S. G. Sergeev

REVERBERATION MAPPING MEASUREMENTS OF BLACK HOLE MASSES IN SIX LOCAL SEYFERT GALAXIES

We present the final results from a high sampling rate, multi-month, spectrophotometric reverberation mapping campaign undertaken to obtain either new or improved Hβ reverberation lag measurements for several relatively low-luminosity active galactic nuclei (AGNs). We have reliably measured the time delay between variations in the continuum and Hβ emission line in six local Seyfert 1 galaxies. These measurements are used to calculate the mass of the supermassive black hole at the center of each of these AGNs. We place our results in context to the most current calibration of the broad-line region (BLR) RBLR–L relationship, where our results remove outliers and reduce the scatter at the low-luminosity end of this relationship. We also present velocity-resolved Hβ time-delay measurements for our complete sample, though the clearest velocity-resolved kinematic signatures have already been published.

Lag-Luminosity Relationship for Interband Lags between Variations in B, V, R, and I Bands in Active Galactic Nuclei

We determine interband lags between variations in the B band and variations in the V, R, and I bands for 14 active galactic nuclei observed at the Crimean Astrophysical Observatory. The computed lags range from tenths of a day to several days, and it is positive (that is, V, R, and I bands lag behind the B band) in most cases, except for a few cases for the V filter. In some cases, the lag is greater than zero, with more than 3 σ confidence. The lag is systematically less for the V filter than for the red filters, and the lag determined from the cross-correlation function (CCF) centroid is systematically greater than the lag determined from the CCF peak. We find that the lag scales with luminosity as Lb, where b ≈ 0.4-0.5. We attribute this lag to the light time travel effect, so it reflects the geometrical size of the region that emits optical continuum. We consider a model in which optical emission is mainly reprocessed emission that arises in the accretion disk heated by an X-ray source above the disk.

SPACE TELESCOPE AND OPTICAL REVERBERATION MAPPING PROJECT. III. OPTICAL CONTINUUM EMISSION AND BROADBAND TIME DELAYS IN NGC 5548

The LBT is an international collaboration among institutions nin the United States, Italy and Germany. LBT Corporation npartners are: The Ohio State University, and The Research nCorporation, on behalf of The University of Notre Dame, University nof Minnesota and University of Virginia; The University nof Arizona on behalf of the Arizona university system; nIstituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, nGermany, representing the Max-Planck Society, the nAstrophysical Institute Potsdam, and Heidelberg University. nThis paper used data obtained with the MODS spectrographs nbuilt with funding from National Science Foundation (NSF) ngrant AST-9987045 and the NSF Telescope System Instrumentation nProgram (TSIP), with additional funds from the Ohio nBoard of Regents and the Ohio State University Office of Research. nThis paper made use of the modsIDL spectral data nreduction pipeline developed in part with funds provided by nNSF Grant AST - 1108693. nThe Liverpool Telescope is operated on the island of La nPalma by Liverpool John Moores University in the Spanish nObservatorio del Roque de los Muchachos of the Instituto de nAstrofisica de Canarias with financial support from the UK nScience and Technology Facilities Council. nKAIT and its ongoing operation were made possible by donations nfrom Sun Microsystems, Inc., the Hewlett-Packard nCompany, AutoScope Corporation, Lick Observatory, the nNSF, the University of California, the Sylvia and Jim Katzman nFoundation, and the TABASGO Foundation. Research at nLick Observatory is partially supported by a generous gift from nGoogle. nSupport for HST program number GO-13330 was provided nby NASA through a grant from the Space Telescope Science nInstitute, which is operated by the Association of Universities nfor Research in Astronomy, Inc., under NASA contract nNAS5-26555. M.M.F., G.D.R., B.M.P., C.J.G., and R.W.P. nare grateful for the support of the NSF through grant AST- n1008882 to The Ohio State University. A.J.B. and L.P. have nbeen supported by NSF grant AST-1412693. A.V.F. and W.- nK.Z. are grateful for financial assistance from NSF grant AST- n1211916, the TABASGO Foundation, and the Christopher R. nRedlich Fund. M.C. Bentz gratefully acknowledges support nthrough NSF CAREER grant AST-1253702 to Georgia State nUniversity. M.C. Bottorff acknowledges HHMI for support nthrough an undergraduate science education grant to Southwestern nUniversity. K.D.D. is supported by an NSF Fellowship nawarded under grant AST-1302093. R.E. gratefully acknowledges nsupport from NASA under awards NNX13AC26G, nNNX13AC63G, and NNX13AE99G. J.M.G. gratefully acknowledges nsupport from NASA under award NNH13CH61C. nP.B.H. is supported by NSERC. M.I. acknowledges support nfrom the Creative Initiative program, No. 2008-0060544, of nthe National Research Foundation of Korea (NRFK) funded nby the Korean government (MSIP). M.D.J. acknowledges NSF ngrant AST-0618209 used for obtaining the 0.91 m telescope at nWMO. SRON is financially supported by NWO, the Netherlands nOrganization for Scientific Research. B.C.K. is partially nsupported by the UC Center for Galaxy Evolution. C.S.K. acknowledges nthe support of NSF grant AST-1009756. D.C.L. nacknowledges support from NSF grants AST-1009571 and nAST-1210311, under which part of this research (photometric nobservations collected at MLO) was carried out. We thank nNhieu Duong, Harish Khandrika, Richard Mellinger, J. Chuck nHorst, Steven Armen, and Eddie Garcia for assistance with the nMLO observations. P.L. acknowledges support from Fondecyt ngrant #1120328. A.P. acknowledges support from a NSF graduate nfellowship, a UCSB Dean’s Fellowship, and a NASA Einstein nFellowship. J.S.S. acknowledges CNPq, National Council nfor Scientific and Technological Development (Brazil) for npartial support and The Ohio State University for warm hospitality. nT.T. has been supported by NSF grant AST-1412315. nT.T. and B.C.K. acknowledge support from the Packard Foundation nin the form of a Packard Research Fellowship to T.T.; nalso, T.T. thanks the American Academy in Rome and the Observatory nof Monteporzio Catone for kind hospitality. The nDark Cosmology Centre is funded by the Danish National nResearch Foundation. M.V. gratefully acknowledges support nfrom the Danish Council for Independent Research via grant nno. DFF–4002-00275. J.-H.W. acknowledges support by the nNational Research Foundation of Korea (NRF) grant funded nby the Korean government (No. 2010-0027910). E.D.B. is nsupported by Padua University through grants 60A02-5857/13, n60A02-5833/14, 60A02-4434/15, and CPDA133894. K.H. acknowledges nsupport from STFC grant ST/M001296/1. S.A.K. nthanks Dr. I. A. Rakhimov, the Director of Svetloe Observatory, nfor his support and hospitality. nThis research has made use of the NASA/IPAC Extragalactic nDatabase (NED), which is operated by the Jet Propulsion nLaboratory, California Institute of Technology, under contract nwith NASA.

Multiwavelength Monitoring of the Narrow-Line Seyfert 1 Galaxy Arakelian 564. III. Optical Observations and the Optical-UV-X-Ray Connection

We present the results of a 2 yr long optical monitoring program of the narrow-line Seyfert 1 galaxy Ark 564. The majority of this monitoring project was also covered by X-ray observations (RXTE), and for a period of ~50 days, we observed the galaxy in UV (HST) and X-rays (RXTE and ASCA) simultaneously with the ground-based observations. Rapid and large-amplitude variations seen in the X-ray band, on a daily and hourly timescale, were not detected at optical and UV wavelengths, which in turn exhibited much lower variability either on short (1 day) or long (several months) timescales. The only significant optical variations can be described as two 2-4 day events with ~10% flux variations. We detect no significant optical line variations and thus cannot infer a reverberation size for the broad-line region. Similarly, the large X-ray variations seem to vanish when the light curve is smoothed over a period of 30 days. The UV continuum follows the X-rays with a lag of ~0.4 days, and the optical band lags the UV band by ~2 days. No significant correlation was found between the entire X-ray data set and the optical band. Focusing on a 20 day interval around the strongest optical event we detect a significant X-ray-optical correlation with similar events seen in the UV and X-rays. Our data are consistent with reprocessing models on the grounds of the energy emitted in this single event. However, several large X-ray flares produced no corresponding optical emission.

THE BRIGHTEST GAMMA-RAY FLARING BLAZAR IN THE SKY: AGILE AND MULTI-WAVELENGTH OBSERVATIONS OF 3C 454.3 DURING 2010 NOVEMBER

Since 2005, the blazar 3C 454.3 has shown remarkable flaring activity at all frequencies, and during the last four years it has exhibited more than one ?-ray flare per year, becoming the most active ?-ray blazar in the sky. We present for the first time the multi-wavelength AGILE, Swift, INTEGRAL, and GASP-WEBT data collected in order to explain the extraordinary ?-ray flare of 3C 454.3 which occurred in 2010 November. On 2010 November 20 (MJD 55520), 3C 454.3 reached a peak flux (E >100?MeV) of Fp ? = (6.8 ? 1.0) ? 10?5?photons cm?2 s?1? on a timescale of about 12 hr, more than a factor of six higher than the flux of the brightest steady ?-ray source, the Vela pulsar, and more than a factor of three brighter than its previous super-flare on 2009 December 2-3. The multi-wavelength data make possible a thorough study of the present event: the comparison with the previous outbursts indicates a close similarity to the one that occurred in 2009. By comparing the broadband emission before, during, and after the ?-ray flare, we find that the radio, optical, and X-ray emission varies within a factor of 2-3, whereas the ?-ray flux by a factor of 10. This remarkable behavior is modeled by an external Compton component driven by a substantial local enhancement of soft seed photons.

Twelve years of X-ray and optical variability in the Seyfert galaxy NGC 4051

We discuss the origin of the optical variations in the narrow-line Seyfert 1 galaxy NGC 4051 and present the results of a cross-correlation study using X-ray and optical light curves spanning more than 12 years. The emission is highly variable in all wavebands, and the amplitude of the optical variations is found to be smaller than that of the X-rays, even after correcting for the contaminating host galaxy flux falling inside the photometric aperture. The optical power spectrum is best described by an unbroken power-law model with slope α= 1.4+0.6−0.2 and displays lower variability power than the 2–10 keV X-rays on all time-scales probed. We find the light curves to be significantly correlated at an optical delay of 1.2+1.0−0.3 d behind the X-rays. This time-scale is consistent with the light traveltime to the optical emitting region of the accretion disc, suggesting that the optical variations are driven by X-ray reprocessing. We show, however, that a model whereby the optical variations arise from reprocessing by a flat accretion disc cannot account for all the optical variability. There is also a second significant peak in the cross-correlation function, at an optical delay of 39+2.7−8.4 d. The lag is consistent with the dust sublimation radius in this source, suggesting that there is a measurable amount of optical flux coming from the dust torus. We discuss the origin of the additional optical flux in terms of reprocessing of X-rays and reflection of optical light by the dust.

Thirty years of continuum and emission-line variability in NGC 5548

We analyze a total of 827 optical spectra of NGC 5548 obtained over the 30 year period 1972-2001 for the purpose of studying the long-term behavior of the broad Hβ line profile. The variability characteristics, such as mean continuum and emission-line fluxes, rms variability amplitude, autocorrelation functions, and cross-correlation results, are found to be similar for CCD spectra obtained during the period 1989-2001 and for archival pre-CCD spectra from 1972 to 1988. The only significant difference between these two sets of data is that the mean Hβ flux is higher for 1972-1988. While the Hβ profile can vary dramatically on timescales of months to years, the mean profiles for these two periods are similar, but not identical. We searched for correlations among Hβ profile parameters (such as line width, line centroid, blue-to-red ratio of the line wing fluxes) and investigated their relationship to the continuum flux. Only trivial correlations were found, specifically the correlation between continuum and line fluxes and the anticorrelation between line width and line flux, the latter following from the former and from the inverse correlation between line time lag and line width expected for gravitationally dominated motion.

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.

Variability of the Broad Balmer Emission Lines in 3C 390.3 from 1992 to 2000

We describe the results of an optical spectral monitoring campaign on the Seyfert galaxy 3C 390.3 carried out with a CCD spectrograph at the 2.6 m Shajn Telescope of the Crimean Astrophysical Observatory in 1992-2000. Light curves for the Hα and Hβ emission lines and for the continuum in both the Hα and Hβ spectral regions are given. The lag between the continuum and Hβ emission-line variations (specifically the cross-correlation centroid τcent) is found to be τcent = 89 days, more than twice the lag found in an earlier investigation by Dietrich et al. We attribute this discrepancy to the difference between continuum autocorrelation functions for these two time series, which have very different durations. We show that a single emission-line transfer function is able to reproduce both cross-correlation results. The recovered transfer function for the Hβ line has a peak at a lag of 20 days, a tail that extends up to 300 days, and little or no correlation near zero lag. We find that the Hα line, which varies with a markedly lower amplitude than Hβ, has a lag of τcent = 162 days. We find no significant difference in lag between the blue and red wings of either Hα or Hβ, effectively ruling out kinematics dominated by simple radial motion. However, emission-line profile variations were clearly detected over the duration of the monitoring campaign. The mean and rms profiles computed for three selected time intervals are significantly different and show no correlation between profile width and continuum flux. Over the duration of the campaign, the red central part of the line profiles strongly decreased with respect to the total line flux. Moreover, the red bump nearly completely disappeared, while the blue bump has become more prominent. We find that some discrete profile features appear to propagate across the line profile, and we see such features moving in both directions, blue to red and vice versa. Variations in two profile segments at line-of-sight velocity ±(7500-9500) km s-1 are found to be poorly correlated with variations in the continuum or in other profile segments. Our conjecture is that the observed evolution of the Balmer line profiles in 3C 390.3 may be the result of the rotational redistribution of matter in a Keplerian disk and changes in the relative strength of an additional line component that dominates in the red central part of the profile. We conclude that the evolution of the broad-line profiles in 3C 390.3 in the context of the current models of the broad-line region remains unclear.

SPACE TELESCOPE AND OPTICAL REVERBERATION MAPPING PROJECT. IV. ANOMALOUS BEHAVIOR OF THE BROAD ULTRAVIOLET EMISSION LINES IN NGC 5548

NASA through Space Telescope Science Institute [GO-13330]; NASA [NAS5-26555, NNX13AC26G, NNX13AC63G, NNX13AE99G, NNH13CH61C]; National Science Foundation (NSF) [AST-1008882]; NSF [AST-1412693, AST-1211916, AST-1302093, AST0618209, AST-1009756, AST-1009571, AST-1210311, AST-1412315]; TABASGO Foundation; Christopher R. Redlich Fund; NSF CAREER grant [AST-1253702]; NSERC; UK Science and Technology Facilities Council [ST/J001651/1]; Creative Initiative program of the National Research Foundation of Korea (NRFK) - Korean government (MSIP) [2008-0060544]; NWO, the Netherlands Organization for Scientific Research; UC Center for Galaxy Evolution; Fondecyt [1120328]; UCSB; CNPq, National Council for Scientific and Technological Development (Brazil); Packard Foundation; Danish National Research Foundation; Danish Council for Independent Research [DFF4002-00275]; National Research Foundation of Korea (NRF) - Korean government [2010-0027910]; HHMI