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Rosse Telescope

Garret Cotter

Professor of Physics

Research theme

  • Astronomy and astrophysics
  • Particle astrophysics & cosmology

Sub department

  • Astrophysics

Research groups

  • Pulsars, transients and relativistic astrophysics
  • The Square Kilometre Array (SKA)
  • Gamma-ray astronomy
Garret.Cotter@physics.ox.ac.uk
Telephone: 01865 (2)73604
Denys Wilkinson Building, room Dalitz 4
  • About
  • Publications

Optical spectroscopy of blazars for the Cherenkov Telescope Array Observatory - IV

Astronomy & Astrophysics EDP Sciences (2025)

Authors:

B Rajput, P Goldoni, W Max-Moerbeck, E Kasai, DA Williams, C Boisson, S Pita, M Backes, U Barres de Almeida, J Becerra González, G Cotter, F D'Ammando, V Fallah Ramazani, B Hnatyk, O Hervet, E Lindfors, D Mukhi-Nilo, M Nikołajuk, M Splettstoesser, B van Soelen

Abstract:

Blazars, comprising BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars, are the most luminous extragalactic sources that dominate the γ-ray sky. They account for approximately 56% of the sources listed in the recent Fermi -LAT (Large Area Telescope) catalogue (4FGL-DR4). The optical and UV spectra of BL Lacs are nearly featureless, making it difficult to precisely determine their redshifts. Consequently, nearly half of the γ-ray BL Lacs lack reliable redshift measurements. This poses a significant challenge, since redshift is crucial for studying the cosmic evolution of the blazar population and for understanding their intrinsic emission mechanisms. Additionally, it is vital for γ-ray propagation studies, such as indirect evidence of extragalactic background light (EBL), placing constraints on the intergalactic magnetic field (IGMF), and searches for Lorentz invariance violation (LIV) and axion-like particles (ALPs). This paper is the fourth in a series dedicated to determining the redshift of a sample of blazars identified as key targets for future observations with the Cherenkov Telescope Array Observatory (CTAO). The precise determination of the redshifts of these objects plays a crucial role in planning future CTAO observations. We carried out Monte Carlo simulations to identify potential γ-ray blazars with hard spectra detected by the Fermi -LAT telescope that currently lack redshift measurements. These simulations selected the blazars that are anticipated to be detectable by the CTAO within 30 hours or less of exposure assuming an average flux state. In this fourth paper, we report the results of detailed spectroscopic observations of 29 blazars using the ESO/VLT, Keck II, and SALT telescopes. Our analysis involved a thorough search for spectral lines in the spectra of each blazar, and when features of the host galaxy were identified, we modelled its properties. Moreover, we compared the magnitudes of the targets during the observations to their long-term light curves. In the sample studied, 9 of 29 sources were observed with a high signal-to-noise ratio (S/N $>$ 100), while the remaining 20 were observed with a moderate or low S/N. We successfully determined firm redshifts for 12 blazars, ranging from 0.1636 to 1.1427, and identified two lower limit redshifts at z > 1.0196 and z > 1.4454. The remaining 15 BL Lac objects exhibited featureless spectra under the observed S/N.
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Combined dark matter search towards dwarf spheroidal galaxies with Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS

(2025)

Authors:

LAT Collaboration, S Abdollahi, L Baldini, R Bellazzini, B Berenji, E Bissaldi, R Bonino, P Bruel, S Buson, E Charles, AW Chen, S Ciprini, M Crnogorcevic, A Cuoco, F D'Ammando, A de Angelis, M Di Mauro, N Di Lalla, L Di Venere, A Domínguez, SJ Fegan, A Fiori, P Fusco, V Gammaldi, F Gargano, D Gasparrini, F Giacchino, N Giglietto, M Giliberti, F Giordano, M Giroletti, IA Grenier, S Guiriec, M Gustafsson, E Hays, JW Hewitt, D Horan, H Katagiri, M Kuss, J Li, F Longo, F Loparco, L Lorusso, G Martí-Devesa, MN Mazziotta, JE McEnery, I Mereu, M Meyer, PF Michelson, N Mirabal, W Mitthumsiri, T Mizuno, A Morselli, IV Moskalenko, M Negro, N Omodei, M Orienti, E Orlando, G Panzarini, M Persic, M Pesce-Rollins, R Pillera, TA Porter, G Principe, S Rainò, R Rando, M Razzano, O Reimer, M Sánchez-Conde, PM Saz Parkinson, D Serini, DJ Suson, DF Torres, G Zaharijas, HAWC Collaboration, :, A Albert, R Alfaro, C Alvarez, JC Arteaga-Velázquez, D Avila Rojas, HA Ayala Solares, R Babu, E Belmont-Moreno, KS Caballero-Mora, T Capistrán, A Carramiñana, S Casanova, O Chaparro-Amaro, U Cotti, J Cotzomi, S Coutiño de León, E de la Fuente, C de León, R Diaz Hernandez, BL Dingus, MA DuVernois, M Durocher, JC Díaz-Vélez, K Engel, C Espinoza, KL Fan, N Fraija, JA García-González, F Garfias, MM González, JA Goodman, JP Harding, S Hernandez, I Herzog, J Hinton, D Huang, F Hueyotl-Zahuantitla, P Hüntemeyer, A Iriarte, V Joshi, S Kaufmann, D Kieda, GJ Kunde, A Lara, J Lee, H León Vargas, JT Linnemann, AL Longinotti, G Luis-Raya, J Lundeen, K Malone, O Martinez, J Martínez-Castro, H Martínez-Huerta, JA Matthews, P Miranda-Romagnoli, JA Morales-Soto, E Moreno, M Mostafá, A Nayerhoda, L Nellen, MU Nisa, R Noriega-Papaqui, L Olivera-Nieto, N Omodei, A Peisker, Y Pérez Araujo, EG Pérez-Pérez, CD Rho, D Rosa-González, H Salazar, D Salazar-Gallegos, A Sandoval, M Schneider, J Serna-Franco, AJ Smith, Y Son, RW Springer, O Tibolla, K Tollefson, I Torres, R Torres-Escobedo, R Turner, F Ureña-Mena, E Varela, L Villaseñor, X Wang, IJ Watson, K Whitaker, E Willox, S Yu, S Yun-Cárcamo, H Zhou, HESS Collaboration, :, F Aharonian, F Ait Benkhali, C Armand, J Aschersleben, M Backes, V Barbosa Martins, R Batzofin, Y Becherini, D Berge, B Bi, M Böttcher, C Boisson, J Bolmont, M de Bony de Lavergne, J Borowska, M Bouyahiaoui, F Bradascio, M Breuhaus, F Brun, B Bruno, T Bulik, C Burger-Scheidlin, S Caroff, S Casanova, R Cecil, J Celic, M Cerruti, T Chand, S Chandra, A Chen, J Chibueze, O Chibueze, G Cotter, S Dai, J Damascene Mbarubucyeye, A Dmytriiev, V Doroshenko, J-P Ernenwein, G Fichet de Clairfontaine, M Filipovic, G Fontaine, M Füßling, S Funk, S Gabici, S Ghafourizadeh, G Giavitto, D Glawion, JF Glicenstein, G Grolleron, L Haerer, JA Hinton, W Hofmann, TL Holch, M Holler, D Horns, M Jamrozy, F Jankowsky, A Jardin-Blicq, V Joshi, I Jung-Richardt, E Kasai, K Katarzyński, R Khatoon, B Khélifi, W Kluźniak, Nu Komin, D Kostunin, RG Lang, S Le Stum, F Leitl, A Lemière, M Lemoine-Goumard, J-P Lenain, F Leuschner, T Lohse, A Luashvili, I Lypova, J Mackey, D Malyshev, D Malyshev, V Marandon, P Marchegiani, R Marx, M Meyer, A Mitchell, R Moderski, A Montanari, E Moulin, K Nakashima, M de Naurois, J Niemiec, A Priyana Noel, L Oakes, P O'Brien, S Ohm, L Olivera-Nieto, E de Ona Wilhelmi, M Ostrowski, S Panny, M Panter, RD Parsons, V Poireau, DA Prokhorov, G Pühlhofer, A Quirrenbach, P Reichherzer, A Reimer, O Reimer, F Rieger, L Rinchiuso, G Rowell, B Rudak, V Sahakian, S Sailer, A Santangelo, M Sasaki, J Schäfer, U Schwanke, JNS Shapopi, H Sol, A Specovius, S Spencer, Ł Stawarz, R Steenkamp, S Steinmassl, C Steppa, I Sushch, H Suzuki, T Takahashi, T Tanaka, T Tavernier, AM Taylor, R Terrier, C Thorpe-Morgan, C van Eldik, M Vecchi, J Veh, C Venter, J Vink, T Wach, SJ Wagner, A Wierzcholska, Yu Wun Wong, M Zacharias, D Zargaryan, AA Zdziarski, A Zech, S Zouari, N Żywucka, MAGIC Collaboration, :, H Abe, S Abe, VA Acciari, I Agudo, T Aniello, S Ansoldi, LA Antonelli, A Arbet Engels, C Arcaro, M Artero, K Asano, D Baack, A Babić, A Baquero, U Barres de Almeida, JA Barrio, I Batković, J Baxter, J Becerra González, W Bednarek, E Bernardini, M Bernardos, J Bernete, A Berti, C Bigongiari, A Biland, O Blanch, G Bonnoli, Ž Bošnjak, I Burelli, G Busetto, A Campoy Ordaz, A Carosi, R Carosi, M Carretero-Castrillo, AJ Castro-Tirado, G Ceribella, Y Chai, A Cifuentes, S Cikota, E Colombo, JL Contreras, J Cortina, S Covino, G D'Amico, V D'Elia, P Da Vela, F Dazzi, A De Angelis, B De Lotto, A Del Popolo, M Delfino, J Delgado, C Delgado Mendez, D Depaoli, F Di Pierro, L Di Venere, D Dominis Prester, A Donini, D Dorner, M Doro, D Elsaesser, G Emery, J Escudero, L Fariña, A Fattorini, L Foffano, L Font, S Fröse, S Fukami, Y Fukazawa, RJ García López, M Garczarczyk, S Gasparyan, M Gaug, JG Giesbrecht Paiva, N Giglietto, F Giordano, P Gliwny, N Godinović, R Grau, D Green, JG Green, D Hadasch, A Hahn, T Hassan, L Heckmann, J Herrera, D Hrupec, M Hütten, R Imazawa, T Inada, R Iotov, K Ishio, I Jiménez Martínez, J Jormanainen, D Kerszberg, GW Kluge, Y Kobayashi, PM Kouch, H Kubo, J Kushida, M Láinez Lezáun, A Lamastra, F Leone, E Lindfors, S Lombardi, F Longo, R López-Coto, M López-Moya, A López-Oramas, S Loporchio, A Lorini, B Machado de Oliveira Fraga, P Majumdar, M Makariev, G Maneva, N Mang, M Manganaro, S Mangano, K Mannheim, M Mariotti, M Martínez, A Mas-Aguilar, D Mazin, S Menchiari, S Mender, D Miceli, T Miener, JM Miranda, R Mirzoyan, M Molero González, E Molina, HA Mondal, A Moralejo, D Morcuende, C Nanci, V Neustroev, M Nievas Rosillo, C Nigro, K Nilsson, K Nishijima, T Njoh Ekoume, K Noda, S Nozaki, Y Ohtani, A Okumura, J Otero-Santos, S Paiano, M Palatiello, D Paneque, R Paoletti, JM Paredes, L Pavletić, M Persic, M Pihet, G Pirola, F Podobnik, PG Prada Moroni, E Prandini, G Principe, C Priyadarshi, W Rhode, M Ribó, J Rico, C Righi, N Sahakyan, T Saito, K Satalecka, FG Saturni, B Schleicher, K Schmidt, F Schmuckermaier, JL Schubert, T Schweizer, A Sciaccaluga, J Sitarek, V Sliusar, D Sobczynska, A Spolon, A Stamerra, J Strišković, D Strom, M Strzys, Y Suda, S Suutarinen, H Tajima, M Takahashi, R Takeishi, F Tavecchio, P Temnikov, K Terauchi, T Terzić, M Teshima, L Tosti, S Truzzi, A Tutone, S Ubach, J van Scherpenberg, M Vazquez Acosta, S Ventura, V Verguilov, I Viale, CF Vigorito, V Vitale, I Vovk, R Walter, M Will, C Wunderlich, T Yamamoto, VERITAS Collaboration, :, A Acharyya, CB Adams, A Archer, P Bangale, JT Bartkoske, P Batista, W Benbow, JH Buckley, Y Chen, JL Christiansen, AJ Chromey, M Errando, M Escobar Godoy, A Falcone, S Feldman, Q Feng, JP Finley, GM Foote, L Fortson, A Furniss, G Gallagher, C Giuri, W Hanlon, O Hervet, CE Hinrichs, J Hoang, J Holder, Z Hughes, TB Humensky, W Jin, MN Johnson, P Kaaret, M Kertzman, M Kherlakian, D Kieda, TK Kleiner, N Korzoun, F Krennrich, S Kumar, M Lundy, G Maier, CE McGrath, MJ Millard, J Millis, CL Mooney, P Moriarty, R Mukherjee, D Nieto, S O'Brien, RA Ong, M Pohl, E Pueschel, J Quinn, PL Rabinowitz, K Ragan, PT Reynolds, D Ribeiro, E Roache, JL Ryan, I Sadeh, L Saha, M Santander, GH Sembroski, R Shang, M Splettstoesser, D Tak, AK Talluri, JV Tucci, VV Vassiliev, A Weinstein, DA Williams, SL Wong
More details from the publisher

Optical spectroscopy of blazars for the Cherenkov Telescope Array Observatory- IV

(2025)

Authors:

B Rajput, P Goldoni, W Max-Moerbeck, E Kasai, DA Williams, C Boisson, S Pita, M Backes, U Barres de Almeida, J Becerra González, G Cotter, F D'Ammando, V Fallah Ramazani, B Hnatyk, O Hervet, E Lindfors, D Mukhi-Nilo, M Nikołajuk, M Splettstoesser, B Van Soelen
More details from the publisher

The H.E.S.S. extragalactic sky survey with the first decade of observations

(2025)

Authors:

HESS Collaboration, F Aharonian, F Ait Benkhali, J Aschersleben, H Ashkar, M Backes, V Barbosa Martins, R Batzofin, Y Becherini, D Berge, K Bernlöhr, M Böttcher, C Boisson, J Bolmont, M de Bony de Lavergne, J Borowska, M Bouyahiaoui, F Bradascio, R Brose, A Brown, F Brun, B Bruno, T Bulik, C Burger-Scheidlin, T Bylund, S Casanova, J Celic, M Cerruti, T Chand, S Chandra, A Chen, J Chibueze, O Chibueze, G Cotter, P Cristofari, J Damascene Mbarubucyeye, ID Davids, J Devin, J Djuvsland, A Dmytriiev, K Egberts, S Einecke, S Fegan, G Fontaine, S Funk, S Gabici, JF Glicenstein, J Glombitza, P Goswami, G Grolleron, L Haerer, B Heß, JA Hinton, W Hofmann, TL Holch, M Holler, D Horns, Zhiqiu Huang, M Jamrozy, F Jankowsky, A Jardin-Blicq, E Kasai, K Katarzyński, R Khatoon, B Khélifi, Nu Komin, K Kosack, D Kostunin, A Kundu, RG Lang, S Le Stum, A Lemière, M Lemoine-Goumard, J-P Lenain, F Leuschner, A Luashvili, J Mackey, D Malyshev, V Marandon, G Martí-Devesa, R Marx, A Mehta, A Mitchell, R Moderski, L Mohrmann, A Montanari, M de Naurois, J Niemiec, P O'Brien, L Olivera-Nieto, E de Ona Wilhelmi, M Ostrowski, S Panny, M Panter, U Pensec, G Pühlhofer, M Punch, A Quirrenbach, S Ravikularaman, M Regeard, A Reimer, O Reimer, I Reis, H Ren, B Reville, F Rieger, G Rowell, B Rudak, E Ruiz-Velasco, V Sahakian, H Salzmann, DA Sanchez, A Santangelo, M Sasaki, J Schäfer, F Schüssler, JNS Shapopi, A Sharma, H Sol, S Spencer, Ł Stawarz, R Steenkamp, S Steinmassl, C Steppa, H Suzuki, T Takahashi, T Tanaka, AM Taylor, R Terrier, A Thakur, M Tsirou, C van Eldik, M Vecchi, C Venter, J Vink, HJ Völk, T Wach, SJ Wagner, A Wierzcholska, M Zacharias, AA Zdziarski, A Zech, N Żywucka
More details from the publisher

Detection of very-high-energy gamma-ray emission from Eta Carinae during its 2020 periastron passage

(2025)

Authors:

HESS Collaboration, F Aharonian, F Ait Benkhali, J Aschersleben, H Ashkar, V Barbosa Martins, R Batzofin, Y Becherini, D Berge, K Bernlöhr, M Böttcher, C Boisson, J Bolmont, M de Bony de Lavergne, F Bradascio, R Brose, A Brown, F Brun, B Bruno, C Burger-Scheidlin, S Casanova, J Celic, M Cerruti, T Chand, S Chandra, A Chen, J Chibueze, O Chibueze, T Collins, G Cotter, J Damascene Mbarubucyeye, J de Assis Scarpin, J Devin, A Djannati-Ataï, J Djuvsland, A Dmytriiev, K Egberts, S Einecke, J-P Ernenwein, C Escañuela Nieves, K Feijen, M Filipovic, G Fontaine, S Funk, S Gabici, JF Glicenstein, G Grolleron, M-H Grondin, L Haerer, B Heß, JA Hinton, W Hofmann, TL Holch, M Holler, D Horns, Zhiqiu Huang, M Jamrozy, F Jankowsky, A Jardin-Blicq, I Jung-Richardt, K Katarzyński, R Khatoon, B Khélifi, W Kluźniak, Nu Komin, K Kosack, D Kostunin, RG Lang, S Le Stum, A Lemière, M Lemoine-Goumard, J-P Lenain, A Luashvili, J Mackey, D Malyshev, V Marandon, A Marcowith, G Martí-Devesa, R Marx, A Mehta, A Mitchell, R Moderski, MO Moghadam, L Mohrmann, E Moulin, M de Naurois, J Niemiec, S Ohm, L Olivera-Nieto, E de Ona Wilhelmi, M Ostrowski, S Panny, M Panter, RD Parsons, U Pensec, G Pühlhofer, A Quirrenbach, S Ravikularaman, M Regeard, A Reimer, O Reimer, Q Remy, H Ren, B Reville, F Rieger, G Rowell, B Rudak, E Ruiz-Velasco, K Sabri, V Sahakian, H Salzmann, A Santangelo, M Sasaki, J Schäfer, F Schüssler, HM Schutte, JNS Shapopi, S Spencer, Ł Stawarz, R Steenkamp, S Steinmassl, C Steppa, K Streil, T Tanaka, R Terrier, M Tluczykont, M Tsirou, N Tsuji, C van Eldik, M Vecchi, C Venter, T Wach, SJ Wagner, F Werner, R White, A Wierzcholska, M Zacharias, AA Zdziarski, A Zech, N Żywucka
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