arXiv subjects

V. H. Chavushyan

Publications and source records attributed to V. H. Chavushyan.

At least 37 records · Page 2Linked to original sources

arXiv2010

Multi-band properties of superluminal AGN detected by Fermi/LAT

We perform a multi-band statistical analysis of core-dominated superluminal active galactic nuclei (AGN) detected with Fermi Large Area Telescope (LAT). The detection rate of $γ$-ray jets is found to be high for optically bright AGN. There is a significant correlation between the $γ$-ray luminosity and the optical nuclear and radio (15 GHz) luminosities of AGN. We report a well defined positive correlation between the $γ$-ray luminosity and the radio-loudness for quasars and BL Lacertae type objects (BL Lacs). The slope of the best-fit line is significantly different for quasars and BL Lacs. The relations between the optical and radio luminosities and the $γ$-ray loudness are also examined, showing a different behavior for the populations of quasars and BL Lacs. Statistical results suggest that the $γ$-ray, optical and radio emission is generated at different locations and velocity regimes along the parsec-scale jet.

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arXiv2010

Observational evidence for the link between the variable optical continuum and the subparsec-scale jet of the radio galaxy 3C 390.3

The mechanism and the region of generation of variable continuum emission are poorly understood for radio-loud AGN because of a complexity of the nuclear region. High-resolution radio VLBI (very long baseline interferometry) observations allow zooming into a subparsec-scale region of the jet in the radio-loud galaxy 3C 390.3. We combined the radio VLBI and the optical data covering the time period of 14 years to look for a link between optical flares and parsec-scale jet. We identify two stationary and nine moving radio features in the innermost subparsec-scale region of the jet. All nine ejections are associated with optical flares. We found a significant correlation (at a confidence level of $>99.99%$) between the ejected jet components and optical continuum flares. The epochs at which the moving knots pass through the location of a stationary radio feature and the optical light curve reaches the maximum are correlated. The radio events follow the maxima of optical flares with the mean time delay of $0.10\pm0.04$ years. This correlation can be understood if the variable optical continuum emission is generated in the innermost part of the jet. A possible mechanism of the energy release is the ejection of knots of high-energy electrons that are accelerated in the jet flow and generate flares of synchrotron continuum emission in the wide range of frequencies from radio to X-ray bands. In this scenario, the beamed optical continuum emission from the jet and counterjet ionizes a gas in a subrelativistic outflow surrounding the jet, which results in a formation of two outflowing conical regions with broad emission lines (in addition to the conventional broad line region around the central nucleus).

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arXiv2010

Spectral optical monitoring of 3C390.3 in 1995-2007: I. Light curves and flux variation of the continuum and broad lines

Here we present the results of the long-term (1995-2007) spectral monitoring of the broad line radio galaxy \object{3C~390.3}, a well known AGN with the double peaked broad emission lines, usually assumed to be emitted from an accretion disk. To explore dimensions and structure of the BLR, we analyze the light curves of the broad H$α$ and H$β$ line fluxes and the continuum flux. In order to find changes in the BLR, we analyze the H$α$ and H$β$ line profiles, as well as the change in the line profiles during the monitoring period. First we try to find a periodicity in the continuum and H$β$ light curves, finding that there is a good chance for quasi-periodical oscillations. Using the line shapes and their characteristics (as e.g. peaks separation and their intensity ratio, or FWHM) of broad H$β$ and H$α$ lines, we discuss the structure of the BLR. Also, we cross-correlate the continuum flux with H$β$ and H$α$ lines to find dimensions of the BLR. We found that during the monitoring period the broad emission component of the H$α$ and H$β$ lines, and the continuum flux varied by a factor of $\approx $4-5. Also, we detected different structure in the line profiles of H$α$ and H$β$. It seems that an additional central component is present and superposed to the disk emission. In the period of high activity (after 2002), H$β$ became broader than H$α$ and red wing of H$β$ was higher than the one of H$α$. We found time lags of $\sim$95 days between the continuum and H$β$ flux, and about 120 days between the continuum and H$α$ flux. Variation in the line profiles, as well as correlation between the line and continuum flux during the monitoring period is in the favor of the disk origin of the broad lines with the possible contribution of some additional region and/or some kind of perturbation in the disk.

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arXiv2010

Relativistic plasma as the dominant source of the optical continuum emission in the broad-line radio galaxy 3C 120

We report a relation between radio emission in the inner jet of the Seyfert galaxy 3C 120 and optical continuum emission in this galaxy. Combining the optical variability data with multi-epoch high-resolution very long baseline interferometry observations reveals that an optical flare rises when a superluminal component emerges into the jet and its maxima is related to the passage of such component through the location a stationary feature at a distance of ~1.3 parsecs from the jet origin. This indicates that a significant fraction of the optical continuum produced in 3C 120 is non-thermal and it can ionize material in a sub-relativistic wind or outflow. We discuss implications of this finding for the ionization and structure of the broad emission line region, as well as for the use of broad emission lines for determining black hole masses in radio-loud AGN.

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arXiv2009

Long-term variability of the optical spectra of NGC 4151: II. Evolution of the broad Ha and Hb emission-line profiles

Results of the long-term (11 years, from 1996 to 2006) H$α$ and H$β$ line variations of the active galactic nucleus of NGC 4151 are presented. High quality spectra (S/N>50 and R~8A) of H$α$ and H$β$ were investigated. We analyzed line profile variations during monitoring period. Comparing the line profiles of H$α$ and H$β$, we studied different details (bumps, absorption features) in the line profiles. The variations of the different H$α$ and H$β$ line profile segments have been investigated. Also, we analyzed the Balmer decrement for whole line and for line segments. We found that the line profiles were strongly changing during the monitoring period, showing blue and red asymmetries. This indicates a complex BLR geometry of NGC 4151 with, at least, three kinematically distinct regions: one that contributes to the blue line wing, one to the line core and one to the red line wing. Such variation can be caused by an accelerating outflow starting very close to the black hole, where the red part may come from the region {closer to the black hole than the blue part, which is coming} from the region having the highest outflow velocities. Taking into account the fact that the BLR of NGC 4151 has a complex geometry (probably affected by an outflow) and that a portion of the broad line emission seems to have not a pure photoionization origin, one can ask the question whether the study of the BLR by reverberation mapping may be valid in the case of this galaxy.

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arXiv2009

Spectroscopic monitoring of the Blazar 3C 454.3

We performed an optical spectroscopic monitoring of the blazar 3C 454.3 from September 2003 to July 2008. Sixteen optical spectra were obtained during different runs, which constitute the first spectroscopic monitoring done in the rest-frame UV region (z=0.859). An overall flux variation of the MgII (2800 A) by a factor ~ 3 was observed, while the corresponding UV continuum (F_cont at 3000 A) changed by a factor ~ 14. The MgII emission lines respond proportionally to the continuum variations when the source is in a low-activity state. In contrast, near the optical outbursts detected in 2005 and 2007, the MgII emission lines showed little response to the continuum flux variations. During the monitored period the UV FeII flux changed by a factor ~ 6 and correlated with F_cont (r = 0.92). A negative correlation between EW(Mg II) and F_cont was found, i.e. the so-called "Intrinsic Baldwin Effect".

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arXiv2009

Long term variability of the Broad Emission Line profiles in AGN

Results of a long-term monitoring ($\gtrsim 10$ years) of the broad line and continuum fluxes of three Active Galactic Nuclei (AGN), 3C 390.3, NGC 4151, and NGC 5548, are presented. We analyze the H$α$ and H$β$ profile variations during the monitoring period and study different details (as bumps, absorption bands) which can indicate structural changes in the Broad Line Region (BLR). The BLR dimensions are estimated using the time lags between the continuum and the broad lines flux variations. We find that in the case of 3C 390.3 and NGC 5548 a disk geometry can explain both the broad line profiles and their flux variations, while the BLR of NGC 4151 seems more complex and is probably composed of two or three kinematically different regions.

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arXiv2009

The Expanding Nebular Remnant of the Recurrent Nova RS Ophiuchi (2006): II. Modeling of Combined Hubble Space Telescope Imaging and Ground-based Spectroscopy

We report Hubble Space Telescope imaging, obtained 155 and 449 days after the 2006 outburst of the recurrent nova RS Ophiuchi, together with ground-based spectroscopic observations, obtained from the Observatorio Astronómico Nacional en San Pedro Mártir, Baja California, México and at the Observatorio Astrofísico Guillermo Haro, at Cananea, Sonora, México. The observations at the first epoch were used as inputs to model the geometry and kinematic structure of the evolving RS Oph nebular remnant. We find that the modeled remnant comprises two distinct co-aligned bipolar components; a low-velocity, high-density innermost (hour glass) region and a more extended, high-velocity (dumbbell) structure. This overall structure is in agreement with that deduced from radio observations and optical interferometry at earlier epochs. We find that the asymmetry observed in the west lobe is an instrumental effect caused by the profile of the HST filter and hence demonstrate that this lobe is approaching the observer. We then conclude that the system has an inclination to the line of sight of 39$^{+1}_{-10}$ degrees. This is in agreement with the inclination of the binary orbit and lends support to the proposal that this morphology is due to the interaction of the outburst ejecta with either an accretion disk around the central white dwarf and/or a pre-existing red giant wind that is significantly denser in the equatorial regions of the binary than at the poles. The second epoch HST observation was also modeled. However, as no spectra were taken at this epoch, it is more difficult to constrain any model. Nevertheless, we demonstrate that between the two HST epochs the outer dumbbell structure seems to have expanded linearly.

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arXiv2009

Jet-BLR connection in the radio galaxy 3C 390.3

Variations of the optical continuum emission in the radio galaxy 3C 390.3 are compared to the properties of radio emission from the compact, sub-parsec-scale jet in this object. We showed that very long-term variations of optical continuum emission (>10 years) is correlated with the radio emission from the base of the jet located above the disk, while the optical long-term variations (1-2 years) follows the radio flares from the stationary component in the jet with time delay of about 1 year. This stationary feature is most likely to be a standing shock formed in the continuous relativistic flow seen at a distance of ~0.4 parsecs from the base of the jet. To account for the correlations observed we propose a model of the nuclear region of 3C 390.3 in which the beamed continuum emission from the jet and counterjet ionizes material in a subrelativistic outflow surrounding the jet. This results in the formation of two conical regions with double-peaked broad emission lines (in addition to the conventional broad line region around the central nucleus) at a distance ~0.6 parsecs from the central engine.

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arXiv2008

Long-term variability of the optical spectra of NGC 4151: I. Light curves and flux correlations

Results of a long-term spectral monitoring of the active galactic nucleus of NGC 4151 are presented (11 years, from 1996 to 2006). High quality spectra (S/N>50 in the continuum near Halpha and Hbeta) were obtained in the spectral range ~4000 to 7500 Å, with a resolution between 5 and 15 A, using the 6-m and the 1-m SAO's telescopes (Russia), the GHAO's 2.1-m telescope (Cananea, Mexico), and the OAN-SPM's 2.1-m telescope (San-Pedro, Mexico). The observed fluxes of the Halpha, Hbeta, Hgamma and HeII emission lines and of the continuum at the observed wavelength 5117 A, were corrected for the position angle, the seeing and the aperture effects. We found that the continuum and line fluxes varied strongly (up to a factor 6) during the monitoring period. The emission was maximum in 1996-1998, and there were two minima, in 2001 and in 2005. The Halpha, Hgamma and He II fluxes were well correlated with the Hbeta flux. We considered three characteristic periods during which the Hbeta and Halpha profiles were similar: 1996-1999, 2000-2001 and 2002-2006. The line to continuum flux ratios were different; in particular during the first period, the lines were not correlated with the continuum and saturated at high fluxes. In the second and third period, where the continuum flux was small, the Halpha and Hbeta fluxes were well correlated to the continuum flux, meaning that the ionizing continuum was a good extrapolation of the optical continuum. The CCFs are often asymmetrical and the time lags between the lines and the continuum are badly defined indicating the presence of a complex BLR, with dimensions from 1 to 50 light-days.

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arXiv2007

Radio-Optical Study of Double-Peaked AGNs. I. 3C 390.3

We aim to test the model proposed to explain the correlation between the flux density at 15 GHz of a stationary component in the parsec-scale jet and the optical continuum emission in the radio galaxy 3C~390.3. In the model, the double-peaked emission from 3C~390.3 is likely to be generated both near the disk and in a rotating subrelativistic outflow surrounding the jet, due to ionization of the outflow by the beamed continuum emission from the jet. This scenario is chosen since broad-emission lines are observed to vary following changes in the inner radio jet. For recent epochs we have imaged and modelled the radio emission of the inner jet of 3C~390.3, which was observed with very long baseline interferometry at 15 GHz, 22 GHz and 43 GHz, to image the inner part of the parsec-scale jet, locate the exact region where the bulk of the continuum luminosity is generated and search for the mechanism that drives the double-peaked profile emission. We present the preliminary results of testing the model using data from 11 years of active monitoring of 3C~390.3.

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arXiv2007

Probing the physical properties of the NGC 5548 Broad Line Region using Balmer lines

We investigate the physical characteristics of the Broad Line Region (BLR) of NGC 5548 using the Boltzmann plot (BP) method, that we applied on the Balmer lines observed from 1996 to 2004. We find that variability earlier detected in the lines, is also present in the temperature parameter A, obtained from the BP method. Using the BP temperature parameter A to calculate temperature, we find that the average temperature for the considered period was T$\approx$ 10000 K, and that varies from 5000 K (in 2002) to 15000 K (in 1998). This variation correlates with the AGN-component of the optical continuum flux (r=0.85) and may indicate the existence of an accretion disc in the BLR of NGC 5548.

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arXiv2006

Complex emission line region of Mrk 817

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.

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arXiv2004

Radio-optical scrutiny of the central engine in compact AGN

We combine Very-Long-Baseline Interferometry (VLBI) data for $\sim100$ active galactic nuclei (AGN) available from the Very Large Baseline Array (VLBA) 2 cm imaging survey and optical spectroscopy to investigate the relationships in the emission-line region--central engine--radio jet system. Here, we present the diversity of spectral types among the brightest AGN in our sample. We also discuss correlations between the mass of the central engine and properties of the parsec-scale radio jet for 24 AGN selected by the presence of H$β$ broad-emission lines in their spectra.

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arXiv2004

Profile variability of the H-alpha and H-beta broad emission lines in NGC5548

Between 1996 and 2002, we have carried out a spectral monitoring program for the Seyfert galaxy NGC 5548. High quality spectra (S/N>50), covering the spectral range (4000-7500)AA were obtained with the 6 m and 1 m telescopes of SAO (Russia) and with the 2.1 m telescope GHO (Mexico). We found that both the flux in the lines and the continuum gradually decreased, reaching minimum values during May-June 2002. The mean, rms, and the averaged over years, observed and difference line profiles of H-alpha and H-beta reveal the double peaked structure at the radial velocity ~+-1000km/s. The relative intensity of these peaks changes with time. During 1996, the red peak was the brightest, while in 1998 - 2002, the blue peak became the brighter one. In 2000-2002 a distinct third peak appeared in the red wing of H-alpha and H-beta line profiles. The radial velocity of this feature decreased between 2000 and 2002 from ~+2500 km/s to ~+2000 km/s. The fluxes of the various parts of the line profiles are well correlated with each other and also with the continuum flux. Shape changes of the different parts of the broad line are not correlated with continuum variations and, apparently, are not related to reverberation effects. Changes of the integral Balmer decrement are, on average, anticorrelated with the continuum flux variations. This is probably due to an increasing role of collisional excitation as the ionizing flux decreases. Our results favor the formation of the broad Balmer lines in a turbulent accretion disc with large and moving "optically thick" inhomogeneities, capable of reprocessing the central source continuum.

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arXiv2004

Understanding the relationship between the environment of the black hole and the radio jet: optical spectroscopy of compact AGN

We aim to investigate the relationship between radio jet activity on parsec-scales and the characteristics of both the bright active galactic nuclei (AGN) and their broad line regions (BLR). For this purpose, we combine 2cm Very Long Baseline Array observations of AGN with their optical spectral observations. This would enable us to investigate the optical spectra of a set of 172 relativistically beamed, flat-spectrum AGN with the nuclear disk oriented near to the plane of sky. Here, we present first results from optical spectroscopic observations of the brightest AGN from the 2 cm VLBA survey, and show a diversity of their spectral morphologies.

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arXiv2004

Structure and kinematics of candidate double-barred galaxies

Results of optical and NIR spectral and photometric observations of a sample of candidate double-barred galaxies are presented. Velocity fields and velocity dispersion maps of stars and ionized gas, continuum and emission-line images were constructed from integral-field spectroscopy observations carried out at the 6m telescope (BTA) of SAO RAS, with the MPFS spectrograph and the scanning Fabry-Perot Interferometer. NGC2681 was also observed with the long-slit spectrograph of the BTA. Optical and NIR images were obtained at the BTA and at the 2.1m telescope (OAN, México). High-resolution images were retrieved from the HST data archive. Morphological and kinematic features of all 13 sample objects are described in detail. Attention is focused on the interpretation of observed non-circular motions of gas and stars in circumnuclear (one kiloparsec- scale) regions. We have shown first of all that these motions are caused by the gravitational potential of a large-scale bar. NGC3368 and NGC3786 have nuclear bars only, their isophotal twist at larger radii being connected with the bright spiral arms. Three cases of inner polar disks in our sample (NGC2681, NGC3368 and NGC5850) are considered. We found ionized-gas counter-rotation in the central kiloparsec of the lenticular galaxy NGC3945. Seven galaxies (NGC470, NGC2273, NGC2681, NGC3945, NGC5566, NGC5905, and NGC6951) have inner mini-disks nested in large-scale bars. Minispiral structures occur often in these nuclear disks. It is interesting that the majority of the observed, morphological and kinematical, features in the sample galaxies can be explained without the secondary bar hypothesis. Thus we suggest that a dynamically independent secondary bar is a rarer phenomenon than follows from isophotal analysis of the images only.

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arXiv2003

The Leo I Cloud: Secular nuclear evolution of NGC 3379, NGC 3384, and NGC 3368?

The central regions of the three brightest members of the Leo I galaxy group -- NGC 3368, NGC 3379, and NGC 3384 -- are investigated by means of 2D spectroscopy. In all three galaxies we have found separate circumnuclear stellar and gaseous subsystems -- more probably, disks -- whose spatial orientations and spins are connected to the spatial orientation of the supergiant intergalactic HI ring reported previously by Schneider et al. (1983) and Schneider (1985, 1989). In NGC 3368 the global gaseous disk seems also to be inclined to the symmetry plane of the stellar body, being probably of external origin. Although the rather young mean stellar age and spatial orientations of the circumnuclear disks in NGC 3379, NGC 3384, and NGC 3368 could imply their recent formation from material of the intergalactic HI cloud, the time scale of these secondary formation events, of order 3 Gyr, does not support the collision scenario of Rood & Williams (1985), but is rather in line with the ideas of Schneider (1985, 1989) regarding tidal interactions of the galaxies with the HI cloud on timescales of the intergroup orbital motions.

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