Multiwavelength study of the galactic PeVatron candidate LHAASO J2108+5157
Journal
Date Issued
2023
Author(s)
Abe, S.
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Aguasca-Cabot, A.
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Agudo, I.
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Alvarez Crespo, N.
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Aramo, C.
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Arbet-Engels, A.
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Artero, M.
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Asano, K.
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Aubert, P.
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Baktash, A.
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Heller, M.
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Herrera Llorente, J.
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Hirotani, K.
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Hoffmann, D.
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Horns, D.
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Houles, J.
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Hrabovsky, M.
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Hrupec, D.
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Hui, D.
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Hütten, M.
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Bamba, A.
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Imazawa, R.
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Inada, T.
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Inome, Y.
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Ioka, K.
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Iori, M.
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Ishio, K.
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Iwamura, Y.
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Jacquemont, M.
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Jimenez Martinez, I.
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Jurysek, J.
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Baquero Larriva, A.
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Kagaya, M.
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Karas, V.
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Katagiri, H.
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Kataoka, J.
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Kerszberg, D.
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Kobayashi, Y.
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Kong, A.
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Kubo, H.
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Kushida, J.
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Lainez, M.
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Lamanna, G.
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Le Flour, T.
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Linhoff, M.
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Longo, F.
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López-Coto, R.
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López-Moya, M.
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López-Oramas, A.
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Loporchio, S.
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Lorini, A.
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Barres de Almeida, U.
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Luque-Escamilla, P. L.
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Majumdar, P.
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Makariev, M.
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Mandat, D.
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Manganaro, M.
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Manicò, G.
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Mannheim, K.
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Mariotti, M.
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Marquez, P.
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Marsella, G.
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Barrio, J. A.
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Martí, J.
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Martinez, O.
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Martínez, G.
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Martínez, M.
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Marusevec, P.
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Mas-Aguilar, A.
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Maurin, G.
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Mazin, D.
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Mestre Guillen, E.
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Micanovic, S.
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Batkovic, I.
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Miceli, D.
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Miener, T.
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Miranda, J. M.
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Mirzoyan, R.
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Mizuno, T.
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Molero Gonzalez, M.
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Molina, E.
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Montaruli, T.
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Monteiro, I.
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Moralejo, A.
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Baxter, J.
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Morcuende, D.
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Morselli, A.
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Mrakovcic, K.
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Murase, K.
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Nagai, A.
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Nakamori, T.
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Nickel, L.
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Nievas, M.
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Nishijima, K.
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Noda, K.
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Becerra González, J.
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Nosek, D.
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Nozaki, S.
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Ohishi, M.
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Ohtani, Y.
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Okazaki, N.
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Okumura, A.
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Orito, R.
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Otero-Santos, J.
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Palatiello, M.
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Paneque, D.
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Bernardini, E.
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Pantaleo, F. R.
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Paoletti, R.
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Paredes, J. M.
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Pavletić, L.
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Pech, M.
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Pecimotika, M.
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Pietropaolo, E.
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Pirola, G.
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Podobnik, F.
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Poireau, V.
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Bernardos, M. I.
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Polo, M.
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Pons, E.
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Prast, J.
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Priyadarshi, C.
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Prouza, M.
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Rando, R.
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Rhode, W.
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Ribó, M.
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Rizi, V.
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Bernete Medrano, J.
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Rodriguez Fernandez, G.
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Saito, T.
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Sakurai, S.
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Sanchez, D. A.
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Šarić, T.
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Scherpenberg, J.
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Schleicher, B.
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Schmuckermaier, F.
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Schubert, J. L.
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Berti, A.
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Schussler, F.
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Schweizer, T.
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Seglar Arroyo, M.
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Sitarek, J.
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Sliusar, V.
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Spolon, A.
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Strišković, J.
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Strzys, M.
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Suda, Y.
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Sunada, Y.
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Bhattacharjee, P.
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Tajima, H.
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Takahashi, M.
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Takahashi, H.
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Takata, J.
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Takeishi, R.
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Tam, P. H. T.
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Tanaka, S. J.
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Tateishi, D.
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Temnikov, P.
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Terada, Y.
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Biederbeck, N.
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Terauchi, K.
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Terzic, T.
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Teshima, M.
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Tluczykont, M.
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Tokanai, F.
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Torres, D. F.
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Travnicek, P.
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Truzzi, S.
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Uhlrich, G.
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Vacula, M.
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Vázquez Acosta, M.
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Verguilov, V.
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Viale, I.
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Vigliano, A.
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Vigorito, C. F.
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Vitale, V.
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Voutsinas, G.
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Vovk, I.
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Vuillaume, T.
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Bissaldi, E.
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Walter, R.
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Will, M.
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Yamamoto, T.
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Yamazaki, R.
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Yoshida, T.
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Yoshikoshi, T.
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Zywucka (CTA-LST Project), N.
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Balbo, M.
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Eckert, D.
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Tramacere, A.
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Blanch, O.
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Bordas, P.
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Buisson, C.
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Burelli, I.
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Buscemi, M.
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Caroff, S.
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Cassol, F.
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Cauz, D.
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Ceribella, G.
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Chai, Y.
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Cheng, K.
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Chiavassa, A.
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Chikawa, M.
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Chytka, L.
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Cifuentes, A.
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Contreras, J. L.
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Cortina, J.
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Costantini, H.
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D'Amico, G.
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Dalchenko, M.
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De Angelis, A.
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de Bony de Lavergne, M.
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De Lotto, B.
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de Menezes, R.
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Deleglise, G.
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Delgado, C.
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Delgado Mengual, J.
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della Volpe, D.
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Dellaiera, M.
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Di Piano, A.
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Di Pierro, F.
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Di Tria, R.
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Di Venere, L.
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Díaz, C.
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Dominik, R. M.
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Dominis Prester, D.
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Donini, A.
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Dorner, D.
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Doro, M.
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Elsässer, D.
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Emery, G.
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Escudero, J.
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Fallah Ramazani, V.
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Ferrara, G.
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Fiasson, A.
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Freixas Coromina, L.
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Fröse, S.
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Fukami, S.
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Fukazawa, Y.
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Garcia, E.
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Garcia López, R.
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Gasparrini, D.
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Geyer, D.
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Giesbrecht Paiva, J.
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Giglietto, N.
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Giordano, F.
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Gliwny, P.
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Godinovic, N.
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Grau, R.
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Green, D.
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Gunji, S.
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Hackfeld, J.
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Hadasch, D.
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Hahn, A.
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Hashiyama, K.
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Hassan, T.
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Hayashi, K.
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Heckmann, L.
Abstract
Context. Several new ultrahigh-energy (UHE) γ-ray sources have recently been discovered by the Large High Altitude Air Shower Observatory (LHAASO) collaboration. These represent a step forward in the search for the so-called Galactic PeVatrons, the enigmatic sources of the Galactic cosmic rays up to PeV energies. However, it has been shown that multi-TeV γ-ray emission does not necessarily prove the existence of a hadronic accelerator in the source; indeed this emission could also be explained as inverse Compton scattering from electrons in a radiation-dominated environment. A clear distinction between the two major emission mechanisms would only be made possible by taking into account multi-wavelength data and detailed morphology of the source.
Aims: We aim to understand the nature of the unidentified source LHAASO J2108+5157, which is one of the few known UHE sources with no very high-energy (VHE) counterpart.
Methods: We observed LHAASO J2108+5157 in the X-ray band with XMM-Newton in 2021 for a total of 3.8 hours and at TeV energies with the Large-Sized Telescope prototype (LST-1), yielding 49 hours of good-quality data. In addition, we analyzed 12 years of Fermi-LAT data, to better constrain emission of its high-energy (HE) counterpart 4FGL J2108.0+5155. We used naima and jetset software packages to examine the leptonic and hadronic scenario of the multi-wavelength emission of the source.
Results: We found an excess (3.7σ) in the LST-1 data at energies E > 3 TeV. Further analysis of the whole LST-1 energy range, assuming a point-like source, resulted in a hint (2.2σ) of hard emission, which can be described with a single power law with a photon index of Γ = 1.6 ± 0.2 the range of 0.3 − 100 TeV. We did not find any significant extended emission that could be related to a supernova remnant (SNR) or pulsar wind nebula (PWN) in the XMM-Newton data, which puts strong constraints on possible synchrotron emission of relativistic electrons. We revealed a new potential hard source in Fermi-LAT data with a significance of 4σ and a photon index of Γ = 1.9 ± 0.2, which is not spatially correlated with LHAASO J2108+5157, but including it in the source model we were able to improve spectral representation of the HE counterpart 4FGL J2108.0+5155.
Conclusions: The LST-1 and LHAASO observations can be explained as inverse Compton-dominated leptonic emission of relativistic electrons with a cutoff energy of 100−30+70 TeV. The low magnetic field in the source imposed by the X-ray upper limits on synchrotron emission is compatible with a hypothesis of a PWN or a TeV halo. Furthermore, the spectral properties of the HE counterpart are consistent with a Geminga-like pulsar, which would be able to power the VHE-UHE emission. Nevertheless, the lack of a pulsar in the neighborhood of the UHE source is a challenge to the PWN/TeV-halo scenario. The UHE γ rays can also be explained as π0 decay-dominated hadronic emission due to interaction of relativistic protons with one of the two known molecular clouds in the direction of the source. Indeed, the hard spectrum in the LST-1 band is compatible with protons escaping a shock around a middle-aged SNR because of their high low-energy cut-off, but the origin of the HE γ-ray emission remains an open question....
Aims: We aim to understand the nature of the unidentified source LHAASO J2108+5157, which is one of the few known UHE sources with no very high-energy (VHE) counterpart.
Methods: We observed LHAASO J2108+5157 in the X-ray band with XMM-Newton in 2021 for a total of 3.8 hours and at TeV energies with the Large-Sized Telescope prototype (LST-1), yielding 49 hours of good-quality data. In addition, we analyzed 12 years of Fermi-LAT data, to better constrain emission of its high-energy (HE) counterpart 4FGL J2108.0+5155. We used naima and jetset software packages to examine the leptonic and hadronic scenario of the multi-wavelength emission of the source.
Results: We found an excess (3.7σ) in the LST-1 data at energies E > 3 TeV. Further analysis of the whole LST-1 energy range, assuming a point-like source, resulted in a hint (2.2σ) of hard emission, which can be described with a single power law with a photon index of Γ = 1.6 ± 0.2 the range of 0.3 − 100 TeV. We did not find any significant extended emission that could be related to a supernova remnant (SNR) or pulsar wind nebula (PWN) in the XMM-Newton data, which puts strong constraints on possible synchrotron emission of relativistic electrons. We revealed a new potential hard source in Fermi-LAT data with a significance of 4σ and a photon index of Γ = 1.9 ± 0.2, which is not spatially correlated with LHAASO J2108+5157, but including it in the source model we were able to improve spectral representation of the HE counterpart 4FGL J2108.0+5155.
Conclusions: The LST-1 and LHAASO observations can be explained as inverse Compton-dominated leptonic emission of relativistic electrons with a cutoff energy of 100−30+70 TeV. The low magnetic field in the source imposed by the X-ray upper limits on synchrotron emission is compatible with a hypothesis of a PWN or a TeV halo. Furthermore, the spectral properties of the HE counterpart are consistent with a Geminga-like pulsar, which would be able to power the VHE-UHE emission. Nevertheless, the lack of a pulsar in the neighborhood of the UHE source is a challenge to the PWN/TeV-halo scenario. The UHE γ rays can also be explained as π0 decay-dominated hadronic emission due to interaction of relativistic protons with one of the two known molecular clouds in the direction of the source. Indeed, the hard spectrum in the LST-1 band is compatible with protons escaping a shock around a middle-aged SNR because of their high low-energy cut-off, but the origin of the HE γ-ray emission remains an open question....
Volume
673
Start page
A75
Issn Identifier
0004-6361
Rights
open.access
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