@article {291, title = {{Discovery of off-axis jet structure of TeV blazar Mrk 501 with mm-VLBI}}, journal = {\aap}, volume = {586}, year = {2016}, pages = {A113}, keywords = {BL Lacertae objects: individual: Markarian 501, galaxies: active, galaxies: jets, radio continuum: galaxies}, doi = {10.1051/0004-6361/201526541}, author = {Koyama, S. and Kino, M. and Giroletti, M. and Doi, A. and Giovannini, G. and Orienti, M. and Hada, K. and Ros, E. and Niinuma, K. and Nagai, H. and Savolainen, T. and Krichbaum, T.~P. and Perez-Torres, M.~A.} } @book {181, title = {{The Spanish Square Kilometre Array White Book}}, series = {ArXiv e-prints}, year = {2015}, keywords = {Astrophysics - Instrumentation and Methods for Astrophysics}, url = {http://adsabs.harvard.edu/abs/2015arXiv150603474A}, author = {Acosta-Pulido, J.~A. and Agudo, I. and Alberdi, A. and Alcolea, J. and Alfaro, E.~J. and Alonso-Herrero, A. and Anglada, G. and Arnalte-Mur, P. and Ascasibar, Y. and Ascaso, B. and Azulay, R. and Bachiller, R. and Baez-Rubio, A. and Battaner, E. and Blasco, J. and Brook, C.~B. and Bujarrabal, V. and Busquet, G. and Caballero-Garcia, M.~D. and Carrasco-Gonzalez, C. and Casares, J. and Castro-Tirado, A.~J. and Colina, L. and Colomer, F. and de Gregorio-Monsalvo, I. and del Olmo, A. and Desmurs, J.-F. and Diego, J.~M. and Dominguez-Tenreiro, R. and Estalella, R. and Fernandez-Soto, A. and Florido, E. and Font, J. and Font, J.~A. and Fuente, A. and Garc{\'\i}a-Benito, R. and Garcia-Burillo, S. and Garc{\'\i}a-Lorenzo, B. and Gil de Paz, A. and Girart, J.~M. and Goicoechea, J.~R. and G{\'o}mez, J.~F. and Gonzalez-Garcia, M. and Gonz{\'a}lez-Mart{\'\i}n, O. and Gonzalez-Serrano, J.~I. and Gorgas, J. and Gorosabel, J. and Guijarro, A. and Guirado, J.~C. and Hern{\'a}ndez-Garc{\'\i}a, L. and Hernandez-Monteagudo, C. and Herranz, D. and R. Herrero-Illana and Hu, Y.-D. and Huelamo, N. and Huertas-Company, M. and Iglesias-Paramo, J. and Jeong, S. and Jimenez-Serra, I. and Knapen, J.~H. and Lineros, R.~A. and Lisenfeld, U. and Marcaide, J.~M. and Marquez, I. and Marti, J. and Marti, J.~M. and Mart{\'\i}-Vidal, I. and Martinez-Gonzalez, E. and Martin-Pintado, J. and Masegosa, J. and Mayen-Gijon, J.~M. and Mezcua, M. and Migliari, S. and Mimica, P. and Mold{\'o}n, J. and Morata, O. and Negueruela, I. and Oates, S.~R. and Osorio, M. and Palau, A. and Paredes, J.~M. and Perea, J. and P{\'e}rez-Gonz{\'a}lez, P.~G. and Perez-Montero, E. and M. A. P{\'e}rez-Torres and Perucho, M. and Planelles, S. and Pons, J.~A. and Prieto, A. and Quilis, V. and Ramirez-Moreta, P. and Ramos Almeida, C. and Rea, N. and Rib{\'o}, M. and Rioja, M.~J. and Rodriguez Espinosa, J.~M. and Ros, E. and Rubi{\~n}o-Martin, J.~A. and Ruiz-Granados, B. and Sabater, J. and Sanchez, S. and Sanchez-Contreras, C. and Sanchez-Monge, A. and Sanchez-Ramirez, R. and Sintes, A.~M. and Solanes, J.~M. and Sopuerta, C.~F. and Tafalla, M. and Tello, J.~C. and Tercero, B. and Toribio, M.~C. and Torrelles, J.~M. and Torres, M.~A.~P. and Usero, A. and Verdes-Montenegro, L. and Vidal-Garcia, A. and Vielva, P. and Vilchez, J. and Zhang, B.-B.} } @article {2014ApJ...792...38P, title = {{Constraints on the Progenitor System and the Environs of SN 2014J from Deep Radio Observations}}, journal = {The Astrophysical Journal}, volume = {792}, year = {2014}, pages = {38}, abstract = {We report deep EVN and eMERLIN observations of the Type Ia SN 2014J in the nearby galaxy M82. Our observations represent, together with JVLA observations of SNe 2011fe and 2014J, the most sensitive radio studies of Type Ia SNe ever. By combining data and a proper modeling of the radio emission, we constrain the mass-loss rate from the progenitor system of SN 2014J to $\backslash$dot$\{$M$\}$ $\backslash$lesssim 7.0$\backslash$times 10\^{}$\{$-10$\}$ $\{$$\backslash$,$\{$M\_$\{$$\backslash$odot $\}$ $\backslash$,yr\^{}$\{$-1$\}$$\}$$\}$ (for a wind speed of 100 km s$^{-1}$). If the medium around the supernova is uniform, then n $_{ISM}$ {\l}t}\~{} 1.3 cm$^{-3}$, which is the most stringent limit for the (uniform) density around a Type Ia SN. Our deep upper limits favor a double-degenerate (DD) scenario{\mdash}involving two WD stars{\mdash}for the progenitor system of SN 2014J, as such systems have less circumstellar gas than our upper limits. By contrast, most single-degenerate (SD) scenarios, i.e., the wide family of progenitor systems where a red giant, main-sequence, or sub-giant star donates mass to an exploding WD, are ruled out by our observations. (While completing our work, we noticed that a paper by Margutti et al. was submitted to The Astrophysical Journal. From a non-detection of X-ray emission from SN 2014J, the authors obtain limits of $\backslash$dot$\{$M$\}$ $\backslash$lesssim 1.2 $\backslash$times 10\^{}$\{$-9$\}$ M $_{\&sun;}$ yr$^{-1}$ (for a wind speed of 100 km s$^{-1}$) and n $_{ISM}$ {\l}t}\~{} 3.5 cm$^{-3}$, for the {$\rho$}vpropr $^{-2}$ wind and constant density cases, respectively. As these limits are less constraining than ours, the findings by Margutti et al. do not alter our conclusions. The X-ray results are, however, important to rule out free-free and synchrotron self-absorption as a reason for the radio non-detections.) Our estimates on the limits on the gas density surrounding SN2011fe, using the flux density limits from Chomiuk et al., agree well with their results. Although we discuss the possibilities of an SD scenario passing observational tests, as well as uncertainties in the modeling of the radio emission, the evidence from SNe 2011fe and 2014J points in the direction of a DD scenario for both.}, keywords = {stars: mass-loss, supernovae: individual: SN2011fe SN2014J}, doi = {10.1088/0004-637X/792/1/38}, url = {http://adsabs.harvard.edu/abs/2014ApJ...792...38P}, author = {M. A. P{\'e}rez-Torres and Lundqvist, P. and Beswick, R.~J. and Bj{\"o}rnsson, C.~I. and Muxlow, T.~W.~B. and Paragi, Z. and Ryder, S. and Alberdi, A. and Fransson, C. and Marcaide, J.~M. and Mart{\'\i}-Vidal, I. and Ros, E. and Argo, M.~K. and Guirado, J.~C.} } @article {2012A\&A...537A..93R, title = {{VLBI imaging of M 81* at 43 GHz}}, journal = {Astronomy and Astrophysics}, volume = {537}, year = {2012}, month = {jan}, pages = {A93}, abstract = {Context. The nearby spiral galaxy M 81 harbours in its core a low-luminosity active galactic nucleus (LLAGN), and appears to be closely related to the more distant and powerful active galactic nuclei (AGNs) seen in quasars and radio galaxies. The intrinsic size of this object is unknown because of too much scattering, and it has shown a core-jet morphology with weak extended emission rotating with wavelength.
Aims: The proximity of M 81 (D = 3.63 Mpc) allows for a detailed investigation of its nucleus. The nucleus is four orders of magnitude more luminous than the Galactic centre, and is therefore considered to be a link between Sgr A$^{*}$ and the more powerful nuclei of radio galaxies and quasars. Our main goal was to determine the size of M 81{\l}owast} at a shorter wavelength to directly test whether the frequency-size dependent law {$\Theta$} {\prop} {$ν$}$^{-0.8}$ is still valid for wavelengths shorter than 1 cm. In addition, we also aimed to confirm the rotation of the source as a function of frequency.
Methods: We observed the continuum 7 mm radio emission of M 81{\l}owast} with the Very Long Baseline Array on Sep. 13, 2002, using nearby calibrators to apply their interferometric observables to the target source to increase the chances of detection. The source was detected on all baselines and hybrid mapping was possible.
Results: We present the first 7 mm VLBI image of the core of M 81{\l}owast}, which is the highest resolution image ever of this source. Modelling the interferometric visibilities with two Gaussian functions sets constraints on the angular size of its core down to 38 microarcseconds, corresponding to a maximum (projected) linear size of 138 AU, and shows extended emission towards the NE with a position angle of \~{}50{\deg}. A fit of a one Gaussian elliptical function yields a position angle of 28 {\plusmn} 8 degrees for its elongated, compact structure. Combining the 7 mm size with earlier measurements at other frequencies, we determine a frequency-size dependence of {$\Theta$} {\prop} {$ν$}$^{(-0.88 {\textpm} 0.04)}$.
Conclusions: Our VLBI imaging of M 81{\l}owast} has clearly detected its core-jet structure, and has allowed us to estimate a size for its core, with a minimum size of 138 AU ({\ap}100 Schwarzschild radii). Our work opens the way for future observations of M 81{\l}owast} at high-angular resolution, including the monitoring of its structure, given that much higher bandwidths are currently available on the interferometric networks. In particular, this would allow one to test for possible proper motions of the core or of its components in the inner jet of M 81{\l}owast}, and for the speed of the detected jet components.}, keywords = {galaxies: active, galaxies: individual: M 81, galaxies: nuclei, instrumentation: interferometers, radio continuum: galaxies}, doi = {10.1051/0004-6361/201118399}, url = {http://adsabs.harvard.edu/abs/2012A\%26A...537A..93R}, author = {Ros, E. and M. A. P{\'e}rez-Torres} } @article {2011A\&A...533C...1M, title = {{Coherence loss in phase-referenced VLBI observations (Corrigendum)}}, journal = {Astronomy and Astrophysics}, volume = {533}, year = {2011}, month = {sep}, pages = {C1}, abstract = {We report an erratum in an equation that models the relation of the limiting dynamic range to the angular distance between target and calibrator.}, keywords = {addenda, atmospheric effects, errata, instrumentation: interferometers, techniques: interferometric}, doi = {10.1051/0004-6361/201014203e}, url = {http://adsabs.harvard.edu/abs/2011A\%26A...533C...1M}, author = {Mart{\'\i}-Vidal, I. and Ros, E. and M. A. P{\'e}rez-Torres and Guirado, J.~C. and Jim{\'e}nez-Monferrer, S. and Marcaide, J.~M.} } @article {2011A\&A...533A.111M, title = {{Detection of jet precession in the active nucleus of M 81}}, journal = {Astronomy and Astrophysics}, volume = {533}, year = {2011}, month = {sep}, pages = {A111}, abstract = {We report on very-long-baseline-interferometry (VLBI) monitoring observations of the low-luminosity active galactic nucleus (LLAGN) in the galaxy M 81 at the frequencies of 1.7, 2.3, 5.0, and 8.4 GHz. The observations reported here are phase-referenced to the supernova SN 1993J (located in the same galaxy) and cover from late 1993 to late 2005. The large amount of available observations allows us to study the stability of the AGN position in the frame of its host galaxy at different frequencies and chromatic effects in the jet morphology, together with their time evolution. The source consists at all frequencies of a slightly resolved core and a small jet extension towards the northeast direction (position angle of \~{}65 degrees) in agreement with previous publications. We find that the position of the intensity peak in the images at 8.4 GHz is very stable in the galactic frame of M 81 (proper motion upper limit about 10 {$μ$}as per year). We confirm previous reports that the peaks at all frequencies are systematically shifted among them, possibly due to opacity effects in the jet as predicted by the standard relativistic jet model. We use this model, under plausible assumptions, to estimate the magnetic field in the jet close to the jet base and the mass of the central black hole. We obtain a black-hole mass of \~{}2 {\times} 10$^{7}$ M$_{\&sun;}$, comparable to estimates previously reported using different approaches, but the magnetic fields obtained are 10$^{3}$-10$^{4}$ times lower than previous estimates. We find that the positions of the cores at 1.7, 2.3, and 5.0 GHz are less stable than that at 8.4 GHz and evolve systematically, shifting southward at a rate of several tens of {$μ$}as per year. The evolution in the jet orientation seems to be related to changes in the inclination of the cores at all frequencies. These results can be interpreted as due to a precessing jet. The evolving jet orientation also seems to be related to a flare in the peak flux densities at 5.0 and 8.4 GHz, which lasts \~{}4 years (from mid 1997 to mid 2001). An increase in the accretion rate of the black hole, and its correlation with the jet luminosity via the disk-jet connection model, seems insufficient to explain this long flare and the simultaneous evolution in the jet orientation. A continued monitoring of the flux density and the jet structure evolution in this LLAGN will be necessary to further confirm our jet precession model.}, keywords = {astrometry, galaxies: active, galaxies: individual: M 81, galaxies: jets, radiation mechanisms: non-thermal, radio continuum: galaxies}, doi = {10.1051/0004-6361/201117211}, url = {http://adsabs.harvard.edu/abs/2011A\%26A...533A.111M}, author = {Mart{\'\i}-Vidal, I. and Marcaide, J.~M. and Alberdi, A. and M. A. P{\'e}rez-Torres and Ros, E. and Guirado, J.~C.} } @article {2011ApJ...736..131A, title = {{Fermi Large Area Telescope Observations of Markarian 421: The Missing Piece of its Spectral Energy Distribution}}, journal = {The Astrophysical Journal}, volume = {736}, year = {2011}, month = {aug}, pages = {131}, abstract = {We report on the {$\gamma$}-ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk 421) during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) {$\gamma$}-ray spectrum above 0.3 GeV can be well described by a power-law function with photon index {$\Gamma$} = 1.78 {\plusmn} 0.02 and average photon flux F({\gt} 0.3 GeV) = (7.23 {\plusmn} 0.16) {\times} 10$^{-8}$ ph cm$^{-2}$ s$^{-1}$. Over this time period, the Fermi-LAT spectrum above 0.3 GeV was evaluated on seven-day-long time intervals, showing significant variations in the photon flux (up to a factor \~{}3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in {$\gamma$}-rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk 421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk 421 showed a low activity at all wavebands. The extensive multi-instrument (radio to TeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.}, keywords = {acceleration of particles, BL Lacertae objects: general, BL Lacertae objects: individual: Mrk 421, galaxies: active, gamma rays: general, radiation mechanisms: non-thermal}, doi = {10.1088/0004-637X/736/2/131}, url = {http://adsabs.harvard.edu/abs/2011ApJ...736..131A}, author = {Abdo, A.~A. and Ackermann, M. and Ajello, M. and Baldini, L. and Ballet, J. and Barbiellini, G. and Bastieri, D. and Bechtol, K. and Bellazzini, R. and Berenji, B. and Blandford, R.~D. and Bloom, E.~D. and Bonamente, E. and Borgland, A.~W. and Bouvier, A. and Bregeon, J. and Brez, A. and Brigida, M. and Bruel, P. and Buehler, R. and Buson, S. and Caliandro, G.~A. and Cameron, R.~A. and Cannon, A. and Caraveo, P.~A. and Carrigan, S. and Casandjian, J.~M. and Cavazzuti, E. and Cecchi, C. and {\c C}elik, {\"O}. and Charles, E. and Chekhtman, A. and Chiang, J. and Ciprini, S. and Claus, R. and Cohen-Tanugi, J. and Conrad, J. and Cutini, S. and De Angelis, A. and de Palma, F. and Dermer, C.~D. and Silva, E.~d.~C.~e. and Drell, P.~S. and Dubois, R. and Dumora, D. and Escande, L. and Favuzzi, C. and Fegan, S.~J. and Finke, J. and Focke, W.~B. and Fortin, P. and Frailis, M. and Fuhrmann, L. and Fukazawa, Y. and Fukuyama, T. and Funk, S. and Fusco, P. and Gargano, F. and Gasparrini, D. and Gehrels, N. and Georganopoulos, M. and Germani, S. and Giebels, B. and Giglietto, N. and Giommi, P. and Giordano, F. and Giroletti, M. and Glanzman, T. and Godfrey, G. and Grenier, I.~A. and Guiriec, S. and Hadasch, D. and Hayashida, M. and Hays, E. and Horan, D. and Hughes, R.~E. and J{\'o}hannesson, G. and Johnson, A.~S. and Johnson, W.~N. and Kadler, M. and Kamae, T. and Katagiri, H. and Kataoka, J. and Kn{\"o}dlseder, J. and Kuss, M. and Lande, J. and Latronico, L. and Lee, S.-H. and Longo, F. and Loparco, F. and Lott, B. and Lovellette, M.~N. and Lubrano, P. and Madejski, G.~M. and Makeev, A. and Max-Moerbeck, W. and Mazziotta, M.~N. and McEnery, J.~E. and M{\'e}hault, J. and Michelson, P.~F. and Mitthumsiri, W. and Mizuno, T. and Monte, C. and Monzani, M.~E. and Morselli, A. and Moskalenko, I.~V. and Murgia, S. and Nakamori, T. and Naumann-Godo, M. and Nishino, S. and Nolan, P.~L. and Norris, J.~P. and Nuss, E. and Ohsugi, T. and Okumura, A. and Omodei, N. and Orlando, E. and Ormes, J.~F. and Ozaki, M. and Paneque, D. and Panetta, J.~H. and Parent, D. and Pavlidou, V. and Pearson, T.~J. and Pelassa, V. and Pepe, M. and Pesce-Rollins, M. and Pierbattista, M. and Piron, F. and Porter, T.~A. and Rain{\`o}, S. and Rando, R. and Razzano, M. and Readhead, A. and Reimer, A. and Reimer, O. and Reyes, L.~C. and Richards, J.~L. and Ritz, S. and Roth, M. and Sadrozinski, H.~F.-W. and Sanchez, D. and Sander, A. and Sgr{\`o}, C. and Siskind, E.~J. and Smith, P.~D. and Spandre, G. and Spinelli, P. and Stawarz, {\L}. and Stevenson, M. and Strickman, M.~S. and Suson, D.~J. and Takahashi, H. and Takahashi, T. and Tanaka, T. and Thayer, J.~G. and Thayer, J.~B. and Thompson, D.~J. and Tibaldo, L. and Torres, D.~F. and Tosti, G. and Tramacere, A. and Troja, E. and Usher, T.~L. and Vandenbroucke, J. and Vasileiou, V. and Vianello, G. and Vilchez, N. and Vitale, V. and Waite, A.~P. and Wang, P. and Wehrle, A.~E. and Winer, B.~L. and Wood, K.~S. and Yang, Z. and Yatsu, Y. and Ylinen, T. and Zensus, J.~A. and Ziegler, M. and Fermi LAT Collaboration and Aleksi{\'c}, J. and Antonelli, L.~A. and Antoranz, P. and Backes, M. and Barrio, J.~A. and Becerra Gonz{\'a}lez, J. and Bednarek, W. and Berdyugin, A. and Berger, K. and Bernardini, E. and Biland, A. and Blanch, O. and Bock, R.~K. and Boller, A. and Bonnoli, G. and Bordas, P. and Borla Tridon, D. and Bosch-Ramon, V. and Bose, D. and Braun, I. and Bretz, T. and Camara, M. and Carmona, E. and Carosi, A. and Colin, P. and Colombo, E. and Contreras, J.~L. and Cortina, J. and Covino, S. and Dazzi, F. and De Angelis, A. and De Cea del Pozo, E. and Delgado Mendez, C. and De Lotto, B. and De Maria, M. and De Sabata, F. and Diago Ortega, A. and Doert, M. and Dom{\'\i}nguez, A. and Dominis Prester, D. and Dorner, D. and Doro, M. and Elsaesser, D. and Ferenc, D. and Fonseca, M.~V. and Font, L. and Garc{\'\i}a L{\'o}pez, R.~J. and Garczarczyk, M. and Gaug, M. and Giavitto, G. and Godinovi, N. and Hadasch, D. and Herrero, A. and Hildebrand, D. and H{\"o}hne-M{\"o}nch, D. and Hose, J. and Hrupec, D. and Jogler, T. and Klepser, S. and Kr{\"a}henb{\"u}hl, T. and Kranich, D. and Krause, J. and La Barbera, A. and Leonardo, E. and Lindfors, E. and Lombardi, S. and L{\'o}pez, M. and Lorenz, E. and Majumdar, P. and Makariev, E. and Maneva, G. and Mankuzhiyil, N. and Mannheim, K. and Maraschi, L. and Mariotti, M. and Mart{\'\i}nez, M. and Mazin, D. and Meucci, M. and Miranda, J.~M. and Mirzoyan, R. and Miyamoto, H. and Mold{\'o}n, J. and Moralejo, A. and Nieto, D. and Nilsson, K. and Orito, R. and Oya, I. and Paoletti, R. and Paredes, J.~M. and Partini, S. and Pasanen, M. and Pauss, F. and Pegna, R.~G. and M. A. P{\'e}rez-Torres and Persic, M. and Peruzzo, J. and Pochon, J. and Prada, F. and Prada Moroni, P.~G. and Prandini, E. and Puchades, N. and Puljak, I. and Reichardt, T. and Rhode, W. and Rib{\'o}, M. and Rico, J. and Rissi, M. and R{\"u}gamer, S. and Saggion, A. and Saito, K. and Saito, T.~Y. and Salvati, M. and S{\'a}nchez-Conde, M. and Satalecka, K. and Scalzotto, V. and Scapin, V. and Schultz, C. and Schweizer, T. and Shayduk, M. and Shore, S.~N. and Sierpowska-Bartosik, A. and Sillanp{\"a}{\"a}, A. and Sitarek, J. and Sobczynska, D. and Spanier, F. and Spiro, S. and Stamerra, A. and Steinke, B. and Storz, J. and Strah, N. and Struebig, J.~C. and Suri{\'c}, T. and Takalo, L.~O. and Tavecchio, F. and Temnikov, P. and Terzi{\'c}, T. and Tescaro, D. and Teshima, M. and Vankov, H. and Wagner, R.~M. and Weitzel, Q. and Zabalza, V. and Zandanel, F. and Zanin, R. and MAGIC Collaboration and Villata, M. and Raiteri, C. and Aller, H.~D. and Aller, M.~F. and Chen, W.~P. and Jordan, B. and Koptelova, E. and Kurtanidze, O.~M. and L{\"a}hteenm{\"a}ki, A. and McBreen, B. and Larionov, V.~M. and Lin, C.~S. and Nikolashvili, M.~G. and Reinthal, R. and Angelakis, E. and Capalbi, M. and Carrami{\~n}ana, A. and Carrasco, L. and Cassaro, P. and Cesarini, A. and Falcone, A. and Gurwell, M.~A. and Hovatta, T. and Kovalev, Y.~A. and Kovalev, Y.~Y. and Krichbaum, T.~P. and Krimm, H.~A. and Lister, M.~L. and Moody, J.~W. and Maccaferri, G. and Mori, Y. and Nestoras, I. and Orlati, A. and Pace, C. and Pagani, C. and Pearson, R. and Perri, M. and Piner, B.~G. and Ros, E. and Sadun, A.~C. and Sakamoto, T. and Tammi, J. and Zook, A.} } @article {2011ApJ...727..129A, title = {{Insights into the High-energy {$\gamma$}-ray Emission of Markarian 501 from Extensive Multifrequency Observations in the Fermi Era}}, journal = {The Astrophysical Journal}, volume = {727}, year = {2011}, month = {feb}, pages = {129}, abstract = {We report on the {$\gamma$}-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) {$\gamma$}-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 {\plusmn} 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 {\plusmn} 0.14, and the softest one is 2.51 {\plusmn} 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15{\mdash}August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size lsim0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (sime10$^{44}$ erg s$^{-1}$) constitutes only a small fraction (\~{}10$^{-3}$) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude.}, keywords = {acceleration of particles, BL Lacertae objects: general, BL Lacertae objects: individual: Mrk 501, galaxies: active, gamma rays: general, radiation mechanisms: non-thermal}, doi = {10.1088/0004-637X/727/2/129}, url = {http://adsabs.harvard.edu/abs/2011ApJ...727..129A}, author = {Abdo, A.~A. and Ackermann, M. and Ajello, M. and Allafort, A. and Baldini, L. and Ballet, J. and Barbiellini, G. and Baring, M.~G. and Bastieri, D. and Bechtol, K. and Bellazzini, R. and Berenji, B. and Blandford, R.~D. and Bloom, E.~D. and Bonamente, E. and Borgland, A.~W. and Bouvier, A. and Brandt, T.~J. and Bregeon, J. and Brez, A. and Brigida, M. and Bruel, P. and Buehler, R. and Buson, S. and Caliandro, G.~A. and Cameron, R.~A. and Cannon, A. and Caraveo, P.~A. and Carrigan, S. and Casandjian, J.~M. and Cavazzuti, E. and Cecchi, C. and {\c C}elik, {\"O}. and Charles, E. and Chekhtman, A. and Cheung, C.~C. and Chiang, J. and Ciprini, S. and Claus, R. and Cohen-Tanugi, J. and Conrad, J. and Cutini, S. and Dermer, C.~D. and de Palma, F. and Silva, E.~d.~C.~e. and Drell, P.~S. and Dubois, R. and Dumora, D. and Favuzzi, C. and Fegan, S.~J. and Ferrara, E.~C. and Focke, W.~B. and Fortin, P. and Frailis, M. and Fuhrmann, L. and Fukazawa, Y. and Funk, S. and Fusco, P. and Gargano, F. and Gasparrini, D. and Gehrels, N. and Germani, S. and Giglietto, N. and Giordano, F. and Giroletti, M. and Glanzman, T. and Godfrey, G. and Grenier, I.~A. and Guillemot, L. and Guiriec, S. and Hayashida, M. and Hays, E. and Horan, D. and Hughes, R.~E. and J{\'o}hannesson, G. and Johnson, A.~S. and Johnson, W.~N. and Kadler, M. and Kamae, T. and Katagiri, H. and Kataoka, J. and Kn{\"o}dlseder, J. and Kuss, M. and Lande, J. and Latronico, L. and Lee, S.-H. and Lemoine-Goumard, M. and Longo, F. and Loparco, F. and Lott, B. and Lovellette, M.~N. and Lubrano, P. and Madejski, G.~M. and Makeev, A. and Max-Moerbeck, W. and Mazziotta, M.~N. and McEnery, J.~E. and M{\'e}hault, J. and Michelson, P.~F. and Mitthumsiri, W. and Mizuno, T. and Moiseev, A.~A. and Monte, C. and Monzani, M.~E. and Morselli, A. and Moskalenko, I.~V. and Murgia, S. and Naumann-Godo, M. and Nishino, S. and Nolan, P.~L. and Norris, J.~P. and Nuss, E. and Ohsugi, T. and Okumura, A. and Omodei, N. and Orlando, E. and Ormes, J.~F. and Paneque, D. and Panetta, J.~H. and Parent, D. and Pavlidou, V. and Pearson, T.~J. and Pelassa, V. and Pepe, M. and Pesce-Rollins, M. and Piron, F. and Porter, T.~A. and Rain{\`o}, S. and Rando, R. and Razzano, M. and Readhead, A. and Reimer, A. and Reimer, O. and Richards, J.~L. and Ripken, J. and Ritz, S. and Roth, M. and Sadrozinski, H.~F.-W. and Sanchez, D. and Sander, A. and Scargle, J.~D. and Sgr{\`o}, C. and Siskind, E.~J. and Smith, P.~D. and Spandre, G. and Spinelli, P. and Stawarz, {\L}. and Stevenson, M. and Strickman, M.~S. and Sokolovsky, K.~V. and Suson, D.~J. and Takahashi, H. and Takahashi, T. and Tanaka, T. and Thayer, J.~B. and Thayer, J.~G. and Thompson, D.~J. and Tibaldo, L. and Torres, D.~F. and Tosti, G. and Tramacere, A. and Uchiyama, Y. and Usher, T.~L. and Vandenbroucke, J. and Vasileiou, V. and Vilchez, N. and Vitale, V. and Waite, A.~P. and Wang, P. and Wehrle, A.~E. and Winer, B.~L. and Wood, K.~S. and Yang, Z. and Ylinen, T. and Zensus, J.~A. and Ziegler, M. and Fermi LAT Collaboration and Aleksi{\'c}, J. and Antonelli, L.~A. and Antoranz, P. and Backes, M. and Barrio, J.~A. and Becerra Gonz{\'a}lez, J. and Bednarek, W. and Berdyugin, A. and Berger, K. and Bernardini, E. and Biland, A. and Blanch, O. and Bock, R.~K. and Boller, A. and Bonnoli, G. and Bordas, P. and Borla Tridon, D. and Bosch-Ramon, V. and Bose, D. and Braun, I. and Bretz, T. and Camara, M. and Carmona, E. and Carosi, A. and Colin, P. and Colombo, E. and Contreras, J.~L. and Cortina, J. and Covino, S. and Dazzi, F. and De Angelis, A. and De Cea del Pozo, E. and De Lotto, B. and De Maria, M. and De Sabata, F. and Delgado Mendez, C. and Diago Ortega, A. and Doert, M. and Dom{\'\i}nguez, A. and Dominis Prester, D. and Dorner, D. and Doro, M. and Elsaesser, D. and Ferenc, D. and Fonseca, M.~V. and Font, L. and Garc{\'\i}a L{\'o}pez, R.~J. and Garczarczyk, M. and Gaug, M. and Giavitto, G. and Godinovi, N. and Hadasch, D. and Herrero, A. and Hildebrand, D. and H{\"o}hne-M{\"o}nch, D. and Hose, J. and Hrupec, D. and Jogler, T. and Klepser, S. and Kr{\"a}henb{\"u}hl, T. and Kranich, D. and Krause, J. and La Barbera, A. and Leonardo, E. and Lindfors, E. and Lombardi, S. and L{\'o}pez, M. and Lorenz, E. and Majumdar, P. and Makariev, E. and Maneva, G. and Mankuzhiyil, N. and Mannheim, K. and Maraschi, L. and Mariotti, M. and Mart{\'\i}nez, M. and Mazin, D. and Meucci, M. and Miranda, J.~M. and Mirzoyan, R. and Miyamoto, H. and Mold{\'o}n, J. and Moralejo, A. and Nieto, D. and Nilsson, K. and Orito, R. and Oya, I. and Paoletti, R. and Paredes, J.~M. and Partini, S. and Pasanen, M. and Pauss, F. and Pegna, R.~G. and M. A. P{\'e}rez-Torres and Persic, M. and Peruzzo, J. and Pochon, J. and Prada Moroni, P.~G. and Prada, F. and Prandini, E. and Puchades, N. and Puljak, I. and Reichardt, T. and Reinthal, R. and Rhode, W. and Rib{\'o}, M. and Rico, J. and Rissi, M. and R{\"u}gamer, S. and Saggion, A. and Saito, K. and Saito, T.~Y. and Salvati, M. and S{\'a}nchez-Conde, M. and Satalecka, K. and Scalzotto, V. and Scapin, V. and Schultz, C. and Schweizer, T. and Shayduk, M. and Shore, S.~N. and Sierpowska-Bartosik, A. and Sillanp{\"a}{\"a}, A. and Sitarek, J. and Sobczynska, D. and Spanier, F. and Spiro, S. and Stamerra, A. and Steinke, B. and Storz, J. and Strah, N. and Struebig, J.~C. and Suri{\'c}, T. and Takalo, L.~O. and Tavecchio, F. and Temnikov, P. and Terzi{\'c}, T. and Tescaro, D. and Teshima, M. and Vankov, H. and Wagner, R.~M. and Weitzel, Q. and Zabalza, V. and Zandanel, F. and Zanin, R. and MAGIC Collaboration and Acciari, V.~A. and Arlen, T. and Aune, T. and Benbow, W. and Boltuch, D. and Bradbury, S.~M. and Buckley, J.~H. and Bugaev, V. and Cannon, A. and Cesarini, A. and Ciupik, L. and Cui, W. and Dickherber, R. and Errando, M. and Falcone, A. and Finley, J.~P. and Finnegan, G. and Fortson, L. and Furniss, A. and Galante, N. and Gall, D. and Gillanders, G.~H. and Godambe, S. and Grube, J. and Guenette, R. and Gyuk, G. and Hanna, D. and Holder, J. and Huang, D. and Hui, C.~M. and Humensky, T.~B. and Kaaret, P. and Karlsson, N. and Kertzman, M. and Kieda, D. and Konopelko, A. and Krawczynski, H. and Krennrich, F. and Lang, M.~J. and Maier, G. and McArthur, S. and McCann, A. and McCutcheon, M. and Moriarty, P. and Mukherjee, R. and Ong, R. and Otte, A.~N. and Pandel, D. and Perkins, J.~S. and Pichel, A. and Pohl, M. and Quinn, J. and Ragan, K. and Reyes, L.~C. and Reynolds, P.~T. and Roache, E. and Rose, H.~J. and Rovero, A.~C. and Schroedter, M. and Sembroski, G.~H. and Senturk, G.~D. and Steele, D. and Swordy, S.~P. and Te\v si{\'c}, G. and Theiling, M. and Thibadeau, S. and Varlotta, A. and Vincent, S. and Wakely, S.~P. and Ward, J.~E. and Weekes, T.~C. and Weinstein, A. and Weisgarber, T. and Williams, D.~A. and Wood, M. and Zitzer, B. and VERITAS Collaboration and Villata, M. and Raiteri, C.~M. and Aller, H.~D. and Aller, M.~F. and Arkharov, A.~A. and Blinov, D.~A. and Calcidese, P. and Chen, W.~P. and Efimova, N.~V. and Kimeridze, G. and Konstantinova, T.~S. and Kopatskaya, E.~N. and Koptelova, E. and Kurtanidze, O.~M. and Kurtanidze, S.~O. and L{\"a}hteenm{\"a}ki, A. and Larionov, V.~M. and Larionova, E.~G. and Larionova, L.~V. and Ligustri, R. and Morozova, D.~A. and Nikolashvili, M.~G. and Sigua, L.~A. and Troitsky, I.~S. and Angelakis, E. and Capalbi, M. and Carrami{\~n}ana, A. and Carrasco, L. and Cassaro, P. and de la Fuente, E. and Gurwell, M.~A. and Kovalev, Y.~Y. and Kovalev, Y.~A. and Krichbaum, T.~P. and Krimm, H.~A. and Leto, P. and Lister, M.~L. and Maccaferri, G. and Moody, J.~W. and Mori, Y. and Nestoras, I. and Orlati, A. and Pagani, C. and Pace, C. and Pearson III, R. and Perri, M. and Piner, B.~G. and Pushkarev, A.~B. and Ros, E. and Sadun, A.~C. and Sakamoto, T. and Tornikoski, M. and Yatsu, Y. and Zook, A.} } @article {2011A\&A...526A.142M, title = {{Radio emission of SN1993J: the complete picture. I. Re-analysis of all the available VLBI data}}, journal = {Astronomy and Astrophysics}, volume = {526}, year = {2011}, month = {feb}, pages = {A142}, abstract = {We have performed a complete re-calibration and re-analysis of all the available Very-Long-Baseline-Interferometry (VLBI) observations of supernova SN1993J, following an homogeneous and well-defined methodology. VLBI observations of SN1993J at 69 epochs, spanning 13 years, were performed by two teams, which used different strategies and analysis tools. The results obtained by each group are similar, but their conclusions on the supernova expansion and the shape and evolution of the emitting region differ significantly. From our analysis of the combined set of observations, we have obtained an expansion curve with unprecedented time resolution and coverage. We find that the data from both teams are compatible when analyzed with the same methodology. One expansion index (m$_{3}$ = 0.87 {\plusmn} 0.02) is enough to model the expansion observed at 1.7 GHz, while two expansion indices (m$_{1}$ = 0.933 {\plusmn} 0.010 and m$_{2}$ = 0.796 {\plusmn} 0.005), separated by a break time, t$_{br}$ = 390 {\plusmn} 30 days, are needed to model the data, at frequencies higher than 1.7 GHz, up to day \~{}4000 after explosion. We thus confirm the wavelength dependence of the size of the emitting region reported by one of the groups. We also find that all sizes measured at epochs later than day \~{}4000 after explosion are systematically smaller than our model predictions (i.e., an additional expansion index might be needed to properly model these data). We also estimate the fractional shell width (0.31 {\plusmn} 0.02, average of all epochs and frequencies) and the level of opacity to the radio emission by the ejecta. We find evidence of a spectral-index radial gradient in the supernova shell, which is indicative of a frequency-dependent ejecta opacity. Finally, we study the distribution and evolution of the azimuthal anisotropies (hot spots) found around the radio shell during the expansion. These anisotropies have intensities of \~{}20\% of the mean flux density of the shell, and appear to systematically evolve during the expansion.}, keywords = {galaxies: individual: M 81, radio continuum: stars, supernovae: general, supernovae: individual: SN1993J}, doi = {10.1051/0004-6361/200913831}, url = {http://adsabs.harvard.edu/abs/2011A\%26A...526A.142M}, author = {Mart{\'\i}-Vidal, I. and Marcaide, J.~M. and Alberdi, A. and Guirado, J.~C. and M. A. P{\'e}rez-Torres and Ros, E.} } @article {2011A\&A...526A.143M, title = {{Radio emission of SN1993J: the complete picture. II. Simultaneous fit of expansion and radio light curves}}, journal = {Astronomy and Astrophysics}, volume = {526}, year = {2011}, pages = {A143}, abstract = {We report on a simultaneous modelling of the expansion and radio light curves of the supernova SN1993J. We developed a simulation code capable of generating synthetic expansion and radio light curves of supernovae by taking into consideration the evolution of the expanding shock, magnetic fields, and relativistic electrons, as well as the finite sensitivity of the interferometric arrays used in the observations. Our software successfully fits all the available radio data of SN 1993J with a standard emission model for supernovae, which is extended with some physical considerations, such as an evolution in the opacity of the ejecta material, a radial decline in the magnetic fields within the radiating region, and a changing radial density profile for the circumstellar medium starting from day 3100 after the explosion.}, keywords = {acceleration of particles, galaxies: individual: M 81, radiation mechanisms: non-thermal, radio continuum: stars, supernovae: general, supernovae: individual: SN1993J}, doi = {10.1051/0004-6361/201014517}, url = {http://adsabs.harvard.edu/abs/2011A\%26A...526A.143M}, author = {Mart{\'\i}-Vidal, I. and Marcaide, J.~M. and Alberdi, A. and Guirado, J.~C. and M. A. P{\'e}rez-Torres and Ros, E.} } @article {2011A\&A...535L..10M, title = {{VLBI observations of SN 2011dh: imaging of the youngest radio supernova}}, journal = {Astronomy and Astrophysics}, volume = {535}, year = {2011}, pages = {L10}, abstract = {We report on the VLBI detection of supernova SN 2011dh at 22 GHz using a subset of the EVN array. The observations took place 14 days after the discovery of the supernova, thus resulting in a VLBI image of the youngest radio-loud supernova ever. We provide revised coordinates for the supernova with milli-arcsecond precision, linked to the ICRF. The recovered flux density is a factor \~{}2 below the EVLA flux density reported by other authors at the same frequency and epoch of our observations. This discrepancy could be due to extended emission detected with the EVLA or to calibration problems in the VLBI and/or EVLA observations.}, keywords = {ISM: supernova remnants, radiation mechanisms: non-thermal, radio continuum: general, supernovae: general, supernovae: individual: SN 2011dh}, doi = {10.1051/0004-6361/201118195}, url = {http://adsabs.harvard.edu/abs/2011A\%26A...535L..10M}, author = {Mart{\'\i}-Vidal, I. and Tudose, V. and Paragi, Z. and Yang, J. and Marcaide, J.~M. and Guirado, J.~C. and Ros, E. and Alberdi, A. and M. A. P{\'e}rez-Torres and Argo, M.~K. and van der Horst, A.~J. and Garrett, M.~A. and Stockdale, C.~J. and Weiler, K.~W.} } @article {2010A\&A...515A..53M, title = {{Coherence loss in phase-referenced VLBI observations}}, journal = {Astronomy and Astrophysics}, volume = {515}, year = {2010}, month = {jun}, pages = {A53}, abstract = {Context. Phase-referencing is a standard calibration technique in radio interferometry, particularly suited for the detection of weak sources close to the sensitivity limits of the interferometers. However, effects from a changing atmosphere and inaccuracies in the correlator model may affect the phase-referenced images, and lead to wrong estimates of source flux densities and positions. A systematic observational study of signal decoherence in phase-referencing and its effects in the image plane has not been performed yet.
Aims: We systematically studied how the signal coherence in Very-Long-Baseline-Interferometry (VLBI) observations is affected by a phase-reference calibration at different frequencies and for different calibrator-to-target separations. The results obtained should be of interest for a correct interpretation of many phase-referenced observations with VLBI.
Methods: We observed a set of 13 strong sources (the S5 polar cap sample) at 8.4 and 15 GHz in phase-reference mode with 32 different calibrator/target combinations spanning angular separations between 1.5 and 20.5 degrees. We obtained phase-referenced images and studied how the dynamic range and peak flux-density depend on observing frequency and source separation.
Results: We obtained dynamic ranges and peak flux densities of the phase-referenced images as a function of frequency and separation from the calibrator. We compared our results with models and phenomenological equations previously reported.
Conclusions: The dynamic range of the phase-referenced images is strongly limited by the atmosphere at all frequencies and for all source separations. The limiting dynamic range is inversely proportional to the sine of the calibrator-to-target separation. Not surpriseingly, we also find that the peak flux densities decrease with source separation, relative to those obtained from the self-calibrated images.}, keywords = {atmospheric effects, instrumentation: interferometers, techniques: interferometric}, doi = {10.1051/0004-6361/201014203}, url = {http://adsabs.harvard.edu/abs/2010A\%26A...515A..53M}, author = {Mart{\'\i}-Vidal, I. and Ros, E. and M. A. P{\'e}rez-Torres and Guirado, J.~C. and Jim{\'e}nez-Monferrer, S. and Marcaide, J.~M.} }