Publications by Will Potter


Modelling blazar flaring using a time-dependent fluid jet emission model - an explanation for orphan flares and radio lags

Monthly Notices of the Royal Astronomical Society Oxford University Press 473 (2017) 4107-4121

W Potter

Blazar jets are renowned for their rapid violent variability and multiwavelength flares, however, the physical processes responsible for these flares are not well understood. In this paper we develop a time-dependent inhomogeneous fluid jet emission model for blazars. We model optically thick radio flares for the first time and show that they are delayed with respect to the prompt optically thin emission by ∼ months to decades, with a lag that increases with the jet power and observed wavelength. This lag is caused by a combination of the travel time of the flaring plasma to the optically thin radio emitting sections of the jet and the slow rise time of the radio flare. We predict two types of flares: symmetric flares - with the same rise and decay time, which occur for flares whose duration is shorter than both the radiative lifetime and the geometric path-length delay timescale; extended flares - whose luminosity tracks the power of particle acceleration in the flare, which occur for flares with a duration longer than both the radiative lifetime and geometric delay. Our model naturally produces orphan X-ray and γ-ray flares. These are caused by flares which are only observable above the quiescent jet emission in a narrow band of frequencies. Our model is able to successfully fit to the observed multiwavelength flaring spectra and lightcurves of PKS1502+106 across all wavelengths, using a transient flaring front located within the broad-line region.


Using radiative energy losses to constrain the magnetisation and magnetic reconnection rate at the base of black hole jets

Monthly Notices of the Royal Astronomical Society Oxford University Press 465 (2016) 337-357

W Potter

We calculate the severe radiative energy losses which occur at the base of black hole jets using a relativistic fluid jet model, including in-situ acceleration of non-thermal leptons by magnetic reconnection. Our results demonstrate that including a self-consistent treatment of radiative energy losses is necessary to perform accurate MHD simulations of powerful jets and that jet spectra calculated via post-processing are liable to vastly overestimate the amount of non-thermal emission. If no more than 95% of the initial total jet power is radiated away by the plasma travels as it travels along the length of the jet, we can place a lower bound on the magnetisation of the jet plasma at the base of the jet. For typical powerful jets, we find that the plasma at the jet base is required to be highly magnetised, with at least 10,000 times more energy contained in magnetic fields than in non-thermal leptons. Using a simple power-law model of magnetic reconnection, motivated by simulations of collisionless reconnection, we determine the allowed range of the large-scale average reconnection rate along the jet, by restricting the total radiative energy losses incurred and the distance at which the jet first comes into equipartition. We calculate analytic expressions for the cumulative radiative energy losses due to synchrotron and inverse-Compton emission along jets, and derive analytic formulae for the constraint on the initial magnetisation.


Demonstration of a magnetic Prandtl number disc instability from first principles

Monthly Notices of the Royal Astronomical Society Oxford University Press 472 (2017) 3021–3028-

W Potter, SA Balbus

Understanding what determines the strength of MHD turbulence in accretion discs is a question of fundamental theoretical and observational importance. In this work we investigate whether the dependence of the turbulent accretion disc stress (α) on the magnetic Prandtl number (Pm) is sufficiently sensitive to induce thermal-viscous instability using 3D MHD simulations. We first investigate whether the α-Pm dependence, found by many previous authors, has a physical or numerical origin by conducting a suite of local shearing-box simulations. We find that a definite α-Pm dependence persists when simultaneously increasing numerical resolution and decreasing the absolute values of both the viscous and resistive dissipation coefficients. This points to a physical origin of the α-Pm dependence. Using a further set of simulations which include realistic turbulent heating and radiative cooling, and by giving Pm a realistic physical dependence on the plasma temperature and density, we demonstrate that the α-Pm dependence is sufficiently strong to lead to a local instability. We confirm that the instability manifests itself as an unstable limit cycle by mapping the local thermal-equilibrium curve of the disc. This is the first self-consistent MHD simulation demonstrating the Pm instability from first principles. This result is important because a physical Pm instability could lead to the global propagation of heating and cooling fronts and a transition between disc states on timescales compatible with the observed hard/soft state transitions in black hole binaries.


Erratum: An accretion disc instability induced by a temperature sensitive α parameter [MNRAS, 441, 1 (2014) (681-689)

Monthly Notices of the Royal Astronomical Society 464 (2017) 4544-

WJ Potter, SA Balbus

© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. The paper 'An accretion disc instability induced by a temperaturesensitive a parameter' was originally published in 441(1), 681-689. A serious typesetting error appears in this paper. The symbol for Schwarzschild radius, rs, was incorrectly replaced with the symbol for central temperature, Tc, everywhere in the manuscript. This affects equations (13), (41), (42), (43), (44) and (A9) and many instances in the text highlighted below. Since the resulting online published article is incorrect in so many places, the authors recommend that interested readers refer to the (https://arxiv.org/abs/1404.0013) version of the paper.


Surprises in astrophysical gasdynamics.

Reports on progress in physics. Physical Society (Great Britain) 79 (2016) 066901-

SA Balbus, WJ Potter

Much of astrophysics consists of the study of ionized gas under the influence of gravitational and magnetic fields. Thus, it is not possible to understand the astrophysical universe without a detailed knowledge of the dynamics of magnetized fluids. Fluid dynamics is, however, a notoriously tricky subject, in which it is all too easy for one's a priori intuition to go astray. In this review, we seek to guide the reader through a series of illuminating yet deceptive problems, all with an enlightening twist. We cover a broad range of topics including the instabilities acting in accretion discs, the hydrodynamics governing the convective zone of the Sun, the magnetic shielding of a cooling galaxy cluster, and the behaviour of thermal instabilities and evaporating clouds. The aim of this review is to surprise and intrigue even veteran astrophysical theorists with an idiosyncratic choice of problems and counterintuitive results. At the same time, we endeavour to bring forth the fundamental ideas, to set out important assumptions, and to describe carefully whatever novel techniques may be appropriate to the problem at hand. By beginning at the beginning, and analysing a wide variety of astrophysical settings, we seek not only to make this review suitable for fluid dynamic veterans, but to engage novice recruits as well with what we hope will be an unusual and instructive introduction to the subject.


New constraints on the structure and dynamics of black hole jets

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 453 (2015) 4070-4088

WJ Potter, G Cotter


Differential rotation and radiative equilibrium in the Sun: is the tachocline spreading?

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 448 (2015) 2077-2084

A Caleo, SA Balbus, WJ Potter


An accretion disc instability induced by a temperature sensitive α parameter

Monthly Notices of the Royal Astronomical Society 441 (2014) 681-689

WJ Potter, SA Balbus

In the standard thin-disc formalism, the dimensionless α parameter is usually assumed to be constant. However, there are good theoretical reasons for believing, as well as evidence from simulations, that α is dependent on intrinsic disc properties. In this paper, we analyse the conditions for the stability of a thin accretion disc in which α is a function of the magnetic Prandtl number, the ratio of collisional viscosity to resistivity. In the inner disc, where the free electron opacity and radiation viscosity dominate, the disc is unstable if α is proportional to the magnetic Prandtl number with an exponent >0.5. This is within the range of values for the power-law index found in magnetohydrodynamic simulations with simple energetics. We calculate the evolution of the unstable disc within the α-formalism and show that the physically accessible solutions form a limit cycle, analogous to the behaviour seen in recurrent dwarf novae. It is noteworthy that the time-dependent global behaviour of the instability results in cyclic heating of the inner section of the disc, when parameters appropriate for an X-ray binary system are used. We calculate a model spectrum of the disc in the flaring and quiescent states and show that the behaviour is compatible with X-ray observations of the thermal accretion disc in flaring X-ray binary systems. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


THE COSMIC EVOLUTION OF FERMI BL LACERTAE OBJECTS

ASTROPHYSICAL JOURNAL 780 (2014) ARTN 73

M Ajello, RW Romani, D Gasparrini, MS Shaw, J Bolmer, G Cotter, J Finke, J Greiner, SE Healey, O King, W Max-Moerbeck, PF Michelson, WJ Potter, A Rau, ACS Readhead, JL Richards, P Schady


Synchrotron and inverse-Compton emission from blazar jets - IV.BL Lac type blazars and the physical basis for the blazar sequence

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 436 (2013) 304-314

WJ Potter, G Cotter


Uncovering the physics behind the blazar sequence using a realistic model for jet emission

INNERMOST REGIONS OF RELATIVISTIC JETS AND THEIR MAGNETIC FIELDS 61 (2013) ARTN 05008

WJ Potter, G Cotter


Synchrotron and inverse-Compton emission from blazar jets - II. An accelerating jet model with a geometry set by observations of M87

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 429 (2013) 1189-1205

WJ Potter, G Cotter


SPECTROSCOPY OF THE LARGEST EVER gamma-RAY-SELECTED BL LAC SAMPLE

ASTROPHYSICAL JOURNAL 764 (2013) ARTN 135

MS Shaw, RW Romani, G Cotter, SE Healey, PF Michelson, ACS Readhead, JL Richards, W Max-Moerbeck, OG King, WJ Potter


Synchrotron and inverse-Compton emission from blazar jets - III. Compton-dominant blazars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 431 (2013) 1840-1852

WJ Potter, G Cotter


Introducing the CTA concept

ASTROPARTICLE PHYSICS 43 (2013) 3-18

BS Acharya, M Actis, T Aghajani, G Agnetta, J Aguilar, F Aharonian, M Ajello, A Akhperjanian, M Alcubierre, J Aleksic, R Alfaro, E Aliu, AJ Allafort, D Allan, I Allekotte, E Amato, J Anderson, EO Anguener, LA Antonelli, P Antoranz, A Aravantinos, T Arlen, T Armstrong, H Arnaldi, L Arrabito, K Asano, T Ashton, HG Asorey, Y Awane, H Baba, A Babic, N Baby, J Baehr, A Bais, C Baixeras, S Bajtlik, M Balbo, D Balis, C Balkowski, A Bamba, R Bandiera, A Barber, C Barbier, M Barcelo, A Barnacka, J Barnstedt, U Barres de Almeida, JA Barrio, A Basili, S Basso, D Bastieri, C Bauer, A Baushev, J Becerra, Y Becherini, KC Bechtol, JB Tjus, V Beckmann, W Bednarek, B Behera, M Belluso, W Benbow, J Berdugo, K Berger, F Bernard, T Bernardino, K Bernloehr, N Bhat, S Bhattacharyya, C Bigongiari, A Biland, S Billotta, T Bird, E Birsin, E Bissaldi, J Biteau, M Bitossi, S Blake, O Blanch Bigas, P Blasi, A Bobkov, V Boccone, M Boettcher, L Bogacz, J Bogart, M Bogdan, C Boisson, J Boix Gargallo, J Bolmont, G Bonanno, A Bonardi, T Bonev, P Bonifacio, G Bonnoli, P Bordas, A Borgland, J Borkowski, R Bose, O Botner, A Bottani, L Bouchet, M Bourgeat, C Boutonnet, A Bouvier, S Brau-Nogue, I Braun, T Bretz, M Briggs, T Bringmann, P Brook, P Brun, L Brunetti, T Buanes, J Buckley, R Buehler, V Bugaev, A Bulgarelli, T Bulik, G Busetto, S Buson, K Byrum, M Cailles, R Cameron, J Camprecios, R Canestrari, S Cantu, M Capalbi, P Caraveo, E Carmona, A Carosi, J Carr, P-H Carton, S Casanova, M Casiraghi, O Catalano, S Cavazzani, S Cazaux, M Cerruti, E Chabanne, P Chadwick, C Champion, A Chen, J Chiang, L Chiappetti, M Chikawa, VR Chitnis, F Chollet, J Chudoba, M Cieslar, A Cillis, J Cohen-Tanugi, S Colafrancesco, P Colin, J Calome, S Colonges, M Compin, P Conconi, V Conforti, V Connaughton, J Conrad, JL Contreras, P Coppi, P Corona, D Corti, J Cortina, L Cossio, H Costantini, G Cotter, B Courty, S Couturier, S Covino, G Crimi, SJ Criswell, J Croston, G Cusumano, M Dafonseca, O Dale, M Daniel, J Darling, I Davids, F Dazzi, A De Angelis, V De Caprio, F De Frondat, EM de Gouveia Dal Pino, I de la Calle, GA De La Vega, RDLR Lopez, B De Lotto, A De Luca, JRT de Mello Neto, M de Naurois, Y de Oliveira, E de Ona Wilhelmi, V de Souza, G Decerprit, G Decock, C Deil, E Delagnes, G Deleglise, C Delgado, D Della Volpe, P Demange, G Depaola, A Dettlaff, A Di Paola, F Di Pierro, C Diaz, J Dick, R Dickherber, H Dickinson, V Diez-Blanco, S Digel, D Dimitrov, G Disset, A Djannati-Atai, M Doert, M Dohmke, W Domainko, DD Prester, A Donat, D Dorner, M Doro, J-L Dournaux, G Drake, D Dravins, L Drury, F Dubois, R Dubois, G Dubus, C Dufour, D Dumas, J Dumm, D Durand, J Dyks, M Dyrda, J Ebr, E Edy, K Egberts, P Eger, S Einecke, C Eleftheriadis, S Elles, D Emmanoulopoulos, D Engelhaupt, R Enomoto, J-P Ernenwein, M Errando, A Etchegoyen, P Evans, A Falcone, D Fantinel, K Farakos, C Farnier, G Fasola, B Favill, E Fede, S Federici, S Fegan, F Feinstein, D Ferenc, P Ferrando, M Fesquet, A Fiasson, E Fillin-Martino, D Fink, C Finley, JP Finley, M Fiorini, R Firpo Curcoll, H Flores, D Florin, W Focke, C Foehr, E Fokitis, L Font, G Fontaine, M Fornasa, A Foerster, L Fortson, N Fouque, A Franckowiak, C Fransson, G Fraser, R Frei, IFM Albuquerque, L Fresnillo, C Fruck, Y Fujita, Y Fukazawa, Y Fukui, S Funk, W Gaebele, S Gabici, R Gabriele, A Gadola, N Galante, D Gall, Y Gallant, J Gamez-Garcia, B Garcia, R Garcia Lopez, D Gardiol, D Garrido, L Garrido, D Gascon, M Gaug, J Gaweda, L Gebremedhin, N Geffroy, L Gerard, A Ghedina, M Ghigo, E Giannakaki, F Gianotti, S Giarrusso, G Giavitto, B Giebels, V Gika, P Giommi, N Girard, E Giro, A Giuliani, T Glanzman, J-F Glicenstein, N Godinovic, V Golev, M Gomez Berisso, J Gomez-Ortega, MM Gonzalez, A Gonzalez, F Gonzalez, A Gonzalez Munoz, KS Gothe, M Gougerot, R Graciani, P Grandi, F Granena, J Granot, G Grasseau, R Gredig, A Green, T Greenshaw, T Gregoire, O Grimm, J Grube, M Grudzinska, V Gruev, S Gruenewald, J Grygorczuk, V Guarino, S Gunji, G Gyuk, D Hadasch, R Hagiwara, J Hahn, N Hakansson, A Hallgren, N Hamer Heras, S Hara, MJ Hardcastle, J Harris, T Hassan, K Hatanaka, T Haubold, A Haupt, T Hayakawa, M Hayashida, R Heller, F Henault, G Henri, G Hermann, R Hermel, A Herrero, N Hidaka, J Hinton, D Hoffmann, W Hofmann, P Hofverberg, J Holder, D Horns, D Horville, J Houles, M Hrabovsky, D Hrupec, H Huan, B Huber, J-M Huet, G Hughes, TB Humensky, J Huovelin, A Ibarra, JM Illa, D Impiombato, S Incorvaia, S Inoue, Y Inoue, K Ioka, E Ismailova, C Jablonski, A Jacholkowska, M Jamrozy, M Janiak, P Jean, C Jeanney, JJ Jimenez, T Jogler, T Johnson, L Journet, C Juffroy, I Jung, P Kaaret, S Kabuki, M Kagaya, J Kakuwa, C Kalkuhl, R Kankanyan, A Karastergiou, K Kaercher, M Karczewski, S Karkar, A Kasperek, D Kastana, H Katagiri, J Kataoka, K Katarzynski, U Katz, N Kawanaka, B Kellner-Leidel, H Kelly, E Kendziorra, B Khelifi, DB Kieda, T Kifune, T Kihm, T Kishimoto, K Kitamoto, W Kluzniak, C Knapic, JW Knapp, J Knoedlseder, F Koeck, J Kocot, K Kodani, J-H Koehne, K Kohri, K Kokkotas, D Kolitzus, N Komin, I Kominis, Y Konno, H Koeppel, P Korohoda, K Kosack, G Koss, R Kossakowski, P Kostka, R Koul, G Kowal, S Koyama, J Koziol, T Kraehenbuehl, J Krause, H Krawzcynski, F Krennrich, A Krepps, A Kretzschmann, R Krobot, P Krueger, H Kubo, VA Kudryavtsev, J Kushida, A Kuznetsov, A La Barbera, N La Palombara, V La Parola, G La Rosa, K Lacombe, G Lamanna, J Lande, D Languignon, J Lapington, P Laporte, C Lavalley, T Le Flour, A Le Padellec, S-H Lee, WH Lee, MA Leigui de Oliveira, D Lelas, J-P Lenain, DJ Leopold, T Lerch, L Lessio, B Lieunard, E Lindfors, A Liolios, A Lipniacka, H Lockart, T Lohse, S Lombardi, A Lopatin, M Lopez, R Lopez-Coto, A Lopez-Oramas, A Lorca, E Lorenz, P Lubinski, F Lucarelli, H Luedecke, J Ludwin, PL Luque-Escamilla, W Lustermann, O Luz, E Lyard, MC Maccarone, TJ Maccarone, GM Madejski, A Madhavan, M Mahabir, G Maier, P Majumdar, G Malaguti, S Maltezos, A Manalaysay, A Mancilla, D Mandat, G Maneva, A Mangano, P Manigot, K Mannheim, I Manthos, N Maragos, A Marcowith, M Mariotti, M Marisaldi, S Markoff, A Marszalek, C Martens, J Marti, J-M Martin, P Martin, G Martinez, F Martinez, M Martinez, A Masserot, A Mastichiadis, A Mathieu, H Matsumoto, F Mattana, S Mattiazzo, G Maurin, S Maxfield, J Maya, D Mazin, L Mc Comb, N McCubbin, I McHardy, R McKay, C Medina, C Melioli, D Melkumyan, S Mereghetti, P Mertsch, M Meucci, J Michalowski, P Micolon, A Mihailidis, T Mineo, M Minuti, N Mirabal, F Mirabel, JM Miranda, R Mirzoyan, T Mizuno, B Moal, R Moderski, I Mognet, E Molinari, M Molinaro, T Montaruli, I Monteiro, P Moore, A Moralejo Olaizola, M Mordalska, C Morello, K Mori, F Mottez, Y Moudden, E Moulin, I Mrusek, R Mukherjee, P Munar-Adrover, H Muraishi, K Murase, A Murphy, S Nagataki, T Naito, D Nakajima, T Nakamori, K Nakayama, C Naumann, D Naumann, M Naumann-Godo, P Nayman, D Nedbal, D Neise, L Nellen, V Neustroev, N Neyroud, L Nicastro, J Nicolau-Kuklinski, A Niedzwiecki, J Niemiec, D Nieto, A Nikolaidis, K Nishijima, S Nolan, R Northrop, D Nosek, N Nowak, A Nozato, P O'Brien, Y Ohira, M Ohishi, S Ohm, H Ohoka, T Okuda, A Okumura, J-F Olive, RA Ong, R Orito, M Orr, J Osborne, M Ostrowski, LA Otero, N Otte, E Ovcharov, I Oya, A Ozieblo, L Padilla, S Paiano, D Paillot, A Paizis, S Palanque, M Palatka, J Pallota, K Panagiotidis, J-L Panazol, D Paneque, M Panter, R Paoletti, A Papayannis, G Papyan, JM Paredes, G Pareschi, G Parks, J-M Parraud, D Parsons, MP Arribas, M Pech, G Pedaletti, V Pelassa, D Pelat, MDC Perez, M Persic, P-O Petrucci, B Peyaud, A Pichel, S Pita, F Pizzolato, L Platos, R Platzer, L Pogosyan, M Pohl, G Pojmanski, JD Ponz, W Potter, J Poutanen, E Prandini, J Prast, R Preece, F Profeti, H Prokoph, M Prouza, M Proyetti, I Puerto-Gimenez, G Puehlhofer, I Puljak, M Punch, R Pyziol, EJ Quel, J Quinn, A Quirrenbach, E Racero, PJ Rajda, P Ramon, R Rando, RC Rannot, M Rataj, M Raue, P Reardon, O Reimann, A Reimer, O Reimer, K Reitberger, M Renaud, S Renner, B Reville, W Rhode, M Ribo, M Ribordy, MG Richer, J Rico, J Ridky, F Rieger, P Ringegni, J Ripken, PR Ristori, A Riviere, S Rivoire, L Rob, U Roeser, R Rohlfs, G Rojas, P Romano, W Romaszkan, GE Romero, S Rosen, SR Lees, D Ross, G Rouaix, J Rousselle, S Rousselle, AC Rovero, F Roy, S Royer, B Rudak, C Rulten, M Rupinski, F Russo, F Ryde, B Sacco, EO Saemann, A Saggion, V Safiakian, K Saito, T Saito, Y Saito, N Sakaki, R Sakonaka, A Salini, F Sanchez, M Sanchez-Conde, A Sandoval, H Sandaker, E Sant'Ambrogio, A Santangelo, EM Santos, A Sanuy, L Sapozhnikov, S Sarkar, N Sartore, H Sasaki, K Satalecka, M Sawada, V Scalzotto, V Scapin, M Scarcioffolo, J Schafer, T Schanz, S Schlenstedt, R Schlickeiser, T Schmidt, J Schmoll, P Schovanek, M Schroedter, C Schultz, J Schultze, A Schulz, K Schure, T Schwab, U Schwanke, J Schwarz, S Schwarzburg, T Schweizer, S Schwemmer, A Segreto, J-H Seiradakis, GH Sembroski, K Seweryn, M Sharma, M Shayduk, RC Shellard, J Shi, T Shibata, A Shibuya, E Shum, L Sidoli, M Sidz, J Sieiro, M Sikora, J Silk, A Sillanpaa, BB Singh, J Sitarek, C Skole, R Smareglia, A Smith, D Smith, J Smith, N Smith, D Sobczynska, H Sol, G Sottile, M Sowinski, F Spanier, D Spiga, S Spyrou, V Stamatescu, A Stamerra, R Starling, L Stawarz, R Steenkamp, C Stegmann, S Steiner, N Stergioulas, R Sternberger, M Sterzel, F Stinzing, M Stodulski, U Straumann, E Strazzeri, L Stringhetti, A Suarez, M Suchenek, R Sugawara, K-H Sulanke, S Sun, AD Supanitsky, T Suric, P Sutcliffe, J Sykes, M Szanecki, T Szepieniec, A Szostek, G Tagliaferri, H Tajima, H Takahashi, K Takahashi, L Takalo, H Takami, C Talbot, J Tammi, M Tanaka, S Tanaka, J Tasan, M Tavani, J-P Tavernet, LA Tejedor, I Telezhinsky, P Temnikov, C Tenzer, Y Terada, R Terrier, M Teshima, V Testa, D Tezier, D Thuermann, L Tibaldo, O Tibolla, A Tiengo, M Tluczykont, CJ Todero Peixoto, F Tokanai, M Tokarz, K Toma, K Torii, M Tornikoski, DF Torres, M Torres, G Tosti, T Totani, C Toussenel, G Tovmassian, P Travnicek, M Trifoglio, I Troyano, K Tsinganos, H Ueno, K Umehara, SS Upadhya, T Usher, M Uslenghi, JF Valdes-Galicia, P Vallania, G Vallejo, W van Driel, C van Eldik, J Vandenbrouke, J Vanderwalt, H Vankov, G Vasileiadis, V Vassiliev, D Veberic, I Vegas, S Vercellone, S Vergani, C Veyssiere, JP Vialle, A Viana, M Videla, P Vincent, S Vincent, J Vink, N Vlahakis, L Vlahos, P Vogler, A Vollhardt, H-P von Gunten, S Vorobiov, C Vuerli, V Waegebaert, R Wagner, RG Wagner, S Wagner, SP Wakely, R Walter, T Walther, K Warda, R Warwick, P Wawer, R Wawrzaszek, N Webb, P Wegner, A Weinstein, Q Weitzel, R Welsing, M Werner, H Wetteskind, R White, A Wierzcholska, S Wiesand, M Wilkinson, DA Williams, R Willingale, K Winiarski, R Wischnewski, L Wisniewski, M Wood, A Woernlein, Q Xiong, KK Yadav, H Yamamoto, T Yamamoto, R Yamazaki, S Yanagita, JM Yebras, D Yelos, A Yoshida, T Yoshida, T Yoshikoshi, V Zabalza, M Zacharias, A Zajczyk, R Zanin, A Zdziarski, A Zech, A Zhao, X Zhou, K Zietara, J Ziolkowski, P Ziolkowski, V Zitelli, C Zurbach, P Zychowski, CTA Consortium


Synchrotron and inverse-Compton emission from blazar jets - I. A uniform conical jet model

Monthly Notices of the Royal Astronomical Society 423 (2012) 756-765

WJ Potter, G Cotter

In the first of a series of papers investigating emission from blazar jets from radio to high-energy γ-rays, we revisit the class of models where the jet has a uniform conical ballistic structure. We argue that by using simple developments of these models, in the context of new multifrequency data extending to γ-ray energies, valuable insights may be obtained into the properties that fully realistic models must ultimately have. In this paper we consider the synchrotron and synchrotron-self-Compton emission from the jet, modelling the recent simultaneous multiwavelength observations of BL Lac. This is the first time these components have been fitted simultaneously for a blazar using a conical jet model. In the model we evolve the electron population dynamically along the jet taking into account the synchrotron and inverse-Compton losses. The inverse-Compton emission is calculated using the Klein-Nishina cross-section and a relativistic transformation into the jet frame, and we explicitly show the seed photon population. We integrate synchrotron opacity along the line of sight through the jet plasma, taking into account the emission and opacity of each section of the jet. In agreement with previous studies of radio emission, we find that a conical jet model which conserves magnetic energy produces the characteristic blazar flat radio spectrum; however, we do not require any fine-tuning of the model to achieve this. Of particular note, in our model fit to BL Lac - which at ∼10 37W is a relatively low jet-power source - we find no requirement for significant re-acceleration within the jet to explain the observed spectrum. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


SPECTROSCOPY OF BROAD-LINE BLAZARS FROM 1LAC

ASTROPHYSICAL JOURNAL 748 (2012) ARTN 49

MS Shaw, RW Romani, G Cotter, SE Healey, PF Michelson, ACS Readhead, JL Richards, W Max-Moerbeck, OG King, WJ Potter


Synchrotron and inverse-Compton emission from blazar jets - I. A uniform conical jet model

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 423 (2012) 756-765

WJ Potter, G Cotter


A gauge-invariant approach to interactions in the dark sector

Journal of Cosmology and Astroparticle Physics IOP Publishing 2011 (2011) 005-

WJ Potter, S Chongchitnan

We outline a gauge-invariant framework to calculate cosmological perturbations in dark energy models consisting of a scalar field interacting with dark matter via energy and momentum exchanges. Focusing on three well-known models of quintessence and three common types of dark sector interactions, we calculate the matter and dark energy power spectra as well as the Integrated Sachs-Wolfe (ISW) effect in these models. We show how the presence of dark sector interactions can produce a large-scale enhancement in the matter power spectrum and a boost in the low multipoles of the cosmic microwave background anisotropies. Nevertheless, we find these enhancements to be much more subtle than those found by previous authors who model dark energy using simple ansatz for the equation of state. We also address issues of instabilities and emphasise the importance of momentum exchanges in the dark sector.


Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy

EXPERIMENTAL ASTRONOMY 32 (2011) 193-316

M Actis, G Agnetta, F Aharonian, A Akhperjanian, J Aleksic, E Aliu, D Allan, I Allekotte, F Antico, LA Antonelli, P Antoranz, A Aravantinos, T Arlen, H Arnaldi, S Artmann, K Asano, H Asorey, J Baehr, A Bais, C Baixeras, S Bajtlik, D Balis, A Bamba, C Barbier, M Barcelo, A Barnacka, J Barnstedt, UB de Almeida, JA Barrio, S Basso, D Bastieri, C Bauer, J Becerra, Y Becherini, K Bechtol, J Becker, V Beckmann, W Bednarek, B Behera, M Beilicke, M Belluso, M Benallou, W Benbow, J Berdugo, K Berger, T Bernardino, K Bernloehr, A Biland, S Billotta, T Bird, E Birsin, E Bissaldi, S Blake, O Blanch, AA Bobkov, L Bogacz, M Bogdan, C Boisson, J Boix, J Bolmont, G Bonanno, A Bonardi, T Bonev, J Borkowski, O Botner, A Bottani, M Bourgeat, C Boutonnet, A Bouvier, S Brau-Nogue, I Braun, T Bretz, MS Briggs, P Brun, L Brunetti, H Buckley, V Bugaev, R Buehler, T Bulik, G Busetto, S Buson, K Byrum, M Cailles, R Cameron, R Canestrari, S Cantu, E Carmona, A Carosi, J Carr, PH Carton, M Casiraghi, H Castarede, O Catalano, S Cavazzani, S Cazaux, B Cerruti, M Cerruti, M Chadwick, J Chiang, M Chikawa, M Cieslar, M Ciesielska, A Cillis, C Clerc, P Colin, J Colome, M Compin, P Conconi, V Connaughton, J Conrad, JL Contreras, P Coppi, M Corlier, P Corona, O Corpace, D Corti, J Cortina, H Costantini, G Cotter, B Courty, S Couturier, S Covino, J Croston, G Cusumano, MK Daniel, F Dazzi, A Deangelis, E de Cea del Pozo, EMDG Dal Pino, O de Jager, I de la Calle Perez, G De La Vega, B De Lotto, M de Naurois, EDO Wilhelmi, V de Souza, B Decerprit, C Deil, E Delagnes, G Deleglise, C Delgado, T Dettlaff, A Di Paolo, F Di Pierro, C Diaz, J Dick, H Dickinson, SW Digel, D Dimitrov, G Disset, A Djannati-Ata, M Doert, W Domainko, D Dorner, M Doro, J-L Dournaux, D Dravins, L Drury, F Dubois, R Dubois, G Dubus, C Dufour, D Durand, J Dyks, M Dyrda, E Edy, K Egberts, C Eleftheriadis, S Elles, D Emmanoulopoulos, R Enomoto, J-P Ernenwein, M Errando, A Etchegoyen, AD Falcone, K Farakos, C Farnier, S Federici, F Feinstein, D Ferenc, E Fillin-Martino, D Fink, C Finley, JP Finley, R Firpo, D Florin, C Foehr, E Fokitis, L Font, G Fontaine, A Fontana, A Foerster, L Fortson, N Fouque, C Fransson, GW Fraser, L Fresnillo, C Fruck, Y Fujita, Y Fukazawa, S Funk, W Gaebele, S Gabici, A Gadola, N Galante, Y Gallant, B Garcia, RJ Garcia Lopez, D Garrido, L Garrido, D Gascon, C Gasq, M Gaug, J Gaweda, N Geffroy, C Ghag, A Ghedina, M Ghigo, E Gianakaki, S Giarrusso, G Giavitto, B Giebels, E Giro, P Giubilato, T Glanzman, J-F Glicenstein, M Gochna, V Golev, M Gomez Berisso, A Gonzalez, F Gonzalez, F Granena, R Graciani, J Granot, R Gredig, A Green, T Greenshaw, O Grimm, J Grube, M Grudzinska, J Grygorczuk, V Guarino, L Guglielmi, F Guilloux, S Gunji, G Gyuk, D Hadasch, D Haefner, R Hagiwara, J Hahn, A Hallgren, S Hara, MJ Hardcastle, T Hassan, T Haubold, M Hauser, M Hayashida, R Heller, G Henri, G Hermann, A Herrero, JA Hinton, D Hoffmann, W Hofmann, P Hofverberg, D Horns, D Hrupec, H Huan, B Huber, J-M Huet, G Hughes, K Hultquist, TB Humensky, J-F Huppert, A Ibarra, JM Illa, J Ingjald, S Inoue, Y Inoue, K Ioka, C Jablonski, A Jacholkowska, M Janiak, P Jean, H Jensen, T Jogler, I Jung, P Kaaret, S Kabuki, J Kakuwa, C Kalkuhl, R Kankanyan, M Kapala, A Karastergiou, M Karczewski, S Karkar, N Karlsson, J Kasperek, H Katagiri, K Katarzynski, N Kawanaka, B Kedziora, E Kendziorra, B Khelifi, D Kieda, T Kifune, T Kihm, S Klepser, W Kluzniak, J Knapp, AR Knappy, T Kneiske, J Knoedlseder, F Koeck, K Kodani, K Kohri, K Kokkotas, N Komin, A Konopelko, K Kosack, R Kossakowski, P Kostka, J Kotula, G Kowal, J Koziol, T Kraehenbuehl, J Krause, H Krawczynski, F Krennrich, A Kretzschmann, H Kubo, VA Kudryavtsev, J Kushida, N La Barbera, V La Parola, G La Rosa, A Lopez, G Lamanna, P Laporte, C Lavalley, T Le Flour, A Le Padellec, J-P Lenain, L Lessio, B Lieunard, E Lindfors, A Liolios, T Lohse, S Lombardi, A Lopatin, E Lorenz, P Lubinski, O Luz, E Lyard, MC Maccarone, T Maccarone, G Maier, P Majumdar, S Maltezos, P Malkiewicz, C Mana, A Manalaysay, G Maneva, A Mangano, P Manigot, J Marin, M Mariotti, S Markoff, G Martinez, M Martinez, A Mastichiadis, H Matsumoto, S Mattiazzo, D Mazin, TJL McComb, N McCubbin, I McHardy, C Medina, D Melkumyan, A Mendes, P Mertsch, M Meucci, J Michalowski, P Micolon, T Mineo, N Mirabal, F Mirabel, JM Miranda, R Mirzoyan, T Mizuno, B Moal, R Moderski, E Molinari, I Monteiro, A Moralejo, C Morello, K Mori, G Motta, F Mottez, E Moulin, R Mukherjee, P Munar, H Muraishi, K Murase, AS Murphy, S Nagataki, T Naito, T Nakamori, K Nakayama, C Naumann, D Naumann, P Nayman, D Nedbal, A Niedzwiecki, J Niemiec, A Nikolaidis, K Nishijima, SJ Nolan, N Nowak, PT O'Brien, I Ochoa, Y Ohira, M Ohishi, H Ohka, A Okumura, C Olivetto, RA Ong, R Orito, M Orr, JP Osborne, M Ostrowski, L Otero, AN Otte, E Ovcharov, I Oya, A Ozieblo, S Paiano, J Pallota, JL Panazol, D Paneque, M Panter, R Paoletti, G Papyan, JM Paredes, G Pareschi, RD Parsons, MP Arribas, G Pedaletti, A Pepato, M Persic, PO Petrucci, B Peyaud, W Piechocki, S Pita, G Pivato, L Platos, R Platzer, L Pogosyan, M Pohl, G Pojmanski, JD Ponz, W Potter, E Prandini, R Preece, H Prokoph, G Puehlhofer, M Punch, E Quel, A Quirrenbach, P Rajda, R Rando, M Rataj, M Raue, C Reimann, O Reimann, A Reimer, O Reimer, M Renaud, S Renner, J-M Reymond, W Rhode, M Ribo, M Ribordy, J Rico, F Rieger, P Ringegni, J Ripken, P Ristori, S Rivoire, L Rob, S Rodriguez, U Roeser, P Romano, GE Romero, S Rosier-Lees, AC Rovero, F Roy, S Royer, B Rudak, CB Rulten, J Ruppel, F Russo, F Ryde, B Sacco, A Saggion, V Sahakian, K Saito, T Saito, N Sakaki, E Salazar, A Salini, F Sanchez, MA Sanchez Conde, A Santangelo, EM Santos, A Sanuy, L Sapozhnikov, S Sarkar, V Scalzotto, V Scapin, M Scarcioffolo, T Schanz, S Schlenstedt, R Schlickeiser, T Schmidt, J Schmoll, M Schroedter, C Schultz, J Schultze, A Schulz, U Schwanke, S Schwarzburg, T Schweizer, J Seiradakis, S Selmane, K Seweryn, M Shayduk, RC Shellard, T Shibata, M Sikora, J Silk, A Sillanpaa, J Sitarek, C Skole, N Smith, D Sobczynska, M Sofo Haro, H Sol, F Spanier, D Spiga, S Spyrou, V Stamatescu, A Stamerra, RLC Starling, L Stawarz, R Steenkamp, C Stegmann, S Steiner, N Stergioulas, R Sternberger, F Stinzing, M Stodulski, U Straumann, A Suarez, M Suchenek, R Sugawara, KH Sulanke, S Sun, AD Supanitsky, P Sutcliffe, M Szanecki, T Szepieniec, A Szostek, A Szymkowiak, G Tagliaferri, H Tajima, H Takahashi, K Takahashi, L Takalo, H Takami, RG Talbot, PH Tam, M Tanaka, T Tanimori, M Tavani, J-P Tavernet, C Tchernin, LA Tejedor, I Telezhinsky, P Temnikov, C Tenzer, Y Terada, R Terrier, M Teshima, V Testa, L Tibaldo, O Tibolla, M Tluczykont, CJT Peixoto, F Tokanai, M Tokarz, K Toma, DF Torres, G Tosti, T Totani, F Toussenel, P Vallania, G Vallejo, J van der Walt, C van Eldik, J Vandenbroucke, H Vankov, G Vasileiadis, VV Vassiliev, I Vegas, L Venter, S Vercellone, C Veyssiere, JP Vialle, M Videla, P Vincent, J Vink, N Vlahakis, L Vlahos, P Vogler, A Vollhardt, F Volpe, HP Von Gunten, S Vorobiov, S Wagner, RM Wagner, B Wagner, SP Wakely, P Walter, R Walter, R Warwick, P Wawer, R Wawrzaszek, N Webb, P Wegner, A Weinstein, Q Weitzel, R Welsing, H Wetteskind, R White, A Wierzcholska, MI Wilkinson, DA Williams, M Winde, R Wischnewski, L Wisniewski, A Wolczko, M Wood, Q Xiong, T Yamamoto, K Yamaoka, R Yamazaki, S Yanagita, B Yoffo, M Yonetani, A Yoshida, T Yoshida, T Yoshikoshi, V Zabalza, A Zagdanski, A Zajczyk, A Zdziarski, A Zech, K Zietara, P Ziolkowski, V Zitelli, P Zychowski, CTA Consortium