BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:What can we learn from correlated radio and X-ray variability? DTSTART;VALUE=DATE-TIME:20230626T133000Z DTEND;VALUE=DATE-TIME:20230626T134500Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-863@cern.ch DESCRIPTION:Speakers: Ari Laor (Technion)\nHigh frequency radio emission m ay originate from scales as small as the\ninnermost accretion disk\, and c an thus probe directly the relativistic electrons\nand the magnetic fields in the coronal gas of radio quiet AGN.\n\nI will present simulations of t he time evolution of the distribution functions of\nrelativistic electrons following their injection due to a coronal reconnection event.\nThe elect rons cool through Compton scattering\, producing a pulse of X-ray\nemissio n\, and through synchrotron emission\, producing a pulse of high frequency \nradio emission. Future simultaneous monitoring of X-ray and mm emission may allow \nto probe directly the coronal heating and cooling mechanisms. \n\nI wil also briefly point out the false detections of correlated variab ility when two\nred light curves are correlated\, as we found in a recent study of simultaneous radio\nand X-ray observation of three AGN. I will al so describe how these biases can be \nminimised in future studies.\n\nhtt ps://indico.unina.it/event/61/contributions/863/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/863/ END:VEVENT BEGIN:VEVENT SUMMARY:Review: Continuum reverberation variability of AGN DTSTART;VALUE=DATE-TIME:20230626T074500Z DTEND;VALUE=DATE-TIME:20230626T081500Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-907@cern.ch DESCRIPTION:Speakers: Ian McHardy (University of Southampton)\nDetermining the inner geometry of AGN - i.e. the size and location of the central X- ray emitting corona relative to the accretion disc\, the shape\, size and structure of the disc\, the location of the broad line region and its poss ible connection with disc winds\, the location and structure of obscuring material - remains one of the main challenges of astrophysical research. A part from M87 and SgrA*\, whose very inner regions have been imaged by mil limetre global VLBI\, these inner structures are far too small for direct X-ray or optical imaging. We therefore use the technique of 'reverberation mapping'. Here the time lag between direct X-ray emission and lower energ y (UV/optical) emission\, produced by reprocessing of X-rays by the surrou nding material\, gives us the distance from the central X-ray source to th e surrounding material. By measuring that lag in multiple wavebands\, corr esponding to material at a range of temperatures\, we are able to map out at least the temperature structure of the surround material. We can then c ompare our observed structure with the structure that we expect based on t heoretical models of these structures and hence determine whether the mode ls are correct. I will review the observations that have been carried out and their implications for our understanding of the inner geometries of AG N.\n\nhttps://indico.unina.it/event/61/contributions/907/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/907/ END:VEVENT BEGIN:VEVENT SUMMARY:The multifaceted variability of the Seyfert AGN MCG+08-11-11 DTSTART;VALUE=DATE-TIME:20230626T083000Z DTEND;VALUE=DATE-TIME:20230626T084500Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-881@cern.ch DESCRIPTION:Speakers: Daniel Kynoch (University of Southampton)\nOver the last decade reverberation mapping (RM) campaigns of active galactic nuclei (AGN) have enabled us to probe their inner regions in unprecedented detai l. Whilst observations have broadly confirmed that the short-term variabil ity of the accretion disc is driven by variations in the X-ray corona a nu mber of puzzles have also emerged\, including: the contribution of the bro ad line region (BLR) to measured lags\; the implied large disc sizes\; the role of disc winds as obscurers or additional reprocessors\; and unexpect edly long X-ray to UV lags.\n \nTo address these issues I present resul ts from a superb new multi-wavelength data set on the bright Seyfert galax y MCG$+$08$-$11$-$11. This major\, high-cadence monitoring campaign\, cond ucted with *Swift* and ground-based observatories\, captured the source in an unusually highly-variable phase compared with previous observations: r apid\, large-amplitude flux changes are observed at all wavelengths. We fi nd that the X-ray and UV-optical lightcurves are much more highly-correlat ed than typically found in similar RM studies. The wavelength-dependent la gs form a spectrum that approximates disc reprocessing predictions. The be haviour of the source was markedly different during an optical RM campaign conducted just a year prior in which only slow and moderate flux changes were seen\; the resultant lag spectrum was very much steeper during this p eriod\, likely because of a stronger contribution from the BLR. Our new r esults further emphasise that a simple\, static reprocessing geometry cann ot explain the observed variability: even in the same source\, different r everberating components (or processes) dominate at different times. This r ich data set provides a golden opportunity to grapple with the dynamic and complex nature of AGN variability\, and I discuss the broader implication s.\n\nhttps://indico.unina.it/event/61/contributions/881/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/881/ END:VEVENT BEGIN:VEVENT SUMMARY:The Ultraviolet/optical Variability and Its Implication for the Ph ysical Processes in Quasars DTSTART;VALUE=DATE-TIME:20230626T084500Z DTEND;VALUE=DATE-TIME:20230626T090000Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-877@cern.ch DESCRIPTION:Speakers: Wenyong Kang (University of Science and Technology o f China)\nQuasars are a class of objects in the Universe with very apparen t flux variation. UV/optical variability of such sources has attracted par ticular attention. The radiation in this band is thought to come from the accretion disk. As the central dynamical region of a quasar\, the accretio n disk is theoretically believed to be related to structures such as the c orona and emission line region. Studying the correlations between UV/optic al variability and physical processes occurring in these structures can he lp to constrain and improve the relevant physical models. \n\nWe make a on e-parameter characterization of UV/optical variability amplitude of quasar s using the famous Sloan Digital Sky Survey 10-year light curves in the St ripe 82 region\, and explores the statistical correlations between AGN UV/ optical variability (from the accretion disk) and X-ray emission (from cor ona)\, and between the variability and UV/optical line emission (from line emitting regions). We find that there is an intrinsic positive correlatio n between UV/optical variability and X-ray loudness\, and this correlation occurs mainly at long timescales. This result prefers the physical pictur e depicted by the thermal fluctuation model of accretion disk\, i.e.\, bot h the corona heating and UV/optical variability are related to magnetic tu rbulence in the accretion disk. Then we find a positive intrinsic correlat ion between the variability amplitude and the equivalent width for the bro ad Mg II line\, the C IV line and the [O III] 5007 line. We point out that the possible physical reason behind such correlation could be: a more var iable accretion disk will have a harder and bluer spectral energy distribu tion and therefore increases the emission line equivalent width\; on the o ther hand\, a more variable accretion disk may launch more clouds\, thus i ncreasing the covering factor of emission line region. \n\nIn the future\, with the rapid progress of time-domain surveys\, more extensive/systemati cal studies of AGN variability could significantly promote our understandi ng of AGN variability and relevant physical processes.\n\nhttps://indico.u nina.it/event/61/contributions/877/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/877/ END:VEVENT BEGIN:VEVENT SUMMARY:AGN Continuum Reverberation Mapping DTSTART;VALUE=DATE-TIME:20230626T090000Z DTEND;VALUE=DATE-TIME:20230626T091500Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-880@cern.ch DESCRIPTION:Speakers: Hengxiao Guo ()\nReverberation mapping (RM) is a pow erful tool to explore the unresolved central region of active galactic nuc leus (AGN)\, e.g.\, accretion disk. Determining the structure of accretion disks in AGN is fundamental to understanding the growth of supermassive b lack holes\, confirming the standard thin disk theory\, and examining the X-ray reprocessing variability model. However\, recent continuum RM sugges ts that the observed accretion disk size is around three times larger than prediction. In this talk\, I will introduce our recent continuum RM resul ts of bright AGNs in ZTF and the well-known dwarf galaxy NGC 4395. We foun d that the continuum lag is dominated by the diffuse continuum emission\, which may account for the disk-size discrepancy. In addition\, we will int roduce a new method to measure the reverberation black hole mass via conti nuum RM.\n\nhttps://indico.unina.it/event/61/contributions/880/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/880/ END:VEVENT BEGIN:VEVENT SUMMARY:The AGN Variability Archive - AVA: A legacy database of intensive broadband reverberation mapping experiments DTSTART;VALUE=DATE-TIME:20230626T081500Z DTEND;VALUE=DATE-TIME:20230626T083000Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-875@cern.ch DESCRIPTION:Speakers: Juan Hernandez Santisteban (University of St Andrews )\nAGN variability carries information about the geometry of the accretion flow which is usually unaccessible to direct imaging methods. In particul ar\, the reverberation signals at optical wavelengths of reprocessed high- energy photons provide insight into the size of the disc itself as well as inclination\, mass accretion rate and the temperature profile of the disc itself. Over the last decade\, we have developed the intensive broadband reverberation mapping technique combining the capabilities of Swift and La s Cumbres Observatory (LCO) to perform long-term (multiple years)\, high-c adence (sub-day)\, multi-wavelength (X-rays to NIR) experiments on ~30 loc al AGN. These IBRM experiments have enabled stringent tests on the predict ions of accretion theory and shown disagreements\, catapulting new avenues to understand AGN variability. In this talk\, I will review the main outc omes of the past IBRM campaigns\, with particular focus on a high Eddingto n accretion source PG 1119+120. Our spectral and temporal decomposition al lowed us to retrieve the signal of two components\; a fast signal consiste nt with the X-ray reprocessing scenario\, and a slow signal with a spectra l energy distribution consistent with diffuse continuum emission from the broad-line region. I will also present the launch of our open-source datab ase - AGN Variability Archive (AVA). This legacy database of processed lig ht curves and spectra of ~10 years of observations taken by both Swift and LCO will enable further studies in accretion flows of supermassive black holes.\n\nhttps://indico.unina.it/event/61/contributions/875/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/875/ END:VEVENT BEGIN:VEVENT SUMMARY:Revisiting the dust torus size - luminosity relationship in AGN ba sed on the mid-infrared reverberation mapping data DTSTART;VALUE=DATE-TIME:20230626T130000Z DTEND;VALUE=DATE-TIME:20230626T131500Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-878@cern.ch DESCRIPTION:Speakers: Amit Kumar Mandal (Seoul National University\, Seoul )\nWe measured the dust torus  size of 86 quasars with bolometric AGN lu minosity in the range 10^43.4 to 10^46.4 erg/s  by determining the lag b etween the optical continuum emission obtained from ground-based optical s urveys\, i.e.\, CRTS\, ASAS-SN\, PTF and ZTF\, and the mid-infrared contin uum observed with the W1 and W2 bands from the Wide-field Infrared Survey Explorer (WISE) survey. By combining the new measurements with our re-anal yzed measurements of the sample in the literature\, we constrain the torus size - AGN luminosity relation over a large dynamic range of luminosities (i.e.\, 10^43.4 to 10^47.6 erg/s) with a slope of 0.31 and 0.32\, dependi ng on mid-infrared band W1 and W2-band\, respectively. We corrected the ac cretion disk contamination in the observed MIR light flux\, obtaining a sl ightly changed slope of 0.37 and 0.31 for W1 and W2-band lags\, respective ly. While the new slope is shallower than the value of 0.5 expected from thermal equilibrium model\, it is in good agreement with that obtained fro m the interferometric observations available in the literature. We also fo und wavelength dependent lags (from K to W1\, W2)\, suggesting a stratifie d structure of the dust torus\, such that emissions in different infrared wavelengths come from the different regions of the torus.\n\nhttps://indic o.unina.it/event/61/contributions/878/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/878/ END:VEVENT BEGIN:VEVENT SUMMARY:Searching for X-ray eclipses in NGC 6814 using dense optical/UV to X-ray monitoring with Swift DTSTART;VALUE=DATE-TIME:20230626T131500Z DTEND;VALUE=DATE-TIME:20230626T133000Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-882@cern.ch DESCRIPTION:Speakers: Adam Gonzalez (Saint Mary's University)\nNGC 6814 is a nearby ($z = 0.005$) Seyfert 1.5 galaxy that we recently showed had und ergone a rapid X-ray occultation event during an *XMM-Newton* observation from 2016. The X-ray eclipse of high column ($N_{\\mathrm{H}} \\approx 10^ {23}~\\mathrm{cm}^{-2}$)\, mildly ionised ($\\log\\xi \\approx 1~\\mathrm{ erg~cm~s^{-1}}$) matter lasted ~45ks\, with ingress and egress each lastin g ~14ks\, revealing a partially covered X-ray region we estimated to be ~2 5 gravitational radii across. From August to November 2022 we observed NGC 6814 3-4 times per day with *Swift* to search for new X-ray eclipses to b etter understand the environment in this AGN. We present here a new analys is of the 2016 *XMM-Newton* data using X-ray colour-colour diagrams that r eveal an inhomogeneous\, clumpy obscurer\, which is likely embedded within an extended\, large scale structure based on simultaneous and long-term * Swift* coverage. Our 2022 *Swift* campaign reveals no new X-ray eclipses\, but offers a rich data set with which we conduct the first thermal reverb eration analysis of this AGN. We find highly correlated optical/UV to X-ra y variability that exhibits a significantly flatter time-lag spectrum than the predicted 4/3 power law relation of a standard X-ray illuminated accr etion disc. Furthermore\, we find that during the 2016 X-ray eclipse X-ray s de-correlate from optical/UV variation before resuming highly correlated broad band variability ~30 days later.\n\nhttps://indico.unina.it/event/6 1/contributions/882/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/882/ END:VEVENT BEGIN:VEVENT SUMMARY:Long and short term\, X-ray/optical/UV time-lags in AGN DTSTART;VALUE=DATE-TIME:20230626T100000Z DTEND;VALUE=DATE-TIME:20230626T101500Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-876@cern.ch DESCRIPTION:Speakers: Iossif Papadakis ()\nRecent multi-wavelength surveys of a few AGN have given us the opportunity to constrain well the cross-co rrelation between the X-rays and the UV/optical variations in these object s. The variations in the UV lead the variations detected at longer wavelen gths in almost all cases where good quality light curves\, in many waveban ds\, exist. However\, there have been indications that the optical variati ons lead the UV variations on the longest sampled time scales in a few obj ects. This could indicate the presence of accretion rate variations which propagate inwards. We use well sampled\, long light curves of a few Seyfer t galaxies to compute the time lags on both long and short time scales. We will present the results regarding the dependence of the observed time-la gs on the probed time-scale\, and we will discuss possible constraints on various models for the observed optical/UV variations in AGN.\n\nhttps://i ndico.unina.it/event/61/contributions/876/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/876/ END:VEVENT BEGIN:VEVENT SUMMARY:Modelling thermal reverberation in active galactic nuclei DTSTART;VALUE=DATE-TIME:20230626T104500Z DTEND;VALUE=DATE-TIME:20230626T110000Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-862@cern.ch DESCRIPTION:Speakers: Elias Kammoun (IRAP - CNRS)\nSeveral active galactic nuclei (AGN) show UV/optical variability lagging behind the X-ray emissio n by a few days. The simplest and most straightforward interpretation is t hat the variable X-ray flux from the corona illuminates the accretion disc below where it is partially reflected and observed as fast X-ray reverber ation signal\, and partially absorbed and thermalised in the disc\, which produces a slow UV and optical reverberation signal. Since the corona is t hought to be centrally located and very small compared to the accretion di sc\, it first illuminates the hottest inner parts of the accretion disc an d later on its colder further out areas. Thus one expects to see the origi nal X-ray fluctuations to be firstly followed by variations in the UV and then in the optical wavebands.\n\n\nIn this talk\, I will present our newl y developed full GR-ray-tracing code that computes the thermally reverbera ted UV/optical continuum responding to X-ray illumination by a compact cor ona. Our code considers the mutual interaction of the accretion disc and t he X–ray corona. I will discuss how the properties of the system (e.g.\, black hole spin\, accretion rate\, corona height\, etc.) affect the UV/op tical time lags. I will also present our results from modelling the observ ed lags obtained from long monitoring of bright local AGN.\n\nhttps://indi co.unina.it/event/61/contributions/862/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/862/ END:VEVENT BEGIN:VEVENT SUMMARY:The Optical-to-X-ray continuum variability of AGN: thermal fluctua tion rather than reprocessing? DTSTART;VALUE=DATE-TIME:20230626T103000Z DTEND;VALUE=DATE-TIME:20230626T104500Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-861@cern.ch DESCRIPTION:Speakers: Zhen-Yi Cai ()\nFrom optical to X-ray\, the variable continuum emissions of AGN are generally found to be correlated with vari ations at longer wavelengths lagging the shorter ones. Both the correlatio n and the lag-wavelength relation are usually understood within the widesp read X-ray reprocessing scenario. However\, both of them do not always pre serve and challenge the reprocessing scenario. In recent years\, we (Cai e t al. 2016\, 2018\, 2020) upgrade the inhomogeneous thermal fluctuation mo del proposed by Dexter & Agol (2011)\, by introducing a common larger-scal e fluctuation (as a result of the propagation and mixing of local fluctuat ions\, likely\, by magnetic fields allover the accretion disk) and suggest ing a new origin for the continuum lag (as a result of the differential re gression capability of local fluctuations responding to the large-scale fl uctuation). Now\, the new thermal fluctuation scenario can account for sev eral observational properties of AGN variability\, including the correlati on and lag across the X-ray/UV/optical and the timescale-dependent color v ariation\, and may shed new light on comprehending the UV/optical continuu m variations and the relation to X-ray for AGN.\n\nhttps://indico.unina.it /event/61/contributions/861/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/861/ END:VEVENT BEGIN:VEVENT SUMMARY:Probing Accretion Disk Structure with Long Lags in AGN Photometry DTSTART;VALUE=DATE-TIME:20230626T094500Z DTEND;VALUE=DATE-TIME:20230626T100000Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-860@cern.ch DESCRIPTION:Speakers: Amy Secunda (Princeton University)\nI will discuss t he use of longer timescale “negative” lags\, where the variability in high frequency bands lags the corresponding variability at low frequency\, as a probe of accretion disk structure. Traditional reverberation mapping uses lags of variations in AGN photometry from high frequency to low freq uency wavebands on the light-crossing timescale which come from the reproc essing of light in different temperature regions of the disk. The long neg ative lag\, on the other hand\, is due to fluctuations in the outer part o f the UV/optical region of the disk that are accreted inward on the inflow timescale. Because the inflow rate also depends on disk properties\, unli ke the speed of light\, these long lags can provide additional information about disk structure. Standard disk models predict the inflow timescale i s on the order of hundreds of years. However\, recent 3D radiation magneto hydrodynamic simulations of AGN disks and analysis of high-cadence\, long baseline observations of Fairall 9 suggest that in the UV/optical region o f the disk\, the inflow timescale can be on the order of only 100 days\, n ot years. This much shorter lag timescale would make the detection of long lags possible with long baseline observations from instruments such as SW IFT or Vera C. Rubin Observatory. I will outline the underlying theory of these long lags\, show results from 3D radiation magnetohydrodynamic simul ations of disk models beyond the standard disk model\, and also present so me candidate long lags.\n\nhttps://indico.unina.it/event/61/contributions/ 860/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/860/ END:VEVENT BEGIN:VEVENT SUMMARY:Looking beyond the lamppost: a new method of understanding AGN con tinuum variability DTSTART;VALUE=DATE-TIME:20230626T101500Z DTEND;VALUE=DATE-TIME:20230626T103000Z DTSTAMP;VALUE=DATE-TIME:20260417T182756Z UID:indico-contribution-184-859@cern.ch DESCRIPTION:Speakers: Jack Neustadt (The Ohio State University)\nThe varia bility of Active Galactic Nuclei (AGNs) has been studied for decades\, wit h the UV/optical continuum observed to stochastically fluctuate at the 10% level over timescales of weeks to months. Fundamentally\, this variabilit y should be driven by temperature fluctuations in the accretion disc surro unding the central black hole. Where multiband lightcurves are available \, the variability is similar in all bands\, but the bluer wavelengths var y earlier than the redder wavelengths with delays typical of the light tra vel time across the disc. These observations have led to the commonly use d "lamppost" model\, where central luminosity fluctuations - typically lin ked with X-ray emission - irradiate the disc to drive the UV/optical varia bility. However\, it seems unlikely that this is the only source of vari ability in the disc. We introduce a new approach to understanding disc va riability where we invert the multiband UV/optical lightcurves of AGNs int o “maps” of the disc resolved in time and in radius under the assumpti on of axisymmetry. In addition to a lamppost "signal"\, we see strong ev idence for small amplitude\, slow-moving temperature fluctuations. We sugg est that these fluctuations dominate AGN variability on long timescales\, a hypothesis that will be tested by Rubin/LSST in the near future. This n ew method for understanding disc variability can also be used to probe oth er issues\, such as the degree to which unrecognized emission from the bro ad line region (BLR) contaminates continuum lightcurves.\n\nhttps://indico .unina.it/event/61/contributions/859/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/859/ END:VEVENT END:VCALENDAR