A parsec-scale faint jet in the nearby changing-look Seyfert galaxy Mrk 590
J. Yang, I. van Bemmel, Z. Paragi, S. Komossa, F. Yuan, X. Yang, T. An, J.Y. Koay, C. Reynolds, J.B.R. Oonk, X. Liu, Q. Wu
MMNRAS , 1–5 (2015) Preprint 13 January 2021 Compiled using MNRAS L A TEX style file v3.0
A parsec-scale faint jet in the nearby changing-look Seyfert galaxy Mrk 590
Jun Yang, ★ , Ilse van Bemmel, Zsolt Paragi, S. Komossa, Feng Yuan, Xiaolong Yang, Tao An, J. Y. Koay, C. Reynolds, J. B. R. Oonk, , , Xiang Liu and Qingwen Wu Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala, Sweden Joint Institute for VLBI ERIC (JIVE), Postbus 2, NL-7990 AA Dwingeloo, the Netherlands Max-Planck-Insitut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany Shanghai Astronomical Observatory, Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 200030 Shanghai, China Institute of Astronomy and Astrophysics, Academia Sinica, Section 4, Roosevelt Rd., Taipei 10617, Taiwan CSIRO Astronomy and Space Science, Kensington 6151, Australia SURFsara, PO Box 94613, NL-1090 GP Amsterdam, the Netherlands Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, the Netherlands Netherlands Institute for Radio Astronomy (ASTRON), NL-7991 PD Dwingeloo, the Netherlands Xinjiang Astronomical Observatory, Key Laboratory of Radio Astronomy, Chinese Academy of Sciences,150 Science 1-Street, 830011 Urumqi, China Department of Astronomy, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
Accepted XXX. Received YYY; in original form ZZZ
ABSTRACT
Broad Balmer emission lines in active galactic nuclei (AGN) may display dramatic changes in amplitude, even disappearanceand re-appearance in some sources. As a nearby galaxy at a redshift of 𝑧 = . ∼ ∼ ∼ Key words: galaxies: active – galaxies: individual: Mrk 590 – galaxies: jets – galaxies: Seyfert – radio continuum: galaxies
Variations of the mass-accretion rate may give rise to differentclasses of emission-line nuclei of galaxies (e.g. Elitzur et al. 2014;Noda & Done 2018). This scenario has been further supported bythe findings of some optical changing-look active galactic nuclei(AGN) that cannot be explained as a consequence of variable ab-sorption, e.g. the Seyfert galaxies Mrk 590 (Denney et al. 2014)and Mrk 1018 (McElroy et al. 2016; Noda & Done 2018), and thequasar SDSS J015957.64 + ★ E-mail: [email protected]
The existing observations show that intensive accretion eventsmay trigger episodic ejections and launch (mildly) relativistic jetsat speeds > ∼ 𝑐 (e.g. Marscher et al. 2002; Fender et al. 2009).The accretion-ejection activity has been observed in the outburstsof many Galactic stellar-mass black hole X-ray binaries in particularduring the transition from the X-ray low to high states (e.g. Fenderet al. 2009; Yang et al. 2010, 2011; Miller-Jones et al. 2019), a fewtidal disruption events of SMBHs (e.g. Yang et al. 2016; Mattilaet al. 2018), some nearby AGN (e.g. Marscher et al. 2002; Argo et al.2015) and short-lived radio sources (5–20 yr, Mooley et al. 2016;Wołowska et al. 2017). VLBI observations of a few SMBHs accretingclose to or above the Eddington accretion rate also reveal significantpc-scale jet activities while with faint radio cores (e.g. Yang et al.2019, 2020, 2021). Some theoretical models have been proposed toexplain episodic ejections (e.g. Wu 2009; Yuan et al. 2009).Mrk 590 (alternatively, NGC 863) is a face-on Seyfert spiral galaxyat a redshift of 𝑧 = . 𝛽 emission lines di-minished in 2006 (Denney et al. 2014), while reappeared with a lowamplitude in 2017 (Raimundo et al. 2019). There was also a large con- © a r X i v : . [ a s t r o - ph . H E ] J a n J. Yang et al. tinuum luminosity variation in optical, UV, and X-ray wavelengths.The central AGN brightened by a factor of ∼
10 between 1970s and1990s, then faded by a factor of ∼
100 at optical and UV wavelengthsbetween the mid-1990s and 2013 (Denney et al. 2014).At radio wavelengths, Mrk 590 has not only a radio-emitting hostgalaxy but also a kpc-scale compact radio nucleus (Koay et al.2016b). The Multi-Element Radio Linked Interferometer Network(MERLIN) observations on 1995 December 9 reported that the com-pact nucleus had a total flux density 6 . ± . < ∼
90 mas (Thean et al. 2001). The radio nucleus had acorrelation amplitude of ∼ . ± .
08 mJy at 1.8 GHz and a veryflat spectrum between 1.8 and 8.4 GHz on 2015 June 23. Combinedwith early sub-arcsecond-resolution radio observations (Ulvestad &Wilson 1984; Becker et al. 1995; Kukula et al. 1995; Kinney et al.2000), Koay et al. (2016b) showed that the radio nucleus also exhib-ited a coincident outburst peaking between the 1980s and 1990s. Thehigh-resolution Very Long Baseline Array (VLBA) observations at1.6 and 8.4 GHz found a pc-scale compact radio core (Koay et al.2016b). To search for potential faint jet activity launched by the ac-creting SMBH during and after the outburst, we performed deep verylong baseline interferometry (VLBI) observations of Mrk 590 withthe European VLBI Network (EVN).The Letter is organised in the following sequence. We introduceour EVN observations and data reduction in Section 2 and presentour VLBI imaging results of Mrk 590 in Section 3. We interpretthe observed radio structure as the central SMBH accretion-ejectionactivity and discuss potential implications from our findings in Sec-tion 4. Throughout the paper, a standard Λ CDM cosmological modelwith 𝐻 = 71 km s − Mpc − , Ω m = 0.27, Ω Λ = 0.73 is adopted. TheVLBI images have a scale of 0.5 pc mas − . We observed Mrk 590 three times with the EVN at 1.66 GHz in2015. The basic experiment parameters are listed in Table 1. Theparticipating stations were Effelsberg ( EF ), phased-up array of theWesterbork Synthesis Radio Telescope ( WB ), Westerbork single an-tenna ( W1 ), Jodrell Bank MK II ( JB ), Hartebeesthoek ( HH ), Onsala( ON ), Toruń ( TR ), Medicina ( MC ), Shanghai ( SH ), Tianma ( T6 ), Svet-loe ( SV ), Badary ( BD ), Zelenchukskaya ( ZC ), Robeldo ( RO , 70-m dish,only left-circular polarisation available), Sardinia ( SR ) and Urumqi( UR ). At the time of the observations, both T6 and SR were newlyconstructed telescopes. They ran the VLBI observations in the risk-sharing mode. All the experiments used the available maximum datarate 1024 Mbps (16 MHz filters, 2 bit quantisation, 16 sub-bandsin dual polarisation). The first two experiments were performed inthe 𝑒 -VLBI mode (Szomoru 2008). The raw data were transferredto JIVE (Joint Institute for VLBI, ERIC) via broad-band connec-tions and then correlated in real time by the EVN software correlator(SFXC, Keimpema et al. 2015). The last experiment EY023 wascarried out in the traditional disk-recording mode to include moretelescopes and gain a better ( 𝑢 , 𝑣 ) coverage. All the experiments werecorrelated with typical correlation parameters (1 or 2-s integrationtime, 32 or 64 points per subbands) used for continuum experiments.During the observations of Mrk 590, we selected J0216 − h m . s − ◦ (cid:48) . (cid:48)(cid:48) 𝜎 ra = .
15 mas, 𝜎 dec = .
30 mas),in agreement with the positions reported by the 3rd realisation ofInternational Celestial Reference Frame (ICRF3, Charlot, P. et al.2020) and the second data release (DR2) of the optical
Gaia astrom-etry (Gaia Collaboration et al. 2018). It has an unresolved structurewith a correlation amplitude of ∼ ∼ ∼ − ∼ ∼ + + − − ACCOR accordingto the auto-correlation amplitude. (3) The amplitude calibration wasinitially done with properly smoothed antenna monitoring data (sys-tem temperatures and gain curves) or nominal system equivalent fluxdensities in case of missing these data. We also corrected some sub-band dependent constant amplitude errors derived by the amplitudeself-calibration in difmap (Shepherd et al. 1994) in the later re-run ofthe calibration with the aips task
SNCOR . (4) The ionospheric disper-sive delays were corrected according to maps of total electron contentprovided by Global Positioning System (GPS) satellite observations.(5) The phase errors due to the antenna parallactic angle variationswere removed. (6) We aligned the phases across the subbands viaiteratively running fringe-fitting with a short scan of the calibratordata. After the phase alignment, we combined all the subbands in theStokes 𝑅𝑅 and 𝐿𝐿 , ran the fringe-fitting with a sensitive station asthe reference station ( EF or WB ) and applied the solutions to all therelated sources. (7) The bandpass calibration was performed. All theabove calibration steps were scripted in the ParselTongue interface(Kettenis et al. 2006).The de-convolution was performed in difmap (Shepherd et al.1994). The calibrator imaging procedure was performed through anumber of iterations of model fitting with a group of delta functions,i.e., point source models, and the self-calibration in difmap. We re-ran the fringe-fitting and the amplitude and phase self-calibration inaips with the input source model made in difmap. All these solutionswere also transferred to the target data via linear interpolation.The phase-referencing calibrator J0216 − ∼ ∼ ∼
115 mJy at 1.66 GHz in the three epochs. The fluxdensities were slightly lower than the value (128 mJy) reported byICRF3 observations at 2.3 GHz on 2015 January 23.Our target source Mrk 590 was detected in all the epochs. However,we noticed that there were significant phase fluctuations on rathershort time scales > ∼ ◦ and 24 ◦ ) tothe Sun. These phase issues caused poor phase connections betweenthe calibrator and the target and significant phase coherence loss( > ∼
40 per cent). The dirty maps had rather low peak brightness: ∼ ∼ − with uniform grid weighting. Because of thenon-optimal ( 𝑢 , 𝑣 ) coverage, the dirty beam had multiple strong side- MNRAS , 1–5 (2015) et in Mrk 590 Table 1.
Short summary of the EVN observations of Mrk 590 at 1.66 GHz. The two-letter codes for the participating stations are explained in Section 2.Date Participating EVN stations Project code (mode) Phase-referencing2015 Jan 13
EF, WB, JB, HH, ON, TR
EY022 ( 𝑒 -VLBI) Poor2015 May 13 EF, WB, JB, HH, ON, TR, MC, SH, T6
EY022B ( 𝑒 -VLBI) Poor2015 Oct 16 EF, W1, JB, HH, ON, TR, MC, SH, T6, SV, BD, ZC, RO, SR, UR
EY023 (disk-recording VLBI) Success lobes. In view of the two problems, it was hard to detect any secondaryfeature (e.g. the component N in Fig. 1). Thus, the results were notreported in the paper. In the last epoch, SR and UR had no fringes, SH had a linear polarisation signal, T6 had significant amplitudefluctuations on rather short time scale of a few seconds in the parallel-hand correlation data of Stokes 𝐿𝐿 , TR had a problem with trackingMrk 590 in the last three hours and ON had significantly residualerrors likely due to some unexpected ionospheric activity at the highlatitude. All these problematic data were excluded. Moreover, wenoticed that T6 had a certain systematic noise in the remaining Stokes 𝑅𝑅 data and lowered down its data weight by a factor of 0.25 withthe aips task WTMOD . Because most stations ran the observations (19h– 3h UT) at night (the Sun distance 164 ◦ ), the phase varied slowlyand smoothly, and the phase interpolations worked precisely in thelast epoch. The phase-referencing calibration between the calibratorsJ0217 − − Fig. 1 shows the clean map of Mrk 590 made with the uniform gridweighting and without running the phase self-calibration. Enabled bythe high resolution in particular in the north-south direction, Mrk 590shows a significantly elongated structure. To quantify the radial ex-tension, we decomposed the structure into two components, markedas N and S. After peeling off the peak feature S, the extension Nhas a signal to noise ratio (SNR) of about seven in the residual map.During the de-convolution process, we added windows carefully andtimely to avoid cleaning components at the positions of strong (80percent) side lobes. The clean algorithm gives a total flux density of1 . ± .
16 mJy. In the flux density uncertainty, we included ten percent of the flux densities as the systematic errors. Compared to thevalue (2.75 ± <
5) of a faint ( < ∼ − ) MERLIN constraint on the size < ∼
90 mas(Thean et al. 2001). In the 1.6-GHz VLBA image (Koay et al. 2016b),both the total flux density and the peak brightness were likely over-estimated by a factor of about two because the phase self-calibrationwas tried to remove significant residual phase errors.We fit two point sources to the visibility data. The best-fit pointsources have flux densities 1 . ± .
12 mJy for S and 0 . ± .
06 mJyfor N, and a separation of 2 . ± . ∼ . ± . ± . Gaia
DR2 astrometry results with a point source model are also listed inTable 2. The EVN astrometry results are consistent with the optical D ec ( J2000 ) RA (J2000)02 14 33.5630 33.5610 33.5590-00 46 00.16500.17500.18500.195 SN p c EVN at 1.6 GHz +Mrk 590
Figure 1.
The EVN 1.6-GHz image of the nearby changing-look Seyfertgalaxy Mrk 590 on 2015 October 16. The contours start from 2.5 𝜎 and in-crease by factors of −
1, 1, 2, 4 and 8. The map was made with uniform weight-ing. The beam full width at half maximum (FWHM) is 5.48 × atposition angle (PA) 78 . ◦
0. The first contour is 0.083 mJy beam − and the peakbrightness is 0.107 mJy beam − . The white cross denotes the optical centroidreported by the Gaia astrometry.
Gaia DR2 position (Gaia Collaboration et al. 2018) and the VLBAastrometry results at 1.6 and 8.4 GHz (Koay et al. 2016b). Becauseof instrumental limitations, it is hard to fit the structure to the morecomplex model, e.g. two circular Gaussian models or an ellipticalGaussian model.The average brightness temperature 𝑇 b of the entire radio structureis estimated (e.g., Condon et al. 1982) as 𝑇 b = . × 𝑆 int 𝜈 𝜃 ( + 𝑧 ) , (1)where 𝑆 int is the integrated flux density in mJy, 𝜈 obs is the observingfrequency in GHz, 𝜃 size is the FWHM of the best-fit circular Gaussianmodel in mas, and 𝑧 is the redshift. Because the source is unresolvedin the east-west direction, the size estimate is very likely an upperlimit. So, the brightness temperature estimate should be taken as alower limit, i.e. 𝑇 b > ∼ × K. The elongated radio structure can be naturally interpreted as a faintjet in Mrk 590. According to the positional consistency between ourVLBI astrometry and the
Gaia astrometry, the structure represents theparsec- and sub-parsec-scale AGN activity powered by the centralaccreting SMBH. Based on the total flux densities: 3 . ± . . ± . 𝑆 𝜈 ∝ 𝜈 . ± . and thus hosts a partiallysynchrotron self-absorbed jet base. MNRAS000
Gaia astrometry, the structure represents theparsec- and sub-parsec-scale AGN activity powered by the centralaccreting SMBH. Based on the total flux densities: 3 . ± . . ± . 𝑆 𝜈 ∝ 𝜈 . ± . and thus hosts a partiallysynchrotron self-absorbed jet base. MNRAS000 , 1–5 (2015)
J. Yang et al.
Table 2.
List of the high-precision astrometry results of Mrk 590 presented by the optical
Gaia
DR2 (Gaia Collaboration et al. 2018) and our EVN phase-referencing observations at 1.66 GHz. The position errors 𝜎 ra and 𝜎 dec include both the formal error 𝜎 f and the systematic error 𝜎 s .Technique Right Ascension 𝜎 ra ( 𝜎 f , 𝜎 s ) Declination 𝜎 dec ( 𝜎 f , 𝜎 s ) Comment on 𝜎 s (J2000) (mas) (J2000) (mas)Optical Gaia astrometry (DR2) 02 h m . s ± . ± . − ◦ (cid:48) . (cid:48)(cid:48) ± . ± . h m . s ± . ± . − ◦ (cid:48) . (cid:48)(cid:48) ± . ± . − The jet direction is fully consistent with the direction of the nucleargas outflows extending up to ∼ ∼ × erg s − . Thus, it can be identified as alow-radio-power jet (e.g. Kunert-Bajraszewska et al. 2010; An &Baan 2012). According to the fundamental plane relation of blackhole activity (Körding et al. 2006), its low radio luminosity can bereasonably explained as a consequence of its relatively low blackhole mass and low X-ray luminosity (Koay et al. 2016b) in the lowaccretion rate state. Compared to the radio luminosities of nearbygalaxies, e.g. ∼ –10 erg s − (280 galaxies, Baldi et al. 2021),the radio luminosity of Mrk 590 is a typical value.The linear structure has a total radio luminosity below the maxi-mum luminosity, 𝐿 R ∼ . erg s − , observed in the young super-novae (Weiler et al. 2002). However, it cannot be explained as youngsupernovae or supernova remnants (e.g. Varenius et al. 2019). Opticalobservations show that there is no sign of star-forming activity in thenuclear region (Raimundo et al. 2019). Furthermore, the moleculargas mass in the inner 150 pc is very low, < ∼ . × M (cid:12) (Koay et al.2016a). Mrk 590 underwent a giant outburst and then a slow fading from radioto X-ray bands over the last fifty years (Denney et al. 2014; Koay et al.2016b). Among the known changing-look AGN, Mrk 590 is the firstcase displaying the coincident radio variability (Koay et al. 2016b).At radio, it reached 6 . ± . . ± . < ∼
45 yr, show an apparentseparation speed of > ∼ 𝑐 with respect to the component S, and keepfading slowly for the rest of its life. Since the intensive accretion wasa very short active phase, the jet might be short of the energy supplyand then die rapidly as a short-lived jet (Wołowska et al. 2017). Tostrengthen or exclude the association, it requires future multi-epoch deep VLBI observations to search for its proper motion and fluxdensity variability.Mrk 590 had a low accretion rate of 𝐿 bol / 𝐿 Edd ∼ − in thelow luminosity state (Koay et al. 2016b) while reached a very highaccretion rate of 𝐿 bol / 𝐿 Edd ∼ − (Peterson et al. 2004) during theoutburst. Based on a small sample of faded changing-look quasars,(Ruan et al. 2019) has recently found a V-shaped evolution patternin the plot of the UV-to-X-ray spectral index versus the Eddingtonratio. The behaviour is in agreement with the prediction of the AGNaccretion state transition generated by Sobolewska et al. (2011) basedon stellar-mass black holes in X-ray binaries. The critical accretionrate to discriminate high and low states is likely ∼ − (Ruan et al.2019). This is also consistent with the value observed in stellar-massblack hole X-ray binaries (e.g. McClintock & Remillard 2006). If theunified X-ray outburst model in black hole X-ray binaries (Fenderet al. 2009) is applicable to Mrk 590, the early brightening wouldrepresent a transition from the low to high accretion rates, and thecomponent N might be ejected during the state transition. If theejection activity resembles the situation observed by Marscher et al.(2002) in 3C 120, multiple ejection events might have occurred notonly during the outburst but also during the follow-up fading stage.The rapid disappearance and re-appearance of broad Balmer linesin Mrk 590 most likely results from the variable accretion instead ofline-of-sight obscuration by gas and dust (Denney et al. 2014; Koayet al. 2016b; Mathur et al. 2018). This is mainly because of the de-tection of the coincident radio variability (Koay et al. 2016b) and theabscence of intrinsic absorption in the X-ray spectrum (e.g. Mathuret al. 2018). Our finding of the small faint jet provides additionalsupport for the variable accretion scenario. ACKNOWLEDGEMENTS 𝑒 -VLBI research infrastructure in Europe is supported by the Eu-ropean Union’s Seventh Framework Programme (FP7/2007-2013)under grant agreement number RI-261525 NEXPReS. The Euro-pean VLBI Network (EVN) is a joint facility of independent Eu-ropean, African, Asian, and North American radio astronomy insti-tutes. Scientific results from data presented in this publication arederived from the following EVN project codes: EY022 and EY023.The research leading to these results has received funding from theEuropean Commission Seventh Framework Programme (FP/2007-2013) under grant agreement No. 283393 (RadioNet3). This workhas made use of data from the European Space Agency (ESA) mis-sion Gaia ( ), processed bythe Gaia
Data Processing and Analysis Consortium (DPAC, ). Fund-ing for the DPAC has been provided by national institutions, in par-ticular the institutions participating in the
Gaia
Multilateral Agree-ment. This research has made use of the NASA/IPAC ExtragalacticDatabase (NED), which is operated by the Jet Propulsion Laboratory,California Institute of Technology, under contract with the National
MNRAS , 1–5 (2015) et in Mrk 590 Aeronautics and Space Administration. This research has made useof NASA’s Astrophysics Data System Bibliographic Services.
DATA AVAILABILITY
The correlation data of EY022 and EY023 underlying this arti-cle are available in the EVN data archive ( ). The calibrated visibility data will be sharedon reasonable request to the corresponding author.
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