Author: "A. Strigachev" / Journal: monthly notices of the royal astronomical society - Searchworks@Jio Institute Digital Library Search Results

Your search keyword '"A. Strigachev"' showing total 89 results

Start Over Author "A. Strigachev" Journal monthly notices of the royal astronomical society

89 results on '"A. Strigachev"'

1. 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
Full Text: View/download PDF

2. Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

Author: V M Larionov, S G Jorstad, A P Marscher, M Villata, C M Raiteri, P S Smith, I Agudo, S S Savchenko, D A Morozova, J A Acosta-Pulido, M F Aller, H D Aller, T S Andreeva, A A Arkharov, R Bachev, G Bonnoli, G A Borman, V Bozhilov, P Calcidese, M I Carnerero, D Carosati, C Casadio, W-P Chen, G Damljanovic, A V Dementyev, A Di Paola, A Frasca, A Fuentes, J L Gómez, P Gónzalez-Morales, A Giunta, T S Grishina, M A Gurwell, V A Hagen-Thorn, T Hovatta, S Ibryamov, M Joshi, S Kiehlmann, J-Y Kim, G N Kimeridze, E N Kopatskaya, Yu A Kovalev, Y Y Kovalev, O M Kurtanidze, S O Kurtanidze, A Lähteenmäki, C Lázaro, L V Larionova, E G Larionova, G Leto, A Marchini, K Matsumoto, B Mihov, M Minev, M G Mingaliev, D Mirzaqulov, R V Muñoz Dimitrova, I Myserlis, A A Nikiforova, M G Nikolashvili, N A Nizhelsky, E Ovcharov, L D Pressburger, I A Rakhimov, S Righini, N Rizzi, K Sadakane, A C Sadun, M R Samal, R Z Sanchez, E Semkov, S G Sergeev, L A Sigua, L Slavcheva-Mihova, P Sola, Yu V Sotnikova, A Strigachev, C Thum, E Traianou, Yu V Troitskaya, I S Troitsky, P G Tsybulev, A A Vasilyev, O Vince, Z R Weaver, K E Williamson, and G V Zhekanis
Published: 2020
Full Text: View/download PDF

3. Optical intra-day variability of the blazar S5 0716+714

Author: Tripathi, Tushar, primary, Gupta, Alok C, additional, Takey, Ali, additional, Bachev, Rumen, additional, Vince, Oliver, additional, Strigachev, Anton, additional, Kushwaha, Pankaj, additional, Elhosseiny, E G, additional, Wiita, Paul J, additional, Damljanovic, G, additional, Dhiman, Vinit, additional, Fouad, A, additional, Gaur, Haritma, additional, Gu, Minfeng, additional, Hamed, G E, additional, Kishore, Shubham, additional, Kurtenkov, A, additional, Rastogi, Shantanu, additional, Semkov, E, additional, Zead, I, additional, and Zhang, Zhongli, additional
Published: 2023
Full Text: View/download PDF

4. Multiband optical variability on diverse time-scales of the TeV blazar TXS 0506 + 056, the first cosmic neutrino source

Author: Dhiman, Vinit, primary, Gupta, Alok C, additional, Bachev, Rumen, additional, Wiita, Paul J, additional, Cellone, Sergio A, additional, Strigachev, A, additional, Gaur, Haritma, additional, Darriba, A, additional, Bisen, D P, additional, Locatelli, G, additional, Mammana, L A, additional, and Semkov, E, additional
Published: 2023
Full Text: View/download PDF

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

Author: Raiteri, C M, primary, Villata, M, additional, Carnerero, M I, additional, Savchenko, S S, additional, Kurtanidze, S O, additional, Vlasyuk, V V, additional, Marchini, A, additional, Matsumoto, K, additional, Lorey, C, additional, Joner, M D, additional, Gazeas, K, additional, Carosati, D, additional, Mirzaqulov, D O, additional, Acosta Pulido, J A, additional, Agudo, I, additional, Bachev, R, additional, Benítez, E, additional, Borman, G A, additional, Calcidese, P, additional, Chen, W P, additional, Damljanovic, G, additional, Ehgamberdiev, S A, additional, Elsässer, D, additional, Feige, M, additional, Frasca, A, additional, Gaur, H, additional, Grishina, T S, additional, Gupta, A C, additional, Hiriart, D, additional, Holland, M, additional, Horst, B, additional, Ibryamov, S, additional, Ivanidze, R Z, additional, Jensen, J, additional, Jithesh, V, additional, Jovanovic, M D, additional, Kiehlmann, S, additional, Kimeridze, G N, additional, Kishore, S, additional, Kopatskaya, E N, additional, Kurtanidze, O M, additional, Larionova, E G, additional, Lin, H C, additional, Mannheim, K, additional, Marinelli, C, additional, Moreira Reyes, J, additional, Morozova, D A, additional, Nikolashvili, M G, additional, Reinhart, D, additional, Romanov, F D, additional, Semkov, E, additional, Seufert, J, additional, Shishkina, E V, additional, Sigua, L A, additional, Skalidis, R, additional, Spiridonova, O I, additional, Stojanovic, M, additional, Strigachev, A, additional, Troitskaya, Y V, additional, Troitskiy, I S, additional, Tsai, A, additional, Vasilyev, A A, additional, Vince, O, additional, Vrontaki, K, additional, Wani, K, additional, Watts, D, additional, and Zhovtan, A V, additional
Published: 2023
Full Text: View/download PDF

6. Intra-night optical flux and polarization variability of BL Lacertae during its 2020–2021 high state

Author: Rumen Bachev, Tushar Tripathi, Alok C Gupta, Pankaj Kushwaha, Anton Strigachev, Alexander Kurtenkov, Yanko Nikolov, Svetlana Boeva, Goran Damljanovic, Oliver Vince, Milan Stojanovic, Shubham Kishore, Haritma Gaur, Vinit Dhiman, Junhui Fan, Nibedita Kalita, Borislav Spassov, and Evgeni Semkov
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: In this work, we report the presence of rapid intra-night optical variations in both -- flux and polarization of the blazar BL Lacertae during its unprecedented 2020--2021 high state of brightness. The object showed significant flux variability and some color changes, but no firmly detectable time delays between the optical bands. The linear polarization was also highly variable in both -- polarization degree and angle (EVPA). The object was observed from several observatories throughout the world, covering in a total of almost 300 hours during 66 nights. Based on our results, we suggest, that the changing Doppler factor of an ensemble of independent emitting regions, travelling along a curved jet that at some point happens to be closely aligned with the line of sight can successfully reproduce our observations during this outburst. This is one of the most extensive variability studies of the optical polarization of a blazar on intra-night timescales., 23 pages,7 figures, 5 Tables (2 as appendix). Accepted for publication in MNRAS
Published: 2023
Full Text: View/download PDF

7. Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013–2017

Author: F D’Ammando, C M Raiteri, M Villata, J A Acosta-Pulido, I Agudo, A A Arkharov, R Bachev, G V Baida, E Benítez, G A Borman, W Boschin, V Bozhilov, M S Butuzova, P Calcidese, M I Carnerero, D Carosati, C Casadio, N Castro-Segura, W-P Chen, G Damljanovic, A Di Paola, J Echevarría, N V Efimova, Sh A Ehgamberdiev, C Espinosa, A Fuentes, A Giunta, J L Gómez, T S Grishina, M A Gurwell, D Hiriart, H Jermak, B Jordan, S G Jorstad, M Joshi, G N Kimeridze, E N Kopatskaya, K Kuratov, O M Kurtanidze, S O Kurtanidze, A Lähteenmäki, V M Larionov, E G Larionova, L V Larionova, C Lázaro, C S Lin, M P Malmrose, A P Marscher, K Matsumoto, B McBreen, R Michel, B Mihov, M Minev, D O Mirzaqulov, S N Molina, J W Moody, D A Morozova, S V Nazarov, A A Nikiforova, M G Nikolashvili, J M Ohlert, N Okhmat, E Ovcharov, F Pinna, T A Polakis, C Protasio, T Pursimo, F J Redondo-Lorenzo, N Rizzi, G Rodriguez-Coira, K Sadakane, A C Sadun, M R Samal, S S Savchenko, E Semkov, L Sigua, B A Skiff, L Slavcheva-Mihova, P S Smith, I A Steele, A Strigachev, J Tammi, C Thum, M Tornikoski, Yu V Troitskaya, I S Troitsky, A A Vasilyev, O Vince, T Hovatta, S Kiehlmann, W Max-Moerbeck, A C S Readhead, R Reeves, T J Pearson, T Mufakharov, Yu V Sotnikova, and M G Mingaliev
Published: 2019
Full Text: View/download PDF

8. The beamed jet and quasar core of the distant blazar 4C 71.07

Author: C M Raiteri, M Villata, M I Carnerero, J A Acosta-Pulido, D O Mirzaqulov, V M Larionov, P Romano, S Vercellone, I Agudo, A A Arkharov, U Bach, R Bachev, S Baitieri, G A Borman, W Boschin, V Bozhilov, M S Butuzova, P Calcidese, D Carosati, C Casadio, W-P Chen, G Damljanovic, A Di Paola, V T Doroshenko, N V Efimova, Sh A Ehgamberdiev, M Giroletti, J L Gómez, T S Grishina, S Ibryamov, H Jermak, S G Jorstad, G N Kimeridze, S A Klimanov, E N Kopatskaya, O M Kurtanidze, S O Kurtanidze, A Lähteenmäki, E G Larionova, A P Marscher, B Mihov, M Minev, S N Molina, J W Moody, D A Morozova, S V Nazarov, A A Nikiforova, M G Nikolashvili, E Ovcharov, S Peneva, S Righini, N Rizzi, A C Sadun, M R Samal, S S Savchenko, E Semkov, L A Sigua, L Slavcheva-Mihova, I A Steele, A Strigachev, M Tornikoski, Yu V Troitskaya, I S Troitsky, and O Vince
Published: 2019
Full Text: View/download PDF

9. Multiband optical variability of the TeV blazar PG 1553 + 113 in 2019

Author: Vinit Dhiman, Alok C Gupta, Sofia O Kurtanidze, I Eglitis, A Strigachev, G Damljanovic, Paul J Wiita, Minfeng Gu, Haritma Gaur, Oliver Vince, R Bachev, D P Bisen, S Ibryamov, R Z Ivanidze, Miljana D Jovanovic, Omar M Kurtanidze, M G Nikolashvili, E Semkov, B Spassov, M Stojanovic, Beatriz Villarroel, Haiguang Xu, and Zhongli Zhang
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Space and Planetary Science, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report the flux and spectral variability of PG 1553+113 on intra-night (IDV) to short-term timescales using BVRI data collected over 91 nights from 28 February to 8 November 2019 employing ten optical telescopes: three in Bulgaria, two each in India and Serbia, and one each in Greece, Georgia, and Latvia. We monitored the blazar quasi-simultaneously for 16 nights in the V and R bands and 8 nights in the V, R, I bands and examined the light curves (LCs) for intra-day flux and colour variations using two powerful tests: the power-enhanced F-test and the nested ANOVA test. The source was found to be significantly (> 99%) variable in 4 nights out of 27 in R-band, 1 out of 16 in V-band, and 1 out of 6 nights in I-band. No temporal variations in the colours were observed on IDV timescale. During the course of these observations the total variation in R-band was 0.89 mag observed. We also investigated the spectral energy distribution (SED) using B, V, R, and I band data. We found optical spectral indices in the range of 0.878+-0.029 to 1.106+-0.065 by fitting a power law to these SEDs of PG 1553+113. We found that the source follows a bluer-when-brighter trend on IDV timescales. We discuss possible physical causes of the observed spectral variability., 13 pages,8 figures, 7 tables, Accepted for publication in MNRAS
Published: 2022
Full Text: View/download PDF

10. Optical intraday variability of the blazar S5 0716+714.

Author: Tripathi, Tushar, Gupta, Alok C, Takey, Ali, Bachev, Rumen, Vince, Oliver, Strigachev, Anton, Kushwaha, Pankaj, Elhosseiny, E G, Wiita, Paul J, Damljanovic, G, Dhiman, Vinit, Fouad, A, Gaur, Haritma, Gu, Minfeng, Hamed, G E, Kishore, Shubham, Kurtenkov, A, Rastogi, Shantanu, Semkov, E, and Zead, I
Subjects: BL Lacertae objects, ACTIVE galaxies
Abstract: We present an extensive recent multiband optical photometric observations of the blazar S5 0716+714 carried out over 53 nights with two telescopes in India, two in Bulgaria, one in Serbia, and one in Egypt during 2019 November – 2022 December. We collected 1401, 689, 14726, and 165 photometric image frames in B, V, R , and I bands, respectively. We monitored the blazar quasi-simultaneously during three nights in B, V, R , and I bands; four nights in B, V , and R ; two nights in V, R , and I ; five nights in B and R ; and two nights in V and R bands. We also took 37 nights of data only in R band. Single band data are used to study intraday flux variability and two or more bands quasi-simultaneous observations allow us to search for colour variation in the source. We employ the power-enhanced F -test and the nested ANOVA test to search for genuine flux and colour variations in the light curves of the blazar on intraday time-scales. Out of 12, 11, 53, and 5 nights observations, intraday variations with amplitudes between ∼3 and ∼20 per cent are detected in 9, 8, 31 and 3 nights in B, V, R , and I bands, respectively, corresponding to duty cycles of 75, 73, 58, and 60 per cent. These duty cycles are lower than those typically measured at earlier times. On these time-scales colour variations with both bluer-when-brighter and redder-when-brighter are seen, though nights with no measurable colour variation are also present. We briefly discuss possible explanations for this observed intraday variability. [ABSTRACT FROM AUTHOR]
Published: 2024
Full Text: View/download PDF

11. Multiband optical variability on diverse time-scales of the TeV blazar TXS 0506 + 056, the first cosmic neutrino source.

Author: Dhiman, Vinit, Gupta, Alok C, Bachev, Rumen, Wiita, Paul J, Cellone, Sergio A, Strigachev, A, Gaur, Haritma, Darriba, A, Bisen, D P, Locatelli, G, Mammana, L A, and Semkov, E
Subjects: BL Lacertae objects, NEUTRINOS, OPTICAL telescopes, ACTIVE galaxies
Abstract: We report the first extensive optical flux and spectral variability study of the TeV blazar TXS 0506 + 056 on intranight to long-term time-scales using BVRI data collected over 220 nights between 2017 January 21 to 2022 April 9 using eight optical ground-based telescopes. In our search for intraday variability (IDV), we have employed two statistical analysis techniques, the nested ANOVA test and the power enhanced F -test. We found the source was variable in 8 nights out of 35 in the R -band and in 2 of 14 in the V -band yielding duty cycles (DC) of 22.8 per cent and 14.3 per cent, respectively. Clear colour variation in V − R was seen in only 1 out of 14 observing nights, but no IDV was found in the more limited B, I , and B − I data. During our monitoring period the source showed a 1.18 mag variation in the R -band and similar variations are clearly seen at all optical wavelengths. We extracted the optical (BVRI) SEDs of the blazar for 44 nights when observations were carried out in all four of those wavebands. The mean spectral index (α) was determined to be 0.897 ± 0.171. [ABSTRACT FROM AUTHOR]
Published: 2024
Full Text: View/download PDF

12. Intra-night optical flux and polarization variability of BL Lacertae during its 2020 − 2021 high state

Author: Bachev, Rumen, primary, Tripathi, Tushar, additional, Gupta, Alok C, additional, Kushwaha, Pankaj, additional, Strigachev, Anton, additional, Kurtenkov, Alexander, additional, Nikolov, Yanko, additional, Boeva, Svetlana, additional, Damljanovic, Goran, additional, Vince, Oliver, additional, Stojanovic, Milan, additional, Kishore, Shubham, additional, Gaur, Haritma, additional, Dhiman, Vinit, additional, Fan, Junhui, additional, Kalita, Nibedita, additional, Spassov, Borislav, additional, and Semkov, Evgeni, additional
Published: 2023
Full Text: View/download PDF

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

Author: Raiteri, C M, primary, Villata, M, additional, Jorstad, S G, additional, Marscher, A P, additional, Acosta Pulido, J A, additional, Carosati, D, additional, Chen, W P, additional, Joner, M D, additional, Kurtanidze, S O, additional, Lorey, C, additional, Marchini, A, additional, Matsumoto, K, additional, Mirzaqulov, D O, additional, Savchenko, S S, additional, Strigachev, A, additional, Vince, O, additional, Aceti, P, additional, Apolonio, G, additional, Arena, C, additional, Arkharov, A, additional, Bachev, R, additional, Bader, N, additional, Banfi, M, additional, Bonnoli, G, additional, Borman, G A, additional, Bozhilov, V, additional, Brown, L F, additional, Carbonell, W, additional, Carnerero, M I, additional, Damljanovic, G, additional, Dhiman, V, additional, Ehgamberdiev, S A, additional, Elsaesser, D, additional, Feige, M, additional, Gabellini, D, additional, Galán, D, additional, Galli, G, additional, Gaur, H, additional, Gazeas, K, additional, Grishina, T S, additional, Gupta, A C, additional, Hagen-Thorn, V A, additional, Hallum, M K, additional, Hart, M, additional, Hasuda, K, additional, Heidemann, K, additional, Horst, B, additional, Hou, W-J, additional, Ibryamov, S, additional, Ivanidze, R Z, additional, Jovanovic, M D, additional, Kimeridze, G N, additional, Kishore, S, additional, Klimanov, S, additional, Kopatskaya, E N, additional, Kurtanidze, O M, additional, Kushwaha, P, additional, Lane, D J, additional, Larionova, E G, additional, Leonini, S, additional, Lin, H C, additional, Mannheim, K, additional, Marino, G, additional, Minev, M, additional, Modaressi, A, additional, Morozova, D A, additional, Mortari, F, additional, Nazarov, S V, additional, Nikolashvili, M G, additional, Otero Santos, J, additional, Ovcharov, E, additional, Papini, R, additional, Pinter, V, additional, Privitera, C A, additional, Pursimo, T, additional, Reinhart, D, additional, Roberts, J, additional, Romanov, F D, additional, Rosenlehner, K, additional, Sakamoto, T, additional, Salvaggio, F, additional, Schoch, K, additional, Semkov, E, additional, Seufert, J, additional, Shakhovskoy, D, additional, Sigua, L A, additional, Singh, C, additional, Steineke, R, additional, Stojanovic, M, additional, Tripathi, T, additional, Troitskaya, Y V, additional, Troitskiy, I S, additional, Tsai, A, additional, Valcheva, A, additional, Vasilyev, A A, additional, Vrontaki, K, additional, Weaver, Z R, additional, Wooley, J H F, additional, Zaharieva, E, additional, and Zhovtan, A V, additional
Published: 2023
Full Text: View/download PDF

14. Multiband optical variability of the TeV blazar PG 1553 + 113 in 2019

Author: Dhiman, Vinit, primary, Gupta, Alok C, additional, Kurtanidze, Sofia O, additional, Eglitis, I, additional, Strigachev, A, additional, Damljanovic, G, additional, Wiita, Paul J, additional, Gu, Minfeng, additional, Gaur, Haritma, additional, Vince, Oliver, additional, Bachev, R, additional, Bisen, D P, additional, Ibryamov, S, additional, Ivanidze, R Z, additional, Jovanovic, Miljana D, additional, Kurtanidze, Omar M, additional, Nikolashvili, M G, additional, Semkov, E, additional, Spassov, B, additional, Stojanovic, M, additional, Villarroel, Beatriz, additional, Xu, Haiguang, additional, and Zhang, Zhongli, additional
Published: 2022
Full Text: View/download PDF

15. Intra-night optical flux and polarization variability of BL Lacertae during its 2020–2021 high state.

Author: Bachev, Rumen, Tripathi, Tushar, Gupta, Alok C, Kushwaha, Pankaj, Strigachev, Anton, Kurtenkov, Alexander, Nikolov, Yanko, Boeva, Svetlana, Damljanovic, Goran, Vince, Oliver, Stojanovic, Milan, Kishore, Shubham, Gaur, Haritma, Dhiman, Vinit, Fan, Junhui, Kalita, Nibedita, Spassov, Borislav, and Semkov, Evgeni
Subjects: BL Lacertae objects, POLARIZATION (Electricity), BREWSTER'S angle, OPTICAL polarization
Abstract: In this work, we report the presence of rapid intra-night optical variations in both flux and polarization of the blazar BL Lacertae during its unprecedented 2020–2021 high state of brightness. The object showed significant flux variability and some colour changes, but no firmly detectable time delays between the optical bands. The linear polarization was also highly variable in both polarization degree and angle (electric vector polarization angle). The object was observed from several observatories throughout the world, covering a total of almost 300 h during 66 nights. Based on our results, we suggest that the changing Doppler factor of an ensemble of independent emitting regions, travelling along a curved jet that at some point happens to be closely aligned with the line of sight, can successfully reproduce our observations during this outburst. This is one of the most extensive variability studies of the optical polarization of a blazar on intra-night time-scales. [ABSTRACT FROM AUTHOR]
Published: 2023
Full Text: View/download PDF

16. Rapid X-ray variability in Mkn 421 during a multiwavelength campaign

Author: Markowitz, Alex G, primary, Nalewajko, Krzysztof, additional, Bhatta, Gopal, additional, Dewangan, Gulab C, additional, Chandra, Sunil, additional, Dorner, Daniela, additional, Schleicher, Bernd, additional, Pajdosz-Śmierciak, Urszula, additional, Stawarz, Łukasz, additional, Zola, Staszek, additional, Ostrowski, Michał, additional, Carosati, Daniele, additional, Krishnan, Saikruba, additional, Bachev, Rumen, additional, Benítez, Erika, additional, Gazeas, Kosmas, additional, Hiriart, David, additional, Hu, Shao-Ming, additional, Larionov, Valeri, additional, Marchini, Alessandro, additional, Matsumoto, Katsura, additional, Nikiforova, A A, additional, Pursimo, Tapio, additional, Raiteri, Claudia M, additional, Reichart, Daniel E, additional, Rodriguez, Diego, additional, Semkov, Evgeni, additional, Strigachev, Anton, additional, Sugiura, Yuki, additional, Villata, Massimo, additional, Webb, James R, additional, Arbet-Engels, Axel, additional, Baack, Dominik, additional, Balbo, Matteo, additional, Biland, Adrian, additional, Bretz, Thomas, additional, Buss, Jens, additional, Eisenberger, Laura, additional, Elsaesser, Dominik, additional, Hildebrand, Dorothee, additional, Iotov, Roman, additional, Kalenski, Adelina, additional, Mannheim, Karl, additional, Mitchell, Alison, additional, Neise, Dominik, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Rhode, Wolfgang, additional, Sliusar, Vitalii, additional, and Walter, Roland, additional
Published: 2022
Full Text: View/download PDF

17. Multiband optical variability of the TeV blazar PG 1553 + 113 in 2019.

Author: Dhiman, Vinit, Gupta, Alok C, Kurtanidze, Sofia O, Eglitis, I, Strigachev, A, Damljanovic, G, Wiita, Paul J, Gu, Minfeng, Gaur, Haritma, Vince, Oliver, Bachev, R, Bisen, D P, Ibryamov, S, Ivanidze, R Z, Jovanovic, Miljana D, Kurtanidze, Omar M, Nikolashvili, M G, Semkov, E, Spassov, B, and Stojanovic, M
Subjects: SPECTRAL energy distribution, BL Lacertae objects, OPTICAL telescopes, LIGHT curves, ACTIVE galaxies
Abstract: We report the flux and spectral variability of PG 1553 + 113 on intra-night (IDV) to short-term time-scales using BVRI data collected over 91 nights from 28 February to 8 November 2019 employing 10 optical telescopes: three in Bulgaria, two each in India and Serbia, and one each in Greece, Georgia, and Latvia. We monitored the blazar quasi-simultaneously for 16 nights in the V and R bands and 8 nights in the V, R, I bands and examined the light curves (LCs) for intra-day flux and colour variations using two powerful tests: the power-enhanced F-test and the nested ANOVA test. The source was found to be significantly (>99 per cent) variable in 4 nights out of 27 in R-band, 1 out of 16 in V-band, and 1 out of 6 nights in I-band. No temporal variations in the colours were observed on IDV time-scale. During the course of these observations the total variation in R-band was 0.89 mag observed. We also investigated the spectral energy distribution (SED) using B-, V-, R-, and I-band data. We found optical spectral indices in the range of 0.878 ± 0.029 to 1.106 ± 0.065 by fitting a power law (F ν∝ν−α) to these SEDs of PG 1553 + 113. We found that the source follows a bluer-when-brighter trend on IDV time-scales. We discuss possible physical causes of the observed spectral variability. [ABSTRACT FROM AUTHOR]
Published: 2023
Full Text: View/download PDF

18. The complex variability of blazars: time-scales and periodicity analysis in S4 0954+65

Author: Raiteri, C M, primary, Villata, M, additional, Larionov, V M, additional, Jorstad, S G, additional, Marscher, A P, additional, Weaver, Z R, additional, Acosta-Pulido, J A, additional, Agudo, I, additional, Andreeva, T, additional, Arkharov, A, additional, Bachev, R, additional, Benítez, E, additional, Berton, M, additional, Björklund, I, additional, Borman, G A, additional, Bozhilov, V, additional, Carnerero, M I, additional, Carosati, D, additional, Casadio, C, additional, Chen, W P, additional, Damljanovic, G, additional, D’Ammando, F, additional, Escudero, J, additional, Fuentes, A, additional, Giroletti, M, additional, Grishina, T S, additional, Gupta, A C, additional, Hagen-Thorn, V A, additional, Hart, M, additional, Hiriart, D, additional, Hou, W-J, additional, Ivanov, D, additional, Kim, J-Y, additional, Kimeridze, G N, additional, Konstantopoulou, C, additional, Kopatskaya, E N, additional, Kurtanidze, O M, additional, Kurtanidze, S O, additional, Lähteenmäki, A, additional, Larionova, E G, additional, Larionova, L V, additional, Marchili, N, additional, Markovic, G, additional, Minev, M, additional, Morozova, D A, additional, Myserlis, I, additional, Nakamura, M, additional, Nikiforova, A A, additional, Nikolashvili, M G, additional, Otero-Santos, J, additional, Ovcharov, E, additional, Pursimo, T, additional, Rahimov, I, additional, Righini, S, additional, Sakamoto, T, additional, Savchenko, S S, additional, Semkov, E H, additional, Shakhovskoy, D, additional, Sigua, L A, additional, Stojanovic, M, additional, Strigachev, A, additional, Thum, C, additional, Tornikoski, M, additional, Traianou, E, additional, Troitskaya, Y V, additional, Troitskiy, I S, additional, Tsai, A, additional, Valcheva, A, additional, Vasilyev, A A, additional, Vince, O, additional, and Zaharieva, E, additional
Published: 2021
Full Text: View/download PDF

19. Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

Author: Larionov, V M, primary, Jorstad, S G, additional, Marscher, A P, additional, Villata, M, additional, Raiteri, C M, additional, Smith, P S, additional, Agudo, I, additional, Savchenko, S S, additional, Morozova, D A, additional, Acosta-Pulido, J A, additional, Aller, M F, additional, Aller, H D, additional, Andreeva, T S, additional, Arkharov, A A, additional, Bachev, R, additional, Bonnoli, G, additional, Borman, G A, additional, Bozhilov, V, additional, Calcidese, P, additional, Carnerero, M I, additional, Carosati, D, additional, Casadio, C, additional, Chen, W-P, additional, Damljanovic, G, additional, Dementyev, A V, additional, Di Paola, A, additional, Frasca, A, additional, Fuentes, A, additional, Gómez, J L, additional, Gónzalez-Morales, P, additional, Giunta, A, additional, Grishina, T S, additional, Gurwell, M A, additional, Hagen-Thorn, V A, additional, Hovatta, T, additional, Ibryamov, S, additional, Joshi, M, additional, Kiehlmann, S, additional, Kim, J-Y, additional, Kimeridze, G N, additional, Kopatskaya, E N, additional, Kovalev, Yu A, additional, Kovalev, Y Y, additional, Kurtanidze, O M, additional, Kurtanidze, S O, additional, Lähteenmäki, A, additional, Lázaro, C, additional, Larionova, L V, additional, Larionova, E G, additional, Leto, G, additional, Marchini, A, additional, Matsumoto, K, additional, Mihov, B, additional, Minev, M, additional, Mingaliev, M G, additional, Mirzaqulov, D, additional, Muñoz Dimitrova, R V, additional, Myserlis, I, additional, Nikiforova, A A, additional, Nikolashvili, M G, additional, Nizhelsky, N A, additional, Ovcharov, E, additional, Pressburger, L D, additional, Rakhimov, I A, additional, Righini, S, additional, Rizzi, N, additional, Sadakane, K, additional, Sadun, A C, additional, Samal, M R, additional, Sanchez, R Z, additional, Semkov, E, additional, Sergeev, S G, additional, Sigua, L A, additional, Slavcheva-Mihova, L, additional, Sola, P, additional, Sotnikova, Yu V, additional, Strigachev, A, additional, Thum, C, additional, Traianou, E, additional, Troitskaya, Yu V, additional, Troitsky, I S, additional, Tsybulev, P G, additional, Vasilyev, A A, additional, Vince, O, additional, Weaver, Z R, additional, Williamson, K E, additional, and Zhekanis, G V, additional
Published: 2020
Full Text: View/download PDF

20. Dissecting the long-term emission behaviour of the BL Lac object Mrk 421

Author: P. A. González-Morales, Valeri M. Larionov, Filippo D'Ammando, C. Lázaro, Sergey S. Savchenko, Ivan Agudo, V. Bozhilov, A. B. Grinon-Marin, Michael D. Joner, F. J. Redondo-Lorenzo, Sol N. Molina, Svetlana Boeva, A. Pastor Yabar, C. Pace, C. Protasio, M. G. Nikolashvili, M. J. Arévalo, E. Eswaraiah, D. A. Morozova, E. N. Kopatskaya, Sofia O. Kurtanidze, O. Vince, Carolina Casadio, Evgeni Ovcharov, Yu. V. Troitskaya, Joseph Moody, G. Gantchev, Svetlana G. Jorstad, Ekaterina Koptelova, L. Slavcheva-Mihova, A. A. Vasilyev, B. Jordan, Marcus Holden, Sunay Ibryamov, Ivan S. Troitsky, R. Ligustri, Kari Nilsson, Rumen Bachev, Wen Ping Chen, Elena G. Larionova, Alan P. Marscher, N. Rizzi, J. Barnes, F. Pinna, B. McBreen, G. Rodriguez-Coira, J. A. Acosta-Pulido, D. Carosati, Georgi Latev, A. C. Sadun, T. S. Grishina, J. A. Ros, Goran Damljanović, Evgeni Semkov, Neelam Panwar, Manasvita Joshi, H. C. Lin, Boyko Mihov, E. Forné, José L. Gómez, C. Martínez-Lombilla, M. I. Carnerero, A. Strigachev, Nathan Smith, O. M. Kurtanidze, Paul S. Smith, M. Villata, L. V. Larionova, C. M. Raiteri, R. Pearson, Ministerio de Economía y Competitividad (España), Russian Science Foundation, Junta de Andalucía, Bulgarian Academy of Sciences, Ministry of Education, Science and Technological Development (Serbia), and National Aeronautics and Space Administration (US)
Subjects: Galaxies: active, Galaxies: jets, Astrophysics::High Energy Astrophysical Phenomena, jets [galaxies], Library science, FOS: Physical sciences, 7. Clean energy, 01 natural sciences, Observatory, 0103 physical sciences, 010303 astronomy & astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), individual: Mrk 421 [BL Lacertae objects], ta115, 010308 nuclear & particles physics, general [BL Lacertae objects], Astronomy and Astrophysics, BL Lacertae objects: general, Joint research, 13. Climate action, Space and Planetary Science, active [galaxies], BL Lacertae objects: individual: Mrk 421, Christian ministry, Astrophysics - High Energy Astrophysical Phenomena, active, Galaxies: jets [Galaxies]
Abstract: We report on long-term multiwavelength monitoring of blazar Mrk 421 by the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration and Steward Observatory, and by the Swift and Fermi satellites. We study the source behaviour in the period 2007-2015, characterized by several extreme flares. The ratio between the optical, X-ray and γ-ray fluxes is very variable. The γ-ray flux variations show a fair correlation with the optical ones starting from 2012. We analyse spectropolarimetric data and find wavelength-dependence of the polarization degree (P), which is compatible with the presence of the host galaxy, and no wavelength dependence of the electric vector polarization angle (EVPA). Optical polarimetry shows a lack of simple correlation between P and flux and wide rotations of the EVPA. We build broad-band spectral energy distributions with simultaneous near-infrared and optical data from the GASP-WEBT and ultraviolet and X-ray data from the Swift satellite. They show strong variability in both flux and X-ray spectral shape and suggest a shift of the synchrotron peak up to a factor of ~50 in frequency. The interpretation of the flux and spectral variability is compatible with jet models including at least two emitting regions that can change their orientation with respect to the line of sight.© 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society., The Abastumani team acknowledges financial support by Shota Rustaveli NSF under contract FR/577/6-320/13. The research at BU was supported in part by US National Science Foundation grant AST-1615796 and NASA Fermi Guest Investigator grant NNX14AQ58G. This study makes use of 43 GHz VLBA data from the VLBA-BU Blazar Monitoring Program (VLBA-BUBLAZAR; http://www.bu.edu/blazars/VLBAproject.html), funded by NASA through the Fermi Guest Investigator Program. The PRISM camera at the Lowell Observatory was developed by K. Janes et al. at the BU and Lowell Observatory, with funding from the NSF, BU and Lowell Observatory. This research has made use of data from the MOJAVE data base, which is maintained by the MOJAVE team (Lister et al. 2009). The St. Petersburg University team acknowledges support from Russian RFBR grant 15-02-00949 and St. Petersburg University research grant 6.38.335.2015. This paper is partly based on observations carried out at the German Spanish Calar Alto Observatory, which is jointly operated by the MPIA and the IAA-CSIC. IA research is supported by a Ramon y Cajal grant of the Spanish Ministerio de Economia y Competitividad (MINECO). Acquisition of the MAPCAT data was supported in part by MINECO through grants AYA2010-14844, AYA2013-40825-P and AYA2016-80889-P, and by the Regional Government of Andalucia through grant P09-FQM-4784. This research was partially supported by the Scientific Research Fund of the Bulgarian Ministry of Education and Sciences under grants DO 02-137 (BIn-13/09) and DN 08/1. The Skinakas Observatory is a collaborative project of the University of Crete, the Foundation for Research and Technology - Hellas and the Max-Planck-Institut fur Extrater-restrische Physik. GD and OV gratefully acknowledge the observing grant support from the Institute of Astronomy and Rozhen National Astronomical Observatory, Bulgaria Academy of Sciences, via the bilateral joint research project 'Observations of ICRF radio-sources visible in optical domain' (the head is Dr G. Damljanovic). This work is a part of the Projects No 176011 ('Dynamics and kinematics of celestial bodies and systems'), No 176004 ('Stellar physics') and No 176021 ('Visible and invisible matter in nearby galaxies: theory and observations') supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia. The Serbian station is the Astronomical Station Vidojevica (ASV) with the 60-cm ASV telescope (and from this year, the 1.4-m ASV one). This research was supported partly by funds of the project RD-08-81 of the Shumen University.
Published: 2017

21. Multiband optical variability of the blazar OJ 287 during its outbursts in 2015–2016

Author: Kensei Shiki, Yuka Kanda, Haritma Gaur, Jun-Hui Fan, Givi N. Kimeridze, Makoto Uemura, Z. Zhang, R. A. Chigladze, Alka Mishra, Tatsuya Nakaoka, Minfeng Gu, Georgi Latev, M. G. Nikolashvili, Miho Kawabata, Lorand A. Sigua, Rumen Bachev, Aditi Agarwal, O. M. Kurtanidze, Paul J. Wiita, Ryosuke Itoh, Ashwani Pandey, O. Vince, Goran Damljanović, Evgeni Semkov, J. Hirochi, A. Strigachev, Sofia O. Kurtanidze, Pankaj Kushwaha, R. G. Chanishvili, R. V. Munoz Dimitrova, Taisei Abe, Alok C. Gupta, Beatriz Villarroel, and B. Spassov
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010308 nuclear & particles physics, FOS: Physical sciences, Astronomy, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, 13. Climate action, Space and Planetary Science, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, Blazar, 010303 astronomy & astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present recent optical photometric observations of the blazar OJ 287 taken during September 2015 -- May 2016. Our intense observations of the blazar started in November 2015 and continued until May 2016 and included detection of the large optical outburst in December 2016 that was predicted using the binary black hole model for OJ 287. For our observing campaign, we used a total of 9 ground based optical telescopes of which one is in Japan, one is in India, three are in Bulgaria, one is in Serbia, one is in Georgia, and two are in the USA. These observations were carried out in 102 nights with a total of ~ 1000 image frames in BVRI bands, though the majority were in the R band. We detected a second comparably strong flare in March 2016. In addition, we investigated multi-band flux variations, colour variations, and spectral changes in the blazar on diverse timescales as they are useful in understanding the emission mechanisms. We briefly discuss the possible physical mechanisms most likely responsible for the observed flux, colour and spectral variability., 11 pages, 6 figures, 4 tables; Accepted for publication in MNRAS
Published: 2016
Full Text: View/download PDF

22. Kepler light-curve analysis of the blazar W2R 1926+42

Author: Rumen Bachev, Prashanth Mohan, Anton Strigachev, and Alok C. Gupta
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Jet (fluid), 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Phase (waves), FOS: Physical sciences, Spectral density, Astronomy and Astrophysics, Astrophysics, Light curve, 01 natural sciences, Power law, Black hole, Base (group theory), Space and Planetary Science, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, Blazar, 010303 astronomy & astrophysics
Abstract: We study the long term Kepler light curve of the blazar W2R 1926+42 ($\sim$ 1.6 years) which indicates a variety of variability properties during different intervals of observation. The normalized excess variance, $F_{\rm var}$ ranges from 1.8 % in the quiescent phase and 43.3 % in the outburst phase. We find no significant deviation from linearity in the $F_{\rm var}$-flux relation. Time series analysis is conducted using the Fourier power spectrum and the wavelet analysis methods to study the power spectral density (PSD) shape, infer characteristic timescales and statistically significant quasi-periodic oscillations (QPOs). A bending power law with an associated timescale of $T_B = 6.2^{+6.4}_{-3.1}$ hours is inferred in the PSD analysis. We obtain a black hole mass of $M_\bullet = (1.5 - 5.9) \times 10^7 M_\odot$ for the first time using $F_{\rm var}$ and the bend timescale for this source. From a mean outburst lifetime of days, we infer a distance from the jet base $r \leq 1.75$ pc indicating that the outburst originates due to a shock. A possible QPO peaked at 9.1 days and lasting 3.4 cycles is inferred from the wavelet analysis. Assuming that the QPO is a true feature, $r = (152 - 378)~ G M_\bullet/c^2$ and supported by the other timing analysis products such as a weighted mean PSD slope of $-1.5 \pm 0.2$ from the PSD analysis, we argue that the observed variability and the weak and short duration QPO could be due to jet based processes including orbital features in a relativistic helical jet and others such as shocks and turbulence., 14 pages, 6 figures, 2 tables; Accepted for publication in MNRAS
Published: 2015
Full Text: View/download PDF

23. The beamed jet and quasar core of the distant blazar 4C 71.07

Author: Raiteri, C M, primary, Villata, M, additional, Carnerero, M I, additional, Acosta-Pulido, J A, additional, Mirzaqulov, D O, additional, Larionov, V M, additional, Romano, P, additional, Vercellone, S, additional, Agudo, I, additional, Arkharov, A A, additional, Bach, U, additional, Bachev, R, additional, Baitieri, S, additional, Borman, G A, additional, Boschin, W, additional, Bozhilov, V, additional, Butuzova, M S, additional, Calcidese, P, additional, Carosati, D, additional, Casadio, C, additional, Chen, W-P, additional, Damljanovic, G, additional, Di Paola, A, additional, Doroshenko, V T, additional, Efimova, N V, additional, Ehgamberdiev, Sh A, additional, Giroletti, M, additional, Gómez, J L, additional, Grishina, T S, additional, Ibryamov, S, additional, Jermak, H, additional, Jorstad, S G, additional, Kimeridze, G N, additional, Klimanov, S A, additional, Kopatskaya, E N, additional, Kurtanidze, O M, additional, Kurtanidze, S O, additional, Lähteenmäki, A, additional, Larionova, E G, additional, Marscher, A P, additional, Mihov, B, additional, Minev, M, additional, Molina, S N, additional, Moody, J W, additional, Morozova, D A, additional, Nazarov, S V, additional, Nikiforova, A A, additional, Nikolashvili, M G, additional, Ovcharov, E, additional, Peneva, S, additional, Righini, S, additional, Rizzi, N, additional, Sadun, A C, additional, Samal, M R, additional, Savchenko, S S, additional, Semkov, E, additional, Sigua, L A, additional, Slavcheva-Mihova, L, additional, Steele, I A, additional, Strigachev, A, additional, Tornikoski, M, additional, Troitskaya, Yu V, additional, Troitsky, I S, additional, and Vince, O, additional
Published: 2019
Full Text: View/download PDF

24. Optical Variability of TeV Blazars on long time-scales

Author: Gaur, Haritma, primary, Gupta, Alok C, additional, Bachev, R, additional, Strigachev, A, additional, Semkov, E, additional, Wiita, P J, additional, Kurtanidze, O M, additional, Darriba, A, additional, Damljanovic, G, additional, Chanishvili, R G, additional, Ibryamov, S, additional, Kurtanidze, S O, additional, Nikolashvili, M G, additional, Sigua, L A, additional, and Vince, O, additional
Published: 2019
Full Text: View/download PDF

25. The ever-surprising blazar OJ 287: multi-wavelength study and appearance of a new component in X-rays

Author: Kushwaha, Pankaj, primary, Gupta, Alok C, additional, Wiita, Paul J, additional, Pal, Main, additional, Gaur, Haritma, additional, de Gouveia Dal Pino, E M, additional, Kurtanidze, O M, additional, Semkov, E, additional, Damljanovic, G, additional, Hu, S M, additional, Uemura, M, additional, Vince, O, additional, Darriba, A, additional, Gu, M F, additional, Bachev, R, additional, Chen, Xu, additional, Itoh, R, additional, Kawabata, M, additional, Kurtanidze, S O, additional, Nakaoka, T, additional, Nikolashvili, M G, additional, Sigua, L A, additional, Strigachev, A, additional, and Zhang, Z, additional
Published: 2018
Full Text: View/download PDF

26. Optical flux and spectral variability of blazars

Author: Haritma Gaur, Boyko Mihov, G. Latev, Anton Strigachev, Alok C. Gupta, R. Bachev, Svetlana Boeva, Evgeni Semkov, S. Peneva, L. Slavcheva-Mihova, Paul J. Wiita, and U. S. Pandey
Subjects: Physics, Spectral flux, Space and Planetary Science, Optical frequencies, Spectral slope, Flux, Astronomy and Astrophysics, Quasar, Astrophysics, Blazar, Full sample, Spectral line
Abstract: We report the results of optical monitoring for a sample of 11 blazars including 10 BL Lacs and 1 Flat Spectrum Radio Quasar (FSRQ). We have measured the multiband optical flux and colour variations in these blazars on intra-day and short-term timescales of months and have limited data for 2 more blazars. These photometric observations were made during 2009 to 2011, using six optical telescopes, four in Bulgaria, one in Greece and one in India. On short-term timescales we found significant flux variations in 9 of the sources and colour variations in 3 of them. Intra-day variability was detected on 6 nights for 2 sources out of the 18 nights and 4 sources for which we collected such data. These new optical observations of these blazars plus data from our previous published papers (for 3 more blazars) were used to analyze their spectral flux distributions in the optical frequency range. Our full sample for this purpose includes 6 high-synchrotron-frequency-peaked BL Lacs (HSPs), 3 intermediate-synchrotron-frequency-peaked BL Lacs (ISPs) and 6 low-synchrotron-frequency-peaked BL Lacs (LSPs; including both BL Lacs and FSRQs). We also investigated the spectral slope variability and found that the average spectral slopes of LSPs show a good accordance with the Synchrotron Self-Compton (SSC) loss dominated model. Our analysis supports previous studies that found that the spectra of the HSPs and FSRQs have significant additional emission components. The spectra of all these HSPs and LSPs get flatter when they become brighter, while for FSRQs the opposite appears to hold. This supports the hypothesis that there is a significant thermal contribution to the optical spectrum for FSRQs.
Published: 2012
Full Text: View/download PDF

27. Multiwavelength intraday variability of the BL Lacertae S5 0716+714

Author: Pardeep Mohan, Omar M. Kurtanidze, Evgeni Semkov, Krisztina É. Gabányi, Bindu Rani, Helmut Wiesemeyer, Rumen Bachev, N. Palma, J. A. Zensus, A. Strigachev, Sofia O. Kurtanidze, B. McBreen, J. M. Ohlert, T. Pursimo, Haritma Gaur, Thomas P. Krichbaum, James R. Webb, Kirill Sokolovsky, Markus Böttcher, N. Marchili, Alok C. Gupta, M. G. Nikolashvili, Arun V. Mangalam, L. Fuhrmann, Uwe Bach, I. Agudo, G. Nestoras, C.-U. Lee, X. Liu, Keith Hawkins, Paul J. Wiita, Stoyanka Peneva, Givi N. Kimeridze, and Roberto Nesci
Subjects: Physics, Wavelength, Scintillation, Opacity, Space and Planetary Science, Astrophysics::High Energy Astrophysical Phenomena, Spectral energy distribution, Synchrotron radiation, Astronomy and Astrophysics, Astrophysics, Radio spectrum, BL Lac object, Fermi Gamma-ray Space Telescope
Abstract: We report results from a 1 week multi-wavelength campaign to monitor the BL Lac object S5 0716+714 (on December 9-16, 2009). In the radio bands the source shows rapid (~ (0.5-1.5) day) intra-day variability with peak amplitudes of up to ~ 10 %. The variability at 2.8 cm leads by about 1 day the variability at 6 cm and 11 cm. This time lag and more rapid variations suggests an intrinsic contribution to the source's intraday variability at 2.8 cm, while at 6 cm and 11 cm interstellar scintillation (ISS) seems to predominate. Large and quasi-sinusoidal variations of ~ 0.8 mag were detected in the V, R and I-bands. The X-ray data (0.2-10 keV) do not reveal significant variability on a 4 day time scale, favoring reprocessed inverse-Compton over synchrotron radiation in this band. The characteristic variability time scales in radio and optical bands are similar. A quasi-periodic variation (QPO) of 0.9 - 1.1 days in the optical data may be present, but if so it is marginal and limited to 2.2 cycles. Cross-correlations between radio and optical are discussed. The lack of a strong radio-optical correlation indicates different physical causes of variability (ISS at long radio wavelengths, source intrinsic origin in the optical), and is consistent with a high jet opacity and a compact synchrotron component peaking at ~= 100 GHz in an ongoing very prominent flux density outburst. For the campaign period, we construct a quasi-simultaneous spectral energy distribution (SED), including gamma-ray data from the FERMI satellite. We obtain lower limits for the relativistic Doppler-boosting of delta >= 12-26, which for a BL\,Lac type object, is remarkably high.
Published: 2012
Full Text: View/download PDF

28. The nature of the intra-night optical variability in blazars

Author: L. Slavcheva-Mihova, Svetlana Boeva, Boyko Mihov, Alok C. Gupta, Anton Strigachev, Haritma Gaur, R. Bachev, and Evgeni Semkov
Subjects: Physics, Amplitude, Space and Planetary Science, Sample (material), Astronomy and Astrophysics, Astrophysics, Blazar
Abstract: In this paper we present results of a short-term optical monitoring of 13 blazars. The objects were monitored mostly in the R-band for a total of ~ 160 hours between 2006 and 2011. We study the nature of the short-term variations and show that most of them could be described as slow, smooth, and (almost) linear changes of up to ~ 0.1 mag/hour, but many objects show no short-term variations at all. In fact, we found only ~ 2 per cent chance to observe variability of more than 0.1 mag/hour for the sample we observed. Hints for quasi-periodic oscillations at very low amplitude levels are also found for some objects. We briefly discuss some of the possible mechanisms to generate the intra-night variability and the quasi-periodic oscillations.
Published: 2012
Full Text: View/download PDF

29. Quasi-simultaneous two-band optical variability of the blazars 1ES 1959+650 and 1ES 2344+514

Author: Paul J. Wiita, N. Kacharov, Haritma Gaur, S. Peneva, Alok C. Gupta, Boyko Mihov, Evgeni Ovcharov, Anton Strigachev, Evgeni Semkov, R. Bachev, and Svetlana Boeva
Subjects: Physics, Two band, Space and Planetary Science, Astronomy and Astrophysics, Astrophysics, Blazar
Abstract: We report the results of quasi-simultaneous two filter optical monitoring of two high-energy peaked blazars, 1ES 1959+650 and 1ES 2344+514, to search for microvariability and short-term variability (STV). We carried out optical photometric monitoring of these sources in an alternating sequence of B and R pass-bands, and have 24 and 19 nights of new data for these two sources, respectively. No genuine microvariability (intra-night variability) was detected in either of these sources. This non-detection of intra-night variations is in agreement with the conclusions of previous studies that high-energy peaked BL Lacs are intrinsically less variable than low-energy peaked BL Lacs in the optical bands. We also report the results of STV studies for these two sources between July 2009 and August 2010. Genuine STV is found for the source 1ES 1959+650 but not for 1ES 2344+514. We briefly discuss possible reasons for the difference between the intra-night variability behaviour of high- and low-energy peaked blazars.
Published: 2012
Full Text: View/download PDF

30. Spectral energy distribution variation in BL Lacs and flat spectrum radio quasars

Author: Paul J. Wiita, A. Strigachev, Evgeni Semkov, Svetlana Boeva, Filippo D'Ammando, Mark Gurwell, S. Peneva, Evgeni Ovcharov, Bindu Rani, Rumen Bachev, Boyko Mihov, and Alok C. Gupta
Subjects: Physics, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Spectral density, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Electron, Curvature, 01 natural sciences, Spectral line, Synchrotron, law.invention, symbols.namesake, Space and Planetary Science, law, 0103 physical sciences, symbols, Spectral energy distribution, Blazar, 010303 astronomy & astrophysics, Doppler effect
Abstract: We present the results of our study of spectral energy distributions (SEDs) of a sample of ten low- to intermediate-synchrotron-peaked blazars. We investigate some of the physical parameters most likely responsible for the observed short-term variations in blazars. To do so, we focus on the study of changes in the SEDs of blazars corresponding to changes in their respective optical fluxes. We model the observed spectra of blazars from radio to optical frequencies using a synchrotron model that entails a log-parabolic distribution of electron energies. A significant correlation among the two fitted spectral parameters ($a$, $b$) of log-parabolic curves and a negative trend among the peak frequency and spectral curvature parameter, $b$, emphasize that the SEDs of blazars are fitted well by log-parabolic curves. On considering each model parameter that could be responsible for changes in the observed SEDs of these blazars, we find that changes in the jet Doppler factors are most important.
Published: 2011
Full Text: View/download PDF

31. Multiwavelength temporal and spectral variability of the blazar OJ 287 during and after the 2015 December flare: a major accretion disc contribution

Author: Kushwaha, Pankaj, primary, Gupta, Alok C., additional, Wiita, Paul J., additional, Gaur, Haritma, additional, de Gouveia Dal Pino, E. M., additional, Bhagwan, Jai, additional, Kurtanidze, O. M., additional, Larionov, V. M., additional, Damljanovic, G., additional, Uemura, M., additional, Semkov, E., additional, Strigachev, A., additional, Bachev, R., additional, Vince, O., additional, Gu, Minfeng, additional, Zhang, Z., additional, Abe, T., additional, Agarwal, A., additional, Borman, G. A., additional, Fan, J. H., additional, Grishina, T. S., additional, Hirochi, J., additional, Itoh, R., additional, Kawabata, M., additional, Kopatskaya, E. N., additional, Kurtanidze, S. O., additional, Larionova, E. G., additional, Larionova, L. V., additional, Mishra, A., additional, Morozova, D. A., additional, Nakaoka, T., additional, Nikolashvili, M. G., additional, Savchenko, S. S., additional, Troitskaya, Yu. V., additional, Troitsky, I. S., additional, and Vasilyev, A. A., additional
Published: 2017
Full Text: View/download PDF

32. Dissecting the long-term emission behaviour of the BL Lac object Mrk 421

Author: Carnerero, M. I., primary, Raiteri, C. M., additional, Villata, M., additional, Acosta-Pulido, J. A., additional, Larionov, V. M., additional, Smith, P. S., additional, D'Ammando, F., additional, Agudo, I., additional, Arévalo, M. J., additional, Bachev, R., additional, Barnes, J., additional, Boeva, S., additional, Bozhilov, V., additional, Carosati, D., additional, Casadio, C., additional, Chen, W. P., additional, Damljanovic, G., additional, Eswaraiah, E., additional, Forné, E., additional, Gantchev, G., additional, Gómez, J. L., additional, González-Morales, P. A., additional, Griñón-Marín, A. B., additional, Grishina, T. S., additional, Holden, M., additional, Ibryamov, S., additional, Joner, M. D., additional, Jordan, B., additional, Jorstad, S. G., additional, Joshi, M., additional, Kopatskaya, E. N., additional, Koptelova, E., additional, Kurtanidze, O. M., additional, Kurtanidze, S. O., additional, Larionova, E. G., additional, Larionova, L. V., additional, Latev, G., additional, Lázaro, C., additional, Ligustri, R., additional, Lin, H. C., additional, Marscher, A. P., additional, Martínez-Lombilla, C., additional, McBreen, B., additional, Mihov, B., additional, Molina, S. N., additional, Moody, J. W., additional, Morozova, D. A., additional, Nikolashvili, M. G., additional, Nilsson, K., additional, Ovcharov, E., additional, Pace, C., additional, Panwar, N., additional, Pastor Yabar, A., additional, Pearson, R. L., additional, Pinna, F., additional, Protasio, C., additional, Rizzi, N., additional, Redondo-Lorenzo, F. J., additional, Rodríguez-Coira, G., additional, Ros, J. A., additional, Sadun, A. C., additional, Savchenko, S. S., additional, Semkov, E., additional, Slavcheva-Mihova, L., additional, Smith, N., additional, Strigachev, A., additional, Troitskaya, Yu. V., additional, Troitsky, I. S., additional, Vasilyev, A. A., additional, and Vince, O., additional
Published: 2017
Full Text: View/download PDF

33. A peculiar multiwavelength flare in the blazar 3C 454.3

Author: Gupta, Alok C., primary, Mangalam, Arun, additional, Wiita, Paul J., additional, Kushwaha, P., additional, Gaur, H., additional, Zhang, H., additional, Gu, M. F., additional, Liao, M., additional, Dewangan, G. C., additional, Ho, L. C., additional, Mohan, P., additional, Umeura, M., additional, Sasada, M., additional, Volvach, A. E., additional, Agarwal, A., additional, Aller, M. F., additional, Aller, H. D., additional, Bachev, R., additional, Lähteenmäki, A., additional, Semkov, E., additional, Strigachev, A., additional, Tornikoski, M., additional, and Volvach, L. N., additional
Published: 2017
Full Text: View/download PDF

34. Intra-night variability of the blazar CTA 102 during its 2012 and 2016 giant outbursts

Author: Bachev, R., primary, Popov, V., additional, Strigachev, A., additional, Semkov, E., additional, Ibryamov, S., additional, Spassov, B., additional, Latev, G., additional, Muñoz Dimitrova, R. V., additional, and Boeva, S., additional
Published: 2017
Full Text: View/download PDF

35. Synchrotron emission from the blazar PG 1553+113. An analysis of its flux and polarization variability

Author: Raiteri, C. M., primary, Nicastro, F., additional, Stamerra, A., additional, Villata, M., additional, Larionov, V. M., additional, Blinov, D., additional, Acosta-Pulido, J. A., additional, Arévalo, M. J., additional, Arkharov, A. A., additional, Bachev, R., additional, Borman, G. A., additional, Carnerero, M. I., additional, Carosati, D., additional, Cecconi, M., additional, Chen, W.-P., additional, Damljanovic, G., additional, Di Paola, A., additional, Ehgamberdiev, Sh. A., additional, Frasca, A., additional, Giroletti, M., additional, González-Morales, P. A., additional, Griñon-Marín, A. B., additional, Grishina, T. S., additional, Huang, P.-C., additional, Ibryamov, S., additional, Klimanov, S. A., additional, Kopatskaya, E. N., additional, Kurtanidze, O. M., additional, Kurtanidze, S. O., additional, Lähteenmäki, A., additional, Larionova, E. G., additional, Larionova, L. V., additional, Lázaro, C., additional, Leto, G., additional, Liodakis, I., additional, Martínez-Lombilla, C., additional, Mihov, B., additional, Mirzaqulov, D. O., additional, Mokrushina, A. A., additional, Moody, J. W., additional, Morozova, D. A., additional, Nazarov, S. V., additional, Nikolashvili, M. G., additional, Ohlert, J. M., additional, Panopoulou, G. V., additional, Pastor Yabar, A., additional, Pinna, F., additional, Protasio, C., additional, Rizzi, N., additional, Sadun, A. C., additional, Savchenko, S. S., additional, Semkov, E., additional, Sigua, L. A., additional, Slavcheva-Mihova, L., additional, Strigachev, A., additional, Tornikoski, M., additional, Troitskaya, Yu. V., additional, Troitsky, I. S., additional, Vasilyev, A. A., additional, Vera, R. J. C., additional, Vince, O., additional, and Zanmar Sanchez, R., additional
Published: 2016
Full Text: View/download PDF

36. Short-term optical variability of high-redshift quasi-stellar objects

Author: Rumen Bachev, Evgeni Semkov, and Anton Strigachev
Subjects: Physics, Accretion rate, Space and Planetary Science, Wavelength range, Astrophysics::High Energy Astrophysical Phenomena, Astronomy and Astrophysics, Time resolution, Quasar, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Redshift, Statistical evidence
Abstract: This paper presents results of a search for short-term variability in the optical band of selected high-luminosity, high-redshift radio-quiet quasars. Each quasar has been monitored typically for 2 – 4 hours with a time resolution of 2 – 5 minutes and a photometric accuracy of about 0. m 01 – 0. m 02. Due to the significant redshift (z > 2), the covered wavelength range falls into the UV region (typically 1500 – 2500u We found no statistical evidence for any continuum variations larger than 0. 01 – 0. 02 for any of the monitored objects. Our results suggest that the presence of a short-term variability in radio-quiet quasars is unlikely even in the UV region, contrary to reports by other authors. This conclusion holds true at least for high-luminosity (large black hole mass and accretion rate?) objects. The results are consistent with the idea that significant short-term (less than 1 hour) variations in AGN, where observed, should be attributed primarily to processes in a relativistic jet.
Published: 2005
Full Text: View/download PDF

37. Multiwavelength behaviour of the blazar OJ 248 from radio to gamma-rays

Author: M. I. Carnerero, Sofia O. Kurtanidze, J. A. Acosta-Pulido, E. N. Kopatskaya, Paolo Leto, C. S. Lin, A. B. Grinon-Marin, Sol N. Molina, D. A. Morozova, H. C. Lin, R. Bachev, Neelam Panwar, A. I. Manilla-Robles, M. Orienti, Valeri M. Larionov, Marcello Giroletti, J. L. Gomez, P. A. González-Morales, Antoniya Valcheva, Carolina Casadio, Anne Lähteenmäki, Helmut Wiesemeyer, Uwe Bach, Goran Damljanović, Corrado Trigilio, Y. T. Metodieva, D. O. Mirzaqulov, Sunay Ibryamov, Elena G. Larionova, A. Bueno Bueno, T. S. Grishina, H. Y. Hsiao, V. Ramakrishnan, G. Umana, D. Carosati, Wen Ping Chen, Arkady A. Arkharov, V. Bozhilov, Ivan Agudo, Mark Gurwell, A. Pastor Yabar, I. M. McHardy, David Hiriart, Carla Buemi, Manasvita Joshi, A. Strigachev, Alan P. Marscher, S. G. Jorstad, A. Di Paola, Lorand A. Sigua, L. V. Larionova, M. J. Arévalo, N. V. Efimova, D. Blinov, Erika Benítez, C. M. Raiteri, Brian W. Taylor, Omar M. Kurtanidze, I. Puerto Giménez, Evgeni Ovcharov, Yu. V. Troitskaya, M. G. Nikolashvili, Sergio Velasco, Ann E. Wehrle, A. A. Mokrushina, Paul S. Smith, M. Villata, Ivan S. Troitsky, Sh. A. Ehgamberdiev, Merja Tornikoski, M. Rossini, G. M. Richter, Filippo D'Ammando, C. Lázaro, O. Vince, Carnerero MI, Raiteri CM, Villata M, Acosta-Pulido JA, DAmmando F, Smith PS, Larionov VM, Agudo I, Arevalo MJ, Arkharov AA, Bach U, Bachev R, Benitez E, Blinov DA, Bozhilov V, Buemi CS, Bueno AB, Carosati D, Casadio C, Chen WP, Damljanovic G, Di Paola A, Efimova NV, Ehgamberdiev SA, Giroletti M, Gomez JL, Gonzalez-Morales PA, Grinon-Marin AB, Grishina TS, Gurwell MA, Hiriart D, Hsiao HY, Ibryamov S, Jorstad SG, Joshi M, Kopatskaya EN, Kurtanidze OM, Kurtanidze SO, Lahteenmaki A, Larionova EG, Larionova LV, Lazaro C, Leto P, Lin CS, Lin HC, Manilla-Robles AI, Marscher AP, McHardy IM, Metodieva Y, Mirzaqulov DO, Mokrushina AA, Molina SN, Morozova DA, Nikolashvili MG, Orienti M, Ovcharov E, Panwar N, Yabar AP, Gimenez IP, Ramakrishnan V, Richter GM, Rossini M, Sigua LA, Strigachev A, Taylor B, Tornikoski M, Trigilio C, Troitskaya YV, Troitsky IS, Umana G, Valcheva A, Velasco S, Vince O, Wehrle AE, Wiesemeyer H, Anne Lähteenmäki Group, Department of Radio Science and Engineering, Aalto-yliopisto, and Aalto University
Subjects: active [Galaxies], Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, ta221, galaxies: active, ta1171, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, law.invention, Telescope, Observatory, law, quasars: general, Emission spectrum, Blazar, ta216, Physics, individual: OJ 248 [Quasars], ta115, ta213, ta114, Linear polarization, quasars: individual: OJ 248, Astronomy, Astronomy and Astrophysics, general [Quasars], galaxies: active, galaxies: jets, quasars: general, quasars: individual: OJ 248, galaxies: jets, Light curve, Astrophysics - Astrophysics of Galaxies, Space and Planetary Science, jets [Galaxies], Astrophysics - High Energy Astrophysical Phenomena, Fermi Gamma-ray Space Telescope
Abstract: We present an analysis of the multiwavelength behaviour of the blazar OJ 248 at z = 0.939 in the period 2006-2013. We use low-energy data (optical, near-infrared, and radio) obtained by 21 observatories participating in the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT), as well as data from the Swift (optical-UV and X-rays) and Fermi (gamma-rays) satellites, to study flux and spectral variability and correlations among emissions in different bands. We take into account the effect of absorption by the Damped Lyman Alpha intervening system at z = 0.525. Two major outbursts were observed in 2006-2007 and in 2012-2013 at optical and near-IR wavelengths, while in the high-frequency radio light curves prominent radio outbursts are visible peaking at the end of 2010 and beginning of 2013, revealing a complex radio-optical correlation. Cross-correlation analysis suggests a delay of the optical variations after the gamma-ray ones of about a month, which is a peculiar behaviour in blazars. We also analyse optical polarimetric and spectroscopic data. The average polarization percentage P is less than 3 per cent, but it reaches about 19 per cent during the early stage of the 2012-2013 outburst. A vague correlation of P with brightness is observed. There is no preferred electric vector polarisation angle and during the outburst the linear polarization vector shows wide rotations in both directions, suggesting a complex behaviour or structure of the jet and possible turbulence. The analysis of 140 optical spectra acquired at the Steward Observatory reveals a strong Mg II broad emission line with an essentially stable flux of 6.2 e-15 erg cm-2 s-1 and a full width at half-maximum of 2053 km s-1., Comment: 16 pages, 20 figures, 2 tables, in press for MNRAS
Published: 2015

38. Multiband optical variability of the blazar OJ 287 during its outbursts in 2015–2016

Author: Gupta, Alok C., primary, Agarwal, Aditi, additional, Mishra, Alka, additional, Gaur, H., additional, Wiita, P. J., additional, Gu, M. F., additional, Kurtanidze, O. M., additional, Damljanovic, G., additional, Uemura, M., additional, Semkov, E., additional, Strigachev, A., additional, Bachev, R., additional, Vince, O., additional, Zhang, Z., additional, Villarroel, B., additional, Kushwaha, P., additional, Pandey, A., additional, Abe, T., additional, Chanishvili, R., additional, Chigladze, R. A., additional, Fan, J. H., additional, Hirochi, J., additional, Itoh, R., additional, Kanda, Y., additional, Kawabata, M., additional, Kimeridze, G. N., additional, Kurtanidze, S. O., additional, Latev, G., additional, Dimitrova, R. V. Muñoz, additional, Nakaoka, T., additional, Nikolashvili, M. G., additional, Shiki, K., additional, Sigua, L. A., additional, and Spassov, B., additional
Published: 2016
Full Text: View/download PDF

39. Exceptional outburst of the blazar CTA 102 in 2012: the GASP–WEBT campaign and its extension

Author: Larionov, V. M., primary, Villata, M., additional, Raiteri, C. M., additional, Jorstad, S. G., additional, Marscher, A. P., additional, Agudo, I., additional, Smith, P. S., additional, Acosta-Pulido, J. A., additional, ˙arévalo, M. J., additional, Arkharov, A. A., additional, Bachev, R., additional, Blinov, D. A., additional, Borisov, G., additional, Borman, G. A., additional, Bozhilov, V., additional, Bueno, A., additional, Carnerero, M. I., additional, Carosati, D., additional, Casadio, C., additional, Chen, W. P., additional, Clemens, D. P., additional, Di Paola, A., additional, Ehgamberdiev, Sh. A., additional, Gómez, J. L., additional, González-Morales, P. A., additional, Griñón-Marín, A., additional, Grishina, T. S., additional, Hagen-Thorn, V. A., additional, Ibryamov, S., additional, Itoh, R., additional, Joshi, M., additional, Kopatskaya, E. N., additional, Koptelova, E., additional, Lázaro, C., additional, Larionova, E. G., additional, Larionova, L. V., additional, Manilla-Robles, A., additional, Metodieva, Y., additional, Milanova, Yu. V., additional, Mirzaqulov, D. O., additional, Molina, S. N., additional, Morozova, D. A., additional, Nazarov, S. V., additional, Ovcharov, E., additional, Peneva, S., additional, Ros, J. A., additional, Sadun, A. C., additional, Savchenko, S. S., additional, Semkov, E., additional, Sergeev, S. G., additional, Strigachev, A., additional, Troitskaya, Yu. V., additional, and Troitsky, I. S., additional
Published: 2016
Full Text: View/download PDF

40. Multiband optical variability of three TeV blazars on diverse time-scales

Author: Gupta, Alok C., primary, Agarwal, A., additional, Bhagwan, J., additional, Strigachev, A., additional, Bachev, R., additional, Semkov, E., additional, Gaur, H., additional, Damljanovic, G., additional, Vince, O., additional, and Wiita, Paul J., additional
Published: 2016
Full Text: View/download PDF

41. Kepler light-curve analysis of the blazar W2R 1926+42

Author: Mohan, P., primary, Gupta, Alok C., additional, Bachev, Rumen, additional, and Strigachev, Anton, additional
Published: 2015
Full Text: View/download PDF

42. Multiwavelength temporal and spectral variability of the blazar OJ 287 during and after the 2015 December flare: a major accretion disc contribution.

Author: Kushwaha, Pankaj, Gupta, Alok C., Wiita, Paul J., Gaur, Haritma, de Gouveia Dal Pino, E. M., Bhagwan, Jai, Kurtanidze, O. M., Larionov, V. M., Damljanovic, G., Uemura, M., Semkov, E., Strigachev, A., Bachev, R., Vince, O., Minfeng Gu, Zhang, Z., Abe, T., Agarwal, A., Borman, G. A., and Fan, J. H.
Subjects: ACCRETION (Astrophysics), FLARES, SPECTRAL energy distribution, BINARY black holes, SUPERMASSIVE black holes, COMPTON scattering
Abstract: We present a multiwavelength spectral and temporal analysis of the blazar OJ 287 during its recent activity between 2015 December and 2016 May, showing strong variability in the nearinfrared (NIR) to X-ray energies with detection at γ -ray energies as well. Most of the optical flux variations exhibit strong changes in polarization angle and degree. All the interband time lags are consistent with simultaneous emissions. Interestingly, on days with excellent data coverage in the NIR-UV bands, the spectral energy distributions (SEDs) show signatures of bumps in the visible-UV bands, never seen before in this source. The optical bump can be explained as accretion-disc emission associated with the primary black hole of mass ~1.8 × 1010 M☉ while the little bump feature in the optical-UV appears consistent with line emission. Further, the broad-band SEDs extracted during the first flare and during a quiescent period during this span show very different γ -ray spectra compared to previously observed flare or quiescent spectra. The probable thermal bump in the visible seems to have been clearly present since 2013 May, as found by examining all available NIR-optical observations, and favours the binary supermassive black hole model. The simultaneous multiwavelength variability and relatively weak γ -ray emission that shows a shift in the SED peak is consistent with γ -ray emission originating from inverse Compton scattering of photons from the line emission that apparently contributes to the little blue bump. [ABSTRACT FROM AUTHOR]
Published: 2018
Full Text: View/download PDF

43. Multiband optical variability of the blazar S5 0716+714 in outburst state during 2014–2015

Author: Agarwal, Aditi, primary, Gupta, Alok C., additional, Bachev, R., additional, Strigachev, A., additional, Semkov, E., additional, Wiita, Paul J., additional, Fan, J. H., additional, Pandey, U. S., additional, Boeva, S., additional, and Spassov, B., additional
Published: 2015
Full Text: View/download PDF

44. The WEBT campaign on the BL Lac object PG 1553+113 in 2013. An analysis of the enigmatic synchrotron emission

Author: Raiteri, C. M., primary, Stamerra, A., additional, Villata, M., additional, Larionov, V. M., additional, Acosta-Pulido, J. A., additional, Arévalo, M. J., additional, Arkharov, A. A., additional, Bachev, R., additional, Benítez, E., additional, Bozhilov, V. V., additional, Borman, G. A., additional, Buemi, C. S., additional, Calcidese, P., additional, Carnerero, M. I., additional, Carosati, D., additional, Chigladze, R. A., additional, Damljanovic, G., additional, Di Paola, A., additional, Doroshenko, V. T., additional, Efimova, N. V., additional, Ehgamberdiev, Sh. A., additional, Giroletti, M., additional, González-Morales, P. A., additional, Grinon-Marin, A. B., additional, Grishina, T. S., additional, Hiriart, D., additional, Ibryamov, S., additional, Klimanov, S. A., additional, Kopatskaya, E. N., additional, Kurtanidze, O. M., additional, Kurtanidze, S. O., additional, Kurtenkov, A. A., additional, Larionova, L. V., additional, Larionova, E. G., additional, Lázaro, C., additional, Lähteenmäki, A., additional, Leto, P., additional, Markovic, G., additional, Mirzaqulov, D. O., additional, Mokrushina, A. A., additional, Morozova, D. A., additional, Mújica, R., additional, Nazarov, S. V., additional, Nikolashvili, M. G., additional, Ohlert, J. M., additional, Ovcharov, E. P., additional, Paiano, S., additional, Pastor Yabar, A., additional, Prandini, E., additional, Ramakrishnan, V., additional, Sadun, A. C., additional, Semkov, E., additional, Sigua, L. A., additional, Strigachev, A., additional, Tammi, J., additional, Tornikoski, M., additional, Trigilio, C., additional, Troitskaya, Yu. V., additional, Troitsky, I. S., additional, Umana, G., additional, Velasco, S., additional, and Vince, O., additional
Published: 2015
Full Text: View/download PDF

45. Nature of intranight optical variability of BL Lacertae

Author: Gaur, Haritma, primary, Gupta, Alok C., additional, Bachev, R., additional, Strigachev, A., additional, Semkov, E., additional, Böttcher, M., additional, Wiita, P. J., additional, de Diego, J. A., additional, Gu, M. F., additional, Guo, H., additional, Joshi, R., additional, Mihov, B., additional, Palma, N., additional, Peneva, S., additional, Rajasingam, A., additional, and Slavcheva-Mihova, L., additional
Published: 2015
Full Text: View/download PDF

46. Multiband optical–NIR variability of blazars on diverse time-scales

Author: Agarwal, Aditi, primary, Gupta, Alok C., additional, Bachev, R., additional, Strigachev, A., additional, Semkov, E., additional, Wiita, Paul J., additional, Böttcher, M., additional, Boeva, S., additional, Gaur, H., additional, Gu, M. F., additional, Peneva, S., additional, Ibryamov, S., additional, and Pandey, U. S., additional
Published: 2015
Full Text: View/download PDF

47. Multiwavelength behaviour of the blazar OJ 248 from radio to γ-rays★

Author: Carnerero, M. I., primary, Raiteri, C. M., additional, Villata, M., additional, Acosta-Pulido, J. A., additional, D'Ammando, F., additional, Smith, P. S., additional, Larionov, V. M., additional, Agudo, I., additional, Arévalo, M. J., additional, Arkharov, A. A., additional, Bach, U., additional, Bachev, R., additional, Benítez, E., additional, Blinov, D. A., additional, Bozhilov, V., additional, Buemi, C. S., additional, Bueno Bueno, A., additional, Carosati, D., additional, Casadio, C., additional, Chen, W. P., additional, Damljanovic, G., additional, Paola, A. Di, additional, Efimova, N. V., additional, Ehgamberdiev, Sh. A., additional, Giroletti, M., additional, Gómez, J. L., additional, González-Morales, P. A., additional, Grinon-Marin, A. B., additional, Grishina, T. S., additional, Gurwell, M. A., additional, Hiriart, D., additional, Hsiao, H. Y., additional, Ibryamov, S., additional, Jorstad, S. G., additional, Joshi, M., additional, Kopatskaya, E. N., additional, Kurtanidze, O. M., additional, Kurtanidze, S. O., additional, Lähteenmäki, A., additional, Larionova, E. G., additional, Larionova, L. V., additional, Lázaro, C., additional, Leto, P., additional, Lin, C. S., additional, Lin, H. C., additional, Manilla-Robles, A. I., additional, Marscher, A. P., additional, McHardy, I. M., additional, Metodieva, Y., additional, Mirzaqulov, D. O., additional, Mokrushina, A. A., additional, Molina, S. N., additional, Morozova, D. A., additional, Nikolashvili, M. G., additional, Orienti, M., additional, Ovcharov, E., additional, Panwar, N., additional, Pastor Yabar, A., additional, Puerto Giménez, I., additional, Ramakrishnan, V., additional, Richter, G. M., additional, Rossini, M., additional, Sigua, L. A., additional, Strigachev, A., additional, Taylor, B., additional, Tornikoski, M., additional, Trigilio, C., additional, Troitskaya, Yu. V., additional, Troitsky, I. S., additional, Umana, G., additional, Valcheva, A., additional, Velasco, S., additional, Vince, O., additional, Wehrle, A. E., additional, and Wiesemeyer, H., additional
Published: 2015
Full Text: View/download PDF

48. Short-term flux and colour variations in low-energy peaked blazars

Author: Svetla Tsvetkova, Svetlana Boeva, Evgeni Ovcharov, Paul J. Wiita, A. Valcheva, K. A. Stoyanov, B. Spassov, Bindu Rani, Boyko Mihov, Anton Strigachev, Alok C. Gupta, Rumen Bachev, Evgeni Semkov, and S. Peneva
Subjects: Physics, Brightness, Active galactic nucleus, Low energy, Space and Planetary Science, Magnitude (astronomy), Flux, Astronomy and Astrophysics, Quasar, Astrophysics, Blazar, Term (time)
Abstract: We have measured multi-band optical flux and colour variations for a sample of 12 low energy peaked blazars on short, day-to-month, timescales. Our sample contains six BL Lacertae objects and six flat spectrum radio quasars. These photometric observations, made during September 2008 to June 2009, used five optical telescopes, one in India and four in Bulgaria. We detected short term flux variations in eleven of these blazars and colour variability in eight of them. Our data indicate that six blazars (3C 66A, AO 0235+164, S5 0716+714, PKS 0735+178, OJ 287 and 3C 454.3) were observed in preor post-outburst states, that five (PKS 0420 014, 4C 29.45, 3C 279, PKS 1510 089 and BL Lac) were in a low state, while one (3C 273) was in an essentially steady state. The duty cycles for flux and colour variations on short timescales in these low energy peaked blazars are �92 per cent and � 33 per cent, respectively. The colour vs magnitude correlations seen here support the hypothesis that BL Lac objects tend to become bluer with increase in brightness; however, flat spectrum radio quasars may show the opposite trend, and there are exceptions to these trends in both categories of blazar. We briefly discuss emission models for active galactic nuclei that might explain our results.
Published: 2010
Full Text: View/download PDF

49. Multiband optical variability of the blazar OJ 287 during its outbursts in 2015-2016.

Author: Gupta, Alok C., Agarwal, Aditi, Mishra, Alka, Gaur, H., Wiita, P. J., Gu, M. F., Kurtanidze, O. M., Damljanovic, G., Uemura, M., Semkov, E., Strigachev, A., Bachev, R., Vince, O., Zhang, Z., Villarroel, B., Kushwaha, P., Pandey, A., Abe, T., Chanishvili, R., and Chigladze, R. A.
Subjects: BL Lacertae objects, OPTICAL telescopes, ASTRONOMICAL photometry, BINARY black holes, EMISSION spectroscopy
Abstract: We present recent optical photometric observations of the blazar OJ 287 taken during 2015 September-2016 May. Our intense observations of the blazar started in 2015 November and continued until 2016 May and included detection of the large optical outburst in 2015 December that was predicted using the binary black hole model for OJ 287. For our observing campaign, we used a total of nine ground-based optical telescopes of which one is in Japan, one is in India, three are in Bulgaria, one is in Serbia, one is in Georgia, and two are in the USA. These observations were carried out in 102 nights with a total of ~1000 image frames in BVRI bands, though the majority were in the R band. We detected a second comparably strong flare in 2016 March. In addition, we investigated multiband flux variations, colour variations, and spectral changes in the blazar on diverse time-scales as they are useful in understanding the emission mechanisms. We briefly discuss the possible physical mechanisms most likely responsible for the observed flux, colour, and spectral variability. [ABSTRACT FROM AUTHOR]
Published: 2017
Full Text: View/download PDF

50. The awakening of BL Lacertae: observations by Fermi, Swift and the GASP-WEBT★

Author: Raiteri, C. M., primary, Villata, M., additional, D'Ammando, F., additional, Larionov, V. M., additional, Gurwell, M. A., additional, Mirzaqulov, D. O., additional, Smith, P. S., additional, Acosta-Pulido, J. A., additional, Agudo, I., additional, Arévalo, M. J., additional, Bachev, R., additional, Benítez, E., additional, Berdyugin, A., additional, Blinov, D. A., additional, Borman, G. A., additional, Böttcher, M., additional, Bozhilov, V., additional, Carnerero, M. I., additional, Carosati, D., additional, Casadio, C., additional, Chen, W. P., additional, Doroshenko, V. T., additional, Efimov, Yu. S., additional, Efimova, N. V., additional, Ehgamberdiev, Sh. A., additional, Gómez, J. L., additional, González-Morales, P. A., additional, Hiriart, D., additional, Ibryamov, S., additional, Jadhav, Y., additional, Jorstad, S. G., additional, Joshi, M., additional, Kadenius, V., additional, Klimanov, S. A., additional, Kohli, M., additional, Konstantinova, T. S., additional, Kopatskaya, E. N., additional, Koptelova, E., additional, Kimeridze, G., additional, Kurtanidze, O. M., additional, Larionova, E. G., additional, Larionova, L. V., additional, Ligustri, R., additional, Lindfors, E., additional, Marscher, A. P., additional, McBreen, B., additional, McHardy, I. M., additional, Metodieva, Y., additional, Molina, S. N., additional, Morozova, D. A., additional, Nazarov, S. V., additional, Nikolashvili, M. G., additional, Nilsson, K., additional, Okhmat, D. N., additional, Ovcharov, E., additional, Panwar, N., additional, Pasanen, M., additional, Peneva, S., additional, Phipps, J., additional, Pulatova, N. G., additional, Reinthal, R., additional, Ros, J. A., additional, Sadun, A. C., additional, Schwartz, R. D., additional, Semkov, E., additional, Sergeev, S. G., additional, Sigua, L. A., additional, Sillanpää, A., additional, Smith, N., additional, Stoyanov, K., additional, Strigachev, A., additional, Takalo, L. O., additional, Taylor, B., additional, Thum, C., additional, Troitsky, I. S., additional, Valcheva, A., additional, Wehrle, A. E., additional, and Wiesemeyer, H., additional
Published: 2013
Full Text: View/download PDF

Catalog

Books, media, physical & digital resources

See catalog results

Searchworks

Select search scope, currently: Articles Catalog books, media & more in Jio Institute collections Articles journal articles & other e-resources

Search

Search Constraints

Refine your results

Search Limiters

Topic

Publication Year Range

Language

Publication Type

Region

Database

Publisher

89 results on '"A. Strigachev"'

Search Results

Catalog

Select search scope, currently: Articles

Catalog

books, media & more in Jio Institute collections

Articles

journal articles & other e-resources