Sains Malaysiana 49(1)(2020): 189-199

http://dx.doi.org/10.17576/jsm-2020-4901-23

Calon-calon Nukleus Galaksi Aktif Berubah-Rupa pada z ≤ 0.02 dalam Katalog Swift-BAT ke-105 Bulan

(Changing-Look Active Galactic Nuclei Candidates at z ≤ 0.02 in the 105-Month Swift-BAT Catalogue)

MUHAMMAD EZZAT ABDUL HAMID & ADLYKA ANNUAR*

School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia

Diserahkan: 1 Ogos 2019/Diterima: 8 Oktober 2019

ABSTRAK

Nukleus galaksi aktif berubah-rupa (CL AGN) adalah sebuah objek astrofizik yang jarang ditemui. Objek ini mengalami perubahan fluks dan spektra yang dramatik dalam skala masa beberapa tahun atau dekad. Dalam kertas ini, kami mengkaji sampel AGN berhampiran dengan kita yang terletak pada z ≤ 0.02 dalam katalog Swift-BAT ke-105 bulan. Berdasarkan lengkung cahaya sinar-X bertenaga tinggi, kami mendapati bahawa 27 daripada 174 AGN; i.e. (15.5 ± 0.03)%,  dalam sampel kami menunjukkan perubahan fluks yang signifikan berdasarkan ujian statistik. Jumlah ini menunjukkan pertambahan sebanyak dua kali ganda daripada jumlah CL AGN yang dikenal pasti dalam alam semesta setakat ini. Ini mencadangkan bahawa objek tersebut adalah calon CL AGN. Kami juga mengkaji faktor fizikal yang mungkin menyumbang kepada perubahan yang dilihat pada calon tersebut berdasarkan bentuk lengung cahaya dan kajian lepas dan mendapati bahawa bagi satu objek, perubahan yang dilihat berkemungkinan besar disebabkan oleh kejadian gangguan pasang surut. Sementara itu bagi tiga calon, kajian lepas menunjukkan bahawa mereka mengalami perubahan spektra optik atau sinar-X. Ini mencadangkan bahawa calon ini mempunyai struktur torus yang tidak sekata. Hal ini bertentangan dengan apa yang dicadangkan oleh model satuan AGN, menunjukkan bahawa model ini mungkin tidak lagi sesuai digunakan sebagai gambaran umum struktur fizikal sesebuah AGN. Namun begitu, data dan kajian lanjut perlu dijalankan untuk mengenal pasti faktor ini dengan lebih terperinci dan bagi mengkaji faktor untuk calon CL AGN yang selebihnya dalam kajian kami yang selanjutnya.

Kata kunci: Lohong hitam; nukleus galaksi aktif (AGN); sinar X; Swift-BAT

ABSTRACT

Changing-look active galactic nuclei (CL AGN) are relatively rare objects, identified based upon their dramatic flux and spectral changes within a timescale of years or decades. In this paper, we study a sample of nearby AGN within z ≤ 0.02 in the 105-month Swift-BAT catalogue to identify CL AGN using their hard X-ray lightcurves. Based on this, we find that 27 out of 174 AGN; i.e. (15.51 ± 0.03)%, show statistically significant flux changes, suggesting that they are candidates for CL AGN. This number further doubles up the number of CL AGN that we know so far in our universe. We investigate the physical factors that could contribute to the changes seen in these AGN based on the pattern of their lightcurves and past studies, and find that for one object, tidal disruption event is likely the cause. Meanwhile for three of the candidates, past studies have shown that they underwent significant optical or X-ray spectral changes, suggesting that the torus distributions in these AGN are patchy. This is in contradiction with that suggested by the AGN unified model, indicating that this model might no longer be relevant to illustrate the general physical structure of an AGN. However, further data and studies need to be conducted to investigate these factors in more detail. This is also true for the remaining of the CL AGN candidates we identify which we could not investigate the cause due to lack of data and information. This will be our next step for this work.

Keywords: Active galactic nuclei (AGN); black holes; Swift-BAT; X-ray

RUJUKAN

Antonucci, R. 1993. Unified models for active galactic nuclei and quasars. Annu. Rev. Astron. Astrophys. 31: 473-521.

Baumgartner, W.H., Tueller, J., Markwardt, C.B., Skinner, G.K., Barthelmy, S., Mushotzky, R.F., Evans, P.A. & Gehrels, N. 2013. The 70 month swift-BAT all-sky hard X-Ray survey. The Astrophysical Journal Supplement Series 207: 19.

Cohen, R.D., Rudy, R.J., Puetter, J.E., Ake, T.B. & Foltz, C.B. 1986. Variability of Markarian 1018: Seyfert 1.9 to Seyfert 1. The Astrophysical Journal 311: 135-141.

Denney, K.D., De Rosa, G., Croxall, K., Gupta, A., Bentz, M.C., Fausnaugh, M.M., Grier, C.J., Martini, P., Mathur, S., Peterson, B.M., Pogge, R.W. & Shappee, B.J. 2014. The typecasting of active galactic nuclei: Mrk 590 no longer fits the role. The Astrophysical Journal 796: 134.

Edelson, R., Turner, T.J., Pounds, K., Vaughan, S., Markowitz, A., Marshall, H., Dobbie, P. & Warwick, R. 2002. X-Ray spectral variability and rapid variability of the soft X-Ray Spectrum Seyfert 1 Galaxies Arakelian 564 and Ton S180. The Astrophysical Journal 568: 610-626.

Eracleous, M. & Halpern, J.P. 2001. NGC 3065: A certified liner with broad, variable Balmer lines. The Astrophysical Journal 554: 240-244.

Eracleous, M., Livio, M., Halpern, J.P. & Storchi-Bergmann, T. 1995. Elliptical accretion disks in active galactic nuclei. The Astrophysical Journal 438: 610-622.

Lamassa, S.M., Cales, S., Moran, E.C., Myers, A.D., Richards, G.T., Eracleous, M., Heckman, T.M., Gallo, L. & Urry, C.M. 2015. The discovery of the first 'Changing Look' Quasar: New insights into the physics and phenomenology of active galactic nuclei. The Astrophysical Journal 800(2): 144.

Man, J., Liao, Q., Zeng, L. & Wu, L. 2017. Advances in water resources ANOVA-based transformed probabilistic collocation method for Bayesian data-worth analysis. Advances in Water Resources 110: 203-214.

Matt, G., Guainazzi, M. & Maiolino, R. 2003. Changing-look: From Compton-thick to Compton-thin, or the rebirth of fossil active galactic nuclei. Mon. Not. R. Astron. Soc. 342: 422-426.

Merloni, A., Dwelly, T., Salvato, M., Georgakakis, A., Greiner, J., Krumpe, M., Nandra, K., Ponti, G. & Rau, A. 2015. A tidal disruption flare in a massive galaxy? Implications for the fueling mechanisms of nuclear black holes. MNRAS 452: 69-87.

Nandra, K., George, I.M., Mushotzky, R.F., Turner, T.J. & Yaqoob, T. 1997. ASCA observations of Seyfert 1 galaxies. I. Data analysis, imaging, and timing. The Astrophysical Journal 476: 70-82.

Nenkova, M., Elitzur, M., Sirocky, M.M. & Nikutta, R. 2008. AGN Dusty Tori. II. Observational implications of clumpiness. The Astrophysical Journal 685: 160-180.

Oh, K., Koss, M., Markwardt, C.B., Schawinski, K., Baumgartner, W.H., Barthelmy, S.D., Cenko, S.B., Gehrels, N., Mushotzky, R., Petulante, A., Ricci, C., Lien, A. & Trakhtenbrot, B. 2018. The 105-month swift-BAT all-sky hard X-Ray survey. The Astrophysical Journal Supplement Series 235(1): 4.

Oknyansky, V.L., Gaskell, C.M., Huseynov, N.A., Lipunov, V.M. & Shatsky, N.I. 2017. The curtain remains open: NGC 2617 continues in a high state. MNRAS 467: 1496-1504.

Penston, M.V. & Perez, E. 1984. An evolutionary link between Seyfert I and II galaxies? MNRAS 211: 33P.

Peterson, B.M. 2001. Variability of active galactic nuclei. Advanced Lectures on the Starburst-AGN Connection. pp. 3-68.

Ricci, C., Bauer, F.E., Arevalo, P., Boggs, S., Brandt, W.N., Christensen, F.E., Craig, W.W., Hailey, C.J., Harrison, F.A., Koss, M., Markwardt, C.B., Stern, D. & Treister, E. 2016. IC 751: A new changing-look AGN discovered by Nustar 3227. The Astrophysical Journal 820: 5.

Shapovalova, A.I., Burenkov, A.N., Chavushyan, V.H., Kollatschny, W., Bochkarev, N.G., Carrasco, L., Mercado, A., Valdes, J.R. & Vlasuyk, V.V. 2010. Spectral optical monitoring of 3C 390.3 in 1995-2007. A&A 517: A42.

Shappee, B.J., Prieto, J.L., Grupe, D., Kochanek, C.S., Stanek, K.Z., Rosa, G.D., Mathur, S. & Zu, Y. 2014. The man behind the curtain: X-Rays drive the UV through NIR variability in the 2013 active galactic nucleus outburst in NGC 261. The Astrophysical Journal 788: 48.

Soldi, S., Beckmann, V., Baumgartner, W.H., Ponti, G., Shrader, C.R., Lubinski, P., Krimm, H.A., Mattana, F. & Tueller, J. 2013. Long-term variability of AGN at hard X-Rays. Astronomy & Astrophysics 563: 57.

Stern, D., Mckernan, B., Graham, M.J., Ford, K.E.S., Ross, N.P., Meisner, A.M., Assef, R.J., Balokovic´, M., Brightman, M., Dey, A., Drake, A., Djorgovski, S.G., Eisenhardt, P. & Jun, H.D. 2018. A Mid-Ir selected changing-look quasar and physical scenarios for abrupt AGN fading. The Astrophysical Journal 86(4): 27.

Storchi-Bergmann, T., Baldwin, J.A. & Wilson, A.S. 1993. Double-peaked broad line emission from the LINER nucleus of NGC 1097. The Astrophysical Journal 410: L11-L14.

Tohline, J.E. & Osterbrock, D.E. 1976. Variation of the spectrum of the Seyfert Galaxy NGC 7603. The Astrophysical Journal 210: L117-L120.

 Vaughan, S., Edelson, R., Warwick, R.S. & Uttley, P. 2003. On characterising the variability properties of X-Ray light curves from active galaxies. Monthly Notices of the Royal Astronomical Society 345: 1271.

Yang, Q., Wu, X., Fan, X., Jiang, L., Mcgreer, I., Shangguan, J. & Yao, S. 2018. Discovery of 21 new changing-look AGNs in Northern sky. The Astrophysical Journal 862: 109.

*Pengarang untuk surat-menyurat; email: adlyka@ukm.edu.my