D. A. Morozova

Saint Petersburg State University, Sankt-Peterburg, St.-Petersburg, Russia

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Publications (45)98.46 Total impact

  • Proceedings of the International Astronomical Union 09/2015; 10(S313):33-38. DOI:10.1017/S1743921315001829
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    ABSTRACT: We present an analysis of the multiwavelength behaviour of the blazar OJ 248 at z = 0.939 in the period 2006–2013. We use low-energy data (optical, near-infrared, and radio) obtained by 21 observatories participating in the Gamma-Ray Large Area Space Telescope (GLAST)-AGILE Support Program of the Whole Earth Blazar Telescope, as well as data from the Swift (optical–UV and X-rays) and Fermi (γ-rays) satellites, to study flux and spectral variability and correlations among emissions in different bands. We take into account the effect of absorption by the Damped Lyman α intervening system at z = 0.525. Two major outbursts were observed in 2006–2007 and in 2012–2013 at optical and near-IR wavelengths, while in the high-frequency radio light curves prominent radio outbursts are visible peaking at the end of 2010 and beginning of 2013, revealing a complex radio–optical correlation. Cross-correlation analysis suggests a delay of the optical variations after the γ-ray ones of about a month, which is a peculiar behaviour in blazars. We also analyse optical polarimetric and spectroscopic data. The average polarization percentage P is less than 3 per cent, but it reaches ∼19 per cent during the early stage of the 2012–2013 outburst. A vague correlation of P with brightness is observed. There is no preferred electric vector polarization angle and during the outburst the linear polarization vector shows wide rotations in both directions, suggesting a complex behaviour/structure of the jet and possible turbulence. The analysis of 140 optical spectra acquired at the Steward Observatory reveals a strong Mg ii broad emission line with an essentially stable flux of 6.2 × 10− 15 erg cm− 2 s− 1 and a full width at half-maximum of 2053 km s− 1.
    Monthly Notices of the Royal Astronomical Society 07/2015; 450(3):2677. DOI:10.1093/mnras/stv823 · 5.23 Impact Factor
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    ABSTRACT: The results of multi-color photometric and polarization observations of the blazar S4 0954+658 carried out mainly in the Astronomical Institute of St. Petersburg State University and the Central Astronomical Observatory of the Russian Academy of Sciences in 2008-2012 are analyzed. Individual variable components that are responsible for the activity are distinguished; the power-law spectrum and high degree of polarization confirm that the emission is synchrotron radiation. Modeling the observed dependences between the parameters of the polarization and intensity is used to derive parameters of both the constant and the variable components of the radiation. The observed color variability (“the brighter, the bluer”) can be explained by the superposition of a red constant component and a bluer variable component with a constant relative spectral energy distribution.
    Astronomy Reports 06/2015; 59(6):551-562. DOI:10.1134/S1063772915050030 · 0.80 Impact Factor
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    ABSTRACT: A flare from the TeV blazar Mrk 421, occurring in March 2010, was observed for 13 consecutive days from radio to very high energy (VHE; E > 100 GeV) gamma-rays with MAGIC, VERITAS, Whipple, FermiLAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We model the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigate the physical parameters, and evaluate whether the observed broadband SED variability can be associated to variations in the relativistic particle population. Flux variability was remarkable in the X-ray and VHE bands while it was minor or not significant in the other bands. The one-zone SSC model can describe reasonably well the SED of each day for the 13 consecutive days. This flaring activity is also very well described by a two-zone SSC model, where one zone is responsible for the quiescent emission while the other smaller zone, which is spatially separated from the first one, contributes to the daily-variable emission occurring in X-rays and VHE gamma-rays. Both the one-zone SSC and the two-zone SSC models can describe the daily SEDs via the variation of only four or five model parameters, under the hypothesis that the variability is associated mostly to the underlying particle population. This shows that the particle acceleration and cooling mechanism producing the radiating particles could be the main one responsible for the broadband SED variations during the flaring episodes in blazars. The two-zone SSC model provides a better agreement to the observed SED at the narrow peaks of the low- and high-energy bumps during the highest activity, although the reported one-zone SSC model could be further improved by the variation of the parameters related to the emitting region itself ($\delta$, $B$ and $R$), in addition to the parameters related to the particle population.
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    ABSTRACT: We present results of 4 years of VLBA monitoring along with γ-ray and optical R-band photometric observations of 6 blazars (0420-014, 1156+295, 1222+216, PKS 1510-089, 1633+382 and CTA 102). We have analyzed total intensity images obtained with the VLBA at 43 GHz and investigated kinematic evolution of the pc-scale jets of the sources. For all sources we compare flux variations in the VLBI core and bright superluminal knots with γ-ray and optical light curves. The majority of γ-ray flares are coincident with the appearance of a new superluminal knot and/or a flare in the millimeter-wave core and at optical wavelengths. These results support the conclusion that for many flares in blazars the region of the enhanced γ-ray and optical emission is located in the vicinity or downstream of the mm-wave VLBI core.
    Proceedings of the International Astronomical Union 10/2014; 9(S304):249-251. DOI:10.1017/S1743921314003974
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    ABSTRACT: The blazar 1156+295 was active at gamma-ray energies, exhibiting three prominent flares during the year 2010. Here, we present results using the combination of broadband (X-ray through mm single dish) monitoring data and radio band imaging data at 43 GHz on the connection of gamma-ray events to the ejections of superluminal components and other changes in the jet of 1156+295. The kinematics of the jet over the interval 2007.0-2012.5 using 43 GHz Very Long Baseline Array observations, reveal the presence of four moving and one stationary component in the inner region of the blazar jet. The propagation of the third and fourth components in the jet corresponds closely in time to the active phase of the source in gamma rays. We briefly discuss the implications of the structural changes in the jet for the mechanism of gamma-ray production during bright flares. To localise the gamma-ray emission site in the blazar, we performed the correlation analysis between the 43 GHz radio core and the gamma-ray light curve. The time lag obtained from the correlation constrains the gamma-ray emitting region in the parsec-scale jet.
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    Astronomy and Astrophysics 09/2014; 569:A46. DOI:10.1051/0004-6361/201423484 · 4.48 Impact Factor
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    ABSTRACT: We present $\gamma$-ray, X-ray, ultraviolet, optical, and near-infrared light curves of 33 $\gamma$-ray bright blazars over four years that we have been monitoring since 2008 August with multiple optical, ground-based telescopes and the Swift satellite, and augmented by data from the Fermi Gamma-ray Space Telescope and other publicly available data from Swift. The sample consists of 21 flat-spectrum radio quasars (FSRQs) and 12 BL Lac objects (BL Lacs). We identify quiescent and active states of the sources based on their $\gamma$-ray behavior. We derive $\gamma$-ray, X-ray, and optical spectral indices, $\alpha_\gamma$, $\alpha_X$, and $\alpha_o$, respectively ($F_\nu\propto\nu^\alpha$), and construct spectral energy distributions (SEDs) during quiescent and active states. We analyze the relationships between different spectral indices, blazar classes, and activity states. We find (i) significantly steeper $\gamma$-ray spectra of FSRQs than for BL Lacs during quiescent states, but a flattening of the spectra for FSRQs during active states while the BL Lacs show no significant change; (ii) a small difference of $\alpha_X$ within each class between states, with BL Lac X-ray spectra significantly steeper than in FSRQs; (iii) a highly peaked distribution of X-ray spectral slopes of FSRQs at $\sim-$0.60, but a very broad distribution of $\alpha_X$ of BL Lacs during active states; (iv) flattening of the optical spectra of FSRQs during quiescent states, but no statistically significant change of $\alpha_o$ of BL Lacs between states; and (v) a positive correlation between optical and $\gamma$-ray spectral slopes of BL Lacs, with similar values of the slopes. We discuss the findings with respect to the relative prominence of different components of high-energy and optical emission as the flux state changes.
    The Astrophysical Journal 06/2014; 789(2). DOI:10.1088/0004-637X/789/2/135 · 6.28 Impact Factor
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    ABSTRACT: We present the results of optical (R band) photometric and polarimetric monitoring and Very Long Baseline Array (VLBA) imaging of the blazar S4 0954+658, along with Fermi and gamma;-ray data during a multi-waveband outburst in 2011 March-April. After a faint state with a brightness level R ~17.6 mag registered in the first half of January 2011, the optical brightness of the source started to rise and reached ~14.8 mag during the middle of March, showing flare-like behavior. The most spectacular case of intranight variability was observed during the night of 2011 March 9, when the blazar brightened by ~0.7 mag within ~7 hours. During the rise of the flux the position angle of optical polarization rotated smoothly over more than 300$\deg$. At the same time, within 1$\sigma$ uncertainty a new superluminal knot appeared with an apparent speed of 19.0$\pm$0.3 c. We have very strong evidence for association of this knot with the multi-waveband outburst in 2011 March-April. We also analyze the multi-frequency behavior of S4 0954+658 during a number of minor outbursts from August 2008 to April 2012. We find some evidence of connections between at least two more superluminal ejecta and near-simultaneous optical flares.
    The Astronomical Journal 06/2014; 148(3). DOI:10.1088/0004-6256/148/3/42 · 4.05 Impact Factor
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    ABSTRACT: We report on the ongoing outburst of the young variable V1180 Cas, which is known to display characteristics in common with EXor eruptive variables. We present results that support the scenario of an accretion-driven nature of the brightness variations of the object and provide the first evidence of jet structures around the source. We monitored the recent flux variations of the target in the Rc, J, H, and K bands. New optical and near-IR spectra taken during the current high state of V1180 Cas are presented, in conjunction with H2 narrow-band imaging of the source. Observed near-IR colour variations are analogous to those observed in EXors and consistent with excess emission originating from an accretion event. The spectra show numerous emission lines, which indicates accretion, ejection of matter, and an active disc. Using optical and near-IR emission features we derive a mass accretion rate of ~3 E-8 Msun/yr, which is an order of magnitude lower than previous estimates. In addition, a mass loss rate of ~4 E-9 and ~4 E-10 Msun/yr are estimated from atomic forbidden lines and H2, respectively. Our H2 imaging reveals two bright knots of emission around the source and the nearby optically invisible star V1180 Cas B, clearly indicative of mass-loss phenomena. Higher resolution observations of the detected jet will help to clarify whether V1180 Cas is the driving source and to determine the relation between the observed knots.
    Astronomy and Astrophysics 05/2014; 565. DOI:10.1051/0004-6361/201423962 · 4.48 Impact Factor
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    ABSTRACT: We perform optical photometric and polarimetric monitoring of flat spectrum radio quasar (FSRQ) PKS 1222+21 (4C 21.35, z=0.432) using 16" LX-200 telescope (St.Petersburg, Russia) and 70-cm AZT-8 (Crimea, Ukraine). During last month this quasar displays prominent activity. In the nights of 2014 February 24 and 25 it reached a level of R=13.86 and 13.80, correspondingly. These values can be compared to the quiescence level of R~15.7 recorded in 2012-2013.
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    ABSTRACT: Among more than fifty blazars detected in very high energy (VHE, E>100GeV) gamma-rays, only three belong to the subclass of Flat Spectrum Radio Quasars (FSRQs). MAGIC observed FSRQ PKS 1510-089 in February-April 2012 during a high activity state in the high energy (HE, E>100 MeV) gamma-ray band observed by AGILE and Fermi. MAGIC observations result in the detection of a source with significance of 6.0 sigma. In agreement with the previous VHE observations of the source, we find no statistically significant variability during the MAGIC observations in daily, weekly or monthly time scales. The other two known VHE FSRQs have shown daily scale to sub-hour variability. We study the multifrequency behaviour of the source at the epoch of MAGIC observation, collecting quasi-simultaneous data at radio and optical (GASP-WEBT and F-Gamma collaborations, REM, Steward, Perkins, Liverpool, OVRO and VLBA telescopes), X-ray (Swift satellite) and HE gamma-ray frequencies. The gamma-ray SED combining AGILE, Fermi and MAGIC data joins smoothly and shows no hint of a break. The multifrequency light curves suggest a common origin for the millimeter radio and HE gamma-ray emission and the HE gamma-ray flaring starts when the new component is ejected from the 43GHz VLBA core. The quasi-simultaneous multifrequency SED is modelled with a one-zone inverse Compton model. We study two different origins of the seed photons for the inverse Compton scattering, namely the infra-red torus and a slow sheath surrounding the jet around the VLBA core. Both models fit the data well. However, the fast HE gamma-ray variability requires that within the modelled large emitting region, there must exist more compact regions. We suggest that these observed signatures would be most naturally explained by a turbulent plasma flowing at a relativistic speed down the jet and crossing a standing conical shock.
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    ABSTRACT: The Fermi LAT detected an increase in γ-ray activity of the quasar 0836+710 (z=2.17) in Spring 2011 that culminated in a sharp γ-ray flare at the end of 2011 when the source reached a flux of 2.9×10-6 phot s-1cm-2 at 0.1-200 GeV. We monitor the quasar at optical wavelengths in photometric and polarimetric modes, at millimeter and centimeter wavelengths, and with the VLBA at 43 GHz. The optical brightness of the quasar increased by ~0.5 mag in R band and the degree of polarization oscillated between ~1% and ~6% during the highest γ-ray state, while the position angle of polarization rotated by ~300°. We have identified in the VLBA images a strong, highly polarized component that moves with an apparent speed of ~20 c. The component emerged from the core in the beginning of the γ-ray event and reached a flux maximum at the peak of the γ-ray outburst. We present the results of a correlative analysis of variations at different wavelengths along with the kinematic parameters of the parsec scale jet. We discuss the location of the high γ-ray emission in the relativistic jet, as well as the emission mechanisms responsible for γ-ray production.
    The European Physical Journal Conferences 12/2013; 61:04003-. DOI:10.1051/epjconf/20136104003
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    ABSTRACT: Since the launch of the Fermi satellite, BL Lacertae has been moderately active at γ-rays and optical frequencies until 2011 May, when the source started a series of strong flares. The exceptional optical sampling achieved by the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope in collaboration with the Steward Observatory allows us to perform a detailed comparison with the daily γ-ray observations by Fermi. Discrete correlation analysis between the optical and γ-ray emission reveals correlation with a time lag of 0 ± 1 d, which suggests cospatiality of the corresponding jet emitting regions. A better definition of the time lag is hindered by the daily gaps in the sampling of the extremely fast flux variations. In general, optical flares present more structure and develop on longer time-scales than corresponding γ-ray flares. Observations at X-rays and at millimetre wavelengths reveal a common trend, which suggests that the region producing the mm and X-ray radiation is located downstream from the optical and γ-ray-emitting zone in the jet. The mean optical degree of polarization slightly decreases over the considered period and in general it is higher when the flux is lower. The optical electric vector polarization angle (EVPA) shows a preferred orientation of about 15°, nearly aligned with the radio core EVPA and mean jet direction. Oscillations around it increase during the 2011-2012 outburst. We investigate the effects of a geometrical interpretation of the long-term flux variability on the polarization. A helical magnetic field model predicts an evolution of the mean polarization that is in reasonable agreement with the observations. These can be fully explained by introducing slight variations in the compression factor in a transverse shock waves model.
    Monthly Notices of the Royal Astronomical Society 12/2013; 436(2):1530-1545. DOI:10.1093/mnras/stt1672 · 5.23 Impact Factor
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    ABSTRACT: We analyze total and polarized intensity images of the quasar PKS 0420-014 obtained monthly with the VLBA at 43 GHz during 2008-2012 along with γ-ray data provided by the Fermi Large Area Telescope and multi-color photometric and polarimetric measurements collected by different optical telescopes. During this period the quasar underwent a number of optical flares, which were accompanied by rapid rotation of polarization angle, an increase of activity in γ-rays, and the appearance of new superluminal knots in the parsec-scale jet. We investigate the fine structure of the flares at different wavelengths and in polarized light, and determine kinematic parameters of the knots. We compare the rapid evolution of the optical polarization with the polarization of the VLBI core and knots. We interpret the multi-wavelength behavior within a model that places the blazar "dissipation zone" at the millimeter-wave core of the parsec-scale jet.
    The European Physical Journal Conferences 12/2013; 61:07008-. DOI:10.1051/epjconf/20136107008
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    ABSTRACT: We present results of 4 years of VLBA monitoring along with γ-ray and optical R-band photometric observations of 6 BL Lac objects (3C 66A, S5 0716+71, PKS 0735+17, S4 0954+68, W Com, and OT 081). We have analyzed total intensity images obtained with the VLBA at 43 GHz and investigated the kinematic evolution of the parsec scale jets of the sources. For all sources we compare flux variations in the VLBI core and bright superluminal knots with γ-ray and optical light curves. The majority of γ-ray flares have optical counterparts. 67% of the γ-ray events are coincident with the appearance of new superluminal knots and/or flares in the millimeter-wave core. These results support the conclusion that for many flares in blazars the region of the γ-ray and optical emission is located in the vicinity or downstream of the mm-wave VLBI core.
    The European Physical Journal Conferences 12/2013; 61:04018-. DOI:10.1051/epjconf/20136104018
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    ABSTRACT: After a few years of quiescence, the blazar CTA 102 underwent a large outburst in the fall of 2012. The flare has been tracked from γ-rays to near-infrared, including Fermi and Swift data as well as polarimetric data from several observatories. An intensive GASP-WEBT collaboration campaign in optical and NIR bands, with the addition of previously unpublished archival data, allows comparison of this outburst with the previous activity period of this blazar in the early 2000s. We find remarkable similarity between the optical and γ-ray behavior of CTA 102 during the outburst, without any time lag between the two light curves, indicating co-spatiality of the optical and γ-ray emission regions. A strong harder-when-brighter spectral dependence is seen both in γ-rays and optical. The polarimetric behavior of CTA 102 during the outburst conforms with a shock-in-jet interpretation.
    The European Physical Journal Conferences 12/2013; 61:04019-. DOI:10.1051/epjconf/20136104019
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    ABSTRACT: Quasar 3C 279 is known to exhibit episodes of optical polarization angle rotation. We present new, well-sampled optical polarization data for 3C 279 and introduce a method to distinguish between random and deterministic electric vector position angle (EVPA) variations. We observe EVPA rotations in both directions with different amplitudes and find that the EVPA variation shows characteristics of both random and deterministic cases. Our analysis indicates that the EVPA variation is likely dominated by a random process in the low brightness state of the jet and by a deterministic process in the flaring state.
    The European Physical Journal Conferences 11/2013; 61. DOI:10.1051/epjconf/20136106003
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    ABSTRACT: In addition to ATel#5411 and in reference to ATel#5412 and ATel#5418 we report that recently announced flare of the blazar 3C 454.3 seems to have culminated at 2013 September 25. Our optical (AZT-8, Crimea) and NIR (AZT-24, Campo Imperatore, Italy) photometric measurements taken this night yield, correspondingly, R=13.427 at JD2456561.336 and J=11.67 at JD2456561.259. Afterwards we see a clear decline (0.1 mag) in all bands.
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    ABSTRACT: We analyze the multifrequency behavior of the quasar 3C 454.3 during three prominent \gamma-ray outbursts: 2009 Autumn, 2010 Spring, and 2010 Autumn. The data reveal a repeating pattern, including a triple flare structure, in the properties of each \gamma-ray outburst, which implies similar mechanism(s) and location for all three events. The multi-frequency behavior indicates that the lower frequency events are co-spatial with the \gamma-ray outbursts, although the \gamma-ray emission varies on the shortest timescales. We determine that the variability from UV to IR wavelengths during an outburst results from a single synchrotron component whose properties do not change significantly over the different outbursts. Despite a general increase in the degree of optical linear polarization during an outburst, the polarization drops significantly at the peak of the \gamma-ray event, which suggests that both shocks and turbulent processes are involved. We detect two disturbances (knots) with superluminal apparent speeds in the parsec-scale jet associated with the outbursts in 2009 Autumn and 2010 Autumn. The kinematic properties of the knots can explain the difference in amplitudes of the \gamma-ray events, while their millimeter-wave polarization is related to the optical polarization during the outbursts. We interpret the multi-frequency behavior within models involving either a system of standing conical shocks or magnetic reconnection events located in the parsec-scale millimeter-wave core of the jet. We argue that \gamma-ray outbursts with variability timescales as short as ~ 3 hr can occur on parsec scales if flares take place in localized regions such as turbulent cells.
    The Astrophysical Journal 07/2013; 773(2). DOI:10.1088/0004-637X/773/2/147 · 6.28 Impact Factor