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The target source OJ 287
BL Lac object at z=0.3. (1 milli arcsecond = 4.5pc)
It is known to show a rapid variability across a wide range of wavelength.
It exhibits double-peaked periodic optical outburst at a period of approximately 12 yrs.
A binary black hole model suggested[1,2]A secondary body crosses the accretion disk of the primary black hole and produces two impact flashes per period.
The first outburst is a thermal flare which is visible only in the optical regime.
About 1 yr later, the disturbance has propagated down the relativistic jet and results in the growth of new
synchrotron-emitting shocks, which is visible both in optical and radio regimes.
The most resent flares occurred in December 2015[3] and February 2016[4]We here show the monthly VLBI monitoring observations from 2015 October to 2016 April.

Observations & data reduction

Target source

OJ 287VERA common use observations
9 tracks from 2015 October to 2016 AprilFrequency bandK (22 GHz)

Array

VERA

Calibration, data flagging, fringe fitting and imaging wereperformed using the NRAO AIPS software.

Monitoring period

2015 Oct — 2016 AprilCorrelator

NAOJ correlator

Results

04

Radio light curve32
10-1-2-3-4
4Date [yyyy/mm]
2015/112016/01

2016/03

Optical outburst
432

MilliArc seconds

Flux Density [Jy]2016/05

VERA 22GHz

51057300

57350

57400

57450

57500

MJD
Optical variability of OJ 287

Optical light curve

7

Gupta et al. (2017)[5]322340123401234

2015/10/11

2015/11/04

2015/11/28

2015/12/11

2016/01/09

2016/02/10

2016/03/01

2016/03/26

2016/04/15

10-1-2-3-4
4
3

13

12
14

10-1

13
14-2-3-4

15

4

14

20-2
MilliArc seconds-4420-2-415

Our VLBI images show that the 22-GHz radio emission is dominatedby the compact core component at all epochs.

16
14

15

16
7300

7325

7350

7375

7400

7425

7450

7475

7500

7525

The 22-GHz radio emission seemed to increase slightly at the first
optical outburst in Nov/Dec of 2015. After the second optical flare in
Feb/Mar of 2016, the radio flux started to increase to almost twice.

Figure 2. Optical variability light curve of OJ 287. Filled hexagon represent data from Arizona telescopes (A); open triangle for the data from 1.04m India
telescope (B); open and filled square for the data from 2m (C) and 50/70 cm (D) telescopes Rozen, Bulgaria, respectively; filled triangle for the data from 60cm
(E) telescope Belogradchik, Bulgaria; open circle for the data from 60cm (F) telescope, Serbia; filled circle for the data from 70cm (G) telescope, Georgia;
and astrix for the data from 1.5m (H) telescope, Kanata, Japan.

1. Valtaoja et al. (2000), ApJ
531 744
Valtonen et al. (2016). To quantify the spectral variability changes
in the source during its faint state, we generated the SED around JD
2. Valtaoja et al. (2008) Nature2457339.6 (2015452
Nov 13) 851
when the source magnitude reached its
maximum value. We also considered two stages in the post outburst
on JDs 2457369.6 (2015 Dec 13) and 2457372.4 (2015 Dec
3. Shappee et al. (2015),stateTheAstronomer's
Telegram, 8372
15).

put tight constraints on the physical parameters such as the magnetic field, or energies of the relativistic particles in the Doppler
boosted jet. To understand spectral variability in optical range, weused quasi-simultaneous B, V, R, and I data points at five different
states of the source. The outburst state 1 is is taken as that epoch
when the source attained the brightest value in all four bands whichlies near JD 2457361.5 (2015 Dec 5). We note that we do not haveobservations during the preceding two weeks so from our data theactual peak may have been even greater; however, the monitoringby Valtonen et al. (2016) had better coverage during the large flareand showed that it rose during that period and that the maximum
brightness was reached on 2015 Dec 5. As is evident from theSTV LC another very comparable outburst was observed around
JD 2457450.4 (2016 March 2) which we call as outburst state 2
and which is covered well by our observations but not covered by

We have de-reddened the calibrated magnitudes of OJ 287 bysubtracting Galactic absorption values of AB = 0.102 mag, AV =0.077 mag, AR = 0.061 mag, and AI = 0.042 mag (Cardelli et al.
1989; Bessell et al. 1998). We took single data points in B, V, R, andI passbands, corresponding to the JDs for each of the above states
and thus generated optical SEDs at five epochs using our quasisimultaneous B, V, R, and I observations of OJ 287. These SEDs
are displayed in Figure 5. The faintest SED was observed for JD
2457339.6 while the brightest one was observed for JD 2457361.5.

4. Zola et al. (2016), The Astronomer's Telegram, 8667
5. Gupta et al.(2017), MNRAS 465 4423