Two-dimensional correlation analysis of periodicity in active galactic nuclei time series

Kovačević, Andjelka; Ilić, D.

doi:10.1515/astro-2020-0007

Cited by 11 publications

(8 citation statements)

References 20 publications

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“…The CL event observed in 2020 is similar to a previous one that occurred about 4.5 years before (Oknyansky et al 2019b). This time interval is in agreement with regularity in optical variations of the object found by Kovačević et al (2020).…”

Section: Evolution Of the X-ray Spectrumsupporting

confidence: 89%

Multi-Wavelength Monitoring and Reverberation Mapping of a Changing Look Event in the Seyfert Galaxy NGC 3516

Oknyansky,

Brotherton,

Tsygankov

et al. 2021

Preprint

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We present the results of photometric and spectroscopic monitoring campaigns of the changing look AGN NGC 3516 carried out in 2018 to 2020 covering the wavelength range from the X-ray to the optical. The facilities included the telescopes of the CMO SAI MSU, the 2.3-m WIRO telescope, and the XRT and UVOT of S wi f t. We found that NGC 3516 brightened to a high state and could be classified as Sy1.5 during the late spring of 2020. We have measured time delays in the responses of the Balmer and He II λ4686 lines to continuum variations. In the case of the best-characterized broad Hβ line, the delay to continuum variability is about 17 days in the blue wing and is clearly shorter, 9 days, in the red, which is suggestive of inflow. As the broad lines strengthened, the blue side came to dominate the Balmer lines, resulting in very asymmetric profiles with blueshifted peaks during this high state. During the outburst the X-ray flux reached its maximum on 1 April 2020 and it was the highest value ever observed for NGC 3516 by the Swift observatory. The X-ray hard photon index became softer, ∼1.8 in the maximum on 21 Apr 2020 compared to the mean ∼0.7 during earlier epochs before 2020. We have found that the UV and optical variations correlated well (with a small time delay of 1-2 days) with the X-ray until the beginning of April 2020, but later, until the end of Jun. 2020, these variations were not correlated. We suggest that this fact may be a consequence of partial obscuration by Compton-thick clouds crossing the line of sight.

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Section: Evolution Of the X-ray Spectrumsupporting

confidence: 89%

Multi-Wavelength Monitoring and Reverberation Mapping of a Changing Look Event in the Seyfert Galaxy NGC 3516

Oknyansky,

Brotherton,

Tsygankov

et al. 2021

Preprint

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“…Besides the optical variability detected in this work, this source also has the Chandra X-ray catalog variability flag set to 1 (source displays flux variability within one or more observations or between observations in one or more energy bands; Evans et al 2010). For this source, we performed an additional analysis of the periodicity with the 2D hybrid model (Kovačević et al 2018;Kovačević et al 2020) and found that this period and the period calculated with the method explained in Section 3.1 are in excellent agreement. A detailed description of the procedure is given in Appendix C.…”

Section: Plausible Periodically Variable Candidatesmentioning

confidence: 70%

Detecting Long-period Variability in the SDSS Stripe 82 Standards Catalog

Fatović

Palaversa

Tisanić

et al. 2023

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We report the results of a search for long-period (100 < P < 600 days) periodic variability in the SDSS Stripe 82 standards catalog. The SDSS coverage of Stripe 82 enables such a search because there are on average 20 observations per band in ugriz bands for about one million sources, collected over about 6 yr, with a faint limit of r ∼ 22 mag and precisely calibrated 1%–2% photometry. We calculated the periods of variable source candidates in this sample using the Lomb–Scargle periodogram and considered the three highest periodogram peaks in each of the gri filters as relevant. Only those sources with gri periods consistent within 0.1% were later studied. We use the Kuiper statistic to ensure uniform distribution of data points in phased light curves. We present five sources with the spectra consistent with quasar spectra and plausible periodic variability. This SDSS-based search bodes well for future sensitive large-area surveys, such as the Rubin Observatory Legacy Survey of Space and Time, which, due to its larger sky coverage (about a factor of 60) and improved sensitivity (∼2 mag), will be more powerful for finding such sources.

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“…The 2DHybrid combines two techniques continuous wavelet transform and correlation coefficients, to analyze the Gaussian-processed AGN light curves. We have applied the 2DHybrid to our LoTeRM sample (Kovačević et al 2018(Kovačević et al , 2020a finding periodic variations in most of them, but of different origin. In case of the two double-peaked line objects 3C 390.3 and Arp 102B, for which we found a good evidence that they have qualitative different dynamics et al 2018).…”

Section: Oscillatory Patterns In Agn Light Curvesmentioning

confidence: 99%

Investigation of active galactic nuclei in time domain era

Ilic,

Kovacevic,

Popovic

2021

Preprint

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The perfect case for time-domain investigations are active galactic nuclei (AGNs) since they are luminous objects that show strong variability. Key result from the studies of AGNs variability is the estimated mass of a supermassive black hole (SMBH), which resides in the center of an AGN. Moreover, the spectral variability of AGN can be used to study the structure and physics of the broad line region, which in general can be hardly directly observed. Here we review the current status of AGNs variability investigations in Serbia, in the perspectives of the present and future monitoring campaigns.spectroscopy, with its unique capability to study up to 4,000 astronomical objects at once. It will provide spectral light curves of the largest number of quasars, which analysis will enable mapping of the inner regions in AGNs (Shen et al. 2019).This motivates us to do investigations of AGNs using optical spectroscopy in timedomain, of which recent results we give an overview in this Proceedings. We cover topics from: i) long-term monitoring campaign of the sample of near-by AGNs, ii) studies of oscillations in AGN light curves in search for periodic signals, iii) studies of the optically extremely variable AGNs. The findings of our research project are put in the concept of applications and impact to future large surveys, especially the LSST. These investigations are done at the Astronomical Observatory in Belgrade and the Department of Astronomy of the Faculty of Mathematics, University of Belgrade, mainly through the project of "Astrophysical spectroscopy of extragalactic objects", 176001, supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia, which was financed by the end of 2019. This paper is organized as follows: in Sec. 2 we shortly describe the theoretical background of AGN structure, and give the current overview of time-domain investigation of AGNs, in Sec. 3 we list some of the major results of our findings, in Sec. 4 put them in concept of future surveys, and in Sec. 5 a short summary is given. OVERVIEW OF AGNs AND TIME-DOMAIN INVESTIGATIONS 1. ACTIVE GALACTIC NUCLEI

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Two-dimensional correlation analysis of periodicity in active galactic nuclei time series

Cited by 11 publications

References 20 publications

Multi-Wavelength Monitoring and Reverberation Mapping of a Changing Look Event in the Seyfert Galaxy NGC 3516

Multi-Wavelength Monitoring and Reverberation Mapping of a Changing Look Event in the Seyfert Galaxy NGC 3516

Detecting Long-period Variability in the SDSS Stripe 82 Standards Catalog

Investigation of active galactic nuclei in time domain era

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