Search

The upcoming photometric surveys, such as the Rubin Observatory's Legacy Survey of Space and Time (LSST) will monitor unprecedented number of active galactic nuclei (AGN) in a decade long campaign. Motivated by the science goals of LSST, which includes the harnessing of broadband light curves of AGN for photometric reverberation mapping (PhotoRM), we implement the existing formalism to estimate the lagged response of the emission line flux to the continuum variability using only mutli-band photometric light curves. We test the PhotoRM method on a set of 19 artificial light curves simulated using a stochastic model based on the Damped Random Walk process. These light curves are sampled using different observing strategies, including the two proposed by the LSST, in order to compare the accuracy of time-lag retrieval based on different observing cadences. Additionally, we apply the same procedure for time-lag retrieval to the observed photometric light curves of NGC 4395, and compare our results to the existing literature.

We investigate the broad line profiles emitted from a system supermassive binary black hole (SMBBH) having elliptical orbits and low mass ratio of $m_2/m_1\sim 0.1$. Our model assumes a super Eddington accretion flow in the case of a smaller component, whereas the massive component has very small or negligible accretion, therefore supposing that no broad line region (BLR) is attached to it. Thus, the proposed SMBBH system contains one moving BLR, associated with the less massive component and one circum-binary BLR. We study the effect of different total mass of the system (ranging from 10$^6$ to 10$^8$ Solar masses) to the $\mathrm{H\beta}$ line profiles and to the continuum and line light curves. The resulted broad line profiles are asymmetric and shifted, and are varying during the orbital period. The asymmetry in the broad line profiles is discussed in terms of expected differences between the proposed model of the SMBBH with one active component and the scenario of a recoiling black hole. We discuss the periodicity detected in the line and continuum light curves, as well as in the variations of the line asymmetry and shift., Comment: 10 pages, 8 figures, 1 table

Here we present the long-term optical spectral monitoring of a changing-look active galactic nuclei (AGN) NGC 3516 that covers 22 years (from 1996 to 2018). We explore a variability in the broad lines and continuum, finding that the continuum is changing by more than a factor of 2, while the broad lines are varying by more than a factor of 10. The minimum of activity is observed in 2014, when the broad lines almost disappeared. We confirm that NGC 3516 is a changing-look AGN, and the absorption seen in the UV and X-ray may indicate that there is an obscuring region which is responsible for this. The line profiles are also changing. The mean profiles of the broad Halpha and Hbeta lines show shoulder-like structure in the wings, and enhanced peak, that may indicate a complex BLR. The rms-profiles of both lines seem to have the same shape and width of around 4200 km/s, indicating practically the same kinematics in the Halpha and Hbeta emitting regions. Measured time-lags between the continuum and Halpha and Hbeta broad-line variability are ~15 and 17 days, respectively, that in combination with the broad lines width allows us to estimate the NGC 3516 central black hole mass. We find that the black hole mass is 4.73+-1.40 x 10^7M_sun which is in agreement with previous estimates.

We present the variability study of the lowest-luminosity Seyfert 1 galaxy NGC 4395 based on the photometric monitoring campaigns in 2017 and 2018. Using 22 ground-based and space telescopes, we monitored NGC 4395 with a $\sim$5 minute cadence during a period of 10 days and obtained light curves in the UV, V, J, H, and K/Ks bands as well as the H$\alpha$ narrow-band. The RMS variability is $\sim$0.13 mag on \emph{Swift}-UVM2 and V filter light curves, decreasing down to $\sim$0.01 mag on K filter. After correcting for continuum contribution to the H$\alpha$ narrow-band, we measured the time lag of the H$\alpha$ emission line with respect to the V-band continuum as ${55}^{+27}_{-31}$ to ${122}^{+33}_{-67}$ min. in 2017 and ${49}^{+15}_{-14}$ to ${83}^{+13}_{-14}$ min. in 2018, depending on the assumption on the continuum variability amplitude in the H$\alpha$ narrow-band. We obtained no reliable measurements for the continuum-to-continuum lag between UV and V bands and among near-IR bands, due to the large flux uncertainty of UV observations and the limited time baseline. We determined the AGN monochromatic luminosity at 5100\AA\ $\lambda L_\lambda = \left(5.75\pm0.40\right)\times 10^{39}\,\mathrm{erg\,s^{-1}}$, after subtracting the contribution of the nuclear star cluster. While the optical luminosity of NGC 4395 is two orders of magnitude lower than that of other reverberation-mapped AGNs, NGC 4395 follows the size-luminosity relation, albeit with an offset of 0.48 dex ($\geq$2.5$\sigma$) from the previous best-fit relation of Bentz et al. (2013)., Comment: Accepted for publication in ApJ (Feb. 23rd, 2020). 18 pages, 10 figures

The active galactic nuclei (AGN) are among the most powerful sources with an inherent, pronounced and random variation of brightness. The randomness of their time series is so subtle as to blur the border between aperiodic fluctuations and noisy oscillations. This poses challenges to analysing of such time series because neither visual inspection nor pre-exisitng methods can identify well oscillatory signals in them. Thus, there is a need for an objective method for periodicity detection. Here we review our a new data analysis method that combines a two-dimensional correlation (2D) of time series with the powerful methods of Gaussian processes. To demonstrate the utility of this technique, we apply it to two example problems which were not exploited enough: damped rednoised artificial time series mimicking AGN time series and newly published observed time series of changing look AGN (CL AGN) NGC 3516. The method successfully detected periodicities in both types of time series. Identified periodicity of $\sim 4$ yr in NGC 3516 allows us to speculate that if the thermal instability formed in its accretion disc (AD) on a time scale resembling detected periodicity then AD radius could be $\sim 0.0024$ pc., Comment: accepted by Open astronomy

A new combined data of 5 well known type 1 AGN are probed with a novel hybrid method in a search for oscillatory behavior. Additional analysis of artificial light curves obtained from the coupled oscillatory models gives confirmation for detected periods that could have physical background. We find periodic variations in the long-term light curves of 3C 390.3, NGC 4151, NGC 5548 and E1821+643, with correlation coefficients larger than 0.6. We show that oscillatory patterns of two binary black hole candidates NGC 5548 and E1821+643 corresponds to qualitatively different dynamical regimes of chaos and stability, respectively. We demonstrate that absence of oscillatory patterns in Arp 102B could be due to a weak coupling between oscillatory mechanisms. This is the first good evidence that 3C 390.3 and Arp 102B, categorized as double-peaked Balmer line objects, have qualitative different dynamics. Our analysis shows a novelty in the oscillatory dynamical patterns of the light curves of these type 1 AGN.

In this paper we present new optical observations of the galaxy NGC 185 intended to reveal the status of supernova remnants (SNRs) in this dwarf companion of the Andromeda galaxy. Previously, it was reported that this galaxy hosts one SNR. Our deep photometric study with the 2m telescope at Rozhen National Astronomical Observatory using narrow-band H$\alpha$ and [SII] filters revealed complex structure of the interstellar medium in the center of the galaxy. To confirm the classification and to study the kinematics of the detected nebulae, we carried out spectroscopic observations using the SCORPIO multi-mode spectrograph at the 6m telescope at the Special Astrophysical Observatory of the Russian Academy of Science, both in low- and high-resolution modes. We also searched the archival X-ray and radio data for counterparts of the candidate SNRs identified by our optical observations. Our observations imply the presence of one more SNR, one possible HII region previously cataloged as part of an SNR, and the presence of an additional source of shock ionization in one low-brightness PN. We detected enhanced [SII]/H_alpha and [NII]/H_alpha line ratios, as well as relatively high (up to 90 km s$^{-1}$) expansion velocities of the two observed nebulae, motivating their classification as SNRs (with diameters of 45 pc and 50 pc), confirmed by both photometric and spectral observations. The estimated electron density of emission nebulae is 30 - 200 cm$^{-3}$. Archival XMM-Newton observations indicate the presence of an extended, low-brightness, soft source in projection of one of the optical SNRs, whereas the archival VLA radio image shows weak, unresolved emission in the center of NGC 185., Comment: 15 pages, 14 figures, accepted for publication in A&A

We present observations from the short-term intensive optical campaign (from Sep2019 to Jan2020) of the changing-look Seyfert NGC 3516. This active galactic nucleus is known to have strong optical variability and has changed its type in the past. It has been in the low-activity state in the optical since 2013, with some rebrightening from the end of 2015 to the beginning of 2016, after which it remained dormant. We aim to study the photometric and spectral variability of NGC 3516 from the new observations in U- and B-bands and examine the profiles of the optical broad emission lines in order to demonstrate that this object may be entering a new state of activity. NGC 3516 has been monitored intensively for the past 4 months with an automated telescope in U and B filters, enabling accurate photometry of 0.01 precision. Spectral observations were triggered when an increase in brightness was spotted. We support our analysis of past-episodes of violent variability with the UV and X-ray long-term light curves constructed from the archival Swift data. An increase of the photometric magnitude is seen in both U and B filters to a maximum amplitude of 0.25mag and 0.1 mag, respectively. During the flare, we observe stronger forbidden high-ionization iron lines than reported before, as well as the complex broad Ha and Hb lines. This is especially seen in Ha which appears to be double-peaked. It seems that a very broad component of ~10,000 km/s in width in the Balmer lines is appearing. The trends in the optical, UV, and X-ray light curves are similar, with the amplitudes of variability being significantly larger in the case of UV and X-ray bands. The increase of the continuum emission, the variability of the coronal lines, and the very broad component in the Balmer lines may indicate that the AGN of NGC 3516 is finally leaving the low-activity state in which it has been for the last ~3 years., 7 pages, 6 figures, accepted in A&A (corrected after receiving comments from the language editor)

The photometric light curve of PG1302-102 shows periodic variability which makes this object one of the most plausible supermassive black hole binary candidate. Interestingly, the most recent study of its updated optical light curve reports a decrease in significance of periodicity which may suggest that the binary model is less favorable. Here, we model the PG 1302-102 light curve, spanning almost 20 years, with a supermassive black hole binary system in which a perturbation in the accretion disk of more massive component is present. Our model reproduces well the observed light curve with a slight perturbation of a sinusoidal feature and predicts that a slightly larger period than previously reported, of about 1899 days, could arise due to a cold spot in the disk of {\bf more massive} component of a close, unequal-mass ($\frac{\mathrm{m}_{1}}{\mathrm{m}_{2}}=0.1$) black hole binary system. The light curve resembles the pattern of sinusoid-like shape within a few years, which could be confirmed by future observations. In addition, using our hybrid method for periodicity detection, we show that the periods in the observed ($1972\pm 254$ days) and modeled ($1873 \pm \ 250$ days) light curves are within one-sigma, which is also consistent with our physical model prediction and with previous findings. Thus, both the periodic nature and its slight fluctuation of the light curve of PG1302-102 is evident from our physical model and confirmed by the hybrid method for periodicity detection., Accepted to ApJ

The intrinsic Baldwin effect is an anti-correlation between the line equivalent width and the flux of the underlying continuum detected in a single variable active galactic nucleus (AGN). This effect, in spite of the extensive research, is still not well understood, and might give us more information about the physical properties of the line and continuum emission regions in AGNs. Here we present preliminary results of our investigation of the intrinsic Baldwin effect of the broad H$\beta$ line in several Narrow-line Seyfert 1 (NLSy 1) galaxies, for which data were taken from the long-term monitoring campaigns and from the Sloan Digital Sky Survey Reverberation Mapping project.

Here we present an in-depth analysis of the periodicity of the continua and broad emission lines of a quasar E1821+643. We applied non-parametric composite models, the linear sum of stationary and non-stationary Gaussian processes, and quantified contribution of their periodic parts. We found important qualitative differences among the three periodic signals. Periods of $\sim 2200$ and $\sim 4500$ days appear in both continua 5100 \AA \, and 4200 \AA \,, as well as in the H$\gamma$ emission line. Their integer ratio is nearly harmonic $\sim \frac{1}{2}$, suggesting the same physical origin. We discuss the nature of these periods, proposing that the system of two objects in dynamically interaction can be origin of two largest periods., Comment: accepted for publication in Astrophysics and Space Science,13 pages, 6 figures

We present the results of the long-term (20-year period, from 1996 to 2015) optical spectral monitoring of the Seyfert 1 galaxy NGC 7469. The variation in the light-curves of the broad He II {\lambda}4686A H{\beta} and H{\alpha} lines, and the continuum at 5100A and 6300A have been explored. The maximum of activity was in 1998, and the variability in the continuum and lines seems to have two periods of around 1200 and 2600 days, however these periodicities should be taken with caution because of the red-noise. Beside these periods, there are several short-term (1-5 days) flare-like events in the light-curves. There are good correlations between the continuum fluxes and H{\alpha} and H{\beta} line fluxes, but significantly smaller correlation between the He II and continuum. We found that the time-lags between the continuum and broad lines are different for H{\beta} (~20 l.d.) and H{\alpha} (~3 l.d.), and that He II also has a smaller lag (~2-3 l.d.). The H{\alpha} and H{\beta} line profiles show a slight red asymmetry, and the broad line profiles did not changed in the 20-year period. Using the lags and widths of H{\alpha} and H{\beta} we estimated the central black hole mass and found that it is ~(1-6)x$10^7 M_{\odot}$, which is in agreement with previous reverberation estimates., Comment: Accepted in Monthly Notices of the Royal Astronomical Society

It is becoming clear that we can define two different types of nearby AGN belonging to the Seyfert 1 class (S1), on the basis of the match of the intensities of their Broad Balmer Lines (BBL) with the Boltzmann Plots (BP). These two types of S1 galaxies, that we call BP-S1 and NoBP-S1, are characterized, in first approximation, by Broad Line Regions (BLR) with different structural and physical properties. In this communication, we show that these features can be well pointed out by a multi-wavelength analysis of the continuum and of the broad recombination Hydrogen lines, that we carry out on a sample of objects detected at optical and X-ray frequencies. The investigation is addressed to verify whether BP-S1 are the ideal candidates for the study of the kinematical and structural properties of the BLR, in order to derive reliable estimates of the mass of their central engine and to constrain the properties of their nuclear continuum spectrum., Comment: 26 pages, 4 figures (1 multi-paged). Accepted for publication on Advances in Space Research. Contribution to the IX SCSLSA

Here we present an analysis of spectro-polarimetric observations of type 1.5 AGN Mrk 6, performed with 6m telescope SAO RAN in 12 epochs (2010 -- 2013). Additionally, the inter-stellar mater (ISM) polarization has been observed and its contribution to the AGN spectral polarization is taken into account. We measured Stokes parameters and determined the polarization parameters in 12 spectra with and without correction for the ISM polarization. We estimated the time lag between the unpolarized and polarized continuum flux variation of about ~2 days, that indicates a compact scattering region which contributes to the polarized continuum variability. The polarization in H{\alpha} is complex, showing three prominent components in the BLR, one redshifted around +3000 km/s that corresponds to the red shoulder in H{\alpha}, and two blue-shifted around -2000 km/s and -6000 km/s. We found that the ISM polarization has a very significant influence on the measured AGN polarization parameters. After correcting the observations for the ISM polarization we were able to detect the Keplerian motion in the BLR. We give a new method for the black hole mass estimation using spectro-polarimetric observation in the line profile, finding the black hole mass in Mrk 6 of $M_{BH} \sim 1.53 \cdot 10^8 M_{\odot}$, that is in a good agreement with reverberation estimates., Comment: Version submitted to MNRAS, after minor revision

We investigate the virilization of the emission lines Hbeta and Mg II in the sample of 287 Type 1 Active Galactic Nuclei taken from the Sloan Digital Sky Survey database. We explore the connections between the intrinsic line shifts and full widths at different levels of maximal intensity. We found that: (i) Hbeta seems to be a good virial estimator of black hole masses, and an intrinsic redshift of Hbeta is dominantly caused by the gravitational effect, (ii) there is an anti-correlation between the redshift and width of the wings of the Mg II line, (iii) the broad Mg II line can be used as virial estimator only at 50% of the maximal intensity, while the widths and intrinsic shifts of the line wings can not be used for this purpose., Comment: 24 pages, 8 figures, 4 tables, accepted in Astrophysics and Space Science

We report the results of the first long-term (1990-2014) optical spectro-photometric monitoring of a binary black hole candidate QSO E1821+643, a low-redshift high-luminosity radio-quiet quasar. In the monitored period the continua and H$\gamma$ fluxes changed for around two times, while the H$\beta$ flux changed around 1.4 times. We found the periodical variations in the photometric flux with the periods of 1200, 1850 and 4000 days, and 4500 days periodicity in the spectroscopic variations. However, the periodicity of 4000-4500 days covers only one cycle of variation and should be confirmed with a longer monitoring campaign. There is an indication of the period around 1300 days in the spectroscopic light curves, but with small significance level, while the 1850 days period could not be clearly identified in the spectroscopic light curves. The line profiles have not significantly changed, showing an important red asymmetry and broad line peak redshifted around +1000 km s$^{-1}$. However, H$\beta$ shows broader mean profile and has a larger time-lag ($\tau\sim120$ days) than H$\gamma$ ($\tau\sim60$ days). We estimate that the mass of the black hole is $\sim2.6\times10^9\rm M_\odot$. The obtained results are discussed in the frame of the binary black hole hypothesis. To explain the periodicity in the flux variability and high redshift of broad lines we discuss a scenario where dense gas-rich cloudy-like structures are orbiting around a recoiling black hole., Comment: Accepted in ApJS

We present observations of the H I tidal arm near a dwarf galaxy NGC 3077 (member of the M81 galaxy group) in the narrow-band [S II] and Hα filters. Observations were carried out in 2011 March with the 2 m RCC telescope at the NAO Rozhen, Bulgaria. Our search for possible supernova remnant candidates (identified as sources with enhanced [S II] emission relative to their Hα emission) in this region yielded no sources of this kind. Nevertheless, we found a number of objects with significant Hα emission that probably represent uncatalogued, low brightness H II regions.

We present observations of the nearby tidal dwarf galaxy Holmberg IX in M81 galaxy group in narrow band [SII] and H$\alpha$ filters, carried out in March and November 2008 with the 2m RCC telescope at NAO Rozhen, Bulgaria. Our search for resident supernova remnants (identified as sources with enhanced [SII] emission relative to their H$\alpha$ emission) in this galaxy yielded no sources of this kind, besides M&H 10-11 or HoIX X-1. Nevertheless, we found a number of objects with significant H$\alpha$ emission that probably represent uncatalogued HII regions., Comment: 8 pages, 5 figures

We present an extended analysis of the relation between radio surface brightness and diameter -- the so-called $\Sigma-D$ relation for planetary nebulae (PNe). We revise our previous derivation of the theoretical $\Sigma-D$ relation for the evolution of bremsstrahlung surface brightness in order to include the influence of the fast wind from the central star. Different theoretical forms are derived: $\Sigma \propto D^{-1}$ for the first and second phases of evolution and $\Sigma\propto D^{-3}$ for the final stage of evolution. Also, we analyzed several different Galactic PN samples. All samples are influenced by severe selection effects, but Malmquist bias seems to be less influential here than in the supernova remnant (SNR) samples. We derived empirical $\Sigma-D$ relations for 27 sample sets using 6 updated PN papers from which an additional 21 new sets were extracted. Twenty four of these have a trivial form of $\beta \approx 2$. However, we obtain one empirical $\Sigma-D$ relation that may be useful for determining distances to PNe. This relation is obtained by extracting a recent nearby (< 1 kpc) Galactic PN sample.

An analysis of the relation between radio surface brightness and diameter, so-called Sigma-D relation, for planetary nebulae (PNe) is presented: i) the theoretical Sigma-D relation for the evolution of bremsstrahlung surface brightness is derived; ii) contrary to the results obtained earlier for the Galactic supernova remnant (SNR) samples, our results show that the updated sample of Galactic PNe does not severely suffer from volume selection effect - Malmquist bias (same as for the extragalactic SNR samples) and; iii) we conclude that the empirical Sigma-D relation for PNe derived in this paper is not useful for valid determination of distances for all observed PNe with unknown distances., 4 pages, 2 figures

In this paper an analysis of the physical properties of the Broad Line Region (BLR) of the active galaxy NGC 5548 is presented. Using the photoionization code CLOUDY and the measurements of Peterson et al. (2002), the physical conditions of the BLR are simulated and the BLR temperature is obtained. This temperature was compared to the temperature estimated with the Boltzmann-Plot (BP) method (Popovic et al. 2007). It was shown that the measured variability in the BLR temperature could be due to the change in the hydrogen density.

Here we investigate light curves of the continuum and emission lines of five type 1 active galactic nuclei (AGN) from our monitoring campaign, to test time-evolution of their time delays. Using both modeled and observed AGN light curves, we apply Gaussian kernel-based estimator to capture variation of local patterns of their time evolving delays. The largest variations of time delays of all objects occur in the period when continuum or emission lines luminosity is the highest. However, Gaussian kernel-based method shows instability in the case of NGC 5548, 3C 390.3, E1821 + 643 and NGC 4051 possibly due to numerical discrepancies between damped random walk (DRW) time scale of light curves and sliding time windows of the method. The temporal variations of time lags of Arp 102B can correspond to the real nature of the time lag evolution.

The spectral variability of active galactic nuclei (AGN) is one of their key features that enables us to study in more details the structure of AGN emitting regions. Especially, the broad line profiles, that vary both in flux and shape, give us invaluable information about the kinematics and geometry of the broad line region (BLR) where these lines are originating from. We give here a comparative review of the line shape variability in a sample of five type 1 AGN, those with broad emission lines in their spectra, of the data obtained from the international long-term optical monitoring campaign coordinated by the Special Astrophysical Observatory of the Russian Academy of Science. The main aim of this campaign is to study the physics and kinematics of the BLR on a uniform data set, focusing on the problems of the photoionization heating of the BLR and its geometry, where in this paper we give for a first time a comparative analysis of the variabilty of five type 1 AGN, discussing their complex BLR physics and geometry in the framework of the estimates of the supermassive black hole mass in AGN., Accepted in Journal of Astrophysics and Astronomy, Springer

Here we present our investigation of the kinematic structure of the broad emission line region (BLR) in a sample of 14 single-peaked Active Galactic Nuclei (AGN), which have been previously observed in the X-ray (Fe Kα line) and where, according to the X-ray emission, a disk geometry is expected. To explain the BLR complex structure we apply a two component model assuming that line wings originate in a very broad line region (VLRB) and the line core in an intermediate line region (ILR). The VLRB is assumed to be an accretion disk. The model can well describe the complex line shapes of the considered sample of AGN.

In this work we study the physical and kinematical properties of the emission line region of Seyfert 1.5 galaxy Mrk 817 using three sets of observations, among which are high-resolution spectra obtained with the Isaac Newton Telescope on Canary Islands. We find that in Mrk 817 the Narrow (NEL) and Broad Emission Lines (BEL) are very complex, indicating that structure of both the Narrow (NLR) and Broad Line Region (BLR) is complex and consists of at least two sub-regions with different kinematical properties. We find that the BEL can be fitted with the two-component model, where the core of the line is coming from a spherical region with isotropic velocity distribution, and wings might be affected by a low inclined accretion disc (or disc-like emitting region). Also, we discuss the physical properties of the BLR. Moreover, we find that an outflow is present in the NLR, that may be driven by an approaching jet., Comment: 7 pages, 9 figures, accepted for publication in MNRAS

We present here new spectroscopic observations of Mrk 1040 and LEDA 212995 (Mrk 1040 companion) obtained with the Isaac Newton Telescope (INT). The intensity ratios and widths for the narrow emission lines found in LEDA 212995 are typical of H II regions. The red-shift (0.0169$\pm$0.00015) of the object derived from these emission lines is very close to the red-shift of Mrk 1040 (z=0.01665). The weak narrow and broad absorption lines were detected in the H$\alpha$ wavelength band of LEDA 212995 spectra. These absorptions indicate that the companion might be at least partly obscured by Mrk 1040. Using this and previous observations we discuss the possible physical relationship between these two galaxies., Comment: Astronomische Nachrichten, accepted

We investigate the intrinsic Baldwin effect (Beff) of the broad H$\alpha$ and H$\beta$ emission lines for six Type 1 active galactic nuclei (AGNs) with different broad line characteristics: two Seyfert 1 (NGC 4151 and NGC 5548), two AGNs with double-peaked broad line profiles (3C 390.3 and Arp 102B), one narrow line Seyfert 1 (Ark 564), and one high-luminosity quasar with highly red asymmetric broad line profiles (E1821+643). We found that a significant intrinsic Beff was present in all Type 1 AGNs in our sample. Moreover, we do not see strong difference in intrinsic Beff slopes in different types of AGNs which probably have different physical properties, such as inclination, broad line region geometry, or accretion rate. Additionally, we found that the intrinsic Beff was not connected with the global one, which, instead, could not be detected in the broad H$\alpha$ or H$\beta$ emission lines. In the case of NGC 4151, the detected variation of the Beff slope could be due to the change in the site of line formation in the BLR. Finally, the intrinsic Beff might be caused by the additional optical continuum component that is not part of the ionization continuum., Comment: 12 pages, 8 figures, Accepted for publication in A&A

We used the Z-transformed Discrete Correlation Function (ZDCF) and the Stochastic Process Estimation for AGN Reverberation (SPEAR) methods for the time series analysis of the continuum and the H${\alpha}$ and H${\beta}$ line fluxes of a sample of well known type 1 active galactic nuclei (AGNs): Arp 102B, 3C 390.3, NGC 5548, and NGC 4051, where the first two objects are showing double-peaked emission line profiles. The aim of this work is to compare the time lag measurements from these two methods, and check if there is a connection with other emission line properties. We found that the obtained time lags from H$\beta$ are larger than those derived from the H$\alpha$ analysis for Arp 102B, 3C 390.3 and NGC 5548. This may indicate that the H$\beta$ line originates at larger radii in these objects. Moreover, we found that the ZDCF and SPEAR time lags are highly correlated ($r \sim0.87$), and that the error ranges of both ZDCF and SPEAR time lags are correlated with the FWHM of used emission lines ($r\sim 0.7$). This increases the uncertainty of the black hole mass estimates using the virial theorem for AGNs with broader lines., Comment: Accepted for publication in Advances in Space Research

We investigate a long-term (26 years, from 1987 to 2013) variability in the broad spectral line properties of the radio galaxy Arp 102B, an active galaxy with broad double-peaked emission lines. We use observations presented in Paper I (Shapovalova et al. 2013) in the period from 1987 to 2011, and a new set of observations performed in 2012--2013. To explore the BLR geometry, and clarify some contradictions about the nature of the BLR in Arp 102B we explore variations in the H$\alpha$ and H$\beta$ line parameters during the monitored period. We fit the broad lines with three broad Gaussian functions finding the positions and intensities of the blue and red peaks in H$\alpha$ and H$\beta$. Additionally we fit averaged line profiles with the disc model. We find that the broad line profiles are double-peaked and have not been changed significantly in shapes, beside an additional small peak that, from time to time can be seen in the blue part of the H$\alpha$ line. The positions of the blue and red peaks { have not changed significantly during the monitored period. The H$\beta$ line is broader than H$\alpha$ line in the monitored period. The disc model is able to reproduce the H$\beta$ and H$\alpha$ broad line profiles, however, observed variability in the line parameters are not in a good agreement with the emission disc hypothesis. It seems that the BLR of Arp 102B has a disc-like geometry, but the role of an outflow can also play an important role in observed variation of the broad line properties., Comment: 17 pages, Accepted for publication in A&A

Aims. We analyze the ratios of the broad hydrogen Balmer emission lines (from Hα to He) in the context of estimating the physical conditions in the broad line region (BLR) of active galactic nuclei (AGNs). Methods. Our measurements of the ratios of the Balmer emission lines are obtained in three ways: i) using photoionization models obtained with a spectral synthesis code CLOUDY; ii) applying the recombination theory for hydrogenic ions; iii) measuring the lines in observed spectra taken from the Sloan Digital Sky Survey database. We investigate the Balmer line ratios in the framework of the so-called Boltzmann plot (BP), analyzing the physical conditions of the emitting plasma for which we could use the BP method. The BP considers the ratio of Balmer lines normalized to the atomic data of the corresponding line transition, and in that way differs from the Balmer decrement. Results. We find that for a certain range of thermodynamic parameters, there are objects that follow the BP. These AGNs may have a BLR consisting of mostly high density plasma.

Active galactic nuclei (AGNs) are objects hosting in their center a super-massive black hole (SMBH) with an accretion disk surrounded by gas and dust. The mass of an SMBH can be derived from the dynamics of the gas gravitationally bounded to the SMBH. This is the case for the broad line region (BLR), i.e. a photoionized gas in the vicinity of an SMBH that emits broad emission lines (BELs), which properties can be used to estimate the mass of the SMBH. In spite of a number of papers devoted to the BLR research, its true nature is not well known. Therefore, it is still important to investigate the BLR structure (size, geometry, physics, etc.), where one of the aims is to better constrain the mass of the SMBH in the center of AGNs. The BELs are the only signatures of the BLR physics and geometry. They can be clearly identified in AGN spectra and they often show complex profiles. Their fluxes, profiles and ratios can provide much information about the BLR geometry and physics. Moreover, the BELs and continuum flux are very often varying in AGNs. Therefore, an investigation of the BEL flux and profile variability during a long period is another useful tool for mapping the geometrical and dynamical structure of the BLR. In this review we present and discuss some tools and techniques for studying the structure of the BLR using broad emission line properties. peerReviewed

A study of the variability of the broad emission-line parameters of 3C390.3, an active galaxy with the double-peaked emission-line profiles, is presented. We give a detail analysis of variation in the broad Ha and Hb profiles, the ratios, and the Balmer decrement of different line segments. Studying the variability of the line profiles we explore the disk structure, that is assumed to emit the broad double-peaked Ha and Hb emission lines. We divided the observed spectra in two periods (before and after the outburst in 2002) and analyzed separately the variation in these two periods. First we analyzed the spectral emission-line profiles of Ha and Hb, measuring the peak positions. Then, we divided lines into several segments, and we measured the line-segment fluxes. The Balmer decrement variation for total Ha and Hb fluxes, as well as for the line segments has been investigated and discussed. We modeled the line parameters variation using an accretion disk model. We compared the variability in the observed line parameters with the disk model predictions and found that the variation in line profiles and in line segments corresponds to the emission of a disk-like BLR. But, also there is probably one additional emission component that contributes to the Ha and Hb line center. We found that the variation in the line profiles is caused by the variation in the parameters of the disk-like BLR, first of all in the inner (outer) radius which can well explain the line parameter variations in the Period I. The Balmer decrement across the line profile has a bell-like shape, and it is affected not only by physical processes in the disk, but also by different emitting disk dimension of the Ha and Hb line. The geometry of the BLR of 3C390.3 seems to be very complex, and inflows/outflows might be present, but it is evident that the broad line region with disk-like geometry has dominant emission., Comment: Accepted for publication by A&A

Narrow Line Seyfert 1 galaxies represent a distinct category in the larger family of Type 1 Active Galactic Nuclei. The occurrence of emission line profiles not broader than 2000 km/s, combined with luminosity estimates comparable to those of their broad line emitting analogues, suggests that some extreme property is characterizing the fueling of their central engines. Two hypotheses are more commonly considered: on the one hand, it was suggested that the peculiar features of NLS1s might be interpreted as the consequence of a nearly pole-on view over a geometrically flattened source; on the other, there are arguments favoring the interpretation of a relatively low mass black hole, accreting at very high rates. Both explanations provide advantages and drawbacks, but, in spite of the different assumed physics, they agree in identifying NLS1s as the crucial test ground for our understanding of the Broad Line Region structure and dynamics in AGN. Here we report the results obtained investigating asynchronous optical and X-ray spectroscopic observations, respectively extracted from the Sloan Digital Sky Survey and the XMM-Newton science archives, of a sample of both broad and narrow line emitting Seyfert 1 galaxies. Exploiting data collected by the different instruments carried on board XMM, we try to identify the various components which sum up in the observed broad band spectra of the two classes. We discuss the relation that thermal, non-thermal, line emission and broad band absorption components of the X-ray source show with the optical emission line profiles, as interpreted in the framework of a composite Broad Emission Line Region structural model., Comment: 15 pages, 5 figures (Fig. 4 with colors). Proceedings of "Narrow Line Seyfert 1 Galaxies and their Place in the Universe". To appear in Proceedings of Science

Here we discuss the physical conditions in the emission line regions (ELR) of active galactic nuclei (AGN), with the special emphasize on the unresolved problems, e.g. the stratification of the Broad Line Region (BLR) or the failure of the photoionization to explain the strong observed optical Fe II emission. We use here different line fluxes in order to probe the properties of the ELR, such as the hydrogen Balmer lines (Ha to He), the helium lines from two subsequent ionization levels (He II 4686 and He I 5876) and the strongest Fe II lines in the wavelength interval 4400-5400 \AA. We found that the hydrogen Balmer and helium lines can be used for the estimates of the physical parameters of the BLR, and we show that the Fe II emission is mostly emitted from an intermediate line region (ILR), that is located further away from the central continuum source than the BLR., Comment: 8 pages, 9 figures, 2 tables, New Astronomy Reviews (Proceeding of 7th SCSLSA), in press

International audience; We review recent developments in Serbian Virtual Observatory (SerVO) as well as developments surrounding Virtual Atomic and Molecular Data Center. Main components of SerVO are going to be the archive of photographic plates, database of Stark broadening parameters and stellar evolution database. Photographic plates were obtained at Belgrade Observatory from 1936 to 1996. Data for Stark broadening were obtained using semiclassical perturbation and modified semiempirical theories. Stellar evolution database is a mirror of Darthmouth evolution database with improvement and VO compatible outputs.

In this work we investigate the properties of the broad emission line components in the Balmer series of a sample of Type 1 Active Galactic Nuclei (AGN). Using the Boltzmann Plot method as a diagnostic tool for physical conditions in the plasma, we detect a relationship among the kinematical and thermo-dynamical properties of these objects. In order to further clarify the influence of the central engines on the surrounding material, we look for signatures of structure in the broad line emitting regions, that could affect the optical domain of the observed spectra. Using a combination of line profile analysis and kinematical modeling of the emitting plasma, we study how the emission line broadening functions are influenced by different structural configurations. The observed profiles are consistent with flattened structures seen at quite low inclinations, typically smaller than 20 degrees. Since this result is in good agreement with some independent observations at radio frequencies, we apply a new formalism to study the properties of AGN central engines., Comment: 8 pages, 11 figures. Proceedings of the VII Serbian Conference on Spectral Line Shapes in Astrophysics. Accepted by New Astronomy Reviews

In order to contribute to the general effort aiming at the improvement of our knowledge about the physical conditions within the broad-line regions (BLRs) of active galactic nuclei (AGNs), here we present the results achieved by our analysis of the spectral properties of a sample of 90 broad-line-emitting sources, collected from the Sloan Digital Sky Survey database. By focusing our attention mainly on the Balmer series of hydrogen emission lines, which is the dominant feature in the optical wavelength range of many BLR spectra, we extracted several flux and profile measurements, which we related to other source properties, such as optical continuum luminosity, inferred black hole mass, and accretion rate. Using the Boltzmann plot method to investigate the Balmer-line flux ratios as a function of the line profiles, we found that AGNs that emit broader lines typically have larger Hα/Hβ and smaller Hγ/Hβ and Hδ/Hβ line ratios. With the help of some recent investigations, we model the structure of the BLR, and we study the influence of the accretion process on the properties of BLR plasma.

Up to now, all direct observational checks of the theoretical [OIII] 5006.843/4958.511 intensity ratio have been made for photoionized gaseous nebulae spectra. However, in some papers analyzing spectra of quasars, galaxies and AGN, this ratio is obtained as by‐product, used as a checking method or may be derived from published results. Recently, taking into account relativistic corrections to the magnetic dipole operator, Storey and Zeippen obtained the line intensity ratio of 2.98. In order to check that new value using the AGN spectra, we present the measurements of flux ratio of [OIII] λ λ 4959, 5007 A emission lines for a sample of 62 AGN, obtained from SDSS Database and from the published observations. We selected the sample using criteria of high signal to noise ratio and that line shapes of 4959 and 5007 are the same. We found that flux ratio is 2.993 ± 0.014, which is in a good agreement with the theoretical value of 2.98 given by Storey and Zeippen (2000).

We present an investigation of the structure of the emission line region in a sample of 12 single-peaked Active Galactic Nuclei (AGNs). Using the high resolution H-beta and H-alpha line profiles observed with the Isaac Newton Telescope (La Palma) we study the substructure in the lines (such as shoulders or bumps) which can indicate a disk or disk-like emission in Broad Line Regions (BLRs). Applying Gaussian analysis we found that both kinds of emission regions, BLR and NLR, are complex. In this sample the narrow [OIII] lines are composites of two components; NLR1 which have random velocities from \sim 200 to 500 km/s and systematic velocities toward the blue from 20 to 350 km/s, and NLR2 with smaller random velocities (\sim 100-200 km/s) and a redshift corresponding to the cosmological one. The BLR also have complex structure and we apply a two-component model assuming that the line wings originate in a very broad line region (VBLR) and the line core in an intermediate line region (ILR). The VBLR is assumed to be an accretion disk and the ILR a spherical emission region. The model fits very well the H-alpha and H-beta line profiles of the AGNs., Comment: 11 pages, A&A, accpted