GENJI/VERA によるブレーザー OJ287 の VLBI モニター観測
Satoko Sawada-Satoh1, Kazunori Akiyama2, Motoki Kino3, Hiroshi Nagai4, Kotaro Niinuma5, and the GENJI team
1: Mizusawa VLBI Observatory/NAOJ, 2: University of Tokyo, 3: ISAS/JAXA,
4: Chile Observatory/NAOJ, 5: Yamaguchi University

Introduction

Core-Jet Structure

22-GHz Light CurveOJ 287 is known to show a rapid
variability across a wide range ofwavelength. Recent gamma-ray
monitoring by Fermi revealed the highactivity of OJ 287 in 2011 and 2012.
We present the VLBI monitoring
results of blazer OJ 287 at 22 GHzband using the VERA (VLBI
Exploration of Radio Astrometry) in thesame time range from 2010 November
to 2012 September. This research is apart of the monitoring program GENJI(Gamma-ray Emitting Notable AGN
Monitoring by Japanese VLBI; Nagai
et al. 2013, PASJ 65, 24), which is amonitoring program of gamma-ray
bright AGNs with the VERA. Timeinterval of the monitoring is typicallyonce or twice per month.

The core-jet structure is represented bythree components; the core (C1), thejet component (C2) and the inner jetcomponent (C3). The components C1
and C2 could be identified as ‘C’ and‘j’ of the VLBA 43-GHz images (Agudoet al. 2012, 747, 63). Several innermost
jet components could be included into
the components C1 or C3, because
the angular resolution is 5 times lower
than that of the VLBA 43-GHz images.

The 22-GHz light curve of OJ 287 by
GENJI/VERA monitoring from 2010
November to 2012 September reveals
three obvious increasing activities
around 2011 May, 2011 October and2012 March.
In this period, two
pronounced gamma-ray flares in OJ
287 are reported by Fermi LAT. The
two gamma-ray flaring events seem tooccur with/after the two radio
increasing events, unlike the previous
gamma-ray flaring events in 2009
(Agudo et al. 2011, ApJ, 726, L13).

C1C2
C3
C1+C2+C3

Flux Density [Jy]86Fig.1 Light curve of OJ 287 at 22 GHz by GENJI
programme with the VERA. We adopted 10% for
the flux error. Grey rectangles represent the periodsof the gamma-ray flaring event at a 1x10-6 photons
cm-2 s-1 reported by Fermi LAT.

420
2011/01

2011/072012/01

2012/07

Date [yyyy/mm]

2

2010/11/20

2010/11/27

2010/12/24

2011/02/04

Jet Motion

2011/04/22

The angular separation between the components C1 andC2 increased ∼0.8 mas from 2010 November to 2012
September. It corresponds to a superluminal motion with
an apparent velocity of ~8c, applying rectilinear motion.
The superluminal speed is consistent with the velocity(6.7±0.4c) of the jet component ‘j’ measured with theVLBA at 43 GHz. From 2010 November to 2011 April,
the relative position was stalled to the position at (−0.8,−0.7) in fig 3, and then moved along the direction at theposition angle of −160 degree until 2011 November.
After that, the motion of the component C2 rapidlychanged the direction to backward from 2011 November
to 2012 August. The time scale of the jet-direction
variation is shorter than one year. This jet-direction
variation was seen in the high state period of gamma-ray
with two flares in 2011 and 2012. Such a synchronization
between the jet position angle change and the core flux
brightening has been reported in the innermost jet region
mapped with the VLBA 43 GHz monitoring.

0-22

2011/05/07

2011/09/16

2011/09/30

2011/10/21

2011/10/30

2011/11/28

2011/12/10

2011/12/15

2011/12/23

2012/01/16

2012/01/26

2012/02/11

2012/03/08

2012/03/17

2012/03/22

2012/03/26

2012/04/15

2012/04/24

2012/05/02

2012/05/26

0-22

DEC Offset [mas]

0-2
20-2
20-2
2012/05/29

2012/06/07

2012/06/17

2012/07/21

2012/07/22

12/07

0-22

2012/08/13

2012/08/24

2012/09/12

2012/09/13

2012/09/22
C3

C10-2

C2
20-2

20 -2
RA Offset [mas]Fig.2 VERA 22-GHz images of OJ287 from 2010 November
to 2012 September. Images are convolved with a circularbeam size (FWHM) of 0.8 mas, which corresponds to thetypical minor axis of synthesized beam in our observations.
Contours start at 3 mJy beam-1, increasing by a factor of 2.
The structures can be resolved into three components, thecore (C1), the jet component (C2) and the inner jet
component located between C1 and C2 (C3). The component
C2 could be identified as ‘j’ of the VLBA 43-GHz images.

20-2

DEC-Offset [mas]

-0.8
12/01

-1.0

-1.2

11/07

Date [yy/mm]

2-0.6

-1.4
11/01
-1.6
-0.8

-1.0-1.2RA-Offset [mas]43 GHzFig.3 Relative motion of the component C2 with respect to thecomponent C1. Data points are obtained averaging by month from2010 November to 2012 September, expect January, March, June,
July and August in 2011. Positional accuracy is ~0.1 mas.