arXiv subjects

Andjelka B Kovacevic

Publications and source records attributed to Andjelka B Kovacevic.

3 recordsLinked to original sources

arXiv2026

Prospects for Astrobiology and Technosignature Searches with the Vera C. Rubin Observatory Legacy Survey of Space and Time

he Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will repeatedly measure the brightness of billions of astrophysical sources using six colour filters. We test a simple idea: real physical signals tend to appear as coordinated patterns across several measurements, whereas noise does not; we call this behaviour ``coherence''. We illustrate the approach with three LSST-like simulations: (i) five Kuiper Belt Object (KBO) surface/activity states, (ii) 648 exoplanet spectra with an injected vegetation-red-edge-like spectral feature, and (iii) 500 multiband light curves. In idealised simulations, a weakly active KBO is strongly separated from its inactive counterpart when all five colours are combined. The injected red-edge-like feature becomes detectable at effective visible-disc coverage of about 13\%, and stacking about 150 detections could reach 5$σ$. Coherent, natural, and noise-like variability occupy distinct regions. A small Gaia DR3 stellar sample illustrates how colour and stability may help prioritise Galactic search regions.

astro-ph.IM↗

arXiv2020

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

The active galactic nuclei (AGN) are among the most powerful sources with an inherent, pronounced and random variation of brightness. The randomness of their time series is so subtle as to blur the border between aperiodic fluctuations and noisy oscillations. This poses challenges to analysing of such time series because neither visual inspection nor pre-exisitng methods can identify well oscillatory signals in them. Thus, there is a need for an objective method for periodicity detection. Here we review our a new data analysis method that combines a two-dimensional correlation (2D) of time series with the powerful methods of Gaussian processes. To demonstrate the utility of this technique, we apply it to two example problems which were not exploited enough: damped rednoised artificial time series mimicking AGN time series and newly published observed time series of changing look AGN (CL AGN) NGC 3516. The method successfully detected periodicities in both types of time series. Identified periodicity of $\sim 4$ yr in NGC 3516 allows us to speculate that if the thermal instability formed in its accretion disc (AD) on a time scale resembling detected periodicity then AD radius could be $\sim 0.0024$ pc.

astro-ph.GA↗

arXiv2017

Oscillatory patterns in the light curves of 5 long-term monitored type 1 AGN

A new combined data of 5 well known type 1 AGN are probed with a novel hybrid method in a search for oscillatory behavior. Additional analysis of artificial light curves obtained from the coupled oscillatory models gives confirmation for detected periods that could have physical background. We find periodic variations in the long-term light curves of 3C 390.3, NGC 4151, NGC 5548 and E1821+643, with correlation coefficients larger than 0.6. We show that oscillatory patterns of two binary black hole candidates NGC 5548 and E1821+643 corresponds to qualitatively different dynamical regimes of chaos and stability, respectively. We demonstrate that absence of oscillatory patterns in Arp 102B could be due to a weak coupling between oscillatory mechanisms. This is the first good evidence that 3C 390.3 and Arp 102B, categorized as double-peaked Balmer line objects, have qualitative different dynamics. Our analysis shows a novelty in the oscillatory dynamical patterns of the light curves of these type 1 AGN.

astro-ph.GA↗