Detection of RS Oph with LST-1 and modelling of its HE/VHE gamma-ray emission

Abe, K.; Abe, S.; Abhishek, A.; Acero, F.; Aguasca-Cabot, A.; Agudo, I.; Alispach, C.; Alvarez Crespo, N.; Ambrosino, D.; Antonelli, L. A.; Aramo, C.; Arbet-Engels, A.; Arcaro, C.; Asano, K.; Aubert, P.; Baktash, A.; Balbo, M.; Bamba, A.; Baquero Larriva, A.; Barres de Almeida, U.; Barrio, J. A.; Barrios Jiménez, L.; Batkovic, I.; Baxter, J.; Becerra González, J.; Bernardini, E.; Bernete, J.; Berti, A.; Bezshyiko, I.; Bhattacharjee, P.; Bigongiari, C.; Bissaldi, E.; Blanch, O.; Bonnoli, G.; Bordas, P.; Borkowski, G.; Brunelli, G.; Bulgarelli, A.; Bunse, M.; Burelli, I.; Burmistrov, L.; Buscemi, M.; Cardillo, M.; Caroff, S.; Carosi, A.; Carrasco, M. S.; Cassol, F.; Castrejón, N.; Cerasole, D.; Ceribella, G.; Chai, Y.; Cheng, K.; Chiavassa, A.; Chikawa, M.; Chon, G.; Chytka, L.; Cicciari, G. M.; Cifuentes, A.; Contreras, J. L.; Cortina, J.; Costantini, H.; Da Vela, P.; Dalchenko, M.; Dazzi, F.; De Angelis, A.; de Bony de Lavergne, M.; De Lotto, B.; de Menezes, R.; Del Burgo, R.; Del Peral, L.; Delgado, C.; Delgado Mengual, J.; della Volpe, D.; Dellaiera, M.; Di Piano, A.; Di Pierro, F.; Di Tria, R.; Di Venere, L.; Díaz, C.; Dominik, R. M.; Dominis Prester, D.; Donini, A.; Dore, D.; Dorner, D.; Doro, M.; Eisenberger, L.; Elsässer, D.; Emery, G.; Escudero, J.; Fallah Ramazani, V.; Ferrarotto, F.; Fiasson, A.; Foffano, L.; Freixas Coromina, L.; Fröse, S.; Fukazawa, Y.; Garcia López, R.; Gasbarra, C.; Gasparrini, D.; Geyer, D.; Giesbrecht Paiva, J.; Giglietto, N.; Giordano, F.; Gliwny, P.; Godinovic, N.; Grau, R.; Green, D.; Green, J.; Gunji, S.; Günther, P.; Hackfeld, J.; Hadasch, D.; Hahn, A.; Hassan, T.; Hayashi, K.; Heckmann, L.; Heller, M.; Herrera Llorente, J.; Hirotani, K.; Hoffmann, D.; Horns, D.; Houles, J.; Hrabovsky, M.; Hrupec, D.; Hui, D.; Iarlori, M.; Imazawa, R.; Inada, T.; Inome, Y.; Inoue, S.; Ioka, K.; Iori, M.; Iuliano, A.; Jahanvi, J.; Jimenez Martinez, I.; Jimenez Quiles, J.; Jurysek, J.; Kagaya, M.; Kalashev, O.; Karas, V.; Katagiri, H.; Kataoka, J.; Kerszberg, D.; Kobayashi, Y.; Kohri, K.; Kong, A.; Kubo, H.; Kushida, J.; Lacave, B.; Lainez, M.; Lamanna, G.; Lamastra, A.; Lemoigne, L.; Linhoff, M.; Longo, F.; López-Coto, R.; López-Moya, M.; López-Oramas, A.; Loporchio, S.; Lorini, A.; Lozano Bahilo, J.; Luciani, H.; Luque-Escamilla, P. L.; Majumdar, P.; Makariev, M.; Mallamaci, M.; Mandat, D.; Manganaro, M.; Manicò, G.; Mannheim, K.; Marchesi, S.; Mariotti, M.; Marquez, P.; Marsella, G.; Martí, J.; Martinez, O.; Martínez, G.; Martínez, M.; Mas-Aguilar, A.; Maurin, G.; Mazin, D.; Méndez-Gallego, J.; Menon, S.; Mestre Guillen, E.; Micanovic, S.; Miceli, D.; Miener, T.; Miranda, J. M.; Mirzoyan, R.; Mizuno, T.; Molero Gonzalez, M.; Molina, E.; Montaruli, T.; Moralejo, A.; Morcuende, D.; Morselli, A.; Moya, V.; Muraishi, H.; Nagataki, S.; Nakamori, T.; Neronov, A.; Nickel, L.; Nieto Castaño, D.; Nievas Rosillo, M.; Nikolic, L.; Nishijima, K.; Noda, K.; Nosek, D.; Novotny, V.; Nozaki, S.; Ohishi, M.; Ohtani, Y.; Oka, T.; Okumura, A.; Orito, R.; Otero-Santos, J.; Ottanelli, P.; Owen, E.; Palatiello, M.; Paneque, D.; Pantaleo, F. R.; Paoletti, R.; Paredes, J. M.; Pech, M.; Pecimotika, M.; Peresano, M.; Pfeifle, F.; Pietropaolo, E.; Pihet, M.; Pirola, G.; Plard, C.; Podobnik, F.; Pons, E.; Prandini, E.; Prouza, M.; Rainò, S.; Rando, R.; Rhode, W.; Ribó, M.; Righi, C.; Rizi, V.; Rodriguez Fernandez, G.; Rodríguez Frías, M. D.; Romano, P.; Ruina, A.; Ruiz-Velasco, E.; Saito, T.; Sakurai, S.; Sanchez, D. A.; Sano, H.; Šarić, T.; Sato, Y.; Saturni, F. G.; Savchenko, V.; Schiavone, F.; Schleicher, B.; Schmuckermaier, F.; Schubert, J. L.; Schussler, F.; Schweizer, T.; Seglar Arroyo, M.; Siegert, T.; Simongini, A.; Sitarek, J.; Sliusar, V.; Stamerra, A.; Strišković, J.; Strzys, M.; Suda, Y.; Sunny, A.; Tajima, H.; Takahashi, H.; Takahashi, M.; Takata, J.; Takeishi, R.; Tam, P. H. T.; Tanaka, S. J.; Tateishi, D.; Tavernier, T.; Temnikov, P.; Terada, Y.; Terauchi, K.; Terzic, T.; Teshima, M.; Tluczykont, M.; Toennis, C.; Tokanai, F.; Torres, D. F.; Travnicek, P.; Tutone, A.; Vacula, M.; van Scherpenberg, J.; Vázquez Acosta, M.; Ventura, S.; Vercellone, S.; Verna, G.; Viale, I.; Vigliano, A.; Vigorito, C. F.; Visentin, E.; Vitale, V.; Voitsekhovskyi, V.; Voutsinas, G.; Vovk, I.; Vuillaume, T.; Walter, R.; Wan, L.; Will, M.; Wójtowicz, J.; Yamamoto, T.; Yamazaki, R.; Yao, Y.; Yeung, P. K. H.; Yoshida, T.; Yoshikoshi, T.; Zhang, W.; Zywucka, N.

doi:10.1051/0004-6361/202452447

Context. The recurrent nova RS Ophiuchi (RS Oph) underwent a thermonuclear eruption in August 2021. In this event, RS Oph was detected by the High Energy Stereoscopic System (H.E.S.S.), the Major Atmospheric Gamma Imaging Cherenkov (MAGIC), and the first Large-Sized Telescope (LST-1) of the future Cherenkov Telescope Array Observatory (CTAO) at very-high gamma-ray energies above 100 GeV. This means that novae are a new class of very-high-energy (VHE) gamma-ray emitters. Aims. We report the analysis of the RS Oph observations with LST-1. We constrain the particle population that causes the observed emission in hadronic and leptonic scenarios. Additionally, we study the prospects of detecting further novae using LST-1 and the upcoming LST array of CTAO-North. Methods. We conducted target-of-opportunity observations with LST-1 from the first day of this nova event. The data were analysed in the framework of cta-lstchain and Gammapy, the official CTAO-LST reconstruction and analysis packages. One-zone hadronic and leptonic models were considered to model the gamma-ray emission of RS Oph using the spectral information from Fermi-LAT and LST-1, together with public data from the MAGIC and H.E.S.S. telescopes. Results. RS Oph was detected at 6.6σ with LST-1 in the first 6.35 hours of observations following the eruption. The hadronic scenario is preferred over the leptonic scenario considering a proton energy spectrum with a power-law model with an exponential cutoff whose position increases from (0.26 ± 0.08) TeV on day 1 up to (1.6 ± 0.6) TeV on day 4 after the eruption. The deep sensitivity and low energy threshold of the LST-1/LST array will allow us to detect faint novae and increase their discovery rate.