Suspended and restored activities of A Nearby Super Massive Black Hole

J. Wang Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University, Nanning 530004, People始s Republic of China Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China D. W. Xu Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing, China S. S. Sun Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University, Nanning 530004, People始s Republic of China Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China Q. C. Feng Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China T. R. Li Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China P. F. Xiao Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China J. Y. Wei Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing, China

Abstract

The discovery of spectral type transition of active galactic nuclei (AGNs), the so-called “changing-look” (CL) phenomenon, challenges the widely accepted AGN paradigm, not only in the orientation based Unified Model, but also in the standard disk model. In past decades, only a couple of nearby repeat “changing-look” active galactic nuclei (CL-AGNs) have been identified. Here we report spectroscopic observations of UGC 3223 over the course of 18 years, from 2001 onwards. Combining the spectrum taken in 1987 by Stirpe, we have witnessed its type transitions from $1.5\rightarrow 2.0\rightarrow 1.8$ over 32 years, and captured a long-lived (at least 10 years) thorough “turn-off” state with a spectrum typical of a Seyfert 2 galaxy. The long-term thorough “turn-off” state probably suggests a once-dormant and an awakening central engine in UGC3223. We argue the (dis)appearance of the broad Balmer emission lines can be explained by the disk-wind BLR model given the evolution of the calculated Eddington ratio of accretion of the supermassive black hole.

galaxies: nuclei — galaxies: active — quasars: emission lines — quasars: individual (UGC 3223)

^†^†journal: ApJ^†^†facilities: NAOC 2.16m telescope^†^†software: IRAF (Tody 1986, 1993)

1 Introduction

Multi-epoch spectroscopy recently enables us to reveal a batch of the so-called “changing-look” active galactic nuclei (CL-AGNs) that show a spectral type transition between type I, intermediate type and type II within a time scale of an order of years or decades. So far, the CL phenomenon has been identified by spectroscopy in only $\sim$ 80 AGNs, including both “turn-on” and “turn-off” transitions (e.g., Shapovalova et al. 2010; Shappee et al. 2014; LaMassa et al. 2015; McElroy et al. 2016; Runnoe et al. 2016; Gezari et al. 2017; Yang et al. 2018; Ruan et al. 2016; MacLeod et al. 2010, 2016; Wang et al. 2018, 2019; Stern et al. 2018; Frederick et al. 2019; Yan et al. 2019; Trakhtenbrot et al. 2019). Based on the Catalina Real-time Transient Survey, Graham et al. (2019) recently identified 111 “changing-state” quasars according to their optical and mid-infrared photometric behavior and spectroscopic change.

The observed CL phenomenon challenges the traditional understanding of AGNs in two points. At first, there is competing evidence in both middle infrared and polarization supporting that the optical CL phenomenon is due to a variation in accretion rate of a supermassive blackhole (SMBH) (e.g., Sheng et al. 2017, Yang et al. 2018; Wang et al. 2018, 2019b; Gezari et al. 2017; Macleod et al. 2019; Rumbaugh et al. 2018; Stern et al. 2018; Hutsemekers et al. 2019), rather than the orientation effect (e.g., Antonucci 1993). Secondly, there is a viscosity crisis, in which the expected viscous timescale of optical emission coming from the outer accretion is larger than the timescale of the observed CL phenomenon by an order of magnitude (e.g., Lawrence 2018 and references therein). This crisis could be theoretically resolved by introducing a local disk thermal instability (e.g., Husemann et al. 2016; Jiang et al. 2016) or a magnetic field (e.g., Ross et al. 2018; Stern et al. 2018; Dexter & Begelamn 2019).

Even though most of the CL-AGNs are identified in the case of two-epochs spectroscopy, repeat type transitions have been identified in only a few nearby Seyfert galaxies and quasars: Mrk 590, Mrk 1018, NGC 1566, NGC 4151, NGC 7603, Fairall 9 and 3C 390.3 (Marin et al. 2019). Among these objects, only Mrk 590 shows a thorough disappearance of its BLR emission (Denney et al. 2014). We here report a discovery of a new nearby CL-AGN, UGC 3223, with repeat type transition and a prolonged thorough “turn-off” of the activity of the SMBH.

The paper is organized as follows. Section 2 describes our repeat spectroscopic observations and data reductions. The spectral analysis is presented in Section 3. Section 4 presents the results and discussion. A $\Lambda$ CDM cosmology with parameters $H_{0}=70\mathrm{km\ s^{-1}\ Mpc^{-1}}$ , $\Omega_{m}=0.3$ , and $\Omega_{\Lambda}=0.7$ is adopted throughout the paper.

2 Observations and Data Reduction

UGC 3223 (=MCG +01-13-012, R.A.=04^h59^m09^s.4, DEC=+04°58′30″, J2000) is a local AGN at redshift of $z=0.015621$ . It was classified as a Seyfert 1.5 galaxy in the catalog of quasars and active nuclei: 12th edition (Veron-Cetty & Veron 2006), according to the spectroscopy taken in 1987 (Stirpe 1990).

2.1 Spectroscopic observations

The long-slit spectra of UGC 3223 have been taken by us by using the 2.16m telescope (Fan et al. 2016) at Xinglong observatory of National Astronomical Observatories, Chinese Academy of Sciences (NAOC) in four epochs from 2001 to 2019 (See Column(1) in Table 1). The observations were carried out with the Optomechanics Research Inc. spectrograph equipped with a back-illuminated SPEC 1340 $\times$ 400 CCD as detector. A grating of 300 $\mathrm{grooves\ mm^{-1}}$ , and a slit of $2\arcsec$ oriented in the south-north direction were used in the observations. This setup finally leads to a spectral resolution of $\sim 9$ Å as measured from the sky emission lines and comparison arcs. The blazed wavelength was fixed at 6000Å in all the observation runs, which provides a wavelength coverage from 3400-8600Å in the observer frame. In each of the runs, the object was observed twice in succession. The exposure time of each frame ranges from 1500 to 3600 seconds. The wavelength and flux calibrations were carried out by the helium-neon-argon comparison arc taken between the two successive frames, i.e., at the position nearly identical to that of the object, and by the Kitt Peak National Observatory (KPNO) standard stars (Massey et al. 1988), respectively.

2.2 Data reduction

We reduced the two-dimensional spectra by the standard procedures through the IRAF package¹¹1IRAF is distributed by the National Optical Astronomical Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.. At first, the bias subtraction and flat-field correction were applied to each observed frame. In each observation run, the two frames were combined prior to the extraction to enhance the signal-to-noise ratio and to eliminate the contamination of cosmic rays easily. Each extracted 1d spectrum was then calibrated in wavelength and flux by the corresponding comparison arc and standard. The two telluric features A and B around $\lambda$ 7600 and $\lambda$ 6800 due to the $\mathrm{O_{2}}$ molecules were removed from each extracted spectrum by the corresponding standard. The Galactic extinction was then corrected for each extracted spectrum by the extinction magnitude of $A_{V}=0.229$ (Schlafly & Finkbeiner 2011) taken from the NASA/IAPC Extragalactic Database (NED), assuming the $R_{V}=3.1$ extinction law of our Galaxy (Cardelli et al. 1989). The spectra were then transformed to the rest frame according to its redshift. The rest-frame spectra taken at the four different epochs are displayed in Figure 1 (the middle curve in each panel).

Refer to caption — Figure 1: The Xinglong spectra of UGC 3223 taken in the four different epochs. In each panel, the starlight-subtracted spectrum, the observed rest-frame spectrum and the modeled starlight component are displayed by the curves from top to bottom.

3 Spectral Analysis

One can see clearly from the figure a lack of broad H $\alpha$ emission line in the three Xinglong spectra taken in 2001, 2003 and 2011, which is different from the spectrum shown in Stirpe (1990). It is interesting that the broad H $\alpha$ emission and a weak H $\beta$ broad emission return back in the 2019 spectrum. A spectral analysis is performed as follows to quantify the type transition in UGC 3223.

3.1 Removing of The Star Light Component

The starlight component of each of the four spectra is at first modeled by a linear combination of the first seven eigenspectra through a $\chi^{2}$ minimization. The eigenspectra are built from the standard single stellar population spectral library developed by Bruzual & Charlot (2003). An intrinsic extinction due to the host galaxy described by the Galactic extinction curve with $R_{V}=3.1$ is also involved in our fitting. The minimization is carried out over the rest-frame wavelength range from 3700 to 8000Å, except for the regions with strong emission lines, e.g., Balmer lines (both narrow and potential broad components), [O III] $\lambda\lambda$ 4959, 5007, [N II] $\lambda\lambda$ 6548, 6583, [S II] $\lambda\lambda$ 6716, 6731, [O II] $\lambda$ 3727, [O III] $\lambda$ 4363, and [O I] $\lambda$ 6300. Because the absorption features in the observed spectra are dominated by the instrumental profile, the starlight templates are convolved with a fixed Gaussian profile before the minimization. The starlight component, along with the starlight-subtracted spectrum, are shown in Figure 1.

3.2 Line Profile Modeling

In each starlight-subtracted spectrum, we model the emission line profiles by a linear combination of a set of Gaussian profiles in both H $\alpha$ and H $\beta$ regions by the SPECFIT task (Kriss 1994) in the IRAF package. The line flux ratios of the [O III] $\lambda\lambda$ 4959, 5007 and the [N II] $\lambda\lambda$ 6548, 6583 doublets are fixed to their theoretical values, i.e., 1:3. The line modelings are shown in the left and right panels of Figure 2 for the H $\beta$ and H $\alpha$ regions, respectively. In all the spectra except for the one taken in 2019, each Balmer line profile can be well reproduced by a corresponding narrow component. However, a broad component is necessary for fitting the H $\alpha$ line profile of the 2019 spectrum. In addition, a weak H $\beta$ broad component is also required to properly reproduce the 2019 observation. The results of the profile modeling, along with the results quoted from Stirpe (1990) for the 1987 spectrum, are listed in Table 1. All the errors reported in the table correspond to the 1 $\sigma$ significance level, where only the uncertainties caused by the fitting are included.

Date	$F(\mathrm{H\beta_{n}})$	$F(\mathrm{[OIII]\lambda 5007})$	$F(\mathrm{H\alpha_{n}})$	$F(\mathrm{H\beta_{b}})$	FWHM(H $\beta_{\mathrm{b}}$ )	$F(\mathrm{H\alpha_{b}})$	FWHM(H $\alpha_{\mathrm{b}}$ )	$M_{\mathrm{BH}}/M_{\odot}$	$L/L_{\mathrm{Edd}}$
	$\mathrm{10^{-15}\ erg\ s^{-1}\ cm^{-2}}$				$\mathrm{km\ s^{-1}}$	$\mathrm{10^{-15}\ erg\ s^{-1}\ cm^{-2}}$	$\mathrm{km\ s^{-1}}$
(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
1987/01/14^a	12.0	47.9	33.0	85.1	4740	275.4	3980	$2.1\times 10^{7}$	0.014
2001/11/16	$6.5\pm 1.6$	$46.3\pm 3.5$	$56.5\pm 6.4$
2003/10/25	$9.6\pm 1.2$	$51.1\pm 2.4$	$47.1\pm 4.4$
2010/11/09	$9.8\pm 2.0$	$48.3\pm 5.5$	$56.1\pm 4.8$
2019/09/06	$6.7\pm 1.6$	$30.9\pm 2.5$	$30.5\pm 3.2$	$17.6\pm 1.6$	$7600\pm 2600$	$167.5\pm 5.0$	$7800\pm 200$	$(9.8\pm 2.8)\times 10^{7}$	$0.004\pm 0.001$

Suspended and restored activities of A Nearby Super Massive Black Hole

Abstract

1 Introduction

2 Observations and Data Reduction

2.1 Spectroscopic observations

2.2 Data reduction

3 Spectral Analysis

3.1 Removing of The Star Light Component

3.2 Line Profile Modeling

3.3 Blackhole mass and Eddington ratio

4 Results and Discussion

5 Conclusion

References