https://research.matf.bg.ac.rs/handle/123456789/1 2026-05-20T12:39:57Z https://research.matf.bg.ac.rs/handle/123456789/3282 Title: VAR-PZ: Constraining the photometric redshifts of quasars using variability Authors: Satheesh-Sheeba, S.; Assef, R. J.; Anguita, T.; Sánchez-Sáez, P.; Shirley, R.; Ananna, T. T.; Bauer, F. E.; Bobrick, A.; Bornancini, C. G.; Bosman, S. E. I.; Brandt, W. N.; De Cicco, D.; Czerny, B.; Fatović, M.; Ichikawa, K.; Ilić, Dragana; Kovačević, Anđelka; Li, G.; Liao, M.; Rojas-Lilayú, A.; Marculewicz, M.; Marsango, D.; Mazzucchelli, C.; Mkrtchyan, T.; Panda, S.; Peca, A.; Rani, B.; Ricci, C.; Richards, G. T.; Salvato, M.; Schneider, D. P.; Temple, M. J.; Tombesi, F.; Yu, W.; Yoon, I.; Zou, F. Abstract: The Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) is expected to obtain observations of over ten million quasars. The survey’s exceptional cadence and sensitivity will enable a significant fraction of these objects to be monitored in the ugrizy bands, spanning observed wavelengths of approximately 0.3 − 1.0 μm. The unprecedented number of sources makes spectroscopic follow-up for the vast majority of them unfeasible in the near future, so most studies will have to rely on photometric redshift estimates which are traditionally much less reliable for Active Galactic Nuclei (AGNs) than for inactive galaxies. This work presents a novel methodology to constrain the photometric redshift of AGNs that leverages the effects of cosmological time dilation, and of the luminosity and wavelength dependence of AGN variability. Specifically, we assume that the variability can be modeled as a damped random walk (DRW) process, and we adopted a parametric model to characterize the DRW timescale (τ) and asymptotic amplitude of the variability (SF∞) based on the redshift, the rest-frame wavelength, and the AGN luminosity. We constructed variability-based photometric redshift (photo-z) priors by modeling the observed variability using the expected DRW parameters at a given redshift. These variability-based photo-z (VAR-PZ) priors were then combined with traditional spectral energy distribution (SED) fitting to improve the redshift estimates from SED fitting. Validation was performed using observational data from the Sloan Digital Sky Survey (SDSS), demonstrating significant reduction in catastrophic outliers by more than 10% in comparison with SED fitting techniques and improvements in redshift precision. The simulated light curves with both SDSS and LSST-like cadences and baselines confirm that VAR-PZ will be able to constrain the photometric redshifts of SDSS-like AGNs by bringing the outlier fractions down to below 15% from 32% (SED alone) at the end of the survey. 2026-01-01T00:00:00Z https://research.matf.bg.ac.rs/handle/123456789/3281 Title: Informatika a výpočtová technika 4 - učebnica - pre štvrtý ročník gymnázia Authors: Marić, Filip; Zečević, Anđelka 2026-01-01T00:00:00Z https://research.matf.bg.ac.rs/handle/123456789/3280 Title: ASKAP EMU detection of an Odd Radio Circle (ORC) candidate: J094412-751016 (Anglerfish) Authors: Filipović, Miroslav D.; Smeaton, Zachary; Bradley, Aaron; Kothes, Roland; Crawford, Evan J.; Ahmad, Adeel; Akahori, Takuya; Barnes, Luke; Bordiu, Cristobal; Dai, Shi; Duchesne, Stefan William; Gordon, Yjan; Gupta, Nikhel; Hopkins, Andrew; Koribalski, Bärbel Silvia; Lazarević, Sanja; Leahy, Denis; Luken, Kieran; Macgregor, Peter; Mailvaganam, Anilkumar; Mehmood, Saad; Norris, Ray; Novaretti, Nastasia; Park, Laurence; Riggi, Simone; Riseley, Christopher; Rowell, Gavin; Sasaki, Manami; Shabala, Stanislav; Taziaux, Sam; Tothill, Nicholas; Urošević, Dejan; Velović, Velibor; Vernstrom, Tessa; West, Jennifer; Zafar, Tayyaba Abstract: We report diffuse extended radio-continuum emission spatially coinciding with the IR source, WISEA J094409.17 751012.8, and a semi-variable star, V687 Carinae. We use 944 MHz radio data from the large-scale Evolutionary Map of the Universe (EMU) survey to analyse this diffuse emission (EMU J094412 751016), which we nickname 'Anglerfish'. We investigate if the spatially correlated infrared (IR) source, WISEA J094409.17 751012.8, is physically related to Anglerfish. The IR colours of WISEA J094409.17 751012.8 are indicative of an elliptical galaxy, raising the possibility that Anglerfish may belong to the newly discovered class of extragalactic radio sources known as Odd Radio Circles (ORCs) with WISEA J094409.17 751012.8 as the host galaxy. We also investigate the possibility that Anglerfish is physically related to the star, V687 Carinae, and whether it may be a remnant from a previous epoch of stellar mass-loss. We determine that a physical association between the radio emission and the star is unlikely due to the star's weak stellar winds compared to the theoretical expansion velocity of the 'shell'. It is possible that Anglerfish may be a Galactic high-latitude supernova remnant; however, we find that the observed size and luminosity are not consistent with this scenario. We also investigate the ORC scenario, which we deem the most likely scenario based on the Anglerfish's observed properties such as size, brightness, lack of other frequency detections, and possible host galaxy identification. We therefore propose Anglerfish as an ORC candidate, but note that additional radio and optical observations are vital to further constrain the properties and confirm this classification. 2026-04-10T00:00:00Z https://research.matf.bg.ac.rs/handle/123456789/3279 Title: Normal Sub-Riemannian Geodesics Related to Filtrations of Lie Algebras Authors: Jovanović, Božidar; Šukilović, Tijana; Vukmirović, Srđan Abstract: There is a natural way to construct sub-Riemannian structures that depend on n parameters on compact Lie groups. These structures are related to the filtrations of Lie subalgebras $g_0 <g_1 < g_2 < \ldots < g_{n-1}< g_n =g=Lie(G)$. In the case where $n=1$, the explicit solution for normal sub-Riemannian geodesics was provided by Agrachev, Brockett, and Jurjdevic. We extend their solution to apply to general chains of Lie subgroups. Additionally, we describe normal geodesic lines of the induced sub-Riemannian structures on homogeneous spaces $G/K$, where $g_0=Lie(K)$. 2026-01-01T00:00:00Z