Publications by Garret Cotter


Detection of very-high-energy gamma-ray emission from the colliding wind binary eta Car with HESS

ASTRONOMY & ASTROPHYSICS 635 (2020)

H Abdalla, R Adam, F Aharonian, FA Benkhali, EO Anguner, M Arakawa, C Arcaro, C Armand, T Armstrong, H Ashkar, M Backes, VB Martins, M Barnard, Y Becherini, D Berge, K Bernloehr, R Blackwell, M Bottcher, C Boisson, J Bolmont, S Bonnefoy, J Bregeon, M Breuhaus, F Brun, P Brun, M Bryan, M Buchele, T Bulik, T Bylund, S Caroff, A Carosi, S Casanova, M Cerruti, T Chand, S Chandra, A Chen, S Colafrancesco, G Cotter, M Curylo, ID Davids, J Davies, C Deil, J Devin, P dewilt, L Dirson, A Djannati-Atai, A Dmytriiev, A Donath, V Doroshenko, J Dyks, K Egberts, F Eichhorn, G Emery, J-P Ernenwein, S Eschbach, K Feijen, S Fegan, A Fiasson, G Fontaine, S Funk, M Fussling, S Gabici, YA Gallant, F Gate, G Giavitto, L Giunti, D Glawion, JF Glicenstein, D Gottschall, M-H Grondin, J Hahn, M Haupt, G Heinzelmann, G Henri, G Hermann, JA Hinton, W Hofmann, C Hoischen, TL Holch, M Holler, M Horbe, D Horns, D Huber, H Iwasaki, M Jamrozy, D Jankowsky, F Jankowsky, A Jardin-Blicq, V Joshi, I Jung-Richardt, MA Kastendieck, KKP Nski, M Katsuragawa, U Katz, D Khangulyan, B Khelifi, J King, S Klepser, W Kluzniak, N Komin, K Kosack, D Kostunin, M Kreter, G Lamanna, A Lemiere, M Lemoine-Goumard, J-P Lenain, E Leser, C Levy, T Lohse, I Lypova, J Mackey, J Majumdar, D Malyshev, D Malyshev, V Marandon, P Marchegiani, A Marcowith, A Mares, G Marti-Devesa, R Marx, G Maurin, PJ Meintjes, R Moderski, M Mohamed, L Mohrmann, C Moore, P Morris, E Moulin, J Muller, T Murach, S Nakashima, K Nakashima, M de Naurois, H Ndiyavala, F Niederwanger, J Niemiec, L Oakes, P O'Brien, H Odaka, S Ohm, EDO Wilhelmi, M Ostrowski, M Panter, RD Parsons, C Perennes, P-O Petrucci, B Peyaud, Q Piel, S Pita, V Poireau, AP Noel, DA Prokhorov, H Prokoph, G Puhlhofer, M Punch, A Quirrenbach, S Raab, R Rauth, A Reimer, O Reimer, Q Remy, M Renaud, F Rieger, L Rinchiuso, C Romoli, G Rowell, B Rudak, E Ruiz-Velasco, V Sahakian, S Sailer, S Saito, DA Sanchez, A Santangelo, M Sasaki, M Scalici, R Schlickeiser, F Schussler, A Schulz, HM Schutte, U Schwanke, S Schwemmer, M Seglar-Arroyo, M Senniappan, AS Seyffert, N Shafi, K Shiningayamwe, R Simoni, A Sinha, H Sol, A Specovius, S Spencer, M Spir-Jacob, L Stawarz, R Steenkamp, C Stegmann, C Steppa, T Takahashi, T Tavernier, AM Taylor, R Terrier, D Tiziani, M Tluczykont, L Tomankova, C Trichard, M Tsirou, N Tsuji, R Tuffs, Y Uchiyama, DJ van der Walt, C van Eldik, C van Rensburg, B van Soelen, G Vasileiadis, J Veh, C Venter, P Vincent, J Vink, HJ Volk, T Vuillaume, Z Wadiasingh, SJ Wagner, J Watson, F Werner, R White, A Wierzcholska, R Yang, H Yoneda, M Zacharias, R Zanin, AA Zdziarski, A Zech, J Zorn, N Zywucka, HESS Collaboration


Monte Carlo studies for the optimisation of the Cherenkov Telescope Array layout

Astroparticle Physics (2019)

ST Spencer, A Acharyya, I Agudo, EO Angüner, R Alfaro, J Alfaro, C Alispach, R Aloisio, R Alves Batista, J-P Amans, L Amati, E Amato, G Ambrosi, LA Antonelli, C Aramo, T Armstrong, F Arqueros, L Arrabito, K Asano, H Ashkar, C Balazs, M Balbo, B Balmaverde, P Barai, A Barbano, M Barkov, U Barres de Almeida, JA Barrio, D Bastieri, J Becerra González, J Becker Tjus, L Bellizzi, W Benbow, E Bernardini, MI Bernardos, K Bernlöhr, A Berti, M Berton, B Bertucci, V Beshley, B Biasuzzi, C Bigongiari, R Bird, E Bissaldi, J Biteau, O Blanch, J Blazek, C Boisson, G Bonanno, A Bonardi, C Bonavolontá, G Bonnoli, P Bordas, M Böttcher, J Bregeon, A Brill, AM Brown, K Brügge, P Brun, P Bruno, A Bulgarelli, T Bulik, M Burton, A Burtovoi, G Busetto, R Cameron, R Canestrari, M Capalbi, A Caproni, R Capuzzo-Dolcetta, P Caraveo, S Caroff, R Carosi, S Casanova, E Cascone, F Cassol, F Catalani, O Catalano, D Cauz, M Cerruti, S Chaty, A Chen, M Chernyakova, G Chiaro, M Cie´slar, SM Colak, V Conforti, E Congiu, JL Contreras, J Cortina, A Costa, H Costantini, G Cotter, P Cristofari, P Cumani, G Cusumano, A D’Aí, F D’Ammando, L Dangeon, P Da Vela, F Dazzi, A De Angelis, V De Caprio, R de Cássia dos Anjos, F De Frondat, EM de Gouveia Dal Pino, B De Lotto, D De Martino, M de Naurois, E de O na Wilhelmi, F de Palma, V de Souza, M Del Santo, C Delgado, D della Volpe, T Di Girolamo, F Di Pierro, L Di Venere, C Díaz, S Diebold, A Djannati-Ataï, A Dmytriiev, D Dominis Prester, A Donini, D Dorner, M Doro, J-L Dournaux, J Ebr, TRN Ekoume, D Elsässer, G Emery, D Falceta-Goncalves, E Fedorova, S Fegan, Q Feng, G Ferrand, E Fiandrini, A Fiasson, M Filipovic, V Fioretti, M Fiori, S Flis, MV Fonseca, G Fontaine, L Freixas Coromina, S Fukami, Y Fukui, S Funk, M Füßling, D Gaggero, G Galanti, RJ Garcia López, M Garczarczyk, D Gascon, T Gasparetto, M Gaug, A Ghalumyan, F Gianotti, G Giavitto, N Giglietto, F Giordano, M Giroletti, J Gironnet, J-F Glicenstein, R Gnatyk, P Goldoni, JM González, MM González, KN Gourgouliatos, T Grabarczyk, J Granot, D Green, T Greenshaw, M-H Grondin, O Gueta, D Hadasch, T Hassan, M Hayashida, M Heller, O Hervet, J Hinton, N Hiroshima, B Hnatyk, W Hofmann, P Horvath, M Hrabovsky, D Hrupec, TB Humensky, M Hütten, T Inada, F Iocco, M Ionica, M Iori, Y Iwamura, M Jamrozy, P Janecek, D Jankowsky, P Jean, L Jouvin, J Jurysek, P Kaaret, LHS Kadowaki, S Karkar, D Kerszberg, B Khélifi, D Kieda, S Kimeswenger, W Klu´zniak, J Knapp, J Knödlseder, Y Kobayashi, B Koch, J Kocot, N Komin, A Kong, G Kowal, M Krause, H Kubo, J Kushida, P Kushwaha, V La Parola, G La Rosa, M Lallena Arquillo, RG Lang, J Lapington, O Le Blanc, J Lefaucheur, MA Leigui de Oliveira, M Lemoine-Goumard, J-P Lenain, G Leto, R Lico, E Lindfors, T Lohse, S Lombardi, F Longo, A Lopez, M López, A Lopez-Oramas, R López-Coto, S Loporchio, PL Luque-Escamilla, E Lyard, MC Maccarone, E Mach, C Maggio, P Majumdar, G Malaguti, M Mallamaci, D Mandat, G Maneva, M Manganaro, S Mangano, M Marculewicz, M Mariotti, J Martí, M Martínez, G Martínez, H Martínez-Huerta, S Masuda, N Maxted, D Mazin, J-L Meunier, M Meyer, S Micanovic, R Millul, IA Minaya, A Mitchell, T Mizuno, R Moderski, L Mohrmann, T Montaruli, A Moralejo, D Morcuende, G Morlino, A Morselli, E Moulin, R Mukherjee, P Munar, C Mundell, T Murach, A Nagai, T Nagayoshi, T Naito, T Nakamori, R Nemmen, J Niemiec, D Nieto, M Nievas Rosillo, M Niko\lajuk, D Ninci, K Nishijima, K Noda, D Nosek, M Nöthe, S Nozaki, M Ohishi, Y Ohtani, A Okumura, RA Ong, M Orienti, R Orito, M Ostrowski, N Otte, Z Ou, I Oya, A Pagliaro, M Palatiello, M Palatka, R Paoletti, JM Paredes, G Pareschi, N Parmiggiani, RD Parsons, B Patricelli, A Pe’er, M Pech, P Pe nil Del Campo, J Pérez-Romero, M Perri, M Persic, P-O Petrucci, O Petruk, K Pfrang, Q Piel, E Pietropaolo, M Pohl, M Polo, J Poutanen, E Prandini, N Produit, H Prokoph, M Prouza, H Przybilski, G Pühlhofer, M Punch, F Queiroz, A Quirrenbach, S Rainò, R Rando, S Razzaque, O Reimer, N Renault-Tinacci, Y Renier, D Ribeiro, M Ribó, J Rico, F Rieger, V Rizi, G Rodriguez Fernandez, JC Rodriguez-Ramirez, JJ Rodrí-guez Vázquez, P Romano, G Romeo, M Roncadelli, J Rosado, G Rowell, B Rudak, A Rugliancich, C Rulten, I Sadeh, L Saha, T Saito, S Sakurai, F Salesa Greus, P Sangiorgi, H Sano, M Santander, A Santangelo, R Santos-Lima, A Sanuy, K Satalecka, FG Saturni, U Sawangwit, S Schlenstedt, P Schovanek, F Schussler, U Schwanke, E Sciacca, S Scuderi, K Sedlaczek, M Seglar-Arroyo, O Sergijenko, K Seweryn, A Shalchi, RC Shellard, H Siejkowski, A Sillanpää, A Sinha, G Sironi, V Sliusar, A Slowikowska, H Sol, A Specovius, S Spencer, G Spengler, A Stamerra, S Stanič, L Stawarz, S Stefanik, T Stolarczyk, U Straumann, T Suomijarvi, P ´Swierk, T Szepieniec, G Tagliaferri, H Tajima, T Tam, F Tavecchio, L Taylor, LA Tejedor, P Temnikov, T Terzic, V Testa, L Tibaldo, CJ Todero Peixoto, F Tokanai, L Tomankova, D Tonev, DF Torres, G Tosti, L Tosti, N Tothill, F Toussenel, G Tovmassian, P Travnicek, C Trichard, G Umana, V Vagelli, M Valentino, B Vallage, P Vallania, L Valore, J Vandenbroucke, GS Varner, G Vasileiadis, V Vassiliev, M Vázquez Acosta, M Vecchi, S Vercellone, S Vergani, GP Vettolani, A Viana, CF Vigorito, J Vink, V Vitale, H Voelk, A Vollhardt, S Vorobiov, SJ Wagner, R Walter, F Werner, R White, A Wierzcholska, M Will, DA Williams, R Wischnewski, L Yang, T Yoshida, T Yoshikoshi, M Zacharias, L Zampieri, M Zavrtanik, D Zavrtanik, AA Zdziarski, A Zech, H Zechlin, A Zenin, VI Zhdanov, S Zimmer, J Zorn


The feasibility of magnetic reconnection powered blazar flares from synchrotron self-Compton emission

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 486 (2019) 1548-1562

PJ Morris, WJ Potter, G Cotter


Deviations from normal distributions in artificial and real time series: a false positive prescription

Monthly Notices of the Royal Astronomical Society Oxford University Press 489 (2019) 2117–2129-

P Morris, N Chakraborty, G Cotter

<jats:title>ABSTRACT</jats:title> <jats:p>Time-series analysis allows for the determination of the Power Spectral Density (PSD) and Probability Density Function (PDF) for astrophysical sources. The former of these illustrates the distribution of power at various time-scales, typically taking a power-law form, while the latter characterizes the distribution of the underlying stochastic physical processes, with Gaussian and lognormal functional forms both physically motivated. In this paper, we use artificial time series generated using the prescription of Timmer &amp; Koenig to investigate connections between the PDF and PSD. PDFs calculated for these artificial light curves are less likely to be well described by a Gaussian functional form for steep (Γ⪆1) PSD indices due to weak non-stationarity. Using the Fermi LAT monthly light curve of the blazar PKS2155-304 as an example, we prescribe and calculate a false positive rate that indicates how likely the PDF is to be attributed an incorrect functional form. Here, we generate large numbers of artificial light curves with intrinsically normally distributed PDFs and with statistical properties consistent with observations. These are used to evaluate the probabilities that either Gaussian or lognormal functional forms better describe the PDF. We use this prescription to show that PKS2155-304 requires a high prior probability of having a normally distributed PDF, $P(\rm {G})~$ ≥ 0.82, for the calculated PDF to prefer a Gaussian functional form over a lognormal. We present possible choices of prior and evaluate the probability that PKS2155-304 has a lognormally distributed PDF for each.</jats:p>


Science with the Cherenkov Telescope Array

World Scientific, 2019

BS Acharya, I Agudo, R Batista, T Armstrong, G Cotter, A Franco, P Morris, S Sarkar, JJ Watson

The Cherenkov Telescope Array, CTA, will be the major global observatory for very high energy gamma-ray astronomy over the next decade and beyond. The scientific potential of CTA is extremely broad: from understanding the role of relativistic cosmic particles to the search for dark matter. CTA is an explorer of the extreme universe, probing environments from the immediate neighbourhood of black holes to cosmic voids on the largest scales. Covering a huge range in photon energy from 20 GeV to 300 TeV, CTA will improve on all aspects of performance with respect to current instruments. The observatory will operate arrays on sites in both hemispheres to provide full sky coverage and will hence maximize the potential for the rarest phenomena such as very nearby supernovae, gamma-ray bursts or gravitational wave transients. With 99 telescopes on the southern site and 19 telescopes on the northern site, flexible operation will be possible, with sub-arrays available for specific tasks. CTA will have important synergies with many of the new generation of major astronomical and astroparticle observatories. Multi-wavelength and multi-messenger approaches combining CTA data with those from other instruments will lead to a deeper understanding of the broad-band non-thermal properties of target sources. The CTA Observatory will be operated as an open, proposal-driven observatory, with all data available on a public archive after a pre-defined proprietary period. Scientists from institutions worldwide have combined together to form the CTA Consortium. This Consortium has prepared a proposal for a Core Programme of highly motivated observations. The programme, encompassing approximately 40% of the available observing time over the first ten years of CTA operation, is made up of individual Key Science Projects (KSPs), which are presented in this document.


Final characterisation and design of the Gamma-ray Cherenkov Telescope (GCT) for the Cherenkov Telescope Array

GROUND-BASED AND AIRBORNE TELESCOPES VII 10700 (2018) ARTN 1070010

O Le Blanc, G Fasola, JM Huet, R White, A Dmytriiev, H Sol, A Zech, A Abchiche, JP Amans, TP Armstrong, M Barcelo, D Berge, AM Brown, G Buchholtz, PM Chadwick, P Clark, G Cotter, L Dangeon, F De Frondat, P Deiml, JL Dournaux, C Duffy, S Einecke, S Flis, S Funk, G Giavitto, J Gironnet, JA Graham, T Greenshaw, JA Hinton, I Jegouzo, M Kraus, JS Lapington, P Laporte, SA Leach, S Lloyd, IA Minaya, R Morier, A Okumura, H Prokoph, D Ross, G Rowell, CB Rulten, H Schoorlemmer, J Schmoll, ST Spencer, M Stephan, R Stuik, H Tajima, J Thornhill, L Tibaldo, J Vink, JJ Watson, J Williams, A Zink, J Zorn, CTAGCT Project


Characterisation and testing of CHEC-M—A camera prototype for the small-sized telescopes of the Cherenkov telescope array

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Elsevier 904 (2018) 44-63

J Zorn, R White, J Watson, T Armstrong, A Balzer, M Barcelo, D Berge, R Bose, AM Brown, M Bryan, PM Chadwick, P Clark, H Costantini, G Cotter, L Dangeon, M Daniel, A De Franco, P Deiml, G Fasola, S Funk, M Gebyehu, J Gironnet, JA Graham, T Greenshaw, JA Hinton

The Compact High Energy Camera (CHEC) is a camera design for the Small-Sized Telescopes (SSTs; 4 m diameter mirror) of the Cherenkov Telescope Array (CTA). The SSTs are focused on very-high-energy γ-ray detection via atmospheric Cherenkov light detection over a very large area. This implies many individual units and hence cost-effective implementation, as well as shower detection at large impact distance, and hence large field of view (FoV), and efficient image capture in the presence of large time gradients in the shower image detected by the camera. CHEC relies on dual-mirror optics to reduce the plate-scale and make use of 6 × 6 mm2pixels, leading to a low-cost (∼150 k€), compact (0.5 m × 0.5 m), and light (∼45 kg) camera with 2048 pixels providing a camera FoV of ∼9 degrees. The CHEC electronics are based on custom TARGET (TeV array readout with GSa/s sampling and event trigger) application-specific integrated circuits (ASICs) and field programmable gate arrays (FPGAs) sampling incoming signals at a gigasample per second, with flexible camera-level triggering within a single backplane FPGA. CHEC is designed to observe in the γ-ray energy range of 1–300 TeV, and at impact distances up to ∼500 m. To accommodate this and provide full flexibility for later data analysis, full waveforms with 96 samples for all 2048 pixels can be read out at rates up to ∼900 Hz. The first prototype, CHEC-M, based on multi-anode photomultipliers (MAPMs) as photosensors, was commissioned and characterised in the laboratory and during two measurement campaigns on a telescope structure at the Paris Observatory in Meudon. In this paper, the results and conclusions from the laboratory and on-site testing of CHEC-M are presented. They have provided essential input on the system design and on operational and data analysis procedures for a camera of this type. A second full-camera prototype based on Silicon photomultipliers (SiPMs), addressing the drawbacks of CHEC-M identified during the first prototype phase, has already been built and is currently being commissioned and tested in the laboratory.


The GCT camera for the Cherenkov Telescope Array

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 876 (2016) 1-4

JS Lapington, A Abchiche, D Allan, J-P Amans, TP Armstrong, A Balzer, D Berge, C Boisson, J-J Bousquet, R Bose, AM Brown, M Bryan, G Buchholtz, J Buckley, PM Chadwick, H Costantini, G Cotter, MK Daniel, A De Franco, F De Frondat, J-L Dournaux, D Dumas, J-P Ernenwein, G Fasola, S Funk, J Gironnet, JA Graham, T Greenshaw, O Hervet, N Hidaka, JA Hinton, J-M Huet, D Jankowsky, I Jegouzo, T Jogler, T Kawashima, M Kraus, P Laporte, S Leach, J Lefaucheur, S Markoff, T Melse, IA Minaya, L Mohrmann, P Molyneux, P Moore, SJ Nolan, A Okumura, JP Osborne, RD Parsons, S Rosen, D Ross, G Rowell, CB Rulten, Y Sato, F Sayede, J Schmoll, H Schoorlemmer, M Servillat, H Sol, V Stamatescu, M Stephan, R Stuik, J Sykes, H Tajima, J Thornhill, L Tibaldo, C Trichard, G Varner, J Vink, JJ Watson, R White, N Yamane, A Zech, A Zink, J Zorn, CTA Consortium


Redshift measurement of Fermi blazars for the Cherenkov telescope array

AIP Conference Proceedings 1792 (2017)

S Pita, P Goldoni, C Boisson, G Cotter, J Lefaucheur, JP Lenain, E Lindfors, DA Williams

© 2017 Author(s). Blazars are active galactic nuclei, and the most numerous High Energy (HE) and Very High Energy (VHE) γ-ray emitters. Their optical emission is often dominated by non-thermal, and, in the case of BL Lacs, featureless continuum radiation. This makes the determination of their redshift extremely difficult. Indeed, as of today only about 50% of γ-ray blazars have a measured spectroscopic redshift. The knowledge of redshift is fundamental because it allows the precise modeling of the VHE emission and also of its interaction with the extragalactic background light (EBL). The beginning of the Cherenkov Telescope Array (CTA) operations in the near future will allow the detection of several hundreds of new blazars. Using the Fermi catalogue of sources above 50 GeV (2FHL), we performed simulations which indicate that a significant fraction of the 2FHL blazars detectable by CTA will not have a measured redshift. As a matter of fact, the organization of observing campaigns to measure the redshift of these blazars has been recognized as a necessary support for the AGN Key Science Project of CTA. We are planning such an observing campaign. In order to optimize our chances of success, we will perform preliminary deep imaging observations aimed at detecting or setting upper limits to the host galaxy. We will then take spectra of the candidates with the brightest host galaxies. Taking advantage of the recent success of an X-shooter GTO observing campaign, these observations will be different with respect to previous ones due to the use of higher resolution spectrographs and of 8 meter class telescopes. We are starting to submit proposals for these observations. In this paper we briefly describe how candidates are selected and the corresponding observation program.


Gamma-ray Novae: Rare or Nearby?

Monthly Notices of the Royal Astronomical Society Oxford University Press 465 (2016) 1218-1226

P Morris, G Cotter, P Chadwick, A Brown

Classical Novae were revealed as a surprise source of γ-rays in Fermi LAT observations. During the first 8 years since the LAT was launched, 6 novae in total have been detected to &gt;5σ in γ-rays, in contrast to the 69 discovered optically in the same period. We attempt to resolve this discrepancy by assuming all novae are γ-ray emitters, and assigning peak one-day fluxes based on a flat distribution of the known emitters to a simulated population. To determine optical parameters, the spatial distribution and magnitudes of bulge and disc novae in M31 are scaled to the Milky Way, which we approximate as a disc with a 20 kpc20 kpc radius and elliptical bulge with semi major axis 3 kpc3 kpc and axis ratios 2:1 in the xy plane. We approximate Galactic reddening using a double exponential disc with vertical and radial scale heights of rd=5 kpcrd=5 kpc and zd=0.2 kpczd=0.2 kpc, and demonstrate that even such a rudimentary model can easily reproduce the observed fraction of γ-ray novae, implying that these apparently rare sources are in fact nearby and not intrinsically rare. We conclude that classical novae with mR ≤ 12 and within ≈8 kpc≈8 kpc are likely to be discovered in γ-rays using the Fermi LAT.


IC 630: Piercing the Veil of the Nuclear Gas

The Astrophysical Journal 838 (2017) 102-102

M Durré, J Mould, M Schartmann, SA Uddin, G Cotter


Inauguration and first light of the GCT-M prototype for the Cherenkov Telescope Array

6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma2016), Institute of Physics (2017)

JJ Watson, A De Franco, A Abchiche, D Allan, J-P Amans, TP Armstrong, A Balzer, D Berge, C Boisson, J-J Bousquet, AM Brown, M Bryan, G Buchholtz, PM Chadwick, H Costantini, G Cotter, MK Daniel, F De Frondat, J-L Dournaux, D Dumas, J-P Ernenwein, G Fasola, S Funk, J Gironnet, JA Graham

The Gamma-ray Cherenkov Telescope (GCT) is a candidate for the Small Size Telescopes (SSTs) of the Cherenkov Telescope Array (CTA). Its purpose is to extend the sensitivity of CTA to gamma-ray energies reaching 300 TeV. Its dual-mirror optical design and curved focal plane enables the use of a compact camera of 0.4 m diameter, while achieving a field of view of above 8 degrees. Through the use of the digitising TARGET ASICs, the Cherenkov flash is sampled once per nanosecond contin-uously and then digitised when triggering conditions are met within the analogue outputs of the photosensors. Entire waveforms (typically covering 96 ns) for all 2048 pixels are then stored for analysis, allowing for a broad spectrum of investigations to be performed on the data. Two prototypes of the GCT camera are under development, with differing photosensors: Multi-Anode Photomultipliers (MAPMs) and Silicon Photomultipliers (SiPMs). During November 2015, the GCT MAPM (GCT-M) prototype camera was integrated onto the GCT structure at the Observatoire de Paris-Meudon, where it observed the first Cherenkov light detected by a prototype instrument for CTA.


The gamma-ray Cherenkov telescope for the Cherenkov telescope array

6th International Meeting on High Energy Gamma-Ray Astronomy American Instiute of Physics (2017)

L Tibaldo, PM Chadwick, H Costantini, G Cotter, MK Daniels, A De Franco, F De Frondat, J-L Dournaux, D Dumas, J-P Ernenwein, G Fasola, S Funk, J Gironnet, JA Graham, T Greenshaws, O Hervet, N Hidaka, J-M Huet, D Jankowsky, I Jegouzo, T Jogler, M Kraus, JS Lapington, P Laporte, S Markoff

The Cherenkov Telescope Array (CTA) is a forthcoming ground-based observatory for very-high-energy gamma rays. CTA will consist of two arrays of imaging atmospheric Cherenkov telescopes in the Northern and Southern hemispheres, and will combine telescopes of different types to achieve unprecedented performance and energy coverage. The Gamma-ray Cherenkov Telescope (GCT) is one of the small-sized telescopes proposed for CTA to explore the energy range from a few TeV to hundreds of TeV with a field of view ≳ 8° and angular resolution of a few arcminutes. The GCT design features dual-mirror Schwarzschild-Couder optics and a compact camera based on densely-pixelated photodetectors as well as custom electronics. In this contribution we provide an overview of the GCT project with focus on prototype development and testing that is currently ongoing. We present results obtained during the first on-telescope campaign in late 2015 at the Observatoire de Paris-Meudon, during which we recorded the first Cherenkov images from atmospheric showers with the GCT multi-anode photomultiplier camera prototype. We also discuss the development of a second GCT camera prototype with silicon photomultipliers as photosensors, and plans toward a contribution to the realisation of CTA.


Operating performance of the gamma-ray Cherenkov telescope: An end-to-end Schwarzschild-Couder telescope prototype for the Cherenkov Telescope Array

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 845 (2016) 355-358

JL Dournaux, A De Franco, P Laporte, R White, T Greenshaw, H Sol, A Abchiche, D Allan, JP Amans, TP Armstrong, A Balzer, D Berge, C Boisson, JJ Bousquet, AM Brown, M Bryan, G Buchholtz, PM Chadwick, H Costantini, G Cotter, M Daniel, F De Frondat, D Dumas, JP Ernenwein, G Fasola, S Funk, J Gaudemard, JA Graham, J Gironnet, O Hervet, N Hidaka, JA Hinton, JM Huet, I Jegouzo, T Jogler, T Kawashima, M Kraus, JS Lapington, J Lefaucheur, S Markoff, T Melse, L Morhrmann, P Molnyeux, SJ Nolan, A Okumura, RD Parsons, D Ross, G Rowell, Y Sato, F Sayede, J Schmoll, H Schoorlemmer, M Servillat, V Stamatescu, M Stephan, R Stuik, J Sykes, H Tajima, J Thornhill, L Tibaldo, C Trichard, J Vinkh, J Watson, N Yamane, A Zech, A Zink


Prospects for Cherenkov Telescope Array observations of the young supernova remnant RX J1713.7−3946

Astrophysical Journal American Astronomical Society 840 (2017) 74

F Acero, R Aloisio, J Amans, G Cotter, A De Franco, S Sarkar, JJ Watson, E Et al.

We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX J1713.7−3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very high energy (VHE) gamma rays. Special attention is paid to exploring possible spatial (anti)correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H i emission. We present a series of simulated images of RX J1713.7−3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the nonthermal X-ray emission observed by XMM-Newton, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H i observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic versus leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator.


Are gamma-ray novae intrinsically rare or just nearby?

Proceedings of Science Proceedings of Science 312 (2017) 1-6

PJ Morris, G Cotter, AM Brown, PM Chadwick

Fermi LAT data revealed classical novae as unexpected gamma-ray sources, yet only 6 of 69 of those optically detected in the first 8 years of Fermi LAT observations were confirmed as &gt; 5? gamma-ray sources. These proceedings outline Monte Carlo simulations in which a population of Galactic novae were simulated based on spatial distributions and R-band magnitudes based on their M31 counterparts. Interstellar extinction was added using a double exponential disc model, and gamma-ray properties were defined based on those of the original 6 gamma-ray novae. We demonstrate that observations are consistent will all classical novae being gamma-ray sources, and that the gamma-ray sky background is the largest inhibitor when discovering these sources. Furthermore, we predict that all classical novae occurring within ? 8 kpc and with m R ? 12 will be detected using the Fermi LAT.


Cherenkov telescope array extragalactic survey discovery potential and the impact of axion-like particles and secondary gamma rays

ASTROPARTICLE PHYSICS 93 (2017) 8-16

A De Franco, Y Inoue, MA Sanchez-Conde, G Cotter


A survey for H α emission from late L dwarfs and T dwarfs

Astrophysical Journal Institute of Physics 826 (2016) 73-

JS Pineda, G Hallinan, JD Kirkpatrick, G Cotter, MM Kao, KP Mooley

Recently, studies of brown dwarfs have demonstrated that they possess strong magnetic fields and have the potential to produce radio and optical auroral emissions powered by magnetospheric currents. This emission provides the only window on magnetic fields in the coolest brown dwarfs and identifying additional benchmark objects is key to constraining dynamo theory in this regime. To this end, we conducted a new red optical (6300-9700 Å) survey with the Keck telescopes looking for Hα emission from a sample of late L dwarfs and T dwarfs. Our survey gathered optical spectra for 29 targets, 18 of which did not have previous optical spectra in the literature, greatly expanding the number of moderate-resolution (R ∼ 2000) spectra available at these spectral types. Combining our sample with previous surveys, we confirm an Hα detection rate of 9.2± 2.1 3.5 % for L and T dwarfs in the optical spectral range of L4-T8. This detection rate is consistent with the recently measured detection rate for auroral radio emission from Kao et al., suggesting that geometrical selection effects due to the beaming of the radio emission are small or absent. We also provide the first detection of Hα emission from 2MASS 0036+1821, previously notable as the only electron cyclotron maser radio source without a confirmed detection of Hα emission. Finally, we also establish optical standards for spectral types T3 and T4, filling in the previous gap between T2 and T5.


Test bench for front end electronic of the GCT camera for the Cherenkov Telescope Array

JOURNAL OF INSTRUMENTATION 11 (2016) ARTN C02006

A De Franco, G Cotter, CTAC Collaboration


Radio Galaxy Zoo: discovery of a poor cluster through a giant wide-angle tail radio galaxy

Monthly Notices of the Royal Astronomical Society Oxford University Press 460 (2016) 2376-2384

JK Banfield, H Andernach, AD Kapińska, L Rudnick, MJ Hardcastle, G Cotter, S Vaughan, TW Jones, I Heywood, JD Wing, OI Wong, T Matorny, IA Terentev, ÁR López-Sánchez, RP Norris, N Seymour, SS Shabala, KW Willett

We have discovered a previously unreported poor cluster of galaxies (RGZ-CL J0823.2+0333) through an unusual giant wide-angle tail radio galaxy found in the Radio Galaxy Zoo project. We obtained a spectroscopic redshift of z = 0.0897 for the E0-type host galaxy, 2MASX J08231289+0333016, leading to Mr = −22.6 and a 1.4 GHz radio luminosity density of L1.4 = 5.5 × 1024 W Hz−1. These radio and optical luminosities are typical for wide-angle tailed radio galaxies near the borderline between Fanaroff–Riley classes I and II. The projected largest angular size of ≈8 arcmin corresponds to 800 kpc and the full length of the source along the curved jets/trails is 1.1 Mpc in projection. X-ray data from the XMM–Newton archive yield an upper limit on the X-ray luminosity of the thermal emission surrounding RGZ J082312.9+033301 at 1.2–2.6 × 1043 erg s−1 for assumed intracluster medium temperatures of 1.0–5.0 keV. Our analysis of the environment surrounding RGZ J082312.9+033301 indicates that RGZ J082312.9+033301 lies within a poor cluster. The observed radio morphology suggests that (a) the host galaxy is moving at a significant velocity with respect to an ambient medium like that of at least a poor cluster, and that (b) the source may have had two ignition events of the active galactic nucleus with 107 yr in between. This reinforces the idea that an association between RGZ J082312.9+033301 and the newly discovered poor cluster exists.

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