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Multi-color photo-polarimetric observations of OJ 287 during ongoing flare

ATel #8697; Vaidehi S. Paliya, S. Muneer, C. S. Stalin (Indian Institute of Astrophysics, Bengalore, India) A. K. Venkataramana, S. Surendharnath, A. Ramachandran, R. Baskar, A. Muniyandi, M. Muniraj (Vainu Bappu Observatory, IIA, Kavalur, India)
on 15 Feb 2016; 10:04 UT
Credential Certification: Vaidehi S. Paliya (vaidehiratna@gmail.com)

Subjects: Optical, AGN, Blazar

Referred to by ATel #: 8768, 8777, 8778, 8806

We report UBVRI photometric and polarimetric observations of the BL Lac object OJ 287 (z = 0.306) made on 12 February 2016. This object was was recently detected in a high activity state (ATEL#8667). The polarimetry was carried out with a two beam, broadband, three channel polarimeter attached to the 1 m Carl Zeiss telescope at Vainu Bappu Observatory (VBO), Kavalur (G. Srinivasulu, A. V. Raveendran, S. Muneer et al. 2014, Bull. Astr. Soc. India, 42, 165).

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.

February 12; JD 2457431.3

U: P(%) = 16.3 (1.1), PA (deg) = 111 (2.0)

B: P(%) = 18.8 (0.8), PA (deg) = 118 (1.2)

V: P(%) = 19.8 (1.0), PA (deg) = 119 (1.4)

R: P(%) = 19.2 (0.5), PA (deg) = 116 (0.8)

I: P(%) = 16.6 (0.3), PA (deg) = 118 (1.0)

R': P(%) = 18.9 (0.3), PA (deg) = 117 (0.5)

The polarimetric observation listed against the R' band was made in integrated light in the VRI spectral region. The V mag and the broadband colors obtained by us are: V = 14.4, U-B = -0.50, B-V = 0.50, V-R = 0.40, V-I = 1.70. The uncertainty in V is around 0.1 mag, while that of a broadband color is around 0.05 mag.

We also report the temporal brightness variation of OJ 287 on the same night. The photometric observations were made in R band with a TEK 1k x 1k CCD camera attached to the 0.75-m telescope at VBO. Differential R magnitudes of OJ 287 with respect to a comparison star (J2000.0: R.A.= 08:54:54.48, Dec.=20:06:14.40; R = 14.34 mag) is plotted in the top panel of Figure 1. In order to check the constancy in the brightness of the comparison star, we obtained R magnitudes of another star (J2000.0:R.A.=08:54:55.20, Dec.=20:05:42.0; R = 14.65 mag) in the same CCD frame. Differential R magnitudes of both the comparison stars are plotted in the bottom panel of the same figure. No intranight optical variability is detected.