Here we study the flux densities distribution at 1380, 4908 and 15365 MHz, as well as the radio spectral index of 3C 84, a Double Radio source Associated with Galactic Nucleus (DRAGN). 3C 84 is the dominant giant elliptical galaxy in the Perseus cluster, and thus very interesting for our research. This famous radio galaxy Perseus A has Relaxed Double classification because it has the large halo, with the lack of its compact structure. We show its structure (using 2D and 3D flux density plot). Besides, we calculated the radio spectral index, which we then used to investigate the nature and mechanisms of its radiation. The obtained values of spectral indices indicated that the northern hotspot is dominated by synchrotron radiation, while in southern hotspot there are thermal and non-thermal radiations, depending on the studied frequency pairs.BPU11 : 11th International Conference of the Balkan Physical Union : Proceedings book; Aug 11 - Sep 1, 2022S02-AA Astronomy and Astrophysic

Borka Jovanović, Vesna

Borka, Duško

Jovanović, Predrag

English

Here we study the flux densities distribution at 1380, 4908 and 15365 MHz, as well as the radio spectral index of 3C 84, a Double Radio source Associated with Galactic Nucleus (DRAGN). 3C 84 is the dominant giant elliptical galaxy in the Perseus cluster, and thus very interesting for our research. This famous radio galaxy Perseus A has Relaxed Double classification because it has the large halo, with the lack of its compact structure. We show its structure (using 2D and 3D flux density plot). Besides, we calculated the radio spectral index, which we then used to investigate the nature and mechanisms of its radiation. The obtained values of spectral indices indicated that the northern hotspot is dominated by synchrotron radiation, while in southern hotspot there are thermal and non-thermal radiations, depending on the studied frequency pairs.BPU11 : 11th International Conference of the Balkan Physical UnionS02-AA Astronomy and Astrophysic

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PoS(BPU11)043Flux densities and spectral indices of Relaxed Doubleradio galaxy 3C 84Vesna Borka Jovanović,𝑎,∗ Duško Borka𝑎 and Predrag Jovanović𝑏𝑎Department of Theoretical Physics and Condensed Matter Physics (020),Vinča Institute of Nuclear Sciences - National Institute of the Republic of Serbia,University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia𝑏Astronomical Observatory, Volgina 7, P.O. Box 74, 11060 Belgrade, SerbiaE-mail: vborka@vinca.rs, dusborka@vinca.rs, pjovanovic@aob.rsHere we study the flux densities distribution at 1380, 4908 and 15365 MHz, as well as the radiospectral index of 3C 84, a Double Radio source Associated with Galactic Nucleus (DRAGN). 3C84 is the dominant giant elliptical galaxy in the Perseus cluster, and thus very interesting for ourresearch. This famous radio galaxy Perseus A has Relaxed Double classification because it hasthe large halo, with the lack of its compact structure. We show its structure (using 2D and 3D fluxdensity plot). Besides, we calculated the radio spectral index, which we then used to investigatethe nature and mechanisms of its radiation. The obtained values of spectral indices indicated thatthe northern hotspot is dominated by synchrotron radiation, while in southern hotspot there arethermal and non-thermal radiations, depending on the studied frequency pairs.11th International Conference of the Balkan Physical Union (BPU11),28 August - 1 September 2022Belgrade, Serbia∗Speaker© Copyright owned by the author(s) under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). https://pos.sissa.it/PoS(BPU11)043Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84 Vesna Borka Jovanović1. IntroductionThe active galactic nuclei (AGNs) are emitting the most radiation from galaxies [1], and incase of radio galaxies, a lot of their radiation is emitted at radio wavelengths. Radio galaxy containsin its center AGN, a pair of collimated jets of relativistic particles, and jets contain a pair of lobesat their ends. They were discovered by Carl Seyfert in 1943 [2]. Only around 10-15 % of GalacticNuclei are active [3]. More details about this radiation coming from vicinity of supermassive blackholes (SMBH) see in [4]. Radio galaxies according to difference in their spectra have differentoptical-to-radio flux ratios and can be classified as radio-loud and radio-quiet AGNs. The DoubleRadio Sources Associated with Galactic Nuclei (DRAGNs) are manifested as double radio sourcesproduced by outflows (jets) that are launched by processes in AGN. As the environs of a galaxyare not a perfect vacuum the jets push their way through surrounding external media and formthe ”classical” double-lobed structures. The main characteristics of DRAGNs are synchrotronradiation, jets and lobes. Also, DRAGNs are characterized by bright hotspots near the end of eachlobe [1].Based on the degree of correlation between the high and low surface brightness in the lobes ofextragalactic radio sources with their radio luminosity, it is possible to give a classification scheme[5]. This classification given by the Fanaroff and Riley divided radio galaxies in FR I and FR II type,i.e. separated low power and high power radio galaxies, respectively. Radio spectral properties ofradio galaxies is very important feature, that is why a number of radio galaxies were discussed inpapers [6–8] and references therein.The 3C 84 is the famous radio galaxy Perseus A, the dominant giant elliptical galaxy in thePerseus cluster. Its cross-identifications are: NGC 1275; Perseus A; UGC 02669; MRK 1505; MRK9013. It can be said that its radio structure is complicated and therefore it is particularly difficultto image well. In paper [9] the authors propose and discuss the detected jet precession. Also, in[10] it is explained that the subparsec-scale radio structure is dominated by slow-moving featuresin both the eastern and western lanes of the jet, as well as that the jet appears to be accelerated.Here, we study the flux distribution of 3C 84 DRAGN as well as the radio spectral index insome characteristic points. The paper is organized in the following way: in Section 2 we describethe observational data and our method that we used for calculation of radio spectral index. InSection 3 we present and discuss the flux distribution and spectral index of 3C 84 DRAGN. At theend of this section we point out the main conclusions in our study.2. Data and methodIn our study we used publicly available data and images of the source at different frequencies,as well as Leahy’s atlas of double radio-sources (containing data and some very useful information).The radio source 3C 84 was listed in the Third Cambridge Catalogue of Radio Sources, where thenumber after 3C indicates its position in the dataset.Observational data that we used are given in FITS (short for Flexible Image Transport System)format. This is the standard data format and by structure it consists of one or more sets of a Headerand Data Units (called HDUs). In our case we used a two dimensional radio image and otherdata, where each coordinate corresponds to a value for flux density. Using these available flux data2PoS(BPU11)043Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84 Vesna Borka Jovanovićwe show its distribution and obtain spectral indices. For details regarding this type of data, see:https://www.loc.gov/preservation/digital/formats/fdd/fdd000317.shtml.The observations were carried out using ”The Very Large Array” (VLA) and ”The VeryLong Baseline Array” (VLBA) radio telescopes, both operated by the National Radio AstronomyObservatory (NRAO). VLA is located in New Mexico, USA, and from 2012 it is named ”Karl G.Jansky VLA”, while VLBA is located in several US states and can measure the position and distanceof radio sources extremely well due to its high precision observations.It is useful here to notice that we use the calibrated data, i.e. the data and images after they areprocessed using analysis techniques and programs like CLEAN algorithm (see [11] and referencestherein). Particularly, regarding the resolution of the processed data used here, the lowest one of4′′ is at 1380 MHz, while those at 4908 and 15365 MHz are much higher: 0.06 mas and 0.1 mas,respectively.The observed data for 3C 84 radio source have been taken from Leahy’s Atlas of DRAGNs[12]:• J. P. Leahy, A. H. Bridle, R. G. Strom, An Atlas of DRAGNs (2013): http://www.jb.man.ac.uk/atlas/.The atlas contains the basic information concerning the closest 85 of these DRAGNs (radio galaxiesand related objects) from the 3CRR sample of Laing, Riley & Longair (1983) [13].Also, the FITS files for each selected source (at different frequencies) can be found through theNASA/IPAC Extragalactic Database (NED). Database site:• NASA/IPAC Extragalactic Database: http://ned.ipac.caltech.edu/.The method that we used for calculation of radio spectral index we developed for the mainGalactic Loops [14–19], but we extend the same method to extragalactic radio sources [20, 21].As the objects from Leahy’s Atlas are observed with much better resolution, this extension of ourprevious method to much smaller objects was possible.2.1 Radio spectral indexIn radio sources, the flux density 𝑆a dependence on frequency a, is characterized with thepower-law relation:𝑆a ∝ a−𝛼, (1)where 𝛼 is called the ’spectral index’. It is easily obtainable by measuring the flux density atdifferent frequencies and taking the negative slope of the above relation, i.e. it is negative value ofcoefficient of the line:log 𝑆a = log𝐾 − 𝛼 log a, (2)with 𝐾 being constant, and then 𝛼 resulting in:3PoS(BPU11)043Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84 Vesna Borka Jovanović𝛼 = −log(𝑆a1𝑆a2)log(a1a2) . (3)The spectral index can be used to classify radio sources and understand the origin of radioemission. More specifically, if𝛼 > 0.1 the emission is non-thermal (synchrotron) in origin, meaningit does not depend on the temperature of the source, and for 𝛼 < 0 it is thermal (depends only onthe temperature of the source) in origin.3. Results and conclusionsObservations with the RadioAstron space telescope have shown that there are the core shifts inthe jets, and that its position may become frequency dependent. Also, there are strong indicationsfor a precession of the 3C 84 jet. Therefore, the radio spectral index maps are usually calculatedafter image alignment. 1380 MHz49.0049.0549.1049.1549.2049.25α (o)41.2041.2541.3041.3541.4041.45δ (o)0.0050.0250.1250.625Flux (Jy) 48.95 49.05 49.15 49.25  41.2 41.3 41.4 41.50.000.100.200.300.400.500.600.700.800.90α (o)δ (o)Flux (Jy)1380 MHzFigure 1: The flux density 2D plot (left) and 3D plot (right) for 3C 84 at 1380 MHz. 4908 MHz49.95066249.95066749.950672α (o)41.51169241.51169441.51169641.51169841.511700δ (o)0.0080.0160.0320.0640.1280.256Flux (Jy)49.95066249.95066749.95067241.51169041.51169541.5117000.000.050.100.150.200.250.300.350.40α (o)δ (o)Flux (Jy)4908 MHzFigure 2: The same as 1, but for 4908 MHz.4PoS(BPU11)043Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84 Vesna Borka Jovanović 15365 MHz49.95066249.95066749.950672α (o)41.51169241.51169441.51169641.51169841.511700δ (o)0.0050.0250.1250.625Flux (Jy)49.95066249.95066749.95067241.51169041.51169441.5116980.000.501.001.502.002.503.00α (o)δ (o)Flux (Jy)15365 MHzFigure 3: The same as 1, but for 15365 MHz.In Figs. 1 – 3 we show the positions in equatorial RA and DEC coordinates (𝛼, 𝛿) and thedistributions of flux density (in the form of 2D, as well as of 3D plot) of 3C 84 at the followingthree frequencies:• a1 = 1380 MHz (22 cm) – obs. date 1984,• a2 = 4908 MHz (6 cm) – obs. date 1998,• a3 = 15365 MHz (2 cm) – obs. date 1995.The observational data that we used for a1 = 1380 MHz are reduced to epoch B1950, whilethe observational data for a2 = 4908 MHz and a3 = 15365 MHz are reduced to epoch J2000 andfor that reason they are more similar. If we take a look at the RA and DEC coordinates, we can saythat the core shift is really noticeable. Therefore, in order to calculate the spectral indices betweentwo frequencies (at some characteristic points), it was necessary to make the figures alignment. Wecalculated spectral indices of the northern and southern hotspots, between each pair of the threefrequences, and obtained the following results:- northern hotspot: 𝛼12 = 0.64, 𝛼13 = 0.92, 𝛼23 = 1.23;- southern hotspot: 𝛼12 = −1.42, 𝛼13 = −0.72, 𝛼23 = 0.06.We found that the non-thermal (synchrotron) radiation dominates in the northern hotspot ofthe studied source. However, the southern hotspot is dominated by a thermal emission when takinginto account two frequency pairs a1 – a2 and a1 – a3 (due to negative value of 𝛼12 and 𝛼13). Itshould be emphasized here that 𝛼23 is positive, meaning non-thermal radiation. Therefore, in thesouthern hotspot the thermal and non-thermal radiations may be present simultaneously, dependingon the studied frequency pairs.We obtained the flux density of 3C 84 at 1380, 4908 and 15365 MHz. As can be noticedfrom displayed figures, at the very center is an extremely bright flat-spectrum core. The lack ofcompact structure in the halo gives this object its Relaxed Double classification. We also providedthe spectral index values for northern and southern hotspots derived from three pairs of frequencies.The results of this study will be helpful for understanding the evolutionary process of the 3C 84radio source.5PoS(BPU11)043Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84 Vesna Borka JovanovićAcknowledgment. This work is supported by Ministry of Science, Technological Developmentand Innovations of the Republic of Serbia. PJ wishes to acknowledge the support by this Ministrythrough the project contract No. 451-03-68/2022-14/200002.References[1] J. P. Leahy, ”DRAGNs”, in Proceedings: Jets in Extragalactic Radio Sources, Eds. H.-J. Roserand K. Meisenheimer, Lecture Notes in Physics 421, (1993) 1[2] C.K. Seyfert, Nuclear Emission in Spiral Nebulae, Astrophys. J. 97 (1943) 28[3] E. Bempong-Manful, The Nature of Jets in Powerful Radio Galaxies. Master’s thesis Uni-versity of Hertfordshire, Centre for Astrophysics Research School of Physics, Astronomy andMathematics (2017)[4] P. Jovanović, L. Č. Popović, X-ray Emission From Accretion Disks of AGN: Signatures ofSupermassive Black Holes, In: Wachter, A.D., Propst, R.J. (Eds.), Black Holes and GalaxyFormation, (2009) 249[5] B.L. Fanaroff, J.M. Riley, The morphology of extragalactic radio sources of high and lowluminosity, Mon. Not. R. Astron. Soc. 167 (1974) 31P[6] R. Blandford, D. Meier, A. Readhead, Relativistic Jets from Active Galactic Nuclei Ann. Rev.Astron. Astrophys. 57 (2019) 467[7] I. Fernini, VLA observations of 20 FR II radio sources at 8.4 GHz, Astrophys. Space Sci. 364(2019) 167[8] B. Fanaroff et al., A new look at old friends - I. Imaging classical radio galaxies with uGMRTand MeerKAT, Mon. Not. R. Astron. Soc. 505 (2021) 6003[9] S. Britzen, C. Fendt, M. Zajaček, F. Jaron, I. Pashchenko, M. F. Aller, H. D. Aller, 3C 84:Observational Evidence for Precession and a Possible Relation to TeV Emission, Galaxies 7(2019) 72[10] J. A. Hodgson, B. Rani, J. Oh, A. Marsche, S. Jorstad, Y. Mizuno, J. Park, S. S. Lee, S. Trippe,F. Mertens, A Detailed Kinematic Study of 3C 84 and Its Connection to 𝛾-Rays, Astrophys. J.914 (2021) 43[11] A. Pedlar, H. S. Ghataure, R. D. Davies, B. A. Harrison, R. A. Perley, P. C. Crane, S. W.Unger, The radio structure of NGC1275, Mon. Not. R. Astron. Soc. 246 (1990) 477[12] J. P. Leahy, A. H. Bridle, R. G. Strom, An Atlas of DRAGNs - online: http://www.jb.man.ac.uk/atlas/ (2013)[13] R. A. Laing, J. M. Riley, M. S. Longair, Bright radio sources at 178 MHz: Flux densities,optical identifications and the cosmological evolution of powerful radio galaxies, Mon. Not.R. Astron. Soc. 204 (1983) 1516PoS(BPU11)043Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84 Vesna Borka Jovanović[14] V. Borka, Spectral indices of Galactic radio loops between 1420, 820 and 408 MHz, Mon.Not. R. Astron. Soc. 376 (2007) 634[15] V. Borka, J. Milogradov-Turin, D. Urošević, The brightness of the galactic radio loops at 1420MHz: Some indications for the existence of Loops V and VI, Astron. Nachr. 329 (2008) 397[16] V. Borka Jovanović, D. Uročević, Spectral indices of radio loops, J. Phys.: Conf. Ser. 257,(2010) 012030[17] V. Borka Jovanović, Estimation of brightnesses and spectral indices of radio loops, Publ.Astron. Obs. Belgrade 91 (2012) 121[18] D. Borka, V. Borka Jovanović, D. Urošević, Spectra of the HB 21 supernova remnant: Evidenceof spectrum flattening at the low frequencies, Rev. 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Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84

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Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84

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