VERA monitoring of a blazar OJ 287

¹ Mizusawa VLBI Observatory/NAOJ, Hoshigaoka-cho, Mizusawa-ku, Oshu, Iwate, 023-0861 Japan
² The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-8654 Japan
³ ISAS/JAXA, Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, 252-5210 Japan
⁴ NAOJ, Osawa, Mitaka, Tokyo, 181-8588 Japan
⁵ Yamaguchi University, Yoshida, Yamaguchi, Yamaguchi 753-8512

^a e-mail: satoko.ss@nao.ac.jp

Published online: 9 December 2013

Abstract

We present the frequent VLBI monitoring results of blazar OJ 287 at 22 GHz band using the VLBI Exploration of Radio Astrometry (VERA) from 2010 November to 2012 September. Time interval of the monitoring is typically once or twice per month. The 22-GHz light curve of OJ 287 show three obvious increasing activities around 2011 May, 2011 October, and 2012 March, with a timescale of < 4 months. The second radio increasing events occurred at the same time as the γ-ray flare in 2011 October detected by the Fermi Large Area Telescope (LAT), and the third one seemed to precede the γ-ray flares in 2012, exhibiting different behaviour from the previous γ-ray flaring events in 2009. The relative motion of one jet component from the core was rectilinear super luminal motion (~ 8c) from the 2011 February to 2011 November toward the south direction, and then it changed the direction backward. The direction variation of the relative motion was seen from 2011 November to 2012 August, simultaneously with the γ-ray flares. It could be caused by a new ejected component in the innermost region.