Catching profound optical flares in blazars

Flaring episodes in blazars represent one of the most violent processes observed in extra-galactic objects. Studies of such events shed light on the energetics of the physical processes occurring in the innermost regions of blazars, which cannot otherwise be resolved by any current instruments. In this work, we present some of the largest and most rapid flares captured in the optical band in the blazars 3C 279, OJ 49, S4 0954+658, TXS 1156+295 and PG 1553+113. The source flux was observed to increase by nearly ten times within a timescale of a few weeks. We applied several methods of time series analysis and symmetry analysis. Moreover, we also performed searches for periodicity in the light curves of 3C 279, OJ 49 and PG 1553+113 using the Lomb-Scargle method and found plausible indications of quasi-periodic oscillations (QPOs). In particular, the 33- and 22-day periods found in 3C 279, i.e. a 3:2 ratio, are intriguing. These violent events might originate from magnetohydrodynamical instabilities near the base of the jets, triggered by processes modulated by the magnetic field of the accretion disc. We present a qualitative treatment as the possible explanation for the observed large amplitude flux changes in both the source-intrinsic and source-extrinsic scenarios.Comment: 11 pages, 6 figures, MNRAS accepte

Profound optical flares from the relativistic jets of active galactic nuclei

Intense outbursts in blazars are among the most extreme phenomena seen in extragalactic objects. Studying these events can offer important information about the energetic physical processes taking place within the innermost regions of blazars, which are beyond the resolution of current instruments. This work presents some of the largest and most rapid flares detected in the optical band from the sources 3C 279, OJ 49, S4 0954+658, Ton 599, and PG 1553+113, which are mostly TeV blazars. The source flux increased by nearly ten times within a few weeks, indicating the violent nature of these events. Such energetic events might originate from magnetohydrodynamical instabilities near the base of the jets, triggered by processes modulated by the magnetic field of the accretion disc. We explain the emergence of flares owing to the injection of high-energy particles by the shock wave passing along the relativistic jets. Alternatively, the flares may have also arisen due to geometrical effects related to the jets. We discuss both source-intrinsic and source-extrinsic scenarios as possible explanations for the observed large amplitude flux changes.Comment: 8 pages, 2 figures, 38th International Cosmic Ray Conference (ICRC2023) proceeding

Analysis of extensive radio emission around blazars

Niniejsza praca została wykonana w oparciu o wieloczęstotliwościową analizę próbki blazarów,charakteryzujących się rozciągłym promieniowaniem radiowym. W przypadkusześciu obiektów typu BL Lac uzyskane zostały widma strumienia emisji całkowitej,obiektu centralnego oraz dyfuzyjnego halo wraz z mapami indeksu spektralnego. Wartościindeksów spektralnych uzyskane zarówno z dopasowania funkcji liniowej do widm, jaki z map wskazują na starzenie się populacji elektronów wraz ze zwiększaniem odległościod obiektu centralnego. Przyczyny powstawania takich struktur można szukać w dawnejaktywności dżetowej galaktyki macierzystej, jak również produkcji tzw. Pair Halo Cascades.Niemniej jednak, utożsamiając Lacertydy z obiektami typu FR I, radiowe halo mogąstanowić loby obiektów FR I widziane pod niewielkim katem. Dodatkowo, praca zawieraanalizę obiektu SBS B1646+499, dla którego przeprowadzono obserwacje radiowe na 610MHz w celu potwierdzenia rozciągłej struktury otaczającej obiekt.This master’s thesis has been made on the basis of multi-frequency analysis of blazars’sample characterized by an extended radio emission. For six BL Lacertae objects radiospectrum of a total source, central object and halo emission have been obtained alongwith spectral index maps. Spectral indices’ values received from fitting linear functionsto spectra as well as from created maps of the spectral index indicate possible ageing ofthe electron populations with increasing distance from the central object. Cause of suchstructures may be traces of early epochs jets activity, unification of BL Lacs objects andFR I galaxies, likewise Pair Halo Cascades production. In addition, the work presentsan analysis of the object SBS B1646+499 which has been followed by GMRT 610 MHzobservations to confirm the extended structure surrounding the object

Study of large-scale radio structures associated with spiral galaxies

Almost all known powerful extragalactic radio sources, named radio galaxies, are hosted by elliptical (or lenticular) galaxies. However, few examples of strong radio galaxies associated with spiral galaxies have been found in the recent years. In the very centre of a parent galaxy the active galactic nucleus (AGN) can be found. AGN is a small-size, rare formation composed of a supermassive black hole (SMBH; with masses exceeding 10 million Solar masses) surrounded by matter forming an accretion disk, a dusty torus and a corona - heated to millions of degrees and, in some cases, jets of relativistic plasma. These energetic, collimated outflows sometimes blown into huge lobes have their origin near the SMBH and are characterized by a wide range of observed sizes (from dozens of kiloparsecs up to a few megaparsecs). A very important aspect in the study of AGNs is to answer the question why only few powerful, large-scale radio sources are associated with spiral galaxies. Here we present these unique objects with particular interest in radio galaxy B0313$-$192 which is located in Abell 428 galaxy cluster

Multi-frequency study of a double-double radio galaxy J0028+0035

We report the discovery of a double–double radio source (DDRS) J0028+0035. We observed it with LOFAR, GMRT, and the VLA. By combining our observational data with those from the literature, we gathered an appreciable set of radio flux density measurements covering the range from 74 MHz to 14 GHz. This enabled us to carry out an extensive review of physical properties of the source and its dynamical evolution analysis. In particular, we found that, while the age of the large-scale outer lobes is about 245 Myr, the renewal of the jet activity, which is directly responsible for the double–double structure, took place only about 3.6 Myr ago after about 11 Myr long period of quiescence. Another important property typical for DDRSs and also present here is that the injection spectral indices for the inner and the outer pair of lobes are similar. The jet powers in J0028+0035 are similar too. Both these circumstances support our inference that it is, in fact, a DDRS which was not recognized as such so far because of the presence of a coincident compact object close to the inner double so that the centre of J0028+0035 is apparently a triple

Characterising the Extended Morphologies of BL Lacertae Objects at 144 MHz with LOFAR

International audienceWe present a morphological and spectral study of a sample of 99 BL Lac objects using the LOFAR Two-Metre Sky Survey Second Data Release (LDR2). Extended emission has been identified at gigahertz frequencies around BL Lac objects, but with LDR2 it is now possible to systematically study their morphologies at 144 MHz, where more diffuse emission is expected. LDR2 reveals the presence of extended radio structures around 66/99 of the BL Lac nuclei, with angular extents ranging up to 115″, corresponding to spatial extents of 410 kpc. The extended emission is likely to be both unbeamed diffuse emission and beamed emission associated with relativistic bulk motion in jets. The spatial extents and luminosities of the extended emission are consistent with the unification scheme for active galactic nuclei, where BL Lac objects correspond to low-excitation radio galaxies with the jet axis aligned along the line of sight. While extended emission is detected around the majority of BL Lac objects, the median 144–1400 MHz spectral index and core dominance at 144 MHz indicate that the core component contributes ∼42% on average to the total low-frequency flux density. A stronger correlation was found between the 144 MHz core flux density and the γ-ray photon flux (r = 0.69) than between the 144 MHz extended flux density and the γ-ray photon flux (r = 0.42). This suggests that the radio-to-γ-ray connection weakens at low radio frequencies because the population of particles that give rise to the γ-ray flux are distinct from the electrons producing the diffuse synchrotron emission associated with spatially extended features