Browsing by Author "Lindfors, E."

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  • AGILE detection of extreme gamma-ray activity from the blazar PKS 1510-089 during March 2009. Multifrequency analysis
    (2011) "D'Ammando", F.; Raiteri, C.M.; Villata, M.; Romano, P.; Pucella, G.; Krimm, H.A.; Covino, S.; Orienti, M.; Giovannini, G.; Vercellone, S.; Pian, E.; Donnarumma, I.; Vittorini, V.; Tavani, M.; Argan, A.; Barbiellini, G.; Boffelli, F.; Bulgarelli, A.; Caraveo, P.; Cattaneo, P.W.; Chen, A.W.; Cocco, V.; Costa, E.; Del Monte, E.; de Paris, G.; Di Cocco, G.; Evangelista, Y.; Feroci, M.; Ferrari, A.; Fiorini, M.; Froysland, T.; Frutti, M.; Fuschino, F.; Galli, M.; Gianotti, F.; Giuliani, A.; Labanti, C.; Lapshov, I.; Lazzarotto, F.; Lipari, P.; Longo, F.; Marisaldi, M.; Mereghetti, S.; Morselli, A.; Pacciani, L.; Pellizzoni, A.; Perotti, F.; Piano, G.; Picozza, P.; Pilia, M.; Porrovecchio, Geiland; Prest, M.; Rapisarda, M.; Rappoldi, A.; Rubini, A.; Sabatini, S.; Soffitta, P.; Striani, E.; Trifoglio, M.; Trois, A.; Vallazza, E.; Zambra, A.; Zanello, D.; Agudo, I.; Aller, H.D.; Aller, M.F.; Arkharov, A.A.; Bach, U.; Benitez, E.; Berdyugin, A.; Blinov, D.A.; Buemi, C.S.; Chen, W.P.; di Paola, A.; Dolci, M.; Forné, E.; Fuhrmann, L.; Gómez, J.L.; Gurwell, M.A.; Jordan, B.; Jorstad, S.G.; Heidt, J.; Hiriart, D.; Hovatta, T.; Hsiao, H.Y.; Kimeridze, G.; Konstantinova, T.S.; Kopatskaya, E.N.; Koptelova, E.; Kurtanidze, O.M.; Kurtanidze, S.O.; Larionov, V.M.; Lähteenmäki, A.; Leto, P.; Lindfors, E.; Marscher, A.P.; McBreen, B.; McHardy, I.M.; Morozova, D.A.; Nilsson, K.; Pasanen, M.; Roca-Sogorb, M.; Sillanpää, A.; Takalo, L.O.; Tornikoski, M.; Trigilio, C.; Troitsky, I.S.; Umana, G.; Antonelli, Lucio A.; Colafrancesco, S.; Pittori, C.; Santolamazza, P.; Verrecchia, F.; Giommi, P.; Salotti, L.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Another look at the BL Lacertae flux and spectral variability. Observations by GASP-WEBT, XMM-Newton, and Swift in 2008-2009
    (2010) Raiteri, C.M.; Villata, M.; Bruschini, L.; Capetti, A.; Kurtanidze, O.M.; Larionov, V.M.; Romano, P.; Vercellone, S.; Agudo, I.; Aller, H.D.; Aller, M.F.; Arkharov, A.A.; Bach, U.; Berdyugin, A.; Blinov, D.A.; Böttcher, M.; Buemi, C.S.; Calcidese, P.; Carosati, D.; Casas, R.; Chen, W.-P.; Coloma, J.; Diltz, C.; di Paola, A.; Dolci, M.; Efimova, N.V.; Forné, E.; Gómez, J.L.; Gurwell, M.A.; Hakola, A.; Hovatta, T.; Hsiao, H.Y.; Jordan, B.; Jorstad, S.G.; Koptelova, E.; Kurtanidze, S.O.; Lähteenmäki, A.; Larionova, E.G.; Leto, P.; Lindfors, E.; Ligustri, R.; Marscher, A.P.; Morozova, D.A.; Nikolashvili, M.G.; Nilsson, K.; Ros, J.A.; Roustazadeh, P.; Sadun, A.C.; Sillanpää, A.; Sainio, J.; Takalo, L.O.; Tornikoski, M.; Trigilio, C.; Troitsky, I.S.; Umana, G.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Association of IceCube neutrinos with radio sources observed at Owens Valley and Metsähovi Radio Observatories
    (2021-06-10) Hovatta, T.; Lindfors, E.; Kiehlmann, S.; Max-Moerbeck, W.; Hodges, M.; Liodakis, I.; Lähteemäki, A.; Pearson, T. J.; Readhead, A.C.S.; Reeves, R. A.; Suutarinen, S.; Tammi, J.; Tornikoski, M.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Context. Identifying the most likely sources for high-energy neutrino emission has been one of the main topics in high-energy astrophysics ever since the first observation of high-energy neutrinos by the IceCube Neutrino Observatory. Active galactic nuclei with relativistic jets, also known as blazars, have been considered to be one of the main candidates because of their ability to accelerate particles to high energies. Aims. We study the connection between radio emission and IceCube neutrino events using data from the Owens Valley Radio Observatory (OVRO) and Metsähovi Radio Observatory blazar monitoring programs. Methods. We identify sources in our radio monitoring sample that are positionally consistent with IceCube high-energy neutrino events. We estimate their mean flux density and variability amplitudes around the neutrino arrival time, and compare these with values from random samples to establish the significance of our results. Results. We find radio source associations within our samples with 15 high-energy neutrino events detected by IceCube. Nearly half of the associated sources are not detected in the -ray energies, but their radio variability properties and Doppler boosting factors are similar to the -ray detected objects in our sample, meaning that they could still be potential neutrino emitters. We find that the number of strongly flaring objects in our statistically complete OVRO samples is unlikely to be a random coincidence (at 2_ level). Conclusions. Based on our results, we conclude that although it is clear that not all neutrino events are associated with strong radio flaring blazars, observations of large-amplitude radio flares in a blazar at the same time as a neutrino event are unlikely to be a random coincidence.
  • Confronting observations of VHE gamma-ray blazar flares with reconnection models
    (2022-03-18) Jormanainen, J.; Hovatta, T.; Lindfors, E.; Christie, I.; Petropoulou, M.; Liodakis, I.
     A4 Artikkeli konferenssijulkaisussa
    Several models have been suggested to explain the fast gamma-ray variability observed in blazars, but its origin is still debated. One scenario is magnetic reconnection, a process that can efficiently convert magnetic energy to energy of relativistic particles accelerated in the reconnection layer. In our study, we compare results from state-of-the-art particle-in-cell simulations with observations of blazars at Very High Energy (VHE, E > 100 GeV) gamma-rays. Our goal is to test our model predictions on fast gamma-ray variability with data and to constrain the parameter space of the model, such as the magnetic field strength of the unreconnected plasma and the reconnection layer orientation in the blazar jet. For this first comparison, we used the remarkably well-sampled VHE gamma-ray light curve of Mrk 421 observed with the MAGIC and VERITAS telescopes in 2013. The simulated VHE light curves were generated using the observable parameters of Mrk 421, such as the jet power, bulk Lorentz factor, and the jet viewing angle, and sampled as real data. Our results pave the way for future model-to-data comparison with next-generation Cherenkov telescopes, which will help further constrain the different variability models.
  • Discovery of VHE gamma-rays from the blazar 1ES 1215+303 with the MAGIC telescopes and simultaneous multi-wavelength observations
    (2012) Aleksic, J.; Alvarez, E.A.; Antonelli, L.A.; Antoranz, P.; Ansoldi, S.; Asensio, M.; Backes, M.; Barres de Almeida, U.; Barrio, J.A.; Bastieri, D.; Becerra González, J.; Bednarek, W.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bock, R.K.; Boller, A.; Bonnoli, G.; Borla Tridon, D.; Bretz, T.; Cañellas, A.; Carmona, E.; Carosi, A.; Colin, P.; Colombo, E.; Contreras, J.L.; Cortina, J.; Cossio, L.; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caneva, G.; De Cea del Pozo, E.; De Lotto, B.; Delgado Mendez, C.; Diago Ortega, A.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Eisenacher, D.; Elsaesser, D.; Ferenc, D.; Fonseca, M.V.; Font, L.; Fruck, C.; García López, R.J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Giavitto, G.; Godinovic, N.; González Muñoz, A.; Gozzini, S.R.; Hadasch, D.; Häfner, D.; Herrero, A.; Hildebrand, D.; Hose, J.; Hrupec, D.; Huber, B.; Jankowski, F.; Jogler, T.; Kadenius, V.; Kellermann, H.; Klepser, S.; Krähenbühl, T.; Krause, J.; La Barbera, A.; Lelas, D.; Leonardo, E.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Makariev, M.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Mazin, D.; Meucci, M.; Miranda, J.M.; Mirzoyan, R.; Moldón, J.; Moralejo, A.; Munar-Adrover, P.; Niedzwiecki, A.; Nieto, D.; Nilsson, K.; Nowak, N.; Orito, R.; Paiano, S.; Paneque, D.; Paoletti, R.; Pardo, S.; Paredes, J.M.; Partini, S.; Perez-Torres, M.A.; Persic, M.; Pilia, M.; Pochon, J.; Prada, F.; Prada Moroni, P.G.; Prandini, E.; Puerto Gimenez, I.; Puljak, I.; Reichardt, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rügamer, S.; Saggion, A.; Saito, K.; Saito, T.Y.; Salvati, M.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shore, S.N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Spanier, F.; Spiro, S.; Stamatescu, V.; Stamerra, A.; Steinke, B.; Storz, J.; Strah, N.; Sun, S.; Suric, T.; Takalo, L.; Takami, H.; Tavecchio, F.; Temnikov, P.; Terzic, T.; Tescaro, D.; Teshima, M.; Tibolla, O.; Torres, D.F.; Treves, A.; Uellenbeck, M.; Vogler, P.; Wagner, R.M.; Weitzel, Q.; Zabalza, V.; Zandanel, F.; Zanin, R.; Berdyugin, A.; Buson, S.; Järvelä, E.; Larsson, S.; Lähteenmäki, A.; Tammi, J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Distance estimation of gamma-ray-emitting BL Lac objects from imaging observations
    (2024-11-01) Nilsson, K.; Fallah Ramazani, V.; Lindfors, E.; Goldoni, P.; Becerra González, J.; Acosta Pulido, J. A.; Clavero, R.; Otero-Santos, J.; Pursimo, T.; Pita, S.; Kouch, P. M.; Boisson, C.; Backes, M.; Cotter, G.; D'Ammando, F.; Kasai, E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Aims. The direct redshift determination of BL Lac objects is highly challenging as the emission in the optical and near-infrared bands is largely dominated by the non-thermal emission from the relativistic jet, which points very close to our line of sight. Therefore, the optical spectra of BL Lac objects often show no spectral lines from the host galaxy. In this work, we aim to overcome this difficulty by attempting to detect the host galaxy and derive redshift constraints based on assumptions on the galaxy magnitude ('imaging redshifts'). Methods. Imaging redshifts were derived by obtaining deep optical images under good seeing conditions, making it possible to detect the host galaxy as a weak extension of the point-like source. We then derived the imaging redshift by using the host galaxy as a standard candle, employing two different methods. Results. We determine the imaging redshift for 9 out of 17 blazars that we observed as part of this programme. The redshift range of these targets is 0.28-0.60, and the two methods used to derive the redshift give very consistent results within the uncertainties. We also performed a detailed comparison of the imaging redshifts with those obtained using other methods, such as direct spectroscopic constraints or looking for groups of galaxies close to the blazar. We show that the constraints from the different methods are consistent and that combining the three constraints narrows down the redshift. For example, in the case of J2156.0+1818, which is the most distant source for which we detect the host galaxy, the redshift range is narrowed to 0.63 < z < 0.71. This makes the source interesting for future studies of extragalactic background light in the Cherenkov Telescope Array Observatory era.
  • First characterization of the emission behavior of Mrk 421 from radio to very high-energy gamma rays with simultaneous X-ray polarization measurements
    (2024-04-01) Abe, S.; Abhir, J.; Acciari, V. A.; Agudo, I.; Aniello, T.; Ansoldi, S.; Antonelli, L. A.; Arbet-Engels, A.; Arcaro, C.; Artero, M.; Asano, K.; Babić, A.; Baquero, A.; de Almeida, U. Barres; Barrio, J. A.; Batković, I.; Baxter, J.; González, J. Becerra; Bednarek, W.; Bernardini, E.; Bernete, J.; Berti, A.; Besenrieder, J.; Bigongiari, C.; Biland, A.; Blanch, O.; Bonnoli, G.; Bošnjak; Burelli, I.; Busetto, G.; Campoy-Ordaz, A.; Carosi, A.; Carosi, R.; Carretero-Castrillo, M.; Castro-Tirado, A. J.; Ceribella, G.; Chai, Y.; Cifuentes, A.; Cikota, S.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; D'Ammando, F.; D'Amico, G.; D'Elia, V.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; de Menezes, R.; Del Popolo, A.; Delgado, J.; Mendez, C. Delgado; Di Pierro, F.; Di Venere, L.; Prester, D. Dominis; Donini, A.; Dorner, D.; Doro, M.; Elsaesser, D.; Emery, G.; Escudero, J.; Fariña, L.; Fattorini, A.; Foffano, L.; Font, L.; Fröse, S.; Fukami, S.; Fukazawa, Y.; López, R. J.García; Garczarczyk, M.; Gasparyan, S.; Gaug, M.; Paiva, J. G.Giesbrecht; Giglietto, N.; Giordano, F.; Gliwny, P.; Godinović, N.; Gradetzke, T.; Grau, R.; Green, D.; Green, J. G.; Günther, P.; Hadasch, D.; Hahn, A.; Hassan, T.; Heckmann, L.; Herrera, J.; Hrupec, D.; Hütten, M.; Imazawa, R.; Inada, T.; Ishio, K.; Martínez, I. Jiménez; Jormanainen, J.; Kerszberg, D.; Kluge, G. W.; Kobayashi, Y.; Kouch, P. M.; Kubo, H.; Kushida, J.; Lezáun, M. Láinez; Lamastra, A.; Leone, F.; Lindfors, E.; Linhoff, L.; Lombardi, S.; Longo, F.; López-Coto, R.; López-Moya, M.; López-Oramas, A.; Loporchio, S.; Lorini, A.; de Oliveira Fraga, B. Machado; Majumdar, P.; Makariev, M.; Maneva, G.; Mang, N.; Manganaro, M.; Mangano, S.; Mannheim, K.; Mariotti, M.; Martínez, M.; Martínez-Chicharro, M.; Mas-Aguilar, A.; Mazin, D.; Menchiari, S.; Mender, S.; Miceli, D.; Miener, T.; Miranda, J. M.; Mirzoyan, R.; González, M. Molero; Molina, E.; Mondal, H. A.; Moralejo, A.; Morcuende, D.; Nakamori, T.; Nanci, C.; Nava, L.; Neustroev, V.; Nickel, L.; Rosillo, M. Nievas; Nigro, C.; Nikolić, L.; Nilsson, K.; Nishijima, K.; Ekoume, T. Njoh; Noda, K.; Nozaki, S.; Ohtani, Y.; Okumura, A.; Otero-Santos, J.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Pavlović, D.; Peresano, M.; Persic, M.; Pihet, M.; Pirola, G.; Podobnik, F.; Moroni, P. G.Prada; Prandini, E.; Principe, G.; Priyadarshi, C.; Rhode, W.; Ribó, M.; Rico, J.; Righi, C.; Sahakyan, N.; Saito, T.; Satalecka, K.; Saturni, F. G.; Schleicher, B.; Schmidt, K.; Schmuckermaier, F.; Schubert, J. L.; Schweizer, T.; Sciaccaluga, A.; Sitarek, J.; Sliusar, V.; Sobczynska, D.; Stamerra, A.; Strišković, J.; Strom, D.; Strzys, M.; Suda, Y.; Suutarinen, S.; Tajima, H.; Takahashi, M.; Tavecchio, F.; Temnikov, P.; Terauchi, K.; Terzić, T.; Teshima, M.; Tosti, L.; Truzzi, S.; Tutone, A.; Ubach, S.; van Scherpenberg, J.; Acosta, M. Vazquez; Ventura, S.; Viale, I.; Vigorito, C. F.; Vitale, V.; Vovk, I.; Walter, R.; Will, M.; Wunderlich, C.; Yamamoto, T.; Liodakis, I.; Jorstad, S. G.; Di Gesu, L.; Donnarumma, I.; Kim, D. E.; Marscher, A. P.; Middei, R.; Perri, M.; Puccetti, S.; Verrecchia, F.; Leto, C.; De La Calle Pérez, I.; Jiménez-Bailón, E.; Blinov, D.; Bourbah, I. G.; Kiehlmann, S.; Kontopodis, E.; Mandarakas, N.; Skalidis, R.; Vervelaki, A.; Aceituno, F. J.; Agís-González, B.; Sota, A.; Sasada, M.; Kawabata, K. S.; Uemura, M.; Mizuno, T.; Akitaya, H.; Casadio, C.; Myserlis, I.; Sievers, A.; Lähteenmäki, A.; Syrjärinne, I.; Tornikoski, M.; Salomé, Q.; Gurwell, M.; Keating, G. K.; Rao, R.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Aims. We have performed the first broadband study of Mrk 421 from radio to TeV gamma rays with simultaneous measurements of the X-ray polarization from IXPE. Methods. The data were collected as part of an extensive multiwavelength campaign carried out between May and June 2022 using MAGIC, Fermi-LAT, NuSTAR, XMM-Newton, Swift, and several optical and radio telescopes to complement IXPE data. Results. During the IXPE exposures, the measured 0.2-1 TeV flux was close to the quiescent state and ranged from 25% to 50% of the Crab Nebula without intra-night variability. Throughout the campaign, the very high-energy (VHE) and X-ray emission are positively correlated at a 4σ significance level. The IXPE measurements reveal an X-ray polarization degree that is a factor of 2-5 higher than in the optical/radio bands; that implies an energy-stratified jet in which the VHE photons are emitted co-spatially with the X-rays, in the vicinity of a shock front. The June 2022 observations exhibit a rotation of the X-ray polarization angle. Despite no simultaneous VHE coverage being available during a large fraction of the swing, the Swift-XRT monitoring reveals an X-ray flux increase with a clear spectral hardening. This suggests that flares in high synchrotron peaked blazars can be accompanied by a polarization angle rotation, as observed in some flat spectrum radio quasars. Finally, during the polarization angle rotation, NuSTAR data reveal two contiguous spectral hysteresis loops in opposite directions (clockwise and counterclockwise), implying important changes in the particle acceleration efficiency on approximately hour timescales.
  • First multi-wavelength campaign on the gamma-ray-loud active galaxy IC 310
    (2017-07-01) Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.; Arcaro, C.; Babić, A.; Banerjee, B.; Bangale, P.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Berti, A.; Biasuzzi, B.; Biland, A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carosi, R.; Carosi, A.; Chatterjee, A.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Cumani, P.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; Oña-Wilhelmi, E.; Di Pierro, F.; Doert, M.; Domínguez, Alberto; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher Glawion, D.; Elsaesser, D.; Engelkemeier, M.; Fallah Ramazani, V.; Fernández-Barral, A.; Fidalgo, D.; Fonseca, M. V.; Font, L.; Fruck, C.; Galindo, D.; García López, R.J.; Garczarczyk, M.; Gaug, M.; Giammaria, P.; Godinović, N.; Gora, D.; Guberman, D.; Hadasch, D.; Hahn, A.; Hassan, T.; Hayashida, M.; Herrera, J.; Hose, J.; Hrupec, D.; Hughes, G.; Idec, W.; Ishio, K.; Kodani, K.; Konno, Y.; Kubo, H.; Kushida, J.; Lelas, D.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; Majumdar, P.; Makariev, M.; Mallot, K.; Maneva, G.; Manganaro, M.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Mirzoyan, R.; Moralejo, A.; Moretti, E.; Nakajima, D.; Neustroev, V.; Niedzwiecki, A.; Nievas Rosillo, M.; Nilsson, K.; Nishijima, K.; Noda, K.; Nogués, L.; Nöthe, M.; Paiano, S.; Palacio, J.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Paredes-Fortuny, X.; Pedaletti, G.; Peresano, M.; Perri, L.; Persic, M.; Poutanen, J.; Prada Moroni, P.G.; Prandini, E.; Puljak, I.; Rodriguez Garcia, J.; Reichardt, I.; Rhode, W.; Ribó, M.; Rico, J.; Saito, T.; Satalecka, K.; Schroeder, S.; Schweizer, T.; Shore, S. N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Stamerra, A.; Strzys, M.; Surić, T.; Takalo, L.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Torres, D. F.; Torres-Albà, N.; Toyama, T.; Treves, A.; Vanzo, G.; Vazquez Acosta, M.; Vovk, I.; Ward, Eric J; Will, M.; Wu, M. H.; Krauß, Felicia; Schulz, R.; Kadler, M.; Wilms, J.; Ros, E.; Bach, U.; Beuchert, T.; Langejahn, M.; Wendel, C.; Gehrels, N.; Baumgartner, W. H.; Markwardt, C.B.; Müller, C.; Grinberg, V.; Hovatta, T.; Magill, J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Context. The extragalactic very-high-energy gamma-ray sky is rich in blazars. These are jetted active galactic nuclei that are viewed at a small angle to the line-of-sight. Only a handful of objects viewed at a larger angle are so far known to emit above 100 GeV. Multi-wavelength studies of such objects up to the highest energies provide new insights into the particle and radiation processes of active galactic nuclei. Aims. We aim to report the results from the first multi-wavelength campaign observing the TeV detected nucleus of the active galaxy IC 310, whose jet is observed at a moderate viewing angle of 10°-20°. Methods. The multi-instrument campaign was conducted between 2012 November and 2013 January, and involved observations with MAGIC, Fermi, INTEGRAL, Swift, OVRO, MOJAVE and EVN. These observations were complemented with archival data from the AllWISE and 2MASS catalogs. A one-zone synchrotron self-Compton model was applied to describe the broadband spectral energy distribution. Results. IC 310 showed an extraordinary TeV flare at the beginning of the campaign, followed by a low, but still detectable TeV flux. Compared to previous measurements in this energy range, the spectral shape was found to be steeper during the low emission state. Simultaneous observations in the soft X-ray band showed an enhanced energy flux state and a harder-when-brighter spectral shape behavior. No strong correlated flux variability was found in other frequency regimes. The broadband spectral energy distribution obtained from these observations supports the hypothesis of a double-hump structure. Conclusions. The harder-when-brighter trend in the X-ray and VHE emission, observed for the first time during this campaign, is consistent with the behavior expected from a synchrotron self-Compton scenario. The contemporaneous broadband spectral energy distribution is well described with a one-zone synchrotron self-Compton model using parameters that are comparable to those found for other gamma-ray-emitting misaligned blazars.
  • The Great Markarian 421 Flare of 2010 February: Multiwavelength Variability and Correlation Studies
    (2020-02-20) Abeysekara, A. U.; Benbow, W.; Bird, R.; Brill, A.; Brose, R.; Buchovecky, M.; Buckley, J. H.; Christiansen, J. L.; Chromey, A. J.; Daniel, M. K.; Dumm, J.; Falcone, A.; Feng, Q.; Finley, J. P.; Fortson, L.; Furniss, A.; Galante, N.; Gent, A.; Gillanders, G. H.; Giuri, C.; Gueta, O.; Hassan, T.; Hervet, O.; Holder, J.; Hughes, G.; Humensky, T. B.; Johnson, C. A.; Kaaret, P.; Kar, P.; Kelley-Hoskins, N.; Kertzman, M.; Kieda, D.; Krause, M.; Krennrich, F.; Kumar, S.; Lang, M. J.; Moriarty, P.; Mukherjee, R.; Nelson, T.; Nieto, D.; Nievas Rosillo, M.; O'Brien, S.; Ong, R. A.; Otte, A. N.; Park, N.; Petrashyk, A.; Pichel, A.; Pohl, M.; Prado, R. R.; Pueschel, E.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Rovero, A. C.; Rulten, C.; Sadeh, I.; Santander, M.; Sembroski, G. H.; Shahinyan, K.; Stevenson, B.; Sushch, I.; Tyler, J.; Vassiliev, V. V.; Wakely, S. P.; Weinstein, A.; Wells, R. M.; Wilcox, P.; Wilhelm, A.; Williams, D. A.; Zitzer, B.; Acciari, V. A.; Ansoldi, S.; Antonelli, L. A.; Arbet Engels, A.; Baack, D.; Babić, A.; Banerjee, B.; Barres De Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bellizzi, L.; Bernardini, E.; Berti, A.; Besenrieder, J.; Bhattacharyya, W.; Bigongiari, C.; Biland, A.; Blanch, O.; Bonnoli, G.; Busetto, G.; Carosi, R.; Ceribella, G.; Chai, Y.; Cikota, S.; Colak, S. M.; Colin, U.; Colombo, E.; Contreras, J. L.; Cortina, Juan; Covino, S.; D'Elia, V.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; Delfino, M.; Delgado, J.; Di Pierro, F.; Do Souto Espiñera, E.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Elsaesser, D.; Fallah Ramazani, V.; Fattorini, A.; Fernández-Barral, A.; Ferrara, G.; Fidalgo, D.; Foffano, L.; Fonseca, M. V.; Font, L.; Fruck, C.; Galindo, D.; Gallozzi, S.; García López, R. J.; Garczarczyk, M.; Gasparyan, S.; Gaug, M.; Godinović, N.; Green, D.; Guberman, D.; Hadasch, D.; Hahn, A.; Herrera, J.; Hoang, J.; Hrupec, D.; Inoue, S.; Ishio, K.; Iwamura, Y.; Kubo, H.; Kushida, J.; Lamastra, A.; Lelas, D.; Leone, F.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; López-Coto, R.; López-Oramas, A.; Machado De Oliveira Fraga, B.; Maggio, C.; Majumdar, P.; Makariev, M.; Mallamaci, M.; Maneva, G.; Manganaro, M.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Masuda, S.; Mazin, D.; Miceli, D.; Minev, M.; Miranda, J. M.; Mirzoyan, R.; Molina, E.; Moralejo, A.; Morcuende, D.; Moreno, V.; Moretti, E.; Munar-Adrover, P.; Neustroev, V.; Niedzwiecki, A.; Nigro, C.; Nilsson, K.; Ninci, D.; Nishijima, K.; Noda, K.; Nogués, L.; Nöthe, M.; Paiano, S.; Palacio, J.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Penil, P.; Peresano, M.; Persic, M.; Prada Moroni, P. G.; Prandini, E.; Puljak, I.; Rhode, W.; Ribó, M.; Rico, J.; Righi, C.; Rugliancich, A.; Saha, L.; Sahakyan, N.; Saito, T.; Satalecka, K.; Schweizer, T.; Sitarek, J.; Šnidarić, I.; Sobczynska, D.; Somero, A.; Stamerra, A.; Strom, D.; Strzys, M.; Sun, S.; Surić, T.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Teshima, M.; Torres-Alba, N.; Tsujimoto, S.; Van Scherpenberg, J.; Vanzo, G.; Vazquez Acosta, M.; Vovk, I.; Will, Martin; Zarić, D.; Aller, H. D.; Aller, M. F.; Carini, M. T.; Horan, D.; Jordan, B.; Jorstad, S. G.; Kurtanidze, O. M.; Kurtanidze, S. O.; Lahteenmaki, Anne; Larionov, V. M.; Larionova, E. G.; Madejski, G.; Marscher, A. P.; Max-Moerbeck, W.; Moody, J. Ward; Morozova, D. A.; Nikolashvili, M. G.; Raiteri, C. M.; Readhead, A. C.S.; Richards, J. L.; Sadun, A. C.; Sakamoto, T.; Sigua, L. A.; Smith, P. S.; Talvikki, H.; Tammi, Joni; Tornikoski, Merja; Troitsky, I. S.; Villata, M.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of 2010 February, when an extraordinary flare reaching a level of ∼27 Crab Units above 1 TeV was measured in very high energy (VHE) γ-rays with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory. This is the highest flux state for Mrk 421 ever observed in VHE γ-rays. Data are analyzed from a coordinated campaign across multiple instruments, including VHE γ-ray (VERITAS, Major Atmospheric Gamma-ray Imaging Cherenkov), high-energy γ-ray (Fermi-LAT), X-ray (Swift, Rossi X-ray Timing Experiment, MAXI), optical (including the GASP-WEBT collaboration and polarization data), and radio (Metsahovi, Owens Valley Radio Observatory, University of Michigan Radio Astronomy Observatory). Light curves are produced spanning multiple days before and after the peak of the VHE flare, including over several flare "decline" epochs. The main flare statistics allow 2 minute time bins to be constructed in both the VHE and optical bands enabling a cross-correlation analysis that shows evidence for an optical lag of ∼25-55 minutes, the first time-lagged correlation between these bands reported on such short timescales. Limits on the Doppler factor (δ ⪆ 33) and the size of the emission region (δ-1RB≲ 3.8 × 1013cm) are obtained from the fast variability observed by VERITAS during the main flare. Analysis of 10 minute binned VHE and X-ray data over the decline epochs shows an extraordinary range of behavior in the flux-flux relationship, from linear to quadratic to lack of correlation to anticorrelation. Taken together, these detailed observations of an unprecedented flare seen in Mrk 421 are difficult to explain with the classic single-zone synchrotron self-Compton model.
  • The hunt for extraterrestrial high-energy neutrino counterparts
    (2022-09-30) Liodakis, I.; Hovatta, T.; Pavlidou, Vassiliki; Readhead, A. C. S.; Blandford, R. D.; Kiehlmann, S.; Lindfors, E.; Max-Moerbeck, W.; Pearson, T. J.; Petropoulou, M.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The origin of Petaelectronvolt (PeV) astrophysical neutrinos is fundamental to our understanding of the high-energy Universe. Apart from the technical challenges of operating detectors deep below ice, oceans, and lakes, the phenomenological challenges are even greater than those of gravitational waves; the sources are unknown, hard to predict, and we lack clear signatures. Neutrino astronomy therefore represents the greatest challenge faced by the astronomy and physics communities thus far. The possible neutrino sources range from accretion disks and tidal disruption events, to relativistic jets and galaxy clusters with blazar TXS 0506+056 the most compelling association thus far. Since that association, immense effort has been put into proving or disproving that jets are indeed neutrino emitters, but to no avail. By generating simulated neutrino counterpart samples, we explore the potential of detecting a significant correlation of neutrinos with jets from active galactic nuclei. We find that, given the existing challenges, even our best experiments could not have produced a > 3σ result. Larger programs over the next few years will be able to detect a significant correlation only if the brightest radio sources, rather than all jetted active galactic nuclei, are neutrino emitters. We discuss the necessary strategies required to steer future efforts into successful experiments.
  • Insights into the emission of the blazar 1ES 1011+496 through unprecedented broadband observations during 2011 and 2012
    (2016) Aleksić, J.; Ansoldi, S.; Antonelli, L. A.; Antoranz, P.; Arcaro, C.; Babic, A.; Bangale, P.; Barres De Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Biasuzzi, B.; Biland, A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caneva, G.; De Lotto, B.; De Oña Wilhelmi, E.; Delgado Mendez, C.; Di Pierro, F.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher, D.; Elsaesser, D.; Fernández-Barral, A.; Fidalgo, D.; Fonseca, M. V.; Font, L.; Frantzen, K.; Fruck, C.; Galindo, D.; García López, R. J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Godinović, N.; González Muñoz, A.; Gozzini, S. R.; Hadasch, D.; Hanabata, Y.; Hayashida, M.; Herrera, J.; Hose, J.; Hrupec, D.; Idec, W.; Kadenius, V.; Kellermann, H.; Knoetig, M. L.; Kodani, K.; Konno, Y.; Krause, J.; Kubo, H.; Kushida, J.; La Barbera, A.; Lelas, D.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Lozano, I.; Makariev, M.; Mallot, K.; Maneva, G.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Miranda, J. M.; Mirzoyan, R.; Moralejo, A.; Munar-Adrover, P.; Nakajima, D.; Neustroev, V.; Niedzwiecki, A.; Nievas Rosillo, M.; Nilsson, K.; Nishijima, K.; Noda, K.; Orito, R.; Overkemping, A.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Paredes-Fortuny, X.; Persic, M.; Poutanen, J.; Prada Moroni, P. G.; Prandini, E.; Puljak, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rodriguez Garcia, J.; Saito, T.; Saito, K.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schweizer, T.; Shore, S. N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Stamerra, A.; Steinbring, T.; Strzys, M.; Takalo, L.; Takami, H.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Thaele, J.; Torres, D. F.; Toyama, T.; Treves, A.; Vogler, P.; Will, M.; Zanin, R.; Buson, S.; D'Ammando, F.; Lähteenmäki, A.; Hovatta, T.; Kovalev, Y. Y.; Lister, M. L.; Max-Moerbeck, W.; Mundell, C.; Pushkarev, A. B.; Rastorgueva-Foi, E.; Readhead, A. C S; Richards, J. L.; Tammi, J.; Sanchez, D. A.; Tornikoski, M.; Savolainen, Tuomas; Steele, I.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Context. 1ES 1011+496 (z = 0:212) was discovered in very high-energy (VHE, E > 100 GeV) γ rays with MAGIC in 2007. The absence of simultaneous data at lower energies led to an incomplete characterization of the broadband spectral energy distribution (SED). Aims. We study the source properties and the emission mechanisms, probing whether a simple one-zone synchrotron self-Compton (SSC) scenario is able to explain the observed broadband spectrum. Methods. We analyzed data in the range from VHE to radio data from 2011 and 2012 collected by MAGIC, Fermi-LAT, Swift, KVA, OVRO, and Metsähovi in addition to optical polarimetry data and radio maps from the Liverpool Telescope and MOJAVE. Results. The VHE spectrum was fit with a simple power law with a photon index of 3:69 ± 0:22 and a flux above 150 GeV of (1:46 ± 0:16) × 10-11 ph cm-2 s-1. The source 1ES 1011+496 was found to be in a generally quiescent state at all observed wavelengths, showing only moderate variability from radio to X-rays. A low degree of polarization of less than 10% was measured in optical, while some bright features polarized up to 60% were observed in the radio jet. A similar trend in the rotation of the electric vector position angle was found in optical and radio. The radio maps indicated a superluminal motion of 1.8±0.4 c, which is the highest speed statistically significant measured so far in a high-frequency-peaked BL Lac. Conclusions. For the first time, the high-energy bump in the broadband SED of 1ES 1011+496 could be fully characterized from 0.1 GeV to 1 TeV, which permitted a more reliable interpretation within the one-zone SSC scenario. The polarimetry data suggest that at least part of the optical emission has its origin in some of the bright radio features, while the low polarization in optical might be due to the contribution of parts of the radio jet with different orientations of the magnetic field with respect to the optical emission.
  • Investigating Differences in the Palomar-Green Blazar Population Using Polarization
    (2024-12-01) Baghel, Janhavi; Kharb, P.; Hovatta, T.; Ho, Luis C.; Harrison, C.; Lindfors, E.; Silpa, S.; Gulati, S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present polarization images with the Karl G. Jansky Very Large Array (VLA) in A- and B-array configurations at 6 GHz of seven radio-loud (RL) quasars and eight BL Lac objects belonging to the Palomar-Green (PG) “blazar” sample. This completes our arcsecond-scale polarization study of an optically selected volume-limited blazar sample comprising 16 radio-loud quasars and 8 BL Lac objects. Using the VLA, we identify kiloparsec-scale polarization in the cores and jets/lobes of all the blazars, with fractional polarization varying from around 0.8% ± 0.3% to 37% ± 6%. The kiloparsec-scale jets in PG RL quasars are typically aligned along their parsec-scale jets and show apparent magnetic fields parallel to jet directions in their jets/cores and magnetic field compression in their hot spots. The quasars show evidence of interaction with their environment as well as restarted active galactic nucleus activity through morphology, polarization, and spectral indices. These quasi-periodic jet modulations and restarted activity may be indicative of an unstable accretion disk undergoing transition. We find that the polarization characteristics of the BL Lacs are consistent with their jets being reoriented multiple times, with no correlation between their core apparent magnetic field orientations and parsec-scale jet directions. We find that the low synchrotron peaked BL Lacs show polarization and radio morphology features typical of “strong” jet sources as defined by E. T. Meyer et al. for the “blazar envelope scenario,” which posits a division based on jet profiles and velocity gradients rather than total jet power.
  • A Kpc-scale radio polarization study of PG BL Lacs with the uGMRT
    (2024-01-01) Baghel, Janhavi; Kharb, P.; Hovatta, T.; Gulati, Sanna; Lindfors, E.; Silpa, S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present here uGMRT band 4 (∼650 MHz) polarization images of 8 BL Lac objects belonging to the Palomar-Green (PG) ‘blazar’ sample. A large fraction of the sources (∼ 63 per cent) reveal core-halo radio structures with most of the polarization detected in the inner core-jet regions. PG1101 + 385 and PG2254 + 075 exhibit a ‘spine-sheath structure’ in polarization. The core-halo and ‘spine-sheath’ structures are consistent with the Unified Scheme suggestion that BL Lacs are the pole-on beamed counterparts of Fanaroff–Riley (FR) type I radio galaxies. PG1418 + 546 and PG0851 + 203 (OJ287) show the presence of terminal hotspots similar to FR type II radio galaxies. They were also found to be low-spectrally peaked BL Lacs, supportive of the ‘blazar envelope’ scenario for BL Lacs and quasars. Fractional polarization ranges from 1 to 13 per cent in the cores and 2 to 26 per cent in the inner jets/lobes of the sample BL Lacs. Compared to the varied radio morphology of quasars from the PG ‘blazar’ sample, the BL Lacs appear to be less diverse. A comparison of the inferred core magnetic (B-) field structures on arcsec(kpc-) scales w.r.t. the Very Long Baseline Interferometry jet direction does not reveal any preferred orientation, suggesting that if large-scale ordered B-fields exist, they do so on scales smaller than probed by the current observations. However, the presence of polarized emission on arcsec-scales suggests that any mixing of thermal plasma with the synchrotron emitting plasma is insufficient to fully depolarize the emission via the internal depolarization process.
  • Locating the gamma-ray emission site in Fermi/LAT blazars: II. Multifrequency correlations
    (2016) Ramakrishnan, V.; Hovatta, T.; Tornikoski, M.; Nilsson, K.; Lindfors, E.; Balokovic, M.; Lähteenmäki, Anne; Reinthal, R.; Takalo, L.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In an attempt to constrain and understand the emission mechanism of. gamma-rays, we perform a cross-correlation analysis of 15 blazars using light curves inmillimetre, optical and gamma-rays. We use discrete correlation function and consider only correlations significant at the 99 per cent level. A strong correlation was found between 37 and 95 GHz with a near-zero time delay in most of the sources, and similar to 1 month or longer in the rest. A similar result was obtained between the optical and. gamma-ray bands. Of the 15 sources, less than 50 per cent showed a strong correlation between the millimetre and gamma-ray or millimetre and optical bands. The primary reason for the lack of statistically significant correlation is the absence of a major outburst in the millimetre bands of most of the sources during the 2.5 yr time period investigated in our study. This may indicate that only the long-term variations or large flares are correlated between these bands. The variability of the sources at every waveband was also inspected using fractional rms variability (F-var ). The F-var displays an increase with frequency reaching its maximum in the gamma-rays.
  • The long-lasting activity of 3C 454.3 GASP-WEBT and satellite observations in 2008-2010
    (2011) Raiteri, C.M.; Villata, M.; Aller, M.F.; Gurwell, M.A.; Kurtanidze, O.M.; Lähteenmäki, A.; Larionov, V.M.; Romano, P.; Vercellone, S.; Agudo, I.; Aller, H.D.; Arkharov, A.A.; Bach, U.; Benítez, E.; Berdyugin, A.; Blinov, D.A.; Borisova, E.V.; Böttcher, M.; Bravo Calle, O.J.A.; Buemi, C.S.; Calcidese, P.; Carosati, D.; Casas, R.; Chen, W.-P.; Efimova, N.V.; Gómez, J.L.; Gusbar, C.; Hawkins, K.; Heidt, J.; Hiriart, D.; Hsiao, H.Y.; Jordan, B.; Jorstad, S.G.; Joshi, M.; Kimeridze, G.N.; Koptelova, E.; Konstantinova, T.S.; Kopatskaya, E.N.; Kurtanidze, S.O.; Larionova, E.G.; Larionova, L.V.; Leto, P.; Li, Yanrong; Ligustri, R.; Lindfors, E.; Lister, M.; Marscher, A.P.; Molina, S.N.; Morozova, D.A.; Nieppola, E.; Nikolashvili, M.G.; Nilsson, K.; Palma, N.; Pasanen, M.; Reinthal, R.; Roberts, V.; Ros, J.A.; Roustazadeh, P.; Sadun, A.C.; Sakamoto, T.; Schwartz, R.D.; Sigua, L.A.; Sillanpää, A.; Takalo, L.O.; Tammi, J.; Taylor, B.; Tornikoski, M.; Trigilio, C.; Troitsky, I.S.; Umana, G.; Volvach, A.; Yuldasheva, T.A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Long-term optical monitoring of TeV emitting blazars: I. Data analysis
    (2018-12-01) Nilsson, K.; Lindfors, E.; Takalo, L. O.; Reinthal, R.; Berdyugin, A.; Sillanpää, Aimo; Ciprini, S.; Halkola, A.; Heinämäki, P.; Hovatta, T.; Kadenius, V.; Nurmi, P.; Ostorero, L.; Pasanen, M.; Rekola, R.; Saarinen, J.; Sainio, J.; Tuominen, T.; Villforth, C.; Vornanen, T.; Zaprudin, B.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present ten years of R-band monitoring data of 31 northern blazars which were either detected at very high-energy (VHE) gamma rays or listed as potential VHE gamma-ray emitters. The data comprise 11 820 photometric data points in the R-band obtained in 2002-2012. We analyzed the light curves by determining their power spectral density (PSD) slopes assuming a power-law dependence with a single slope β and a Gaussian probability density function (PDF). We used the multiple fragments variance function (MFVF) combined with a forward-casting approach and likelihood analysis to determine the slopes and perform extensive simulations to estimate the uncertainties of the derived slopes. We also looked for periodic variations via Fourier analysis and quantified the false alarm probability through a large number of simulations. Comparing the obtained PSD slopes to values in the literature, we find the slopes in the radio band to be steeper than those in the optical and gamma rays. Our periodicity search yielded one target, Mrk 421, with a significant (p < 5%) period. Finding one significant period among 31 targets is consistent with the expected false alarm rate, but the period found in Mrk 421 is very strong and deserves further consideration.
  • MAGIC detection of short-term variability of the high-peaked BL Lac object 1ES 0806+524
    (2015) Aleksic, J.; Ansoldi, S.; Antonelli, L.A.; Antoranz, P.; Babic, A.; Bangale, P.; Barrio, J.A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Biasuzzi, B.; Biland, A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; Colin, P.; Colombo, E.; Contreras, J.L.; Cortina, J.; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caneva, G.; De Lotto, B.; de Oña Wilhelmi, E.; Delgado Mendez, C.; Di Pierro, F.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher, D.; Elsaesser, D.; Fernández-Barral, A.; Fidalgo, D.; Fonseca, M.V.; Font, L.; Frantzen, K.; Fruck, C.; Galindo, D.; García López, Ramon J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Godinovic, N.; González Muñoz, A.; Gozzini, S.R.; Hadasch, D.; Hanabata, Y.; Hayashida, M.; Herrera, J.; Hose, J.; Hrupec, D.; Idec, W.; Kadenius, V.; Kellermann, H.; Knoetig, M.L.; Kodani, K.; Konno, Yusuke; Krause, J.; Kubo, Hidetoshi; Kushida, J.; La Barbera, A.; Lelas, D.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Lozano, I.; Makariev, M.; Mallot, K.; Maneva, G.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Miranda, J.M.; Mirzoyan, R.; Moralejo, A.; Munar-Adrover, P.; Nakajima, Daisuke; Neustroev, V.; Niedzwiecki, A.; Nievas Rosillo, M.; Nilsson, K.; Nishijima, K.; Noda, K.; Orito, R.; Overkemping, A.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J.M.; Paredes-Fortuny, X.; Persic, M.; Poutanen, J.; Prada Moroni, P.G.; Prandini, E.; Puljak, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, Javier; Rodriguez Garcia, J.; Saito, T.; Saito, K.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shore, S.N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Stamerra, A.; Steinbring, T.; Strzys, M.; Takalo, L.; Takami, H.; Tavecchio, F.; Temnikov, P.; Terzic, T.; Tescaro, D.; Teshima, M.; Thaele, J.; Torres, D.F.; Toyama, T.; Treves, A.; Vogler, P.; Will, M.; Zanin, R.; Berger, K.; Buson, S.; "D'Ammando", F.; Gasparrini, D.; Hovatta, T.; Max-Moerbeck, W.; Readhead, A.; Richards, J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • MAGIC long-term study of the distant TeV blazar PKS 1424+240 in a multiwavelength context
    (2014) Aleksic, J.; Ansoldi, S.; Antonelli, L.A.; Antoranz, P.; Babic, A.; Bangale, P.; Barres de Almeida, U.; Barrio, J.A.; Becerra González, J.; Bednarek, W.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bock, R.K.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; Carreto Fidalgo, D.; Colin, P.; Colombo, E.; Contreras, J.L.; Cortina, Juan; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caneva, G.; De Lotto, B.; Delgado Mendez, C.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher, D.; Elsaesser, D.; Farina, E.; Ferenc, D.; Fonseca, M.V.; Font, L.; Frantzen, K.; Fruck, C.; García López, R.J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Giavitto, G.; Godinovic, N.; González Muñoz, A.; Gozzini, S.R.; Hadasch, D.; Hayashida, M.; Herrero, A.; Hildebrand, D.; Hose, J.; Hrupec, D.; Idec, W.; Kadenius, V.; Kellermann, H.; Kodani, K.; Konno, Y.; Krause, J.; Kubo, H.; Kushida, J.; La Barbera, A.; Lelas, D.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Lozano, I.; Makariev, M.; Mallot, K.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Meucci, M.; Miranda, J.M.; Mirzoyan, R.; Moralejo, A.; Munar-Adrover, P.; Nakajima, D.; Niedzwiecki, A.; Nilsson, K.; Nishijima, K.; Nowak, N.; Orito, R.; Overkemping, A.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J.M.; Paredes-Fortuny, X.; Partini, S.; Persic, M.; Prada, F.; Prada Moroni, P.G.; Prandini, E.; Preziuso, S.; Puljak, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rodriguez Garcia, J.; Rügamer, S.; Saggion, A.; Saito, T.; Saito, K.; Salvati, M.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shore, S.N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Spanier, F.; Stamatescu, V.; Stamerra, A.; Steinbring, T.; Storz, J.; Sun, S.; Suric, T.; Takalo, L.; Takami, H.; Tavecchio, F.; Temnikov, P.; Terzic, T.; Tescaro, D.; Teshima, M.; Thaele, J.; Tibolla, O.; Torres, D.F.; Toyama, T.; Treves, A.; Uellenbeck, M.; Vogler, P.; Wagner, R.M.; Zandanel, F.; Zanin, R.; Cutini, S.; Gasparrini, D.; Furniss, A.; Hovatta, T.; Kankare, E.; Kotilainen, J.; Lister, M.; Lähteenmäki, A.; Max-Moerbeck, W.; Pavlidou, V.; Readhead, A.; Richards, J.; Kangas, Tuomas
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Multiband variability studies and novel broadband SED modeling of Mrk 501 in 2009
    (2017-07-01) Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.; Antoranz, P.; Babic, A.; Banerjee, B.; Bangale, P.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Berti, A.; Biasuzzi, B.; Biland, A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Buson, S.; Carosi, A.; Chatterjee, A.; Clavero, R.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; Oña-Wilhelmi, E.; Di Pierro, F.; Doert, M.; Domínguez, Alberto; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher Glawion, D.; Elsaesser, D.; Engelkemeier, M.; Fallah Ramazani, V.; Fernández-Barral, A.; Fidalgo, D.; Fonseca, M. V.; Font, L.; Frantzen, K.; Fruck, C.; Galindo, D.; García López, R.J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Giammaria, P.; Godinović, N.; González Muñoz, A.; Gora, D.; Guberman, D.; Hadasch, D.; Hahn, A.; Hanabata, Y.; Hayashida, M.; Herrera, J.; Hose, J.; Hrupec, D.; Hughes, G.; Idec, W.; Kodani, K.; Konno, Y.; Kubo, H.; Kushida, J.; La Barbera, A.; Lelas, D.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; López-Coto, R.; Majumdar, P.; Makariev, M.; Mallot, K.; Maneva, G.; Manganaro, M.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Miranda, J. M.; Mirzoyan, R.; Moralejo, A.; Moretti, E.; Nakajima, D.; Neustroev, V.; Niedzwiecki, A.; Nievas Rosillo, M.; Nilsson, K.; Nishijima, K.; Noda, K.; Nogués, L.; Overkemping, A.; Paiano, S.; Palacio, J.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Paredes-Fortuny, X.; Pedaletti, G.; Peresano, M.; Perri, L.; Persic, M.; Poutanen, J.; Prada Moroni, P.G.; Prandini, E.; Puljak, I.; Reichardt, I.; Rhode, W.; Ribó, M.; Rico, J.; Rodriguez Garcia, J.; Saito, T.; Satalecka, K.; Schröder, S.; Schultz, C.; Schweizer, T.; Shore, S. N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Stamerra, A.; Steinbring, T.; Strzys, M.; Surić, T.; Takalo, L.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Thaele, J.; Torres, D. F.; Toyama, T.; Treves, A.; Vanzo, G.; Verguilov, V.; Vovk, I.; Ward, Eric J; Will, M.; Wu, M. H.; Zanin, R.; Abeysekara, A.U.; Archambault, S.; Archer, A.; Benbow, W.; Bird, R.; Buchovecky, M.; Buckley, J.H.; Bugaev, V.; Connolly, M.P.; Cui, W.; Dickinson, H. J.; Falcone, A.; Feng, Q.; Finley, J.P.; Fleischhack, H.; Flinders, A.; Fortson, L.; Gillanders, G.H.; Griffin, S.; Grube, J.; Hütten, M.; Hanna, D.; Holder, J.; Humensky, T.B.; Kaaret, P.; Kar, P.; Kelley-Hoskins, N.; Kertzman, M.; Kieda, D.; Krause, M.; Krennrich, F.; Lang, M.J.; Maier, G.; McCann, A.; Moriarty, P.; Mukherjee, R.; Nieto, D.; O'Brien, S.; Ong, R.A.; Otte, N.; Park, N.; Perkins, J.; Pichel, A.; Pohl, M.; Popkow, A.; Pueschel, E.; Quinn, J.; Ragan, K.; Reynolds, P.T.; Richards, G. T.; Roache, E.; Rovero, A.C.; Rulten, C.; Sadeh, I.; Santander, M.; Sembroski, G.H.; Shahinyan, K.; Telezhinsky, I.; Tucci, J. V.; Tyler, J.; Wakely, S.P.; Weinstein, A.; Wilcox, P.; Wilhelm, A.; Williams, D.A.; Zitzer, B.; Razzaque, S.; Villata, M.; Raiteri, C.M.; Aller, H. D.; Aller, M. F.; Larionov, V. M.; Arkharov, A.; Blinov, Dmitry A.; Efimova, Natalia V.; Grishina, T. S.; Hagen-Thorn, Vladimir A.; Kopatskaya, Evgenia N.; Larionova, Liudmila V.; Larionova, Elena G.; Morozova, Daria A.; Troitsky, Ivan S.; Ligustri, R.; Calcidese, P.; Berdyugin, A.; Kurtanidze, O. M.; Nikolashvili, M. G.; Kimeridze, Givi N.; Sigua, Lorand A.; Kurtanidze, Sofia O.; Chigladze, Revaz A.; Chen, W. P.; Koptelova, E.; Sakamoto, T.; Sadun, A. C.; Moody, J. W.; Pace, C.; Pearson, R.; Yatsu, Y.; Mori, Y.; Carraminyana, A.; Carrasco, L.; de la Fuente, E.; Norris, J. P.; Smith, Paul S.; Wehrle, A.; Gurwell, M. A.; Zook, A.; Pagani, C.; Perri, M.; Capalbi, M.; Cesarini, A.; Krimm, H. A.; Kovalev, Y. Y.; Kovalev, Yu A.; Ros, E.; Pushkarev, Alexander B.; Lister, M. L.; Sokolovsky, K.V.; Kadler, M.; Piner, B. G.; Lähteenmäki, A.; Tornikoski, M.; Angelakis, E.; Krichbaum, T. P.; Nestoras, I.; Fuhrmann, L.; Zensus, J. A.; Cassaro, P.; Orlati, A.; Maccaferri, G.; Leto, P.; Giroletti, M.; Richards, J. L.; Max-Moerbeck, W.; Readhead, A.C.S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Context. We present an extensive study of the BL Lac object Mrk 501 based on a data set collected during the multi-instrument campaign spanning from 2009 March 15 to 2009 August 1, which includes, among other instruments, MAGIC, VERITAS, Whipple 10 m, and Fermi-LAT to cover the γ-ray range from 0.1 GeV to 20 TeV; RXTE and Swift to cover wavelengths from UV tohard X-rays; and GASP-WEBT, which provides coverage of radio and optical wavelengths. Optical polarization measurements were provided for a fraction of the campaign by the Steward and St. Petersburg observatories. We evaluate the variability of the source and interband correlations, the γ-ray flaring activity occurring in May 2009, and interpret the results within two synchrotron self-Compton (SSC) scenarios. Aims. The multiband variability observed during the full campaign is addressed in terms of the fractional variability, and the possible correlations are studied by calculating the discrete correlation function for each pair of energy bands where the significance was evaluated with dedicated Monte Carlo simulations. The space of SSC model parameters is probed following a dedicated grid-scan strategy, allowing for a wide range of models to be tested and offering a study of the degeneracy of model-to-data agreement in the individual model parameters, hence providing a less biased interpretation than the "single-curve SSC model adjustment" typically reported in the literature. Methods. We find an increase in the fractional variability with energy, while no significant interband correlations of flux changes are found on the basis of the acquired data set. The SSC model grid-scan shows that the flaring activity around May 22 cannot be modeled adequately with a one-zone SSC scenario (using an electron energy distribution with two breaks), while it can be suitably described within a two (independent) zone SSC scenario. Here, one zone is responsible for the quiescent emission from the averaged 4.5-month observing period, while the other one, which is spatially separated from the first, dominates the flaring emission occurring at X-rays and very-high-energy (>100 GeV, VHE) γ rays. The flaring activity from May 1, which coincides with a rotation of the electric vector polarization angle (EVPA), cannot be satisfactorily reproduced by either a one-zone or a two-independent-zone SSC model, yet this is partially affected by the lack of strictly simultaneous observations and the presence of large flux changes on sub-hour timescales (detected at VHE γ rays). Results. The higher variability in the VHE emission and lack of correlation with the X-ray emission indicate that, at least during the 4.5-month observing campaign in 2009, the highest energy (and most variable) electrons that are responsible for the VHE γ rays do not make a dominant contribution to the ~1 keV emission. Alternatively, there could be a very variable component contributing to the VHE γ-ray emission in addition to that coming from the SSC scenario. The studies with our dedicated SSC grid-scan show that there is some degeneracy in both the one-zone and the two-zone SSC scenarios probed, with several combinations of model parameters yielding a similar model-to-data agreement, and some parameters better constrained than others. The observed γ-ray flaring activity, with the EVPA rotation coincident with the first γ-ray flare, resembles those reported previously for low frequency peaked blazars, hence suggesting that there are many similarities in the flaring mechanisms of blazars with different jet properties.
  • Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-Ray Blazar PG 1553+113
    (2015) Ackermann, M.; Ajello, M.; Albert, A.; Atwood, W.B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Becerra Gonzalez, J.; Bellazzini, R.; Bissaldi, E.; Blandford, R.D.; Bloom, E.D.; Bonino, R.; Bottacini, E.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G.A.; Cameron, R.A.; Caputo, R.; Caragiulo, M.; Caraveo, P.A.; Cavazzuti, E.; Cecchi, C.; Chekhtman, A.; Chiang, J.; Chiaro, G.; Ciprini, S.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; "D'Ammando", F.; de Angelis, A.; de Palma, F.; Desiante, R.; Di Venere, L.; Domi´nguez, A.; Drell, P.S.; Favuzzi, C.; Fegan, S.J.; Ferrara, E.C.; Focke, W.B.; Fuhrmann, L.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Godfrey, G.; Green, D.; Grenier, I.A.; Grove, J.E.; Guiriec, S.; Harding, A.K.; Hays, E.; Hewitt, J.W.; Hill, A.B.; Horan, D.; Jogler, T.; Jóhannesson, G.; Johnson, A.S.; Kamae, T.; Kuss, M.; Larsson, S.; Latronico, L.; Li, Jian; Li, Liang; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M.N.; Lubrano, P.; Magill, J.; Maldera, S.; Manfreda, A.; Max-Moerbeck, W.; Mayer, M.; Mazziotta, M.N.; McEnery, J.E.; Michelson, P.F.; Mizuno, T.; Monzani, M.E.; Morselli, A.; Moskalenko, I.V.; Murgia, S.; Nuss, E.; Ohno, M.; Ohsugi, T.; Ojha, R.; Omodei, N.; Orlando, E.; Ormes, J.F.; Paneque, D.; Pearson, T.J.; Perkins, J.S.; Perri, M.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Pivato, G.; Porter, T.A.; Rainò, S.; Rando, R.; Razzano, M.; Readhead, A.; Reimer, A.; Reimer, O.; Schulz, A.; Sgrò, C.; Siskind, E.J.; Spada, F.; Spandre, G.; Spinelli, P.; Suson, D.J.; Takahashi, H.; Thayer, J.B.; Thompson, D.J.; Tibaldo, L.; Torres, D.F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Vianello, G.; Wood, K.S.; Wood, M.; Zimmer, S.; Berdyugin, A.; Corbet, R.H.D.; Hovatta, T.; Lindfors, E.; Nilsson, K.; Reinthal, R.; Sillanpää, A.; Stamerra, A.; Takalo, L.O.; Valtonen, M.J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä