BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:A Decade of Near-Infrared Variability in NGC4388: Insights into th e AGN Structure DTSTART;VALUE=DATE-TIME:20230627T153000Z DTEND;VALUE=DATE-TIME:20230627T154500Z DTSTAMP;VALUE=DATE-TIME:20261006T094819Z UID:indico-contribution-188-893@cern.ch DESCRIPTION:Speakers: Luis Gabriel Dahmer Hahn (Shanghai Astronomical Obse rvatory)\nVariability studies of Active Galactic Nuclei (AGNs) have proven to be a powerful diagnostic tool for understanding the physics and proper ties of these objects. They provide insights into the spatial and temporal distribution of the emitting regions\, the structure and dynamics of the accretion disk\, and the properties of the central black hole. Here\, we p resent the results of a ten-year campaign to monitor the near-infrared emi ssion of the Seyfert 1.9/2 nucleus of NGC4388\, covering J and K band spec troscopy. During this period\, the hot dust continuum of the nucleus of th is object varied by up to 200% under certain wavelength ranges. However\, emission lines of low and medium ionization did not change beyond our erro r margin\, whereas we detected variations of almost 100% at the [Ca$_{\\rm VIII}$] coronal line. These results suggest that between 2011 and 2013\, we were able to access an unresolved nuclear region that became obscured a fter 2015. We also mapped continuum and emission lines beyond the nucleus and found no significant variation within this time frame. These maps also indicate that emission lines are distributed along two main directions\, representing the disc and the radio jet. Furthermore\, the ionization of t he emission lines is compatible with photoionization by an AGN in our whol e 8x8 arcsec² field of view. Lastly\, we detected a strong decrease in du st reddening along the radio jet\, suggesting that the AGN is destroying d ust grains in this region.\n\nhttps://indico.unina.it/event/61/contributio ns/893/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/893/ END:VEVENT BEGIN:VEVENT SUMMARY:Review: Optical Variability of AGN with SF and PSD DTSTART;VALUE=DATE-TIME:20230627T150000Z DTEND;VALUE=DATE-TIME:20230627T153000Z DTSTAMP;VALUE=DATE-TIME:20261006T094819Z UID:indico-contribution-188-916@cern.ch DESCRIPTION:Speakers: Szymon Kozlowski (Warsaw University\, Poland)\nI wil l briefly review basic analysis methods used to describe the typical optic al variability of AGN - structure functions and power spectra. I will disc uss the applicability\, usage\, biases\, and limitations of these methods and present some of the results for the OGLE AGN 20-year-long sample.\n\nh ttps://indico.unina.it/event/61/contributions/916/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/916/ END:VEVENT BEGIN:VEVENT SUMMARY:Periodic variability of Stripe 82 quasar light curves DTSTART;VALUE=DATE-TIME:20230627T161500Z DTEND;VALUE=DATE-TIME:20230627T163000Z DTSTAMP;VALUE=DATE-TIME:20261006T094819Z UID:indico-contribution-188-851@cern.ch DESCRIPTION:Speakers: Lovro Palaversa ()\nI am going to present the result s of the search for small-amplitude (A_g > 0.03 mag)\, long-period (100 < P[days] < 600) variability in the SDSS Stripe 82 region. This search led t o the discovery of five quasars with apparently periodic light curves. In addition\, I will discuss the line profile variability (presumably linked to the change in the phase of the optical light curve) of the MgII emissio n line of our strongest periodically variable candidate quasar (P=278 days )\, obtained over the past year. With the data collected so far we were no t yet able to exclude the possibility of the object being system of superm assive binary black holes.\n\nOur search was made possible by the precisel y calibrated (1%-2%) Stripe 82 photometry in SDSS ugriz bands\, which cove red a period of approximately 6 years and reached down to r~22 mag. By ana lyzing the Lomb-Scargle periodograms\, we identified the most promising ca ndidates for periodically variable sources. We then cross-matched these ca ndidates with other surveys across the electromagnetic spectrum (photometr y and spectroscopy) to confirm their variability and type. Our analysis wa s supported by Pan-STARRS and ZTF time series\, which provided observation al data spanning more than 20 years.\n\nAll of the identified candidates w ere quasars\, and the highest-ranked one was flagged as a variable source in the Chandra X-ray catalog. The observed periodic behavior of quasars co uld be attributed to various factors\, such as radio jet precession\, tilt ed or warped accretion disks\, tidal disruption events\, and other accreti on-related effects.\n\nhttps://indico.unina.it/event/61/contributions/851/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/851/ END:VEVENT BEGIN:VEVENT SUMMARY:Revealing Changing-Look Quasar Candidates in SDSS Stripe 82 with S DSS\, Pan-STARRS1\, and ZTF data. DTSTART;VALUE=DATE-TIME:20230627T154500Z DTEND;VALUE=DATE-TIME:20230627T160000Z DTSTAMP;VALUE=DATE-TIME:20261006T094819Z UID:indico-contribution-188-849@cern.ch DESCRIPTION:Speakers: Krzysztof Suberlak (University of Washington)\nWe us e data from the Panoramic Survey Telescope and Rapid Response System 1 Sur vey (Pan-STARRS1\, PS1) to extend the Sloan Digital Sky Survey (SDSS) Stri pe 82 quasar light curves. Combining PS1 and SDSS light curves provides a 15 yr baseline for 9248 quasars–five years longer than prior studies tha t used only SDSS. We fit the light curves with the damped random walk (DRW ) model –  a statistical description of their variability. We correlate the resulting DRW model parameters (asymptotic variability amplitude\, an d characteristic timescale)\, with quasar physical properties (black hole mass\, bolometric luminosity\, and redshift). We also make predictions for the fidelity of DRW model parameter retrieval when light curves will be f urther extended with Zwicky Transient Facility (ZTF) and the Rubin Observa tory Legacy Survey of Space and Time (LSST) data. Finally\, we show how up dated DRW parameters offer an independent method of discovering changing-l ook quasar candidates (CLQSOs). The candidates are outliers in terms of di fferences in magnitude\, and scatter between SDSS and PS1 segments. We ide ntify 40 objects (35 newly reported) exhibiting a tenfold increase in vari ability timescale between SDSS and SDSS - PS1 data. An accompanying large (over 0.5 mag) change in brightness is characteristic of CLQSOs. We summ arize the results of a recent program of spectroscopic follow-up of select CLQSO candidates carried out at the Apache Point Observatory.\n\nhttps:// indico.unina.it/event/61/contributions/849/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/849/ END:VEVENT BEGIN:VEVENT SUMMARY:ZTF constraints on variability from intermediate-mass black hole c andidates DTSTART;VALUE=DATE-TIME:20230627T160000Z DTEND;VALUE=DATE-TIME:20230627T161500Z DTSTAMP;VALUE=DATE-TIME:20261006T094819Z UID:indico-contribution-188-848@cern.ch DESCRIPTION:Speakers: Ernesto Camacho (Instituto de Astrofisica\, Pontific ia Universidad Catolica de Chile. Millennium Institute of Astrophysics MAS \, Nuncio Monsenor Sotero Sanz 100\, Of. 104\, Providencia\, Santiago\, Ch ile)\nIntermediate-mass black holes (IMBHs) are key pieces in the puzzle o f extragalactic and galactic astronomy\, due to their potential to answer questions related the formation and evolution of supermassive black holes and co-evolution with their host galaxies\, among others. Because of the d ifficulties present when detecting and confirming sources as IMBHs\, they have proven to be an elusive population. Accreting BHs are known to show r andom variability in different spectral bands (optical\, UV\, etc.). We ai m to demonstrate the viability of optical variability as a technique to se lect IMBHs candidates and characterize a sample of IMBHs obtained from the literature. Using ZTF forced photometry on the difference image\, and var ious variability features\, we obtain a high-confidence IMBHs candidates s ubgroup. We aim to study the multi-wavelength properties of the selected s ubsample and discuss it's implications in the AGN paradigm.\n\nhttps://ind ico.unina.it/event/61/contributions/848/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/848/ END:VEVENT BEGIN:VEVENT SUMMARY:Ensemble Power Spectral Density of AGN in optical bands DTSTART;VALUE=DATE-TIME:20230627T133000Z DTEND;VALUE=DATE-TIME:20230627T134500Z DTSTAMP;VALUE=DATE-TIME:20261006T094819Z UID:indico-contribution-188-853@cern.ch DESCRIPTION:Speakers: Vincenzo Petrecca (Università di Napoli Federico II )\nVariability of AGN in all wavelengths has been known for decades\, with timescales ranging from days to years. However\, the physical mechanisms driving such variability are still unclear. X-ray Power Spectral Densities (PSDs) are usually well represented by power laws with slopes α ~ -1 at low frequencies\, and α ~ -2 at high frequencies. Similar power-law trend s have also been observed in UV/optical bands\, but with a much lower brea k frequency. Optical variability is typically studied through Structure Fu nction (SF) and modeled with a Damped Random Walk (DRW)\, implying a PSD w ith slopes at low and high frequencies\, α=0\, α=-2\, respectively. Desp ite the good agreement of the DRW model on timescales from several months to a few years\, many works show significant deviations on both longer and shorter timescales\, along with strong uncertainties in determining the p osition of the break. \n\nI will present a completely model independent st udy of AGN optical variability through ensemble PSD analysis on archival d ata. The wealth of information about bolometric luminosities and black hol e masses enable the study of correlations between the variability amplitud e and the AGN physical properties. PSD also has the advantage that its est imates at different frequencies are uncorrelated and with well known stati stical properties. Moreover\, as X-ray variability is usually studied thro ugh PSDs\, using the same tool for optical bands provides better constrain ts on different variability models. Results from this analysis will be fur ther boosted by the upcoming Legacy Survey of Space and Time (LSST)\, whic h will increase both the size of the sample and the temporal baseline\, co mpared to previous surveys.\n\nhttps://indico.unina.it/event/61/contributi ons/853/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/853/ END:VEVENT BEGIN:VEVENT SUMMARY:Extracting AGN variable component properties with long-term optica l photometry DTSTART;VALUE=DATE-TIME:20230627T140000Z DTEND;VALUE=DATE-TIME:20230627T141500Z DTSTAMP;VALUE=DATE-TIME:20261006T094819Z UID:indico-contribution-188-852@cern.ch DESCRIPTION:Speakers: Hartmut Winkler (University of Johannesburg)\nI pres ent initial results from long-term (*U*)*BV*(*u'*)*g'r'* photometry with t he Las Cumbres Observatory robotic telescope network of a sample of ~80 AG N with a cadence of typically 1 month. The sample includes multiple repres entatives from the following AGN sub-categories: NLS1 with strong Fe II em ission\; Seyferts with Keplerian rotator broad line profiles\; Seyferts wi th strong broad He II emission\; obscured AGN\; known Changing-look AGN\; blazars. I utilise the flux variation gradient (FVG) method to determine t he colour of an AGN's variable component. In most cases the FVG method als o enables the separation of the variable and non-variable optical flux con tributions and the estimation of the nuclear reddening. Since commencing t his programme three years ago variations have been confirmed in >80% of th e sample\, and nuclear colours with an accuracy of 0.1 mag or better in *B -V* have been determined for half of the observed AGN. From these colours I determine the intrinsic variable component optical flux distributions an d examine if and how these differ between the AGN sub-categories mentioned earlier. I briefly discuss how this constrains physical models of the var iable parts of these AGN. Additional results include the indication that N LS1 with strong Fe II emission display lower optical variability amplitude s and that the reddening law for the dust obscuring some AGN differs to th at applicable to typical interstellar dust.\n\nhttps://indico.unina.it/eve nt/61/contributions/852/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/852/ END:VEVENT BEGIN:VEVENT SUMMARY:Studying Quasar accretion discs with massive optical variability s urveys DTSTART;VALUE=DATE-TIME:20230627T141500Z DTEND;VALUE=DATE-TIME:20230627T143000Z DTSTAMP;VALUE=DATE-TIME:20261006T094819Z UID:indico-contribution-188-850@cern.ch DESCRIPTION:Speakers: Patricia Arévalo (Instituto de Física y Astronomí a\, Universidad de Valparaíso)\nQuasars optical variability gives us clue s to understand the accretion disc around supermassive black holes. We can expect variability properties to correlate with the main physical propert ies of the accreting black hole\, i.e.\, its mass and accretion rate. It h as been established that the relative amplitude of optical variability ant i-correlates with the accretion rate and luminosity.The dependence of the variance on black hole mass has remained elusive\, and contradicting resul ts\, including positive\, negative\, or no correlation\, have been reporte d. In this work\, we show that the key to these contradictions lies in the timescales of variability studied (e.g.\, the length of the light curves available). By isolating the variance on different timescales as well as m ass and accretion rate bins we show that there is indeed a negative correl ation between black hole mass and variance and that this anti-correlation is stronger for shorter timescale fluctuations. The behavior can be explai ned in terms of a universal variability power spectrum for all quasars\, r esembling a broken power law where the variance is constant at low tempora l frequencies and then drops continuously for frequencies higher than a ch aracteristic frequency f_b\, where f_b correlates with the black hole mass .  Furthermore\, to explain all the variance results presented here\, not only the normalization of this power spectrum must anti-correlate with th e accretion rate\, but also the shape of the power spectra at short timesc ales must depend on this parameter as well. In this talk I will present th e possible interpretations of the dependence of power spectral shape on bo th parameters as well as the data supporting the results.\n\nhttps://indic o.unina.it/event/61/contributions/850/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/850/ END:VEVENT BEGIN:VEVENT SUMMARY:Uncovering Optical Quasar Variability After 20 Years DTSTART;VALUE=DATE-TIME:20230627T134500Z DTEND;VALUE=DATE-TIME:20230627T140000Z DTSTAMP;VALUE=DATE-TIME:20261006T094819Z UID:indico-contribution-188-846@cern.ch DESCRIPTION:Speakers: Zachary Stone (University of Illinois at Urbana Cham paign)\nAll quasars show a common stochastic variability\, seen across var ious observed wavelengths and timescales. The origin of this variability i s still uncertain\, though variability in the optical is thought to stem f rom processes in the accretion disk around the SMBH. Time-series variabili ty analysis presents a unique way to probe a quasar's geometry and dynamic s in this regime without ultra-fine spatial resolution.\n\nOptical quasar variability has been shown to be well-described by the Damped Random Walk (DRW) model\, which is parameterized by a characteristic timescale $\\tau_ {\\rm DRW}$ and amplitude $\\sigma_{\\rm DRW}$. A set of these parameters for a sample of quasars can be used to describe the variability statistica lly\, which can then be related to physical properties of the accretion di sk and its SMBH. For example\, it has been shown that $\\tau_{\\rm DRW}$ c orrelates with the SMBH mass $M_{BH}$.\n\nTo investigate the validity and bias of the DRW model\, in a recent work\, we perform DRW-fitting analysis on multi-band 20-year-long optical quasar light curves for a sample of ne arly 200 quasars\, the longest baseline so far in DRW analysis.\n\nWe find that many of the timescales are still biased\, though they are becoming l ess biased as baselines increase. We also find\, using more flexible model s\, that the group (i.e.\, ensemble) power spectrum of the sample differs from the theoretical DRW model power spectrum on short timescales ($\n\nht tps://indico.unina.it/event/61/contributions/846/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/846/ END:VEVENT BEGIN:VEVENT SUMMARY:Review: AGN Optical/UV Variability: pleasures and pains DTSTART;VALUE=DATE-TIME:20230627T130000Z DTEND;VALUE=DATE-TIME:20230627T133000Z DTSTAMP;VALUE=DATE-TIME:20261006T094819Z UID:indico-contribution-188-905@cern.ch DESCRIPTION:Speakers: Demetra De Cicco (Università degli Studi di Napoli "Federico II")\nVariability characterizes AGN at all wavelengths and is ob served both in continuum and line emission. My talk aims at giving an over view of AGN optical/UV variability\, focusing on the main results and chal lenges from the past decades.\n\nhttps://indico.unina.it/event/61/contribu tions/905/ LOCATION:Centro Congressi Federico II Aula Magna URL:https://indico.unina.it/event/61/contributions/905/ END:VEVENT END:VCALENDAR