015 by Zola et al. 2016 (ATel #8667).

The UBV passbands approximate those of the Johnson's UBV system and the RI passbands, those of the Kron-Cousins system. The degree of linear polarization and position angle obtained are listed below. The probable errors of the measurements are given in the parentheses.

March 8; JD 2457456.2
U: P(%) = 33.0 (1.8), PA (deg) = 62.4 (1.7)
B: P(%) = 28.6 (1.5), PA (deg) = 59.9 (1.6)
R': P(%) = 22.6 (0.2), PA (deg) = 60.8 (0.3)

March 9; JD 2457457.2
R': P(%) = 27.7 (0.5), PA (deg) = 61.2 (0.5)

March 10; JD 2457458.2
U: P(%) = 38.7 (1.4), PA (deg) = 74.3 (1.1)
B: P(%) = 32.1 (1.1), PA (deg) = 64.9 (1.1)
V: P(%) = 27.8 (0.8), PA (deg) = 71.0 (0.9)
R: P(%) = 28.3 (0.8), PA (deg) = 72.5 (0.8)
I: P(%) = 22.5 (0.9), PA (deg) = 67.3 (1.2)
R': P(%) = 27.4 (0.4), PA (deg) = 71.6 (0.4)

March 11; JD 2457459.2
U: P(%) = 32.2 (3.0), PA (deg) = 63.2 (3.1)
B: P(%) = 27.2 (1.6), PA (deg) = 58.6 (1.8)
V: P(%) = 30.0 (0.9), PA (deg) = 63.5 (0.9)
R: P(%) = 23.7 (0.6), PA (deg) = 60.6 (0.8)
R': P(%) = 26.7 (0.4), PA (deg) = 61.1 (0.5)

We estimate the R mag of the object during the present observations to be in the range 14.1-14.3, about 1 mag fainter than that observed on 3 March 2016 (ATel #8768). During the previous polarimetric observations by us (ATel #8697) the R mag of OJ 287 was similar to the above. Both the linear polarization and position angles obtained during the two occasions differ drastically. The present observations indicate that both the linear polarization and position angles show inter-night variations, and that the linear polarization is wavelength-dependent.