• Journal of The Korean Astronomical Society
• /
• v.29 no.spc1
• /
• pp.107-108
• /
• 1996

VRI bands CCD photometric observations of the BL Lac object OJ 287 have been carried out during the period from October, 1994 to May, 1996. OJ 287 underwent two major outbursts during our observations. The first peak (V14.0 mag.) occurred in the first half of November, 1994 and faded out to 16.5 mag within 150 days. The second peak (14.0 mag.) was observed in late December, 1995. The latter peak continued at nearly the same brightness until May, 1996. Such a long lasting outburst has never been reported for OJ 287. Color indices (V - R and V-I) remained nearly constant during the outbursts.

• Journal of The Korean Astronomical Society
• /
• v.34 no.1
• /
• pp.9-15
• /
• 2001

We present the results of optical differential photometry of five blazars [PKS0219+428 (3C66A), PKS 0235+164 (AO 0235+16), H0414+019, PKS 0851+202 (OJ 287) and QSO 1807+698 (3C 371)] that were observed on 7 nights between November 05, 1997 and December 29, 1998, using the B and the V band filters. We have detected microvariations in four blazars (3C66A, AO 0235+16, H04l4+019, and OJ 287). In addition, the light curve of AO 0235+16 has displayed a mini-flare when the brightness of this source was decreasing. Night-to-night variations have also been detected in 3C66A, H04l4+019, and OJ 287. The results of our observations are discussed in the framework of accretion disk phenomena (magnetic flares or hot spots in accretion disks) and jet phenomena (plasma instabilities in jets).

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.429-432
• /
• 2015

We present a kinematic study of the parsec-scale radio jet in OJ 287, one of the most studied BL Lac objects, during ${\gamma}$-ray flares, to explore the relation between parsec-scale radio jet activity and ${\gamma}$-ray emission. The 22-GHz light curve of OJ 287 show three obvious flare events around 2011 May, 2011 October, and 2012 March. The second radio flare occurred during the ${\gamma}$-ray flaring period, and the third radio flare seemed to precede the ${\gamma}$-ray flare by one month. One jet component moved outward with respect to the core component with an apparent superluminal speed (~ 11c) from 2010 November to 2011 November. Then it changed direction, moving apparently inward in 2011 November, when the ${\gamma}$-ray flare occurred. The observed apparent inward motion of the jet at 22 GHz could be caused by a new jet component, unresolved at 22 GHz, in the innermost region.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.241-241
• /
• 2012

MOGABA is a project monitoring of gamma-ray bright AGN(Active Galactic Nuclei). Since May 2011, we have observed total flux, degree of linear polarization, and polarization angle of about twenty AGN once a week at 22, 43 and 86GHz using KVN(Korean VLBI Network) 21m radio telescopes. We have observed variation of total flux of BLLAC and OJ287 from May 2011 to March 2012. We have observed flares of total flux at 22GHz for those sources from October 2011 to November 2011. In this paper we report the variation of total flux, degree of linear polarization and polarization angle at 22, 43, 86GHz for BLLAC and OJ287.

• Journal of Astronomy and Space Sciences
• /
• v.33 no.3
• /
• pp.177-183
• /
• 2016

Active galactic nuclei (AGN) are too compact to be resolved by any existing optical telescope facility, making it difficult to understand their structure and the emission processes responsible for their huge energy output. However, variability, one of their characteristic properties, provides a tool to probe the inner regions of AGN. Blazars are the best candidates for such a study, and hence a considerable amount of effort is being made to investigate variability in these sources across the electromagnetic spectrum. Here, using the Mt. Abu infrared observatory (MIRO) blazar monitoring program, we present intra-night, inter-night, and long term aspects of the variability in S5 0716+71, 3C66A, and OJ 287. These stars show significant variability on short (a few tens of mins, to a few hours, to a few days) to long term (months to years) timescales. Based on the light travel time argument, the shortest variability timescales (micro-variability) provide upper limits to the size of the emission region. While S5 0716 shows a very high duty cycle of variability (> 80 %), 3C66A shows a much lower intra day variability (IDV) duty cycle (< 20 %). All three show rapid variations within 2.5 to 3.5 hr, which, perhaps, are generated near the vicinity of black holes. Assuming this, estimates of the masses of the black holes are made at ~10⁹, 8×10⁸, and 2.7×10⁹ M_⨀ for S5 0716+71, 3C66A, and OJ 287, respectively. Multi-wavelength light-curves for the blazar PKS 1510-089 are discussed to infer the emission processes responsible for the recent flaring episodes in this source.

• The Bulletin of The Korean Astronomical Society
• /
• v.33 no.2
• /
• pp.50.1-50.1
• /
• 2008

• Toxicological Research
• /
• v.17
• /
• pp.281-287
• /
• 2001

The Artichoke extract at 10% was used to add in drinking water to understand its effect on Aflatoxicosis of chickens. The Artichoke extract at the dose of 6 ml per liter of drinking water was given (experiment group) or not (control group) and to Hybro chickens (150 birds), during the first 49 days of life. Also, the chickens were fed with foodstuff containing 200 ppb or 500 ppb Aflatoxin $B_1$. Results showed that, the chickens having Artichoke extract: (1) Had overcome the growth retardation caused by the toxin at concentration of 200 ppb and 500 ppb of Aflatoxin $B_1$ (an addittonal weight gain of about 200-400 g/bird). (2) The feed conversion was improved (a reduction of 200-400 g of feed per kg of bird living weight). (3) Aflatoxicosis lesions were mild in the chickens, which fed 500 ppb of Aflatoxin $B_1$ or not found in those having the toxin 200 ppb. The blood examinations at 28th and 49th days of the trial gave the following results: (1) The Artichoke extract had an effect of suppressing the changes of blood cell numbers, hemoglobin amount. packed cell volume. leukocyte formula that were caused by Aflatoxin $B_1$. (2) The Artichoke extract had an effect of suppressing the diminution oj sugar, protein levels and the increase of the levels of GOT, GPT, alkaline phosphatase and bilirubin in the blood of intoxicated chickens. There was not or very Jew residue of Aflatoxin $B_1$ contained in the liver and muscle of chickens intoxicated by Aflatoxin $B_1$ having Artichoke, that was much lower than the allowed level in animal products.

• Journal of The Korean Astronomical Society
• /
• v.48 no.5
• /
• pp.229-236
• /
• 2015

We report results of investigation of amplitude calibration for very long baseline interferometry (VLBI) observations with Korean VLBI Network (KVN). Amplitude correction factors are estimated based on comparison of KVN observations at 22 GHz correlated by Daejeon hardware correlator and DiFX software correlator in Korea Astronomy and Space Science Institute (KASI) with Very Long Baseline Array (VLBA) observations at 22 GHz by DiFX software correlator in National Radio Astronomy Observatory (NRAO). We used the observations for compact radio sources, 3C 454.3, NRAO 512, OJ 287, BL Lac, 3C 279, 1633+382, and 1510–089, which are almost unresolved for baselines in a range of 350-477 km. Visibility data of the sources obtained with similar baselines at KVN and VLBA are selected, fringe-fitted, calibrated, and compared for their amplitudes. We find that visibility amplitudes of KVN observations should be corrected by factors of 1.10 and 1.35 when correlated by DiFX and Daejeon correlators, respectively. These correction factors are attributed to the combination of two steps of 2-bit quantization in KVN observing systems and characteristics of Daejeon correlator.