Optical and cm Follow‐Ups of the Changing‐Look Event in Mkn 590

In the manuscript, the blue quasar SDSS J105816.19+544310.2 (=SDSS J1058+5443) at redshift 0.479 is reported as so-far the best candidate of true type-2 quasar with disappearance of central BLRs. There are so-far no definite conclusions on the very existence of true type-2 AGN, mainly due to detected optical broad emission lines in high quality spectra of some previously classified candidates of true type-2 AGN. Here, not similar as previous reported candidates for true type-2 AGN among narrow emission-line galaxies with weak AGN activities but strong stellar lights, the definite blue quasar SDSS J1058+5443 can be well confirmed as a true type-2 quasar due to apparent quasar-shape blue continuum emissions but apparent loss of both the optical broad Balmer emission lines and the NUV broad Mg~{\sc ii} emission line. Based on different model functions and F-test statistical technique, after considering blue-shifted optical and UV Fe~{\sc ii} emissions, there are no apparent broad optical Balmer emission lines and/or broad NUV Mg~{\sc ii} line, and the confidence level is smaller than 1sigma to support broad optical and NUV emission lines. Moreover, assumed the Virialization assumption to broad line emission clouds, the re-constructed broad emission lines strongly indicate that the probable intrinsic broad emission lines, if there were, cannot be hidden or overwhelmed in the noises of SDSS spectrum of SDSS J1058+5443. Therefore, SDSS J1058+5443, so-far the best and robust candidate of true type-2 quasar, leads to the further clear conclusion on the very existence of true type-2 AGN.

We present a new model to explain the appearance of red/blue-shifted broad low-ionization emission lines, especially emission lines in optical band, which is commonly considered as an indicator of radial motion of the line emitting gas in broad emission line regions (BLRs) of Active Galactic Nuclei (AGN). We show that partly obscured disk-like BLRs of dbp emitters (AGN with double-peak broad low-ionization emission lines) can also successfully produce shifted standard Gaussian broad balmer emission lines. Then we calculate two kinds of BH masses for AGN with shifted broad balmer emission lines selected from SDSS. We find that the BH masses calculated from M-sigma relation are systematically larger than virial BH masses for the selected objects, even after the correction of internal reddening effects in BLRs. The smaller virial BH masses than BH masses from M-sigma relation for objects with shifted broad emission lines are coincident with what we expect from the partly obscured accretion disk model. Thus, we provide an optional better model to explain the appearance of shifted broad emission lines, especially for those objects with underestimated virial BH masses.

In this paper, a candidate of sub-pc binary black hole (BBH) system is reported in SDSS J1257+2023 through different properties of broad Balmer emission lines. After subtractions of host galaxy contributions, Gaussian functions are applied to measure emission lines in SDSS J1257+2023, leading line width (second moment) 760 km s−1 of broad H β to be 0.69 times of line width 1100 km s−1 of broad H α, quite different from normal line width ratio 1.1 of broad H β to broad H α in quasars. The quite broader component in broad H α in SDSS J1257+2023 can be confirmed with confidence level higher than 5σ through F-test technique, through different model functions applied to measure emission lines. The broad Balmer emission lines having different line widths can be naturally explained by a BBH system with different obscurations on central two independent broad emission line regions. Meanwhile, through Zwicky Transient Facility (ZTF) light curves and corresponding phase folded light curves well described by sinusoidal function, BBH system expected optical quasi-periodic oscillations (QPOs) can be detected with periodicity about 1000 d, confirmed with confidence level higher than 3σ by generalized Lomb–Scargle periodogram. And through Continuous AutoRegressive process simulated light curves, confidence level higher than 2σ can be determined to support the optical QPOs in SDSS J1257+2023 not from intrinsic AGN activities, although the ZTF light curves have short time durations. Moreover, through oversimplified BBH system simulated results, studying different broad Balmer lines as signs of BBH systems in normal quasars with flux ratios around 4 of broad H α to broad H β could be done in near future.

In this paper, the blue quasar SDSS J105816.19+544310.2 (=SDSS J1058+5443) at redshift 0.479 has been reported as the best true type 2 quasar candidate with the disappearance of central broad-line regions. There are no definite conclusions on the very existence of true type 2 active galactic nuclei (AGN), mainly due to detected optical broad emission lines in high-quality spectra of some previously classified true type 2 AGN candidates. Here, unlike previously reported true type 2 AGN candidates among narrow emission-line galaxies with weak AGN activities but strong stellar lights, the definitely blue quasar SDSS J1058+5443 can be well confirmed as a true type 2 quasar due to apparent quasar-shape blue continuum emissions but an apparent loss of both the optical broad Balmer emission lines and the near-UV (NUV) broad Mg ii emission line. Based on different model functions and the F-test statistical technique, after considering blueshifted optical and UV Fe ii emissions, there are no apparent broad optical Balmer emission lines and/or broad NUV Mg ii lines, and the confidence level is smaller than 1σ in support of broad optical and NUV emission lines. Moreover, assuming the virialization assumption to broad-line emission clouds, the reconstructed broad emission lines strongly indicate that the probable intrinsic broad emission lines, if they exist, cannot be hidden or overwhelmed in the noise of the Sloan Digital Sky Survey spectrum of SDSS J1058+5443. Therefore, SDSS J1058+5443 is so far the best and most robust true type 2 quasar candidate, leading to the clear conclusion of the very existence of true type 2 AGN.

In this manuscript, an interesting blue active galactic nuclei (AGNs) SDSS J154751.94+025550 (=SDSS J1547) is reported with very different line profiles of broad Balmer emission lines: double-peaked broad H β but single-peaked broad H α. SDSS J1547 is the first AGN with detailed discussions on very different line profiles of the broad Balmer emission lines, besides the simply mentioned different broad lines in the candidate for a binary black hole (BBH) system in SDSS J0159+0105. The very different line profiles of the broad Balmer emission lines can be well explained by different physical conditions to two central BLRs in a central BBH system in SDSS J1547. Furthermore, the long-term light curve from CSS can be well described by a sinusoidal function with a periodicity about 2159 d, providing further evidence to support the expected central BBH system in SDSS J1547. Therefore, it is interesting to treat different line profiles of broad Balmer emission lines as intrinsic indicators of central BBH systems in broad line AGN. Under assumptions of BBH systems, 0.125 per cent of broad-line AGN can be expected to have very different line profiles of broad Balmer emission lines. Future study on more broad line AGN with very different line profiles of broad Balmer emission lines could provide further clues on the different line profiles of broad Balmer emission lines as indicator of BBH systems.

Using a Gaussian fitting procedure, we have constructed an accurate UV narrow emission line template spectrum for the Seyfert 1 galaxy NGC 5548, from the low-state Hubble Space Telescope/Faint Object Spectrograph UV spectrum taken on 1982 July 5 with the 10 circular aperture. This template spectrum is similar in form to that determined for the prototypical narrow-line Seyfert 2 galaxy NGC 1068. The narrow emission line template spectrum of NGC 5548 has for the first time enabled us to isolate the narrow and broad UV emission lines and thereby to determine firm estimates for the intensities of the broad emission lines for both the low-state spectrum and the HST/FOS archival spectrum obtained from the intensive monitoring campaign undertaken by AGN Watch on 1993 April 19, when the continuum was a factor of ~4.8 brighter. A comparison of the low-state and high-state spectra show that while the narrow UV emission lines are nonvariable over timescales of ~10 months, the broad UV emission lines exhibit large variations in both their strength and shape. By combining a photoionization code with a robust global optimization routine, we have determined global best-fit parameters for the average physical conditions within the broad emission line region gas for both the low- and high-state spectra. By using a best guess estimate for the shape of the ionizing continuum of this source, we find that a single zone photoionization model of the broad emission line region (BLR) cannot simultaneously fit both the emission-line ratios of the strongest UV lines and their variability timescales. However, the line ratios and variability timescales can be reproduced if we assume a stratified BLR, i.e., a BLR that has strong gradients in density (NH ∝ 1/r2, 1011.3-1010.0). These models also suggest that the BLR gas is in a moderately high state of ionization with log10 U ~ -0.6 in the low-state spectrum, rising to ~0.0 in the high state. We find that the observed differences in the broad emission line fluxes and their ratios, between the low- and high-state spectra, are not solely a consequence of changes in the ionizing continuum source luminosity. Rather, they imply in addition, a change in the spectral energy distribution of the ionizing continuum, although changes in either the covering fraction, or composition of the broad emission line region gas, cannot necessarily be ruled out. By constructing a simple two-zone model for the high-ionization lines, we find that in order to reproduce the observed line ratios and line equivalent widths, the gas covering fraction for this source must necessarily be high, ~38% at a radial distance of 2 lt-days and decreasing outward to ~32% at 10 lt-days. This is considerably larger than the typical value of ~10% quoted for active galactic nuclei, derived from the incidence of Lyman edges in high-redshift quasars. Although the statistics for the incidence of Lyman edges in Seyfert 1 galaxies is poorly determined, our derived covering fraction is broadly consistent with the 25% covering fraction estimate obtained from observations with the Hopkins Ultraviolet Telescope.

In this manuscript, the structure of broad emission line regions (BLRs) of well-mapping double-peaked emitter (AGN with broad double-peaked low-ionization emission lines) 3C390.3 is studied. Besides the best fitted results for double-peaked broad optical balmer lines of 3C390.3 by theoretical disk model, we try to find another way to further confirm the origination of double-peaked line from accretion disk. Based on the long-period observed spectra in optical band around 1995 collected from AGN WATCH project, the theoretical disk parameters of disk-like BLRs supposed by elliptical accretion disk model (Eracleous et al. 1995) have been well determined. Through the theoretical disk-like BLRs, characters of observed light-curves of broad double-peaked H$\alpha$ of 3C390.3 can be well reproduced based on the reverberation mapping technique. Thus the accretion disk model is preferred as one better model for BLRs of 3C390.3. Furthermore, we can find that different disk parameters should lead to some different results about size of BLRs of 3C390.3 from the one measured through observational data, which indicates the measured disk parameters are significantly valid for 3C390.3. After that, the precession of theoretical elliptical disk-like BLRs being considered, we can find that the expected line profile in 2000 by theoretical model is consistent with the observed line profile by HST around 2000. Based on the results, we can further believe that the origination of broad double-peaked balmer emission lines of 3C390.3 are from accretion disk around central black hole.

NGC 1275 is one of the most conspicuous active galactic nuclei (AGN) in the local universe. The radio jet currently emits a flux density of ∼10 Jy at ∼1 mm wavelengths, down from the historic high of ∼65 Jy in 1980. Yet, the nature of the AGN in NGC 1275 is still controversial. It has been debated whether this is a broad emission line (BEL) Seyfert galaxy, an obscured Seyfert galaxy, a narrow line radio galaxy, or a BL Lac object. We clearly demonstrate a persistent Hβ BEL over the last 35 yr with a full width at half maximum (FWHM) of 4150–6000 km s−1. We also find a prominent Pα BEL (FWHM ≈ 4770 km s−1) and a weak C iv BEL (FWHM ≈ 4000 km s−1), Hβ/C iv ≈ 2. A far-UV Hubble Space Telescope observation during suppressed jet activity reveals a low luminosity continuum. The Hβ BEL luminosity is typical of broad line Seyfert galaxies with similar far-UV luminosity. X-ray observations indicate a softer ionizing continuum than what would be expected for a broad line Seyfert galaxy with similar far-UV luminosity. This is the opposite of the expectation of advection-dominated accretion. The AGN continuum appears to be thermal emission from a low luminosity, optically thick, accretion flow with a low Eddington ratio, ∼0.0001. The soft, weak, ionizing continuum is consistent with the relatively weak C iv BEL. Evidence that the BEL luminosity is correlated with the jet millimeter-wave luminosity is presented. It appears that the accretion rate regulates jet power.

Gravitational microlensing is a powerful tool allowing one to probe the structure of quasars on sub-parsec scale. We report recent results, focusing on the broad absorption and emission line regions. In particular microlensing reveals the intrinsic absorption hidden in the P Cygni-type line profiles observed in the broad absorption line quasar H1413+117, as well as the existence of an extended continuum source. In addition, polarization microlensing provides constraints on the scattering region. In the quasar Q2237+030, microlensing differently distorts the H$\alpha$ and CIV broad emission line profiles, indicating that the low- and high-ionization broad emission lines must originate from regions with distinct kinematical properties. We also present simulations of the effect of microlensing on line profiles considering simple but representative models of the broad emission line region. Comparison of observations to simulations allows us to conclude that the H$\alpha$ emitting region in Q2237+030 is best represented by a Keplerian disk.

Most massive galaxies contain a supermassive black hole (SMBH) at their centre. When galaxies merge, their SMBHs sink to the centre of the new galaxy, where they are thought to eventually merge. During this process, an SMBH binary is formed. The presence of two sets of broad emission lines in the optical spectrum of an active galactic nucleus (AGN) has been interpreted as evidence for two broad-line regions (BLRs), one surrounding each SMBH in a binary. We modelled the broad Balmer emission lines in the SDSS spectra of 373 extreme variability AGNs using one broad and several narrow Gaussian components. We report on the discovery of SDSS J021647.53 − 011341.5 (hereafter J0216) as a double-peaked broad emission line source. Among the 373 AGNs, there were five sources that are known as double-peaked emission line sources. Three of these have been reported as candidate SMBH binaries in previous studies. We present all six objects and their double-peaked broad Balmer emission lines, and discuss the implications for a tidal disruption event (TDE) interpretation of the extreme variability, assuming the double-peaked sources are SMBH binaries.

Part of results of the multi-epoch intranight optical spectroscopic monitoring of the Markarian 6 nucleus carried out at the telescopes of 6-m of the Special Astrophysical Observatory (Russia), 2.6-m of the Byurakan Astrophysical Observatory (Armenia) and 2-m of the Tautenburg Observatory (Germany) is presented.Observations were made in 1979, 1986, 1988-1991 and 2007-2009 during a total of 33 nights with an average sampling rate of 4 spectra per night. TV-scanner and long-slit spectrographs equipped with Image Tube and CCD detector arrays were used. Altogether we analyzed 110 Hβ and 58 Hα region spectra to search for intranight variability in the broad hydrogen emission line profiles. The typical spectral resolutions were 4 Å for scanner spectra, 6 Å for photographic spectra, and 5 Å and 10 Å for CCD spectra. The S/N ratio at the continuum level near the Hβ and Hα lines was in the range 15–50.The purpose of the search was to look for the characteristic variability signatures of different kinematical models of the broad emission-line region. We considered the centering and guiding errors which can result in differences between spectra.We found variations in the broad Balmer line difference profiles on time scale of hour with the level of significance of 3.6 σ to 5.0 σ. Variations take the form of narrow, small bumps located at the blue and red sides or only at the blue side of the lines. In the intermediate level of broad line flux, the Hβ and Hα profiles show fine structure. Detected profile changes occurred at the same radial velocity shifts as the details in the fine structure.The variability is at least 2 orders of magnitude more rapid than any observed for broad Balmer line profiles in AGNs that we are aware of in the literature.Discovered extremely rapid line-profile variability may be associated with reverberation effects. Two-sided profile changes may indicate the response of circularly rotating hydrogen clouds in the BLR to a light pulse from a central source. One-sided profile variations may be attributed to a response of a non-disk component: the subarcsec scale region of the jet.

Changing-look active galactic nuclei (CLAGNs) show the disappearance and reappearance of broad emission lines in a few years, which challenges the orientation-based AGN unification model. We reduce the X-ray data for five well-studied CLAGNs that show a strong change in broad emission lines in the past several decades. We find that the X-ray photon index, Γ, and the Eddington-scaled X-ray luminosity, L 2–10 keV/L Edd, normally follow negative and positive correlations when the Eddington ratio is lower and higher than a critical value of ∼10−3. We find that the CLAGNs observed with broad Hβ emission lines stay in the positive part of the Γ–L 2–10 keV/L Edd correlation, while the broad Hβ lines become weak or disappear in the anticorrelation part of the Γ–L 2–10 keV/L Edd correlation, which suggests that the evolution of the broad lines should be correlated with the evolution of the underlying accretion process. We further find that the CLAGNs are consistent with the other different types of AGNs in the L bol–L bol/L Edd correlation. These results support that the CLAGNs belong to a special stage of AGNs with a bolometric Eddington ratio ∼1%, where the broad emission lines are easily affected by the strong variation in ionization luminosity that is caused by the transition of accretion modes.

During an intensive Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV monitoring campaign of the Seyfert 1 galaxy NGC 5548 performed from 2014 February to July, the normally highly correlated far UV continuum and broad emission line variations decorrelated for ∼60–70 days, starting ∼75 days after the first HST/COS observation. Following this anomalous state, the flux and variability of the broad emission lines returned to a more normal state. This transient behavior, characterized by significant deficits in flux and equivalent width of the strong broad UV emission lines, is the first of its kind to be unambiguously identified in an active galactic nucleus reverberation mapping campaign. The largest corresponding emission line flux deficits occurred for the high ionization, collisionally excited lines C iv and Si iv(+O iv]), and also He ii(+O iii]), while the anomaly in Lyα was substantially smaller. This pattern of behavior indicates a depletion in the flux of photons with relative to those near 13.6 eV. We suggest two plausible mechanisms for the observed behavior: (i) temporary obscuration of the ionizing continuum incident upon broad line region (BLR) clouds by a moving veil of material lying between the inner accretion disk and inner (BLR), perhaps resulting from an episodic ejection of material from the disk, or (ii) a temporary change in the intrinsic ionizing continuum spectral energy distribution resulting in a deficit of ionizing photons with energies >54 eV, possibly due to a transient restructuring of the Comptonizing atmosphere above the disk. Current evidence appears to favor the latter explanation.

Motivated by the X-ray properties of the galaxy NGC 3065, we have obtained new optical spectra that reveal that it has a low-ionization nuclear emission-line region (LINER) as well as broad Balmer emission lines, establishing it as an active galactic nucleus. We also examined an older spectrum from the CfA Redshift Survey that lacks broad Balmer lines, indicating that these lines appeared sometime after 1980. Thus NGC 3065 joins the set of LINERs with broad, variable Balmer lines, which includes such well-known galaxies as NGC 1097 and M81. Inspired by the sometimes double-peaked profiles of the variable Balmer lines in other LINERs, we speculate that the broad Balmer lines of NGC 3065 also come from an accretion disk. We illustrate the plausibility of this hypothesis by fitting a disk model to the observed Hα profile. We also estimate the mass of the central black hole to be (9 ± 4) × 107 M☉ from the properties of the host galaxy, which leads to the conclusion that the accretion rate is only ~2 × 10-4 times the Eddington value, a property that appears to be common among LINERs. At such a low relative accretion rate, the inner accretion disk can turn into a vertically extended ion torus, which can illuminate the outer thin disk and power the broad-line emission. The reason for the sudden appearance of broad Balmer lines is an open question, although we suggest two possible explanations: (1) tidal disruption of a star or (2) a sudden transition in the structure of the accretion disk.

We report on the radio-quiet quasar SDSS J2125−0813 which obviously emits optical Fe ii emission lines and double-peaked broad Balmer emission lines. Using the accretion disc model for double-peaked, broad, low-ionization emission lines, we reproduce the composite line spectra at the optical band between 4100 and 5600 Å. Broad Fe ii emission lines can be fitted simultaneously with the broad Hβ and Mg i lines, such that all broad lines have an elliptical disc profile with the same disc parameters. This result indicates that the optical Fe ii emission lines originate from the accretion disc near the central black hole which produces the double-peaked broad Balmer emission lines. Furthermore, we find that the object has a dimensionless accretion rate , which is much larger than the accretion rate for the advection-dominated accretion flow (ADAF) mode, and that the energy budget of the accretion disc is enough to power the double-peaked broad Balmer emission lines.