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BL Lacertae object OJ 287 is one of the Blazars, which shows convincing evidence of periodic variations. We have collected the 4.8, 8.0 and 14.5 GHz data for OJ 287 from the University of Michigan Radio Observatory database over three decades. Due to the complexity of the variability data, some algorithms for period searching are not ideal yet. An alternative to traditional periodicity analysis is the ensemble empirical mode decomposition (EEMD). This method can analyze the cyclic components of complicated nonlinear and non-stationary processes. Using the EEMD analysis, the light curve of OJ 287 at radio frequency can be resolved into six independent intrinsic mode functions that have different average periods and trends. We find possible periods of 18.9, 11.9, 5.7 and 2.4 years in 4.8 GHz, 12.2 , 5.2 and 2.4 years in 8.0 GHz and 21.8, 12.0, 4.3 and 2.4 years in 14.5 GHz. The most common periods are 12.0 years and 2.4 years, which imply that the emissions in these bands may originate from the same radiative process. The results also confirm that a radio variability period of OJ 287 is in agreement with the optical variability period of about 12.0 years. The result shows that the components of different variability periods can be separated properly with the EEMD that is a nonlinear and non-stationary signal processing method.
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Keywords:
- OJ 287 /
- variability period /
- ensemble empirical mode decomposition
[1] Tang J, Wu X B 2011 Acta Phys. Sin. 60 119801 (in Chinese) [唐洁, 吴学兵 2011 物理学报 60 119801]
[2] Tang J, Fu M X, Wu X B 2012 Acta Phys. Sin. 61 219501 (in Chinese) [唐洁, 傅明星, 吴学兵 2012 物理学报 61 219501]
[3] Valtonen M J, Lehto H J, Nilsson K, Heidt J Takalo L O 2008 Nature 452 850
[4] Fan J H, Zhang Y W, Qian B C, Tao J, Liu Y, Hua T X 2009 Astrophys. J. Suppl. Ser.181 466
[5] Zhang H J, Zhao G, Zhang X, Bai J M 2010 Sci. China G 53 252
[6] Huang N E, Shen Z, Long S R 1998 Proc. Royal Soc. London A 454 903
[7] Zhao H W, Huang N E 2004 Proc. Royal Soc. London A 460 1597
[8] Fan J H, Liu Y, Qian B C, Tao J, Shen Z Q, Zhang J S, Huang Y, Wang J 2010 Res. Astron. Astrophys. 10 1100
[9] Dai B Z, Li X H, Liu Z M, Zhang B K, Na W W, Wu Y F, Hao J M 2009 Mon. Not. R. Astron. Soc. 392 1181
[10] Dai B Z, Zhang B K, Zhang L 2006 New Astron. 11 471
[11] Tang J, Zhang X 2010 Acta Phys. Sin. 59 7516 (in Chinese) [唐洁, 张雄2010物理学报 59 7516]
[12] Zhang H J, Zhao G, Zhang X, Dong F T, Xie Z H, Yi T F, Zheng Y G, Bao Y Y 2009 Sci. China G 52 1442
[13] Tang J 2012 Acta Astron. Sin. 53 1 (in Chinese) [唐洁 2012 天文学报 53 1]
[14] Sillanpää A, Haarala S, Valtonen M J, Sundelius B, Byrd G G 1988 Astrophys. J. 325 628
[15] Sillanpää A, Takalo L O, Pursimo T, Nilsson K, Heinamaki P, Katajainen S 1996 Astron. Astrophys. 305L 13
[16] Valtonen M, Kidger M, Lehto H, Poyner G 2008 Astron. Astrophys. 477 407
[17] Xie G Z, Yi T F, Li H Z, Zhou S B, Chen L E 2008 Astron. J. 135 2212
[18] Zhang X, Zheng Y G, Zhang H J, Liu Y, Wen Y B, Wang W 2008 Astron. J. 136 1846
[19] Venturi T, Dallacasa D, Orfei A 2001 Astron. Astrophys. 379 755
[20] Boettcher M Fultz K, Aller H D 2009 Astrophys. J. 694 174
[21] Raiteri C M Villata M, Larionov V M 2008 Astron. Astrophys. 480 339
[22] Bai J M, Lee M G 2003 Astrophys. J. 585L 113
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[1] Tang J, Wu X B 2011 Acta Phys. Sin. 60 119801 (in Chinese) [唐洁, 吴学兵 2011 物理学报 60 119801]
[2] Tang J, Fu M X, Wu X B 2012 Acta Phys. Sin. 61 219501 (in Chinese) [唐洁, 傅明星, 吴学兵 2012 物理学报 61 219501]
[3] Valtonen M J, Lehto H J, Nilsson K, Heidt J Takalo L O 2008 Nature 452 850
[4] Fan J H, Zhang Y W, Qian B C, Tao J, Liu Y, Hua T X 2009 Astrophys. J. Suppl. Ser.181 466
[5] Zhang H J, Zhao G, Zhang X, Bai J M 2010 Sci. China G 53 252
[6] Huang N E, Shen Z, Long S R 1998 Proc. Royal Soc. London A 454 903
[7] Zhao H W, Huang N E 2004 Proc. Royal Soc. London A 460 1597
[8] Fan J H, Liu Y, Qian B C, Tao J, Shen Z Q, Zhang J S, Huang Y, Wang J 2010 Res. Astron. Astrophys. 10 1100
[9] Dai B Z, Li X H, Liu Z M, Zhang B K, Na W W, Wu Y F, Hao J M 2009 Mon. Not. R. Astron. Soc. 392 1181
[10] Dai B Z, Zhang B K, Zhang L 2006 New Astron. 11 471
[11] Tang J, Zhang X 2010 Acta Phys. Sin. 59 7516 (in Chinese) [唐洁, 张雄2010物理学报 59 7516]
[12] Zhang H J, Zhao G, Zhang X, Dong F T, Xie Z H, Yi T F, Zheng Y G, Bao Y Y 2009 Sci. China G 52 1442
[13] Tang J 2012 Acta Astron. Sin. 53 1 (in Chinese) [唐洁 2012 天文学报 53 1]
[14] Sillanpää A, Haarala S, Valtonen M J, Sundelius B, Byrd G G 1988 Astrophys. J. 325 628
[15] Sillanpää A, Takalo L O, Pursimo T, Nilsson K, Heinamaki P, Katajainen S 1996 Astron. Astrophys. 305L 13
[16] Valtonen M, Kidger M, Lehto H, Poyner G 2008 Astron. Astrophys. 477 407
[17] Xie G Z, Yi T F, Li H Z, Zhou S B, Chen L E 2008 Astron. J. 135 2212
[18] Zhang X, Zheng Y G, Zhang H J, Liu Y, Wen Y B, Wang W 2008 Astron. J. 136 1846
[19] Venturi T, Dallacasa D, Orfei A 2001 Astron. Astrophys. 379 755
[20] Boettcher M Fultz K, Aller H D 2009 Astrophys. J. 694 174
[21] Raiteri C M Villata M, Larionov V M 2008 Astron. Astrophys. 480 339
[22] Bai J M, Lee M G 2003 Astrophys. J. 585L 113
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