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1. Multiband Optical Variability of the Blazar 3C 454.3 on Diverse Timescales

Author

Karan Dogra, Alok C. Gupta, C. M. Raiteri, M. Villata, Paul J. Wiita, S. O. Kurtanidze, S. G. Jorstad, R. Bachev, G. Damljanovic, C. Lorey, S. S. Savchenko, O. Vince, M. Abdelkareem, F. J. Aceituno, J. A. Acosta-Pulido, I. Agudo, G. Andreuzzi, S. A. Ata, G. V. Baida, L. Barbieri, D. A. Blinov, G. Bonnoli, G. A. Borman, M. I. Carnerero, D. Carosati, V. Casanova, W. P. Chen, Lang Cui, E. G. Elhosseiny, D. Elsaesser, J. Escudero, M. Feige, K. Gazeas, L. E. Gennadievna, T. S. Grishina, Minfeng Gu, V. A. Hagen-Thorn, F. Hemrich, H. Y. Hsiao, M. Ismail, R. Z. Ivanidze, M. D. Jovanovic, T. M. Kamel, G. N. Kimeridze, E. N. Kopatskaya, D. Kuberek, O. M. Kurtanidze, A. Kurtenkov, V. M. Larionov, L. V. Larionova, M. Liao, H. C. Lin, K. Mannheim, A. Marchini, C. Marinelli, A. P. Marscher, D. Morcuende, D. A. Morozova, S. V. Nazarov, M. G. Nikolashvili, D. Reinhart, J. O. Santos, A. Scherbantin, E. Semkov, E. V. Shishkina, L. A. Sigua, A. K. Singh, A. Sota, R. Steineke, M. Stojanovic, A. Strigachev, A. Takey, Amira A. Tawfeek, I. S. Troitskiy, Y. V. Troitskaya, An-Li Tsai, A. A. Vasilyev, K. Vrontaki, Zhongli Zhang, A. V. Zhovtan, N. Zottmann, and Wenwen Zuo

Subjects
Active galactic nuclei, Blazars, Flat-spectrum radio quasars, Markov chain Monte Carlo, Relativistic jets, Supermassive black holes, Astrophysics, QB460-466
Abstract

Due to its peculiar and highly variable nature, the blazar 3C 454.3 has been extensively monitored by the WEBT team. Here, we present for the first time these long-term optical flux and color variability results using data acquired in B , V , R , and I bands over a time span of about two decades. We include data from WEBT collaborators and public archives such as SMARTS, Steward Observatory, and Zwicky Transient Facility. The data are binned and segmented to study the source over this long term when more regular sampling was available. During our study, the long-term spectral variability reveals a redder-when-brighter trend, which, however, stabilizes at a particular brightness cutoff of ∼14.5 mag in the I band, after which it saturates and evolves into a complex state. This trend indicates increasing dominance of jet emission over accretion disk (AD) emission until jet emission completely dominates. Plots of the variation in spectral index (following F _ν ∝ ν ^− ^α ) reveal a bimodal distribution using a one-day binning. These correlate with two extreme phases of 3C 454.3, an outburst or high-flux state and a quiescent or low-flux state, which are respectively jet- and AD-dominated. We have also conducted intraday variability studies of nine light curves and found that six of them are variable. Discrete correlation function analysis between different pairs of optical wave bands peaks at zero lags, indicating cospatial emission in different optical bands.

Published
2024
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2. Multimessenger Characterization of Markarian 501 during Historically Low X-Ray and γ-Ray Activity

Author

H. Abe, S. Abe, V. A. Acciari, I. Agudo, T. Aniello, S. Ansoldi, L. A. Antonelli, A. Arbet-Engels, C. Arcaro, M. Artero, K. Asano, D. Baack, A. Babić, A. Baquero, U. Barres de Almeida, J. A. Barrio, I. Batković, J. Baxter, J. Becerra González, W. Bednarek, E. Bernardini, M. Bernardos, A. Berti, J. Besenrieder, W. Bhattacharyya, C. Bigongiari, A. Biland, O. Blanch, G. Bonnoli, Ž. Bošnjak, I. Burelli, G. Busetto, R. Carosi, M. Carretero-Castrillo, A. J. Castro-Tirado, G. Ceribella, Y. Chai, A. Chilingarian, S. Cikota, E. Colombo, J. L. Contreras, J. Cortina, S. Covino, G. D’Amico, V. D’Elia, P. Da Vela, F. Dazzi, A. De Angelis, B. De Lotto, A. Del Popolo, M. Delfino, J. Delgado, C. Delgado Mendez, D. Depaoli, F. Di Pierro, L. Di Venere, E. Do Souto Espiñeira, D. Dominis Prester, A. Donini, D. Dorner, M. Doro, D. Elsaesser, G. Emery, J. Escudero, V. Fallah Ramazani, L. Fariña, A. Fattorini, L. Foffano, L. Font, C. Fruck, S. Fukami, Y. Fukazawa, R. J. García López, M. Garczarczyk, S. Gasparyan, M. Gaug, J. G. Giesbrecht Paiva, N. Giglietto, F. Giordano, P. Gliwny, N. Godinović, R. Grau, D. Green, J. G. Green, D. Hadasch, A. Hahn, T. Hassan, L. Heckmann, J. Herrera, D. Hrupec, M. Hütten, R. Imazawa, T. Inada, R. Iotov, K. Ishio, I. Jiménez Martínez, J. Jormanainen, D. Kerszberg, Y. Kobayashi, H. Kubo, J. Kushida, A. Lamastra, D. Lelas, F. Leone, E. Lindfors, L. Linhoff, S. Lombardi, F. Longo, R. López-Coto, M. López-Moya, A. López-Oramas, S. Loporchio, A. Lorini, E. Lyard, B. Machado de Oliveira Fraga, P. Majumdar, M. Makariev, G. Maneva, N. Mang, M. Manganaro, S. Mangano, K. Mannheim, M. Mariotti, M. Martínez, A. Mas-Aguilar, D. Mazin, S. Menchiari, S. Mender, S. Mićanović, D. Miceli, T. Miener, J. M. Miranda, R. Mirzoyan, E. Molina, H. A. Mondal, A. Moralejo, D. Morcuende, V. Moreno, T. Nakamori, C. Nanci, L. Nava, V. Neustroev, M. Nievas Rosillo, C. Nigro, K. Nilsson, K. Nishijima, T. Njoh Ekoume, K. Noda, S. Nozaki, Y. Ohtani, T. Oka, A. Okumura, J. Otero-Santos, S. Paiano, M. Palatiello, D. Paneque, R. Paoletti, J. M. Paredes, L. Pavletić, M. Persic, M. Pihet, G. Pirola, F. Podobnik, P. G. Prada Moroni, E. Prandini, G. Principe, C. Priyadarshi, W. Rhode, M. Ribó, J. Rico, C. Righi, A. Rugliancich, N. Sahakyan, T. Saito, S. Sakurai, K. Satalecka, F. G. Saturni, B. Schleicher, K. Schmidt, F. Schmuckermaier, J. L. Schubert, T. Schweizer, J. Sitarek, V. Sliusar, D. Sobczynska, A. Spolon, A. Stamerra, J. Strišković, D. Strom, M. Strzys, Y. Suda, T. Surić, H. Tajima, M. Takahashi, R. Takeishi, F. Tavecchio, P. Temnikov, K. Terauchi, T. Terzić, M. Teshima, L. Tosti, S. Truzzi, A. Tutone, S. Ubach, J. van Scherpenberg, M. Vazquez Acosta, S. Ventura, V. Verguilov, I. Viale, C. F. Vigorito, V. Vitale, I. Vovk, R. Walter, M. Will, C. Wunderlich, T. Yamamoto, D. Zarić, The MAGIC Collaboration, M. Cerruti, J. A. Acosta-Pulido, G. Apolonio, R. Bachev, M. Baloković, E. Benítez, I. Björklund, V. Bozhilov, L. F. Brown, A. Bugg, W. Carbonell, M. I. Carnerero, D. Carosati, C. Casadio, W. Chamani, W. P. Chen, R. A. Chigladze, G. Damljanovic, K. Epps, A. Erkenov, M. Feige, J. Finke, A. Fuentes, K. Gazeas, M. Giroletti, T. S. Grishina, A. C. Gupta, M. A. Gurwell,, E. Heidemann, D. Hiriart, W. J. Hou, T. Hovatta, S. Ibryamov, M. D. Joner, S. G. Jorstad, J. Kania, S. Kiehlmann, G. N. Kimeridze, E. N. Kopatskaya, M. Kopp, M. Korte, B. Kotas, S. Koyama, J. A. Kramer, L. Kunkel, S. O. Kurtanidze, O. M. Kurtanidze, A. Lähteenmäki, J. M. López, V. M. Larionov, E. G. Larionova, L. V. Larionova, C. Leto, C. Lorey, R. Mújica, G. M. Madejski, N. Marchili, A. P. Marscher, M. Minev, A. Modaressi, D. A. Morozova, T. Mufakharov, I. Myserlis, A. A. Nikiforova, M. G. Nikolashvili, E. Ovcharov, M. Perri, C. M. Raiteri, A. C. S. Readhead, A. Reimer, D. Reinhart, S. Righini, K. Rosenlehner, A. C. Sadun, S. S. Savchenko, A. Scherbantin, L. Schneider, K. Schoch, D. Seifert, E. Semkov, L. A. Sigua, C. Singh, P. Sola, Y. Sotnikova, M. Spencer, R. Steineke, M. Stojanovic, A. Strigachev, M. Tornikoski, E. Traianou, A. Tramacere, Yu. V. Troitskaya, I. S. Troitskiy, J. B. Trump, A. Tsai, A. Valcheva, A. A. Vasilyev, F. Verrecchia, M. Villata, O. Vince, K. Vrontaki, Z. R. Weaver, E. Zaharieva, and N. Zottmann

Subjects
Active galaxies, BL Lacertae objects, Markarian galaxies, Active galactic nuclei, Blazars, Astrophysics, QB460-466
Abstract

We study the broadband emission of Mrk 501 using multiwavelength observations from 2017 to 2020 performed with a multitude of instruments, involving, among others, MAGIC, Fermi's Large Area Telescope (LAT), NuSTAR, Swift, GASP-WEBT, and the Owens Valley Radio Observatory. Mrk 501 showed an extremely low broadband activity, which may help to unravel its baseline emission. Nonetheless, significant flux variations are detected at all wave bands, with the highest occurring at X-rays and very-high-energy (VHE) γ -rays. A significant correlation (>3 σ ) between X-rays and VHE γ -rays is measured, supporting leptonic scenarios to explain the variable parts of the emission, also during low activity. This is further supported when we extend our data from 2008 to 2020, and identify, for the first time, significant correlations between the Swift X-Ray Telescope and Fermi-LAT. We additionally find correlations between high-energy γ -rays and radio, with the radio lagging by more than 100 days, placing the γ -ray emission zone upstream of the radio-bright regions in the jet. Furthermore, Mrk 501 showed a historically low activity in X-rays and VHE γ -rays from mid-2017 to mid-2019 with a stable VHE flux (>0.2 TeV) of 5% the emission of the Crab Nebula. The broadband spectral energy distribution (SED) of this 2 yr long low state, the potential baseline emission of Mrk 501, can be characterized with one-zone leptonic models, and with (lepto)-hadronic models fulfilling neutrino flux constraints from IceCube. We explore the time evolution of the SED toward the low state, revealing that the stable baseline emission may be ascribed to a standing shock, and the variable emission to an additional expanding or traveling shock.

Published
2023
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3. Extreme photometric and polarimetric variability of blazar S4 0954+65 at its maximum optical and γ-ray brightness levels

Author

C M Raiteri, M Villata, M I Carnerero, S S Savchenko, S O Kurtanidze, V V Vlasyuk, A Marchini, K Matsumoto, C Lorey, M D Joner, K Gazeas, D Carosati, D O Mirzaqulov, J A Acosta Pulido, I Agudo, R Bachev, E Benítez, G A Borman, P Calcidese, W P Chen, G Damljanovic, S A Ehgamberdiev, D Elsässer, M Feige, A Frasca, H Gaur, T S Grishina, A C Gupta, D Hiriart, M Holland, B Horst, S Ibryamov, R Z Ivanidze, J Jensen, V Jithesh, M D Jovanovic, S Kiehlmann, G N Kimeridze, S Kishore, E N Kopatskaya, O M Kurtanidze, E G Larionova, H C Lin, K Mannheim, C Marinelli, J Moreira Reyes, D A Morozova, M G Nikolashvili, D Reinhart, F D Romanov, E Semkov, J Seufert, E V Shishkina, L A Sigua, R Skalidis, O I Spiridonova, M Stojanovic, A Strigachev, Y V Troitskaya, I S Troitskiy, A Tsai, A A Vasilyev, O Vince, K Vrontaki, K Wani, D Watts, and A V Zhovtan

Published
2023
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4. The optical behaviour of BL Lacertae at its maximum brightness levels: a blend of geometry and energetics

Author

C M Raiteri, M Villata, S G Jorstad, A P Marscher, J A Acosta Pulido, D Carosati, W P Chen, M D Joner, S O Kurtanidze, C Lorey, A Marchini, K Matsumoto, D O Mirzaqulov, S S Savchenko, A Strigachev, O Vince, P Aceti, G Apolonio, C Arena, A Arkharov, R Bachev, N Bader, M Banfi, G Bonnoli, G A Borman, V Bozhilov, L F Brown, W Carbonell, M I Carnerero, G Damljanovic, V Dhiman, S A Ehgamberdiev, D Elsaesser, M Feige, D Gabellini, D Galán, G Galli, H Gaur, K Gazeas, T S Grishina, A C Gupta, V A Hagen-Thorn, M K Hallum, M Hart, K Hasuda, K Heidemann, B Horst, W-J Hou, S Ibryamov, R Z Ivanidze, M D Jovanovic, G N Kimeridze, S Kishore, S Klimanov, E N Kopatskaya, O M Kurtanidze, P Kushwaha, D J Lane, E G Larionova, S Leonini, H C Lin, K Mannheim, G Marino, M Minev, A Modaressi, D A Morozova, F Mortari, S V Nazarov, M G Nikolashvili, J Otero Santos, E Ovcharov, R Papini, V Pinter, C A Privitera, T Pursimo, D Reinhart, J Roberts, F D Romanov, K Rosenlehner, T Sakamoto, F Salvaggio, K Schoch, E Semkov, J Seufert, D Shakhovskoy, L A Sigua, C Singh, R Steineke, M Stojanovic, T Tripathi, Y V Troitskaya, I S Troitskiy, A Tsai, A Valcheva, A A Vasilyev, K Vrontaki, Z R Weaver, J H F Wooley, E Zaharieva, and A V Zhovtan

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Space and Planetary Science, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract

In 2021 BL Lacertae underwent an extraordinary activity phase, which was intensively followed by the Whole Earth Blazar Telescope (WEBT) Collaboration. We present the WEBT optical data in the BVRI bands acquired at 36 observatories around the world. In mid 2021 the source showed its historical maximum, with R = 11.14. The light curves display many episodes of intraday variability, whose amplitude increases with source brightness, in agreement with a geometrical interpretation of the long-term flux behaviour. This is also supported by the long-term spectral variability, with an almost achromatic trend with brightness. In contrast, short-term variations are found to be strongly chromatic and are ascribed to energetic processes in the jet. We also analyse the optical polarimetric behaviour, finding evidence of a strong correlation between the intrinsic fast variations in flux density and those in polarisation degree, with a time delay of about 13 h. This suggests a common physical origin. The overall behaviour of the source can be interpreted as the result of two mechanisms: variability on time scales greater than several days is likely produced by orientation effects, while either shock waves propagating in the jet, or magnetic reconnection, possibly induced by kink instabilities in the jet, can explain variability on shorter time scales. The latter scenario could also account for the appearance of quasi-periodic oscillations, with periods from a few days to a few hours, during outbursts, when the jet is more closely aligned with our line of sight and the time scales are shortened by relativistic effects., Comment: 15 pages, 16 figures, submitted to MNRAS

Published
2023
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5. Structural Characterization of Agonist Binding to an A3 Adenosine Receptor through Biomolecular Simulations and Mutagenesis Experiments

Author

Stamatis, D. Lagarias, P. Barkan, K. Vrontaki, E. Ladds, G. Kolocouris, A.

Abstract

The adenosine A3 receptor (A3R) binds adenosine and is a drug target against cancer cell proliferation. Currently, there is no experimental structure of A3R. Here, we have generated a molecular model of A3R in complex with two agonists, the nonselective 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-β-d-ribofuranuronamide (NECA) and the selective 1-deoxy-1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-N-methyl-β-d-ribofuranuronamide (IB-MECA). Molecular dynamics simulations of the wild-type A3R in complex with both agonists, combined with in vitro mutagenic studies revealed important residues for binding. Further, molecular mechanics-generalized Born surface area calculations were able to distinguish mutations that reduce or negate agonistic activity from those that maintained or increased the activity. Our studies reveal that selectivity of IB-MECA toward A3R requires not only direct interactions with residues within the orthosteric binding area but also with remote residues. Although V1695.30 is considered to be a selectivity filter for A3R binders, when it was mutated to glutamic acid or alanine, the activity of IB-MECA increased by making new van der Waals contacts with TM5. This result may have implications in the design of new A3R agonists. Copyright © 2019 American Chemical Society.

Published
2019

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