Papers - OKUMURA Akira

Multiwavelength study of the galactic PeVatron candidate LHAASO J2108+5157

Abe, S; Aguasca-Cabot, A; Agudo, I; Crespo, NA; Antonelli, LA; Aramo, C; Arbet-Engels, A; Artero, M; Asano, K; Aubert, P; Baktash, A; Bamba, A; Larriva, AB; Baroncelli, L; de Almeida, UB; Barrio, JA; Batkovic, I; Baxter, J; González, JB; Bernardini, E; Bernardos, MI; Medrano, JB; Berti, A; Bhattacharjee, P; Biederbeck, N; Bigongiari, C; Bissaldi, E; Blanch, O; Bordas, P; Buisson, C; Bulgarelli, A; Burelli, I; Buscemi, M; Cardillo, M; Caroff, S; Carosi, A; Cassol, F; Cauz, D; Ceribella, G; Chai, Y; Cheng, K; Chiavassa, A; Chikawa, M; Chytka, L; Cifuentes, A; Contreras, JL; Cortina, J; Costantini, H; D'Amico, G; Dalchenko, M; De Angelis, A; de Lavergne, MD; De Lotto, B; de Menezes, R; Deleglise, G; Delgado, C; Mengual, JD; della Volpe, D; Dellaiera, M; Di Piano, A; Di Pierro, F; Di Tria, R; Di Venere, L; Díaz, C; Dominik, RM; Prester, DD; Donini, A; Dorner, D; Doro, M; Elsässer, D; Emery, G; Escudero, J; Ramazani, VF; Ferrara, G; Fiasson, A; Coromina, LF; Fröse, S; Fukami, S; Fukazawa, Y; Garcia, E; López, RG; Gasparrini, D; Geyer, D; Paiva, JG; Giglietto, N; Giordano, F; Giro, E; Gliwny, P; Godinovic, N; Grau, R; Green, D; Green, J; Gunji, S; Hackfeld, J; Hadasch, D; Hahn, A; Hashiyama, K; Hassan, T; Hayashi, K; Heckmann, L; Heller, M; Llorente, JH; Hirotani, K; Hoffmann, D; Horns, D; Houles, J; Hrabovsky, M; Hrupec, D; Hui, D; Hütten, M; Imazawa, R; Inada, T; Inome, Y; Ioka, K; Iori, M; Ishio, K; Iwamura, Y; Jacquemont, M; Martinez, IJ; Jurysek, J; Kagaya, M; Karas, V; Katagiri, H; Kataoka, J; Kerszberg, D; Kobayashi, Y; Kong, A; Kubo, H; Kushida, J; Lainez, M; Lamanna, G; Lamastra, A; Le Flour, T; Linhoff, M; Longo, F; López-Coto, R; López-Moya, M; López-Oramas, A; Loporchio, S; Lorini, A; Luque-Escamilla, PL; Majumdar, P; Makariev, M; Mandat, D; Manganaro, M; Manicò, G; Mannheim, K; Mariotti, M; Marquez, P; Marsella, G; Martí, J; Martinez, O; Martínez, G; Martínez, M; Marusevec, P; Mas-Aguilar, A; Maurin, G; Mazin, D; Guillen, EM; Micanovic, S; Miceli, D; Miener, T; Miranda, JM; Mirzoyan, R; Mizuno, T; Gonzalez, MM; Molina, E; Montaruli, T; Monteiro, I; Moralejo, A; Morcuende, D; Morselli, A; Mrakovcic, K; Murase, K; Nagai, A; Nakamori, T; Nickel, L; Nievas, M; Nishijima, K; Noda, K; Nosek, D; Nozaki, S; Ohishi, M; Ohtani, Y; Okazaki, N; Okumura, A; Orito, R; Otero-Santos, J; Palatiello, M; Paneque, D; Pantaleo, FR; Paoletti, R; Paredes, JM; Pavletic, L; Pech, M; Pecimotika, M; Pietropaolo, E; Pirola, G; Podobnik, F; Poireau, V; Polo, M; Pons, E; Prandini, E; Prast, J; Priyadarshi, C; Prouza, M; Rando, R; Rhode, W; Ribó, M; Rizi, V; Fernandez, GR; Saito, T; Sakurai, S; Sanchez, DA; Saric, T; Saturni, FG; Scherpenberg, J; Schleicher, B; Schmuckermaier, F; Schubert, JL; Schussler, F; Schweizer, T; Arroyo, MS; Sitarek, J; Sliusar, V; Spolon, A; Striskovic, J; Strzys, M; Suda, Y; Sunada, Y; Tajima, H; Takahashi, M; Takahashi, H; Takata, J; Takeishi, R; Tam, PHT; Tanaka, SJ; Tateishi, D; Temnikov, P; Terada, Y; Terauchi, K; Terzic, T; Teshima, M; Tluczykont, M; Tokanai, F; Torres, DF; Travnicek, P; Truzzi, S; Tutone, A; Uhlrich, G; Vacula, M; Acosta, MV; Verguilov, V; Viale, I; Vigliano, A; Vigorito, CF; Vitale, V; Voutsinas, G; Vovk, I; Vuillaume, T; Walter, R; Will, M; Yamamoto, T; Yamazaki, R; Yoshida, T; Yoshikoshi, T; Zywucka, N; Balbo, M; Eckert, D; Tramacere, A

ASTRONOMY & ASTROPHYSICS   Vol. 673   2023.5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astronomy and Astrophysics  

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 Σ = 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 Σ = 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.

DOI： 10.1051/0004-6361/202245086

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MAGIC observations provide compelling evidence of hadronic multi-TeV emission from the putative PeVatron SNR G106.3+2.7

Abe H., Abe S., Acciari V.A., Agudo I., Aniello T., Ansoldi S., Antonelli L.A., Arbet Engels A., Arcaro C., Artero M., Asano K., Baack D., Babić A., Baquero A., Barres De Almeida U., Barrio J.A., Batković I., Baxter J., Becerra González J., Bednarek W., Bernardini E., Bernardos M., Berti A., Besenrieder J., Bhattacharyya W., Bigongiari C., Biland A., Blanch O., Bonnoli G., Bošnjak , Burelli I., Busetto G., Carosi R., Carretero-Castrillo M., Castro-Tirado A.J., Ceribella G., Chai Y., Chilingarian A., Cikota S., Colombo E., Contreras J.L., Cortina J., Covino S., D'Amico G., D'Elia V., Da Vela P., Dazzi F., De Angelis A., De Lotto B., Del Popolo A., Delfino M., Delgado J., Delgado Mendez C., Depaoli D., Di Pierro F., Di Venere L., Do Souto Espiñeira E., Dominis Prester D., Donini A., Dorner D., Doro M., Elsaesser D., Emery G., Escudero J., Fallah Ramazani V., Fariña L., Fattorini A., Font L., Fruck C., Fukami S., Fukazawa Y., García López R.J., Garczarczyk M., Gasparyan S., Gaug M., Giesbrecht Paiva J.G., Giglietto N., Giordano F., Gliwny P., Godinović N., Grau R., Green D., Green J.G., Hadasch D., Hahn A., Hassan T., Heckmann L., Herrera J., Hrupec D., Hütten M., Imazawa R., Inada T., Iotov R., Ishio K., Jiménez Martínez I., Jormanainen J., Kerszberg D., Kobayashi Y., Kubo H., Kushida J.

Astronomy and Astrophysics   Vol. 671   2023.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astronomy and Astrophysics  

Context. Certain types of supernova remnants (SNRs) in our Galaxy are assumed to be PeVatrons, capable of accelerating cosmic rays (CRs) to ∼ PeV energies. However, conclusive observational evidence for this has not yet been found. The SNR G106.3+2.7, detected at 1- 100 TeV energies by different γ-ray facilities, is one of the most promising PeVatron candidates. This SNR has a cometary shape, which can be divided into a head and a tail region with different physical conditions. However, in which region the 100 TeV emission is produced has not yet been identified because of the limited position accuracy and/or angular resolution of existing observational data. Additionally, it remains unclear as to whether the origin of the γ-ray emission is leptonic or hadronic. Aims. With the better angular resolution provided by new MAGIC data compared to earlier γ-ray datasets, we aim to reveal the acceleration site of PeV particles and the emission mechanism by resolving the SNR G106.3+2.7 with 0.1 resolution at TeV energies. Methods. We observed the SNR G106.3+2.7 using the MAGIC telescopes for 121.7 h in total - after quality cuts - between May 2017 and August 2019. The analysis energy threshold is ∼0.2 TeV, and the angular resolution is 0.07-0.1. We examined the γ-ray spectra of different parts of the emission, whilst benefitting from the unprecedented statistics and angular resolution at these energies provided by our new data. We also used measurements at other wavelengths such as radio, X-rays, GeV γ-rays, and 10 TeV γ-rays to model the emission mechanism precisely. Results. We detect extended γ-ray emission spatially coincident with the radio continuum emission at the head and tail of SNR G106.3+2.7. The fact that we detect a significant γ-ray emission with energies above 6.0 TeV from only the tail region suggests that the emissions above 10 TeV detected with air shower experiments (Milagro, HAWC, Tibet ASγ and LHAASO) are emitted only from the SNR tail. Under this assumption, the multi-wavelength spectrum of the head region can be explained with either hadronic or leptonic models, while the leptonic model for the tail region is in contradiction with the emission above 10 TeV and X-rays. In contrast, the hadronic model could reproduce the observed spectrum at the tail by assuming a proton spectrum with a cutoff energy of ∼1 PeV for that region. Such high-energy emission in this middle-aged SNR (4-10 kyr) can be explained by considering a scenario where protons escaping from the SNR in the past interact with surrounding dense gases at present. Conclusions. The γ-ray emission region detected with the MAGIC telescopes in the SNR G106.3+2.7 is extended and spatially coincident with the radio continuum morphology. The multi-wavelength spectrum of the emission from the tail region suggests proton acceleration up to ∼PeV, while the emission mechanism of the head region could either be hadronic or leptonic.

DOI： 10.1051/0004-6361/202244931

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Gamma-ray observations of MAXI J1820+070 during the 2018 outburst

Abe H., Abe S., Acciari V. A., Aniello T., Ansoldi S., Antonelli L. A., Engels A. Arbet, Arcaro C., Artero M., Asano K., Baack D., Babic A., Baquero A., de Almeida U. Barres, Barrio J. A., Batkovic I, Baxter J., Gonzalez J. Becerra, Bednarek W., Bernardini E., Bernardos M., Berti A., Besenrieder J., Bhattacharyya W., Bigongiari C., Biland A., Blanch O., Bonnoli G., Bosnjak Z., Burelli I, Busetto G., Carosi R., Carretero-Castrillo M., Ceribella G., Chai Y., Chilingarian A., Cikota S., Colombo E., Contreras J. L., Cortina J., Covino S., D'Amico G., D'Elia V, Da Vela P., Dazzi F., De Angelis A., De Lotto B., Del Popolo A., Delfino M., Delgado J., Mendez C. Delgado, Depaoli D., Di Pierro F., Di Venere L., Prester D. Dominis, Donini A., Dorner D., Doro M., Elsaesser D., Emery G., Ramazani V. Fallah, Farina L., Fattorini A., Font L., Fruck C., Fukami S., Fukazawa Y., Lopez R. J. Garcia, Garczarczyk M., Gasparyan S., Gaug M., Paiva J. G. Giesbrecht, Giglietto N., Giordano F., Gliwny P., Godinovic N., Grau R., Green D., Green J. G., Hadasch D., Hahn A., Hassan T., Heckmann L., Herrera J., Hoang J., Hrupec D., Hutten M., Imazawa R., Inada T., Iotov R., Ishio K., Martinez I. Jimenez, Jormanainen J., Kerszberg D., Kobayashi Y., Kubo H., Kushida J., Lamastra A., Lelas D., Leone F., Lindfors E., Linhoff L., Lombardi S., Longo F., Lopez-Coto R., Lopez-Moya M., Lopez-Oramas A., Loporchio S., Lorini A., Lyard E., Fraga B. Machado de Oliveira, Majumdar P., Makariev M., Maneva G., Mang N., Manganaro M., Mangano S., Mannheim K., Mariotti M., Martinez M., Aguilar A. Mas, Mazin D., Menchiari S., Mender S., Micanovic S., Miceli D., Miener T., Miranda J. M., Mirzoyan R., Molina E., Mondal H. A., Moralejo A., Morcuende D., Moreno V, Nakamori T., Nanci C., Nava L., Neustroev V, Rosillo M. Nievas, Nigro C., Nilsson K., Nishijima K., Ekoume T. Njoh, Noda K., Nozaki S., Ohtani Y., Oka T., Okumura A., Otero-Santos J., Paiano S., Palatiello M., Paneque D., Paoletti R., Paredes J. M., Pavletic L., Persic M., Pihet M., Pirola G., Podobnik F., Moroni P. G. Prada, Prandini E., Principe G., Priyadarshi C., Puljak I, Rhode W., Ribo M., Rico J., Righi C., Rugliancich A., Sahakyan N., Saito T., Sakurai S., Satalecka K., Saturni F. G., Schleicher B., Schmidt K., Schmuckermaier F., Schubert J. L., Schweizer T., Sitarek J., Sliusar V, Sobczynska D., Spolon A., Stamerra A., Striskovic J., Strom D., Strzys M., Suda Y., Suric T., Tajima H., Takahashi M., Takeishi R., Tavecchio F., Temnikov P., Terauchi K., Terzic T., Teshima M., Tosti L., Truzzi S., Tutone A., Ubach S., van Scherpenberg J., Acosta M. Vazquez, Ventura S., Verguilov V., Viale I, Vigorito C. F., Vitale V., Vovk I, Walter R., Will M., Wunderlich C., Yamamoto T., Zaric D., Abdalla H., Aharonian F., Benkhali F. Ait, Anguner E. O., Ashkar H., Backes M., Baghmanyan V, Martins V. Barbosa, Batzofin R., Becherini Y., Berge D., Bernloehr K., Bottcher M., Boisson C., Bolmont J., de Lavergne M. de Bony, Bradascio F., Breuhaus M., Brose R., Brun F., Bulik T., Bylund T., Cangemi F., Caroff S., Casanova S., Cerruti M., Chand T., Chandra S., Chen A., Chibueze O. U., Cotter G., Cristofari P., Mbarubucyeye J. Damascene, Devin J., Djannati-Atai A., Dmytriiev A., Egberts K., Ernenwein J-P, Fiasson A., de Clairfontaine G. Fichet, Fontaine G., Fuessling M., Funk S., Gabici S., Ghafourizadeh S., Giavitto G., Glawion D., Glicenstein J. F., Goswami P., Grolleron G., Hinton J. A., Horbe M., Hoischen C., Holch T. L., Holler M., Horns D., Huang Zhiqiu, Jamrozy M., Jankowsky F., Joshi V, Jung-Richardt I, Kasai E., Katarzynski K., Katz U., Khelifi B., Kluzniak W., Komin Nu, Kosack K., Kostunin D., Lang R. G., Le Stum S., Lemiere A., Lemoine-Goumard M., Lenain J-P, Leuschner F., Lohse T., Luashvili A., Lypova I, Mackey J., Majumdar J., Malyshev D., Malyshev D., Marandon V, Marchegiani P., Marti-Devesa G., Marx R., Maurin G., Meyer M., Mitchell A., Moderski R., Mohrmann L., Montanari A., Moulin E., Muller J., Murach T., Nakashima K., de Naurois M., Nayerhoda A., Niemiec J., Noel A. Pniyana, O'Brien P., Ohm S., Olivera-Nieto L., Wilhelmi E. de Ona, Ostrowski M., Panny S., Panter M., Parsons R. D., Poireau V, Prokhorov D. A., Prokoph H., Puehlhofer G., Punch M., Quirrenbach A., Reichherzer P., Reimer A., Reimer O., Renaud M., Rieger F., Rowell G., Rudak B., Ricarte H. Rueda, Ruiz-Velasco E., Sahakian V, Salzmann H., Santangelo A., Sasaki M., Schaefer J., Schussler F., Schutte H. M., Schwanke U., Shapopi J. N. S., Sol H., Specovius A., Spencer S., Stawarz L., Steenkamp R., Steinmassl S., Steppa C., Sushch I, Suzuki H., Takahashi T., Tanaka T., Thorpe-Morgan C., Tluczykont M., Tomankova L., Tsuji N., Uchiyama Y., van Eldik C., van Soelen B., Vecchi M., Veh J., Venter C., Vink J., Wagner S. J., White R., Wierzcholska A., Wong Yu Wun, Yusafzai A., Zacharias M., Zanin R., Zargaryan D., Zdziarski A. A., Zech A., Zhu S. J., Zouari S., Zywucka N., Acharyya A., Adams C. B., Batista P., Benbow W., Capasso M., Christiansen J. L., Chromey A. J., Errando M., Falcone A., Feng Q., Finley J. P., Foote G. M., Fortson L., Furniss A., Gent A., Hanlon W. E., Hervet O., Holder J., Hona B., Humensky T. B., Jin W., Kaaret P., Kertzman M., Kherlakian M., Kleiner T. K., Kumar S., Lang M. J., Lundy M., Maier G., McGrath C. E., Millis J., Moriarty P., Mukherjee R., O'Brien S., Ong R. A., Park N., Patel S. R., Pfrang K., Pohl M., Pueschel E., Quinn J., Ragan K., Reynolds P. T., Ribeiro D., Roache E., Ryan J. L., Sadeh I, Saha L., Santander M., Sembroski G. H., Shang R., Splettstoesser M., Tak D., Tucci J. V, Weinstein A., Williams D. A., Williamson T. J., Bosch-Ramon V, Celma C., Linares M., Russell D. M., Sala G.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   Vol. 517 ( 4 ) page： 4736 - 4751   2022.12

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Monthly Notices of the Royal Astronomical Society  

MAXI J1820+070 is a low-mass X-ray binary with a black hole (BH) as a compact object. This binary underwent an exceptionally bright X-ray outburst from 2018 March to October, showing evidence of a non-thermal particle population through its radio emission during this whole period. The combined results of 59.5 h of observations of the MAXI J1820+070 outburst with the H.E.S.S., MAGIC and VERITAS experiments at energies above 200 GeV are presented, together with Fermi-LAT data between 0.1 and 500 GeV, and multiwavelength observations from radio to X-rays. Gamma-ray emission is not detected from MAXI J1820+070, but the obtained upper limits and the multiwavelength data allow us to put meaningful constraints on the source properties under reasonable assumptions regarding the non-thermal particle population and the jet synchrotron spectrum. In particular, it is possible to show that, if a high-energy (HE) gamma-ray emitting region is present during the hard state of the source, its predicted flux should be at most a factor of 20 below the obtained Fermi-LAT upper limits, and closer to them for magnetic fields significantly below equipartition. During the state transitions, under the plausible assumption that electrons are accelerated up to ∼500 GeV, the multiwavelength data and the gamma-ray upper limits lead consistently to the conclusion that a potential HE and very-HE gamma-ray emitting region should be located at a distance from the BH ranging between 1011 and 1013 cm. Similar outbursts from low-mass X-ray binaries might be detectable in the near future with upcoming instruments such as CTA.

DOI： 10.1093/mnras/stac2686

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Active Galactic Nuclei population studies with the Cherenkov Telescope Array

Abdalla H., Abe H., Abe S., Abusleme A., Acero F., Acharyya A., Acín Portella V., Ackley K., Adam R., Adams C., Adhikari S.S., Aguado-Ruesga I., Agudo I., Aguilera R., Aguirre-Santaella A., Aharonian F., Alberdi A., Alfaro R., Alfaro J., Alispach C., Aloisio R., Alves Batista R., Amans J.P., Amati L., Amato E., Ambrogi L., Ambrosi G., Ambrosio M., Ammendola R., Anderson J., Anduze M., Angüner E.O., Antonelli L.A., Antonuccio V., Antoranz P., Anutarawiramkul R., Aragunde Gutierrez J., Aramo C., Araudo A., Araya M., Arbet-Engels A., Arcaro C., Arendt V., Armand C., Armstrong T., Arqueros F., Arrabito L., Arsioli B., Artero M., Asano K., Ascasíbar Y., Aschersleben J., Ashley M., Attinà P., Aubert P., Singh C.B., Baack D., Babic A., Backes M., Baena V., Bajtlik S., Baktash A., Balazs C., Balbo M., Ballester O., Ballet J., Balmaverde B., Bamba A., Bandiera R., Baquero Larriva A., Barai P., Barbier C., Barbosa Martins V., Barcelo M., Barkov M., Barnard M., Baroncelli L., Barres de Almeida U., Barrio J.A., Bastieri D., Batista P.I., Batkovic I., Bauer C., Bautista-González R., Baxter J., Becciani U., Becerra González J., Becherini Y., Beck G., Becker Tjus J., Bednarek W., Belfiore A., Bellizzi L., Belmont R., Benbow W., Berge D., Bernardini E., Bernardos M.I., Bernlöhr K., Berti A.

Proceedings of Science   Vol. 395   2022.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of Science  

The Cherenkov Telescope Array (CTA) observatory is the next generation of ground-based imaging atmospheric Cherenkov telescopes (IACTs). Building on the strengths of current IACTs, CTA is designed to achieve an order of magnitude improvement in sensitivity, with unprecedented angular and energy resolution. CTA will also increase the energy reach of IACTs, observing photons in the energy range from 20 GeV to beyond 100 TeV. These advances in performance will see CTA heralding in a new era for high-energy astrophysics, with the emphasis shifting from source discovery, to population studies and precision measurements. In this talk we discuss CTA’s ability to conduct source population studies of γ-ray bright active galactic nuclei and how this ability will enhance our understanding on the redshift evolution of this dominant γ-ray source class.

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Monte Carlo Simulations and Validation of NectarCAM, a Medium Sized Telescope Camera for CTA

Armstrong T.P., Costantini H., Glicenstein J.F., Lenain J.P., Schwanke U., Tavernier T., Abdalla H., Abe H., Abe S., Abusleme A., Acero F., Acharyya A., Acín Portella V., Ackley K., Adam R., Adams C., Adhikari S.S., Aguado-Ruesga I., Agudo I., Aguilera R., Aguirre-Santaella A., Aharonian F., Alberdi A., Alfaro R., Alfaro J., Alispach C., Aloisio R., Alves Batista R., Amans J.P., Amati L., Amato E., Ambrogi L., Ambrosi G., Ambrosio M., Ammendola R., Anderson J., Anduze M., Angüner E.O., Antonelli L.A., Antonuccio V., Antoranz P., Anutarawiramkul R., Aragunde Gutierrez J., Aramo C., Araudo A., Araya M., Arbet-Engels A., Arcaro C., Arendt V., Armand C., Armstrong T., Arqueros F., Arrabito L., Arsioli B., Artero M., Asano K., Ascasíbar Y., Aschersleben J., Ashley M., Attinà P., Aubert P., Singh C.B., Baack D., Babic A., Backes M., Baena V., Bajtlik S., Baktash A., Balazs C., Balbo M., Ballester O., Ballet J., Balmaverde B., Bamba A., Bandiera R., Baquero Larriva A., Barai P., Barbier C., Barbosa Martins V., Barcelo M., Barkov M., Barnard M., Baroncelli L., Barres de Almeida U., Barrio J.A., Bastieri D., Batista P.I., Batkovic I., Bauer C., Bautista-González R., Baxter J., Becciani U., Becerra González J., Becherini Y., Beck G., Becker Tjus J., Bednarek W., Belfiore A., Bellizzi L., Belmont R.

Proceedings of Science   Vol. 395   2022.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of Science  

The upcoming Cherenkov Telescope Array (CTA) ground-based gamma-ray observatory will open up our view of the very high energy Universe, offering an improvement in sensitivity of 5-10 times that of previous experiments. NectarCAM is one of the proposed cameras for the Medium-Sized Telescopes (MST) which have been designed to cover the core energy range of CTA, from 100 GeV to 10 TeV. The final camera will be capable of GHz sampling and provide a field of view of 8 degrees with its 265 modules of 7 photomultiplier each (for a total of 1855 pixels). In order to validate the performance of NectarCAM, a partially-equipped prototype has been constructed consisting of only the inner 61-modules. It has so far undergone testing at the integration test-bench facility in CEA Paris-Saclay (France) and on a prototype of the MST structure in Adlershof (Germany). To characterize the performance of the prototype, Monte Carlo simulations were conducted using a detailed model of the 61 module camera in the CORSIKA/sim_telarray framework. This contribution provides an overview of this work including the comparison of trigger and readout performance on test-bench data and trigger and image parameterization performance during on-sky measurements.

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Monitoring the pointing of the prototype LST-1 using star reconstruction in the Cherenkov camera

Foffano L., Carosi A., Dalchenko M., Heller M., Della Volpe D., Montaruli T., Abe H., Aguasca A., Agudo I., Antonelli L.A., Aramo C., Armstrong T., Artero M., Asano K., Ashkar H., Aubert P., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Becerra González J., Bernardos M.I., Berti A., Biederbeck N., Bigongiari C., Blanch O., Bonnoli G., Bordas P., Bose D., Bulgarelli A., Burelli I., Buscemi M., Cardillo M., Caroff S., Cassol F., Cerruti M., Chai Y., Cheng K., Chikawa M., Chytka L., Contreras J.L., Cortina J., Costantini H., De Angelis A., de Bony de Lavergne M., Deleglise G., Delgado C., Delgado Mengual J., Depaoli D., Di Pierro F., Di Venere L., Díaz C., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Elsässer D., Emery G., Escudero J., Fiasson A., Fonseca M.V., Freixas Coromina L., Fukami S., Fukazawa Y., Garcia E., Garcia López R., Giglietto N., Giordano F., Gliwny P., Godinovic N., Green D., Grespan P., Gunji S., Hackfeld J., Hadasch D., Hahn A., Hassan T., Hayashi K., Heckmann L., Herrera Llorente J., Hirotani K., Hoffmann D., Horns D., Houles J., Hrabovsky M., Hrupec D., Hui D., Hütten M., Inada T., Inome Y., Iori M., Ishio K., Iwamura Y., Jacquemont M., Jimenez Martinez I., Jouvin L.

Proceedings of Science   Vol. 395   2022.3

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The first Large-Sized Telescope (LST-1) proposed for the forthcoming Cherenkov Telescope Array (CTA) has started to operate in 2019 in La Palma. The large structure of LST-1 - with a 23 m mirror dish diameter - imposes a strict control of its deformations that could affect the pointing accuracy and its overall performance. According to CTA specifications that are conceived to resolve e.g. the fine structure of galactic sources, the LST post-calibration pointing accuracy should be better than 14 arcseconds. To fulfill this requirement, the telescope pointing precision is monitored with two dedicated CCD cameras located at the dish center. The analysis of their images allows us to disentangle different systematic deformations of the structure. In this work, we investigate a complementary approach that offers the possibility to monitor the pointing of the telescope during the acquisition of sky data. After properly cleaning the events from the Cherenkov showers, the reconstructed positions of the stars imaged in the camera field of view are compared to their nominal expected positions in catalogues. This provides a direct measurement of the telescope pointing, that can be used to cross-check the other methods and as a real-time monitoring of the optical properties of the telescope and of the pointing corrections applied by the bending models. Additionally, this method benefits from not relying on specific hardware or dedicated observations. In this contribution we will illustrate this analysis and show results based on simulations of LST-1.

Scopus

HAWC J2227+610: a potential PeVatron candidate for the CTA in the northern hemisphere

Abdalla H., Abe H., Abe S., Abusleme A., Acero F., Acharyya A., Acín Portella V., Ackley K., Adam R., Adams C., Adhikari S.S., Aguado-Ruesga I., Agudo I., Aguilera R., Aguirre-Santaella A., Aharonian F., Alberdi A., Alfaro R., Alfaro J., Alispach C., Aloisio R., Alves Batista R., Amans J.P., Amati L., Amato E., Ambrogi L., Ambrosi G., Ambrosio M., Ammendola R., Anderson J., Anduze M., Angüner E.O., Antonelli L.A., Antonuccio V., Antoranz P., Anutarawiramkul R., Aragunde Gutierrez J., Aramo C., Araudo A., Araya M., Arbet-Engels A., Arcaro C., Arendt V., Armand C., Armstrong T., Arqueros F., Arrabito L., Arsioli B., Artero M., Asano K., Ascasíbar Y., Aschersleben J., Ashley M., Attinà P., Aubert P., Singh C.B., Baack D., Babic A., Backes M., Baena V., Bajtlik S., Baktash A., Balazs C., Balbo M., Ballester O., Ballet J., Balmaverde B., Bamba A., Bandiera R., Baquero Larriva A., Barai P., Barbier C., Barbosa Martins V., Barcelo M., Barkov M., Barnard M., Baroncelli L., Barres de Almeida U., Barrio J.A., Bastieri D., Batista P.I., Batkovic I., Bauer C., Bautista-González R., Baxter J., Becciani U., Becerra González J., Becherini Y., Beck G., Becker Tjus J., Bednarek W., Belfiore A., Bellizzi L., Belmont R., Benbow W., Berge D., Bernardini E., Bernardos M.I., Bernlöhr K., Berti A.

Proceedings of Science   Vol. 395   2022.3

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Recent observations of the gamma-ray source HAWC J2227+610 by Tibet AS+MD and LHAASO confirm the special interest of this source as a galactic PeVatron candidate in the northern hemisphere. HAWC J2227+610 emits Very High Energy (VHE) gamma-rays up to 500 TeV, from a region coincident with molecular clouds and significantly displaced from the nearby pulsar J2229+6114. Even if this morphology favours an hadronic origin, both leptonic or hadronic models can describe the current VHE gamma-ray emission. The morphology of the source is not well constrained by the present measurements and a better characterisation would greatly help the understanding of the underlying particle acceleration mechanisms. The Cherenkov Telescope Array (CTA) will be the future most sensitive Imaging Atmospheric Cherenkov Telescope and, thanks to its unprecedented angular resolution, could contribute to better constrain the nature of this source. The present work investigates the potentiality of CTA to study the morphology and the spectrum of HAWC J2227+610. For this aim, the source is simulated assuming the hadronic model proposed by the Tibet AS+MD collaboration, recently fitted on multi-wavelength data, and two spatial templates associated to the source nearby molecular clouds. Different CTA layouts and observation times are considered. A 3D map based analysis shows that CTA is able to significantly detect the extension of the source and to attribute higher detection significance to the simulated molecular cloud template compared to the alternative one. CTA data does not allow to disentangle the hadronic and the leptonic emission models. However, it permits to correctly reproduce the simulated parent proton spectrum characterized by a ∼ 500 TeV cutoff.

Scopus

First follow-up of transient events with the CTA Large Size Telescope prototype

Kobayshi Y., Sanchez D., Abe H., Aguasca A., Agudo I., Antonelli L.A., Aramo C., Armstrong T., Artero M., Asano K., Ashkar H., Aubert P., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Becerra González J., Bernardos M.I., Berti A., Biederbeck N., Bigongiari C., Blanch O., Bonnoli G., Bordas P., Bose D., Bulgarelli A., Burelli I., Buscemi M., Cardillo M., Caroff S., Carosi A., Cassol F., Cerruti M., Chai Y., Cheng K., Chikawa M., Chytka L., Contreras J.L., Cortina J., Costantini H., Dalchenko M., De Angelis A., de Bony de Lavergne M., Deleglise G., Delgado C., Delgado Mengual J., della Volpe D., Depaoli D., Di Pierro F., Di Venere L., Díaz C., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Elsässer D., Emery G., Escudero J., Fiasson A., Foffano L., Fonseca M.V., Freixas Coromina L., Fukami S., Fukazawa Y., Garcia E., Garcia López R., Giglietto N., Giordano F., Gliwny P., Godinovic N., Green D., Grespan P., Gunji S., 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., Hütten M., Inada T., Inome Y., Iori M., Ishio K., Iwamura Y., Jacquemont M., Jimenez Martinez I.

Proceedings of Science   Vol. 395   2022.3

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The recent detection of a very high energy (VHE) emission from Gamma-Ray Bursts (GRBs) above 100 GeV performed by the MAGIC and H.E.S.S. collaborations, has represented a significant, long-awaited result for the VHE astrophysics community. Although these results' scientific impact has not yet been fully exploited, the possibility to detect VHE gamma-ray signals from GRBs has always been considered crucial for clarifying the poorly known physics of these objects. Furthermore, the discovery of high-energy neutrinos and gravitational waves associated with astrophysical sources have definitively opened the era of multi-messenger astrophysics, providing unique insights into the physics of extreme cosmic accelerators. In the near future, the Cherenkov Telescope Array (CTA) will play a major role in these observations. Within this framework, the Large Size Telescopes (LSTs) will be the instruments best suited to significantly impact on short time-scale transients follow-up thanks to their fast slewing and large effective area. The observations of the early emission phase of a wide range of transient events with good sensitivity below 100 GeV will allow us to open new opportunities for time-domain astrophysics in an energy range not affected by selective absorption processes typical of other wavelengths. In this contribution, we will report about the observational program and first transients follow-up observations performed by the LST-1 telescope currently in its commissioning phase on La Palma, Canary Islands, the CTA northern hemisphere site.

Scopus

Exploring the population of Galactic very-high-energy γ-ray sources

Steppa C., Egberts K., Abdalla H., Abe H., Abe S., Abusleme A., Acero F., Acharyya A., Acín Portella V., Ackley K., Adam R., Adams C., Adhikari S.S., Aguado-Ruesga I., Agudo I., Aguilera R., Aguirre-Santaella A., Aharonian F., Alberdi A., Alfaro R., Alfaro J., Alispach C., Aloisio R., Alves Batista R., Amans J.P., Amati L., Amato E., Ambrogi L., Ambrosi G., Ambrosio M., Ammendola R., Anderson J., Anduze M., Angüner E.O., Antonelli L.A., Antonuccio V., Antoranz P., Anutarawiramkul R., Aragunde Gutierrez J., Aramo C., Araudo A., Araya M., Arbet-Engels A., Arcaro C., Arendt V., Armand C., Armstrong T., Arqueros F., Arrabito L., Arsioli B., Artero M., Asano K., Ascasíbar Y., Aschersleben J., Ashley M., Attinà P., Aubert P., Singh C.B., Baack D., Babic A., Backes M., Baena V., Bajtlik S., Baktash A., Balazs C., Balbo M., Ballester O., Ballet J., Balmaverde B., Bamba A., Bandiera R., Baquero Larriva A., Barai P., Barbier C., Barbosa Martins V., Barcelo M., Barkov M., Barnard M., Baroncelli L., Barres de Almeida U., Barrio J.A., Bastieri D., Batista P.I., Batkovic I., Bauer C., Bautista-González R., Baxter J., Becciani U., Becerra González J., Becherini Y., Beck G., Becker Tjus J., Bednarek W., Belfiore A., Bellizzi L., Belmont R., Benbow W., Berge D., Bernardini E., Bernardos M.I.

Proceedings of Science   Vol. 395   2022.3

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At very high energies (VHE), the emission of γ rays is dominated by discrete sources. Due to the limited resolution and sensitivity of current-generation instruments, only a small fraction of the total Galactic population of VHE γ-ray sources has been detected significantly. The larger part of the population can be expected to contribute as a diffuse signal alongside emission originating from propagating cosmic rays. Without quantifying the source population, it is not possible to disentangle these two components. Based on the H.E.S.S. Galactic plane survey, a numerical approach has been taken to develop a model of the population of Galactic VHE γ-ray sources, which is shown to account accurately for the observational bias. We present estimates of the absolute number of sources in the Galactic Plane and their contribution to the total VHE γ-ray emission for five different spatial source distributions. Prospects for CTA and its ability to constrain the model are discussed. Finally, first results of an extension of our modelling approach using machine learning to extract more information from the available data set are presented.

Scopus

Development of an advanced SiPM camera for the Large Size Telescope of the Cherenkov Telescope Array Observatory

Bellato M., Bergnoli A., Bernasconi E., Biland A., Charbon E., Corti D., Gascón D., Gómez S., Ziȩtara K., Abe H., Aguasca A., Agudo I., Antonelli L.A., Aramo C., Armstrong T., Artero M., Asano K., Ashkar H., Aubert P., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Becerra González J., Bernardos M.I., Berti A., Biederbeck N., Bigongiari C., Blanch O., Bonnoli G., Bordas P., Bose D., Bulgarelli A., Burelli I., Buscemi M., Cardillo M., Caroff S., Carosi A., Cassol F., Cerruti M., Chai Y., Cheng K., Chikawa M., Chytka L., Contreras J.L., Cortina J., Costantini H., Dalchenko M., De Angelis A., de Bony de Lavergne M., Deleglise G., Delgado C., Delgado Mengual J., della Volpe D., Depaoli D., Di Pierro F., Di Venere L., Díaz C., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Elsässer D., Emery G., Escudero J., Fiasson A., Foffano L., Fonseca M.V., Freixas Coromina L., Fukami S., Fukazawa Y., Garcia E., Garcia López R., Giglietto N., Giordano F., Gliwny P., Godinovic N., Green D., Grespan P., Gunji S., 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., Hütten M.

Proceedings of Science   Vol. 395   2022.3

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Silicon photomultipliers (SiPMs) have become the baseline choice for cameras of the small-sized telescopes (SSTs) of the Cherenkov Telescope Array (CTA). On the other hand, SiPMs are relatively new to the field and covering large surfaces and operating at high data rates still are challenges to outperform photomultipliers (PMTs). The higher sensitivity in the near infra-red and longer signals compared to PMTs result in higher night sky background rate for SiPMs. However, the robustness of the SiPMs represents a unique opportunity to ensure long-term operation with low maintenance and better duty cycle than PMTs. The proposed camera for large size telescopes will feature 0.05◦ pixels, low power and fast front-end electronics and a fully digital readout. In this work, we present the status of dedicated simulations and data analysis for the performance estimation. The design features and the different strategies identified, so far, to tackle the demanding requirements and the improved performance are described.

Scopus

Detection of the Crab Nebula by the prototype Schwarzschild-Couder Telescope

Adams C.B., Ambrosi G., Ambrosio M., Aramo C., Batista P.I., Benbow W., Bertucci B., Bissaldi E., Bitossi M., Boiano A., Bonavolontà C., Bose R., Brill A., Brown A.M., Buckley J.H., Cameron R.A., Canestrari R., Capasso M., Caprai M., Covault C.E., Depaoli D., Di Venere L., Errando M., Fegan S., Feng Q., Fiandrini E., Furniss A., Gent A., Giglietto N., Giordano F., Giro E., Halliday R., Hervet O., Holder J., Humensky T.B., Incardona S., Ionica M., Jin W., Kieda D., Licciulli F., Loporchio S., Marsella G., Masone V., Meagher K., Meures T., Mode B.A.W., Mognet S.A.I., Mukherjee R., Okumura A., Otte N., Pantaleo F.R., Paoletti R., Pareschi G., Di Pierro F., Pueschel E., Ribeiro D., Riitano L., Roache E., Rousselle J., Rugliancich A., Santander M., Shang R., Stiaccini L., Tajima H., Taylor L.P., Tosti L., Tovmassian G., Tripodo G., Vagelli V., Valentino M., Vandenbroucke J., Vassiliev V.V., Williams D.A., Zink A.

Proceedings of Science   Vol. 395   2022.3

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The Schwarzschild-Couder Telescope (SCT) is a medium-sized telescope technology proposed for the Cherenkov Telescope Array. It uses a novel dual-mirror optical design that removes comatic aberrations across its entire field of view. The SCT camera employs high-resolution silicon photomultiplier (SiPM) sensors with a pixel size of 4 arcminutes. A prototype SCT (pSCT) has been constructed at the Fred Lawrence Whipple Observatory in Arizona, USA. An observing campaign in 2020, with a partial camera of 1600 pixels (2.7 degrees by 2.7 degrees field of view) resulted in detection of the Crab Nebula at 8.6 sigma statistical significance. Work on the pSCT camera and optical system is ongoing to improve performance and prepare for an upcoming camera upgrade. The pSCT camera upgrade will replace the current camera modules with improved SiPMs and readout electronics and will expand the camera to its full design field of view of 8 degrees in diameter (11,328 pixels). The fully upgraded pSCT will enable next-generation very-high-energy gamma-ray astrophysics through excellent background rejection and angular resolution. In this presentation we describe first results from the successful operation of the pSCT and future plans.

Scopus

Detection methods for the Cherenkov Telescope Array at very-short exposure times

Di Piano A., Bulgarelli A., Fioretti V., Baroncelli L., Parmiggiani N., Longo F., Stamerra A., López-Oramas A., Stratta G., De Cesare G., Abdalla H., Abe H., Abe S., Abusleme A., Acero F., Acharyya A., Acín Portella V., Ackley K., Adam R., Adams C., Adhikari S.S., Aguado-Ruesga I., Agudo I., Aguilera R., Aguirre-Santaella A., Aharonian F., Alberdi A., Alfaro R., Alfaro J., Alispach C., Aloisio R., Alves Batista R., Amans J.P., Amati L., Amato E., Ambrogi L., Ambrosi G., Ambrosio M., Ammendola R., Anderson J., Anduze M., Angüner E.O., Antonelli L.A., Antonuccio V., Antoranz P., Anutarawiramkul R., Aragunde Gutierrez J., Aramo C., Araudo A., Araya M., Arbet-Engels A., Arcaro C., Arendt V., Armand C., Armstrong T., Arqueros F., Arrabito L., Arsioli B., Artero M., Asano K., Ascasíbar Y., Aschersleben J., Ashley M., Attinà P., Aubert P., Singh C.B., Baack D., Babic A., Backes M., Baena V., Bajtlik S., Baktash A., Balazs C., Balbo M., Ballester O., Ballet J., Balmaverde B., Bamba A., Bandiera R., Baquero Larriva A., Barai P., Barbier C., Barbosa Martins V., Barcelo M., Barkov M., Barnard M., Barres de Almeida U., Barrio J.A., Bastieri D., Batista P.I., Batkovic I., Bauer C., Bautista-González R., Baxter J., Becciani U., Becerra González J., Becherini Y., Beck G., Becker Tjus J., Bednarek W.

Proceedings of Science   Vol. 395   2022.3

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The Cherenkov Telescope Array (CTA) will be the next generation ground-based observatory for very-high-energy (VHE) gamma-ray astronomy, with the deployment of tens of highly sensitive and fast-reacting Cherenkov telescopes. It will cover a wide energy range (20 GeV - 300 TeV) with unprecedented sensitivity. To maximize the scientific return, the observatory will be provided with an online software system that will perform the first analysis of scientific data in real-time. This study investigates the precision and accuracy of available science tools and analysis techniques for the short-term detection of gamma-ray sources, in terms of sky localization, detection significance and, if significant detection is achieved, a first estimation of the integral photon flux. The scope is to evaluate the feasibility of the algorithms' implementation in the real-time analysis of CTA. In this contribution we present a general overview of the methods and some of the results for the test case of the short-term detection of a gamma-ray burst afterglow, as the VHE counterpart of a gravitational wave event.

Scopus

Design and performance of the prototype Schwarzschild-Couder Telescope camera

Taylor L.P., Adams C.B., Ambrosi G., Ambrosio M., Aramo C., Batista P.I., Benbow W., Bertucci B., Bissaldi E., Bitossi M., Boiano A., Bonavolontà C., Bose R., Brill A., Brown A.M., Buckley J.H., Cameron R.A., Capasso M., Caprai M., Covault C.E., Depaoli D., Di Venere L., Errando M., Fegan S., Feng Q., Fiandrini E., Furniss A., Gent A., Giglietto N., Giordano F., Halliday R., Hervet O., Humensky T.B., Incardona S., Ionica M., Jin W., Kieda D., Licciulli F., Loporchio S., Marsella G., Masone V., Meagher K., Meures T., Mode B.A.W., Mognet S.A.I., Mukherjee R., Okumura A., Otte N., Pantaleo F.R., Paoletti R., Pareschi G., Di Pierro F., Pueschel E., Ribeiro D., Riitano L., Roache E., Ross D., Rousselle J., Rugliancich A., Santander M., Shang R., Stiaccini L., Tajima H., Taylor L.P., Tosti L., Tovmassian G., Tripodo G., Vagelli V., Valentino M., Vandenbroucke J., Vassiliev V.V., Watson J.J., White R., Williams D.A., Zink A.

Proceedings of Science   Vol. 395   2022.3

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The Cherenkov Telescope Array (CTA) is the next-generation ground-based observatory for very-high-energy gamma-ray astronomy. An innovative 9.7 m aperture, dual-mirror Schwarzschild-Couder Telescope (SCT) design is a candidate design for CTA Medium-Sized Telescopes. A prototype SCT (pSCT) has been constructed at the Fred Lawrence Whipple Observatory in Arizona, USA. Its camera is currently partially instrumented with 1600 pixels covering a field of view of 2.7 degrees square. The small plate scale of the optical system allows densely packed silicon photomultipliers to be used, which combined with high-density trigger and waveform readout electronics enable the high-resolution camera. The camera's electronics are capable of imaging air shower development at a rate of one billion samples per second. We describe the commissioning and performance of the pSCT camera, including trigger and waveform readout performance, calibration, and absolute GPS time stamping. We also present the upgrade to the camera, which is currently underway. The upgrade will fully populate the focal plane, increasing the field of view to 8 degree diameter, and lower the front-end electronics noise, enabling a lower trigger threshold and improved reconstruction and background rejection.

Scopus

Deep-learning-driven event reconstruction applied to simulated data from a single Large-Sized Telescope of CTA

Abe H., Aguasca A., Agudo I., Antonelli L.A., Aramo C., Armstrong T., Artero M., Asano K., Ashkar H., Aubert P., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Becerra González J., Bernardos M.I., Berti A., Biederbeck N., Bigongiari C., Blanch O., Bonnoli G., Bordas P., Bose D., Bulgarelli A., Burelli I., Buscemi M., Cardillo M., Caroff S., Carosi A., Cassol F., Cerruti M., Chai Y., Cheng K., Chikawa M., Chytka L., Contreras J.L., Cortina J., Costantini H., Dalchenko M., De Angelis A., de Bony de Lavergne M., Deleglise G., Delgado C., Delgado Mengual J., della Volpe D., Depaoli D., Di Pierro F., Di Venere L., Díaz C., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Elsässer D., Emery G., Escudero J., Fiasson A., Foffano L., Fonseca M.V., Freixas Coromina L., Fukami S., Fukazawa Y., Garcia E., Garcia López R., Giglietto N., Giordano F., Gliwny P., Godinovic N., Green D., Grespan P., Gunji S., 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., Hütten M., Inada T., Inome Y., Iori M., Ishio K., Iwamura Y., Jacquemont M., Jimenez Martinez I., Jouvin L., Jurysek J.

Proceedings of Science   Vol. 395   2022.3

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When very-high-energy gamma rays interact high in the Earth's atmosphere, they produce cascades of particles that induce flashes of Cherenkov light. Imaging Atmospheric Cherenkov Telescopes (IACTs) detect these flashes and convert them into shower images that can be analyzed to extract the properties of the primary gamma ray. The dominant background for IACTs is comprised of air shower images produced by cosmic hadrons, with typical noise-to-signal ratios of several orders of magnitude. The standard technique adopted to differentiate between images initiated by gamma rays and those initiated by hadrons is based on classical machine learning algorithms, such as Random Forests, that operate on a set of handcrafted parameters extracted from the images. Likewise, the inference of the energy and the arrival direction of the primary gamma ray is performed using those parameters. State-of-the-art deep learning techniques based on convolutional neural networks (CNNs) have the potential to enhance the event reconstruction performance, since they are able to autonomously extract features from raw images, exploiting the pixel-wise information washed out during the parametrization process. Here we present the results obtained by applying deep learning techniques to the reconstruction of Monte Carlo simulated events from a single, next-generation IACT, the Large-Sized Telescope (LST) of the Cherenkov Telescope Array (CTA). We use CNNs to separate the gamma-ray-induced events from hadronic events and to reconstruct the properties of the former, comparing their performance to the standard reconstruction technique. Three independent implementations of CNN-based event reconstruction models have been utilized in this work, producing consistent results.

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Cross-calibration and combined analysis of the CTA-LST prototype and the MAGIC telescopes

Ohtani Y., Berti A., Depaoli D., Di Pierro F., Green D., Heckmann L., Hütten M., Inada T., López-Coto R., Medina E., Moralejo A., Morcuende D., Pirola G., Strzys M., Suda Y., Vovk I., Abe H., Aguasca A., Agudo I., Antonelli L.A., Aramo C., Armstrong T., Artero M., Asano K., Ashkar H., Aubert P., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Becerra González J., Bernardos M.I., Biederbeck N., Bigongiari C., Blanch O., Bonnoli G., Bordas P., Bose D., Bulgarelli A., Burelli I., Buscemi M., Cardillo M., Caroff S., Carosi A., Cassol F., Cerruti M., Chai Y., Cheng K., Chikawa M., Chytka L., Contreras J.L., Cortina J., Costantini H., Dalchenko M., De Angelis A., de Bony de Lavergne M., Deleglise G., Delgado C., Delgado Mengual J., della Volpe D., Di Venere L., Díaz C., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Elsässer D., Emery G., Escudero J., Fiasson A., Foffano L., Fonseca M.V., Freixas Coromina L., Fukami S., Fukazawa Y., Garcia E., Garcia López R., Giglietto N., Giordano F., Gliwny P., Godinovic N., Grespan P., Gunji S., Hackfeld J., Hadasch D., Hahn A., Hassan T., Hayashi K., Heller M., Herrera Llorente J., Hirotani K., Hoffmann D., Horns D., Houles J., Hrabovsky M., Hrupec D.

Proceedings of Science   Vol. 395   2022.3

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The Cherenkov Telescope Array (CTA) will be the next generation gamma-ray observatory, which will consist of three kinds of telescopes of different sizes. Among those, the Large Size Telescope (LST) will be the most sensitive in the low energy range starting from 20 GeV. The prototype LST (LST-1) proposed for CTA was inaugurated in October 2018 in the northern hemisphere site, La Palma (Spain), and is currently in its commissioning phase. MAGIC is a system of two gamma-ray Cherenkov telescopes of the current generation, located approximately 100 m away from LST-1, that have been operating in stereoscopic mode since 2009. Since LST-1 and MAGIC can observe the same air shower events, we can compare the brightness of showers, estimated energies of gamma rays, and other parameters event by event, which can be used to cross-calibrate the telescopes. Ultimately, by performing combined analyses of the events triggering the three telescopes, we can reconstruct the shower geometry more accurately, leading to better energy and angular resolutions, and a better discrimination of the background showers initiated by cosmic rays. For that purpose, as part of the commissioning of LST-1, we performed joint observations of established gamma-ray sources with LST-1 and MAGIC. Also, we have developed Monte Carlo simulations for such joint observations and an analysis pipeline which finds event coincidence in the offline analysis based on their timestamps. In this work, we present the first detection of an astronomical source, the Crab Nebula, with combined observation of LST-1 and MAGIC. Moreover, we show results of the inter-telescope cross-calibration obtained using Crab Nebula data taken during joint observations with LST-1 and MAGIC.

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Commissioning of the camera of the first Large Size Telescope of the Cherenkov Telescope Array

Saito T., Delgado C., Blanch O., Artero M., Barrio J.A., Cassol F., Diaz C., Hadasch D., Hoffmann D., Houles J., Inome Y., Iori M., Jouvin L., Kerszberg D., Kobayashi Y., Kubo H., Martinez G., Mazin D., Moretti E., Nakamori T., Nozaki S., Oka T., Okumura A., Palatiello M., Polo M., Prast J., Sakurai S., Sunada Y., Takahashi M., Takeishi R., Tejedor L.A., Yamamoto T., Yoshida T., Abe H., Aguasca A., Agudo I., Antonelli L.A., Aramo C., Armstrong T., Asano K., Ashkar H., Aubert P., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Batkovic I., Becerra González J., Bernardos M.I., Berti A., Biederbeck N., Bigongiari C., Bonnoli G., Bordas P., Bose D., Bulgarelli A., Burelli I., Buscemi M., Cardillo M., Caroff S., Carosi A., Cerruti M., Chai Y., Cheng K., Chikawa M., Chytka L., Contreras J.L., Cortina J., Costantini H., Dalchenko M., De Angelis A., de Bony de Lavergne M., Deleglise G., Delgado Mengual J., della Volpe D., Depaoli D., Di Pierro F., Di Venere L., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Elsässer D., Emery G., Escudero J., Fiasson A., Foffano L., Fonseca M.V., Freixas Coromina L., Fukami S., Fukazawa Y., Garcia E., Garcia López R., Giglietto N., Giordano F., Gliwny P., Godinovic N., Green D.

Proceedings of Science   Vol. 395   2022.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of Science  

The first Large Size Telescope (LST-1) of the Cherenkov Telescope Array has been operational since October 2018 at La Palma, Spain. We report on the results obtained during the camera commissioning. The noise level of the readout is determined as a 0.2 p.e. level. The gain of PMTs are well equalized within 2% variation, using the calibration flash system. The effect of the night sky background on the signal readout noise as well as the PMT gain estimation are also well evaluated. Trigger thresholds are optimized for the lowest possible gamma-ray energy threshold and the trigger distribution synchronization has been achieved within 1 ns precision. Automatic rate control realizes the stable observation with 1.5% rate variation over 3 hours. The performance of the novel DAQ system demonstrates a less than 10% dead time for 15 kHz trigger rate even with sophisticated online data correction.

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Camera Calibration of the CTA-LST prototype

Kobayashi Y., Okumura A., Cassol F., Katagiri H., Sitarek J., Gliwny P., Nozaki S., Nogami Y., Abe H., Aguasca A., Agudo I., Antonelli L.A., Aramo C., Armstrong T., Artero M., Asano K., Ashkar H., Aubert P., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Becerra Gonzalez J., Bernardos M.I., Berti A., Biederbeck N., Bigongiari C., Blanch O., Bonnoli G., Bordas P., Bose D., Bulgarelli A., Burelli I., Buscemi M., Cardillo M., Caroff S., Carosi A., Cerruti M., Chai Y., Cheng K., Chikawa M., Chytka L., Contreras J.L., Cortina J., Costantini H., Dalchenko M., De Angelis A., de Bony de Lavergne M., Deleglise G., Delgado C., Delgado Mengual J., della Volpe D., Depaoli D., Di Pierro F., Di Venere L., Daaz C., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Elsaasser D., Emery G., Escudero J., Fiasson A., Foffano L., Fonseca M.V., Freixas Coromina L., Fukami S., Fukazawa Y., Garcia E., Garcia Lapez R., Giglietto N., Giordano F., Godinovic N., Green D., Grespan P., Gunji S., 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., HÃŒtten M., Inada T., Inome Y., Iori M.

Proceedings of Science   Vol. 395   2022.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of Science  

The Cherenkov Telescope Array (CTA) is the next-generation gamma-ray observatory that is expected to reach one order of magnitude better sensitivity than that of current telescope arrays. The Large-Sized Telescopes (LSTs) have an essential role in extending the energy range down to 20 GeV. The prototype LST (LST-1) proposed for CTA was built in La Palma, the northern site of CTA, in 2018. LST-1 is currently in its commissioning phase and moving towards scientific observations. The LST-1 camera consists of 1855 photomultiplier tubes (PMTs) which are sensitive to Cherenkov light. PMT signals are recorded as waveforms sampled at 1 GHz rate with Domino Ring Sampler version 4 (DRS4) chips. Fast sampling is essential to achieve a low energy threshold by minimizing the integration of background light from the night sky. Absolute charge calibration can be performed by the so-called F-factor method, which allows calibration constants to be monitored even during observations. A calibration pipeline of the camera readout has been developed as part of the LST analysis chain. The pipeline performs DRS4 pedestal and timing corrections, as well as the extraction and calibration of charge and time of pulses for subsequent higher-level analysis. The performance of each calibration step is examined, and especially charge and time resolution of the camera readout are evaluated and compared to CTA requirements. We report on the current status of the calibration pipeline, including the performance of each step through to signal reconstruction, and the consistency with Monte Carlo simulations.

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Application of pattern spectra and convolutional neural networks to the analysis of simulated Cherenkov Telescope Array data

Aschersleben J., Peletier R.F., Vecchi M., Wilkinson M.H.F., Abdalla H., Abe H., Abe S., Abusleme A., Acero F., Acharyya A., Acín Portella V., Ackley K., Adam R., Adams C., Adhikari S.S., Aguado-Ruesga I., Agudo I., Aguilera R., Aguirre-Santaella A., Aharonian F., Alberdi A., Alfaro R., Alfaro J., Alispach C., Aloisio R., Alves Batista R., Amans J.P., Amati L., Amato E., Ambrogi L., Ambrosi G., Ambrosio M., Ammendola R., Anderson J., Anduze M., Angüner E.O., Antonelli L.A., Antonuccio V., Antoranz P., Anutarawiramkul R., Aragunde Gutierrez J., Aramo C., Araudo A., Araya M., Arbet-Engels A., Arcaro C., Arendt V., Armand C., Armstrong T., Arqueros F., Arrabito L., Arsioli B., Artero M., Asano K., Ascasíbar Y., Ashley M., Attinà P., Aubert P., Singh C.B., Baack D., Babic A., Backes M., Baena V., Bajtlik S., Baktash A., Balazs C., Balbo M., Ballester O., Ballet J., Balmaverde B., Bamba A., Bandiera R., Baquero Larriva A., Barai P., Barbier C., Barbosa Martins V., Barcelo M., Barkov M., Barnard M., Baroncelli L., Barres de Almeida U., Barrio J.A., Bastieri D., Batista P.I., Batkovic I., Bauer C., Bautista-González R., Baxter J., Becciani U., Becerra González J., Becherini Y., Beck G., Becker Tjus J., Bednarek W., Belfiore A., Bellizzi L., Belmont R., Benbow W., Berge D., Bernardini E.

Proceedings of Science   Vol. 395   2022.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of Science  

The Cherenkov Telescope Array (CTA) will be the next generation gamma-ray observatory and will be the major global instrument for very-high-energy astronomy over the next decade, offering 5 − 10 × better flux sensitivity than current generation gamma-ray telescopes. Each telescope will provide a snapshot of gamma-ray induced particle showers by capturing the induced Cherenkov emission at ground level. The simulation of such events provides images that can be used as training data for convolutional neural networks (CNNs) to determine the energy of the initial gamma rays. Compared to other state-of-the-art algorithms, analyses based on CNNs promise to further enhance the performance to be achieved by CTA. Pattern spectra are commonly used tools for image classification and provide the distributions of the shapes and sizes of various objects comprising an image. The use of relatively shallow CNNs on pattern spectra would automatically select relevant combinations of features within an image, taking advantage of the 2D nature of pattern spectra. In this work, we generate pattern spectra from simulated gamma-ray events instead of using the raw images themselves in order to train our CNN for energy reconstruction. This is different from other relevant learning and feature selection methods that have been tried in the past. Thereby, we aim to obtain a significantly faster and less computationally intensive algorithm, with minimal loss of performance.

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Analysis of the Cherenkov Telescope Array first Large-Sized Telescope real data using convolutional neural networks

Vuillaume T., Jacquemont M., de Bony de Lavergne M., Sanchez D.A., Poireau V., Maurin G., Benoit A., Lambert P., Lamanna G., Abe H., Aguasca A., Agudo I., Antonelli L.A., Aramo C., Armstrong T., Artero M., Asano K., Ashkar H., Aubert P., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Becerra González J., Bernardos M.I., Berti A., Biederbeck N., Bigongiari C., Blanch O., Bonnoli G., Bordas P., Bose D., Bulgarelli A., Burelli I., Buscemi M., Cardillo M., Caroff S., Carosi A., Cassol F., Cerruti M., Chai Y., Cheng K., Chikawa M., Chytka L., Contreras J.L., Cortina J., Costantini H., Dalchenko M., De Angelis A., Deleglise G., Delgado C., Delgado Mengual J., della Volpe D., Depaoli D., Di Pierro F., Di Venere L., Díaz C., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Elsässer D., Emery G., Escudero J., Fiasson A., Foffano L., Fonseca M.V., Freixas Coromina L., Fukami S., Fukazawa Y., Garcia E., Garcia López R., Giglietto N., Giordano F., Gliwny P., Godinovic N., Green D., Grespan P., Gunji S., 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., Hütten M., Inada T.

Proceedings of Science   Vol. 395   2022.3

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The Cherenkov Telescope Array (CTA) is the future ground-based gamma-ray observatory and will be composed of two arrays of imaging atmospheric Cherenkov telescopes (IACTs) located in the Northern and Southern hemispheres respectively. The first CTA prototype telescope built on-site, the Large-Sized Telescope (LST-1), is under commissioning in La Palma and has already taken data on numerous known sources. IACTs detect the faint flash of Cherenkov light indirectly produced after a very energetic gamma-ray photon has interacted with the atmosphere and generated an atmospheric shower. Reconstruction of the characteristics of the primary photons is usually done using a parameterization up to the third order of the light distribution of the images. In order to go beyond this classical method, new approaches are being developed using state-of-the-art methods based on convolutional neural networks (CNN) to reconstruct the properties of each event (incoming direction, energy and particle type) directly from the telescope images. While promising, these methods are notoriously difficult to apply to real data due to differences (such as different levels of night sky background) between Monte Carlo (MC) data used to train the network and real data. The GammaLearn project, based on these CNN approaches, has already shown an increase in sensitivity on MC simulations for LST-1 as well as a lower energy threshold. This work applies the GammaLearn network to real data acquired by LST-1 and compares the results to the classical approach that uses random forests trained on extracted image parameters. The improvements on the background rejection, event direction, and energy reconstruction are discussed in this contribution.

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Performance of a proposed event-type based analysis for the Cherenkov Telescope Array

Hassan T., Abdalla H., Abe H., Abe S., Abusleme A., Acero F., Acharyya A., Acín Portella V., Ackley K., Adam R., Adams C., Adhikari S.S., Aguado-Ruesga I., Agudo I., Aguilera R., Aguirre-Santaella A., Aharonian F., Alberdi A., Alfaro R., Alfaro J., Alispach C., Aloisio R., Alves Batista R., Amans J.P., Amati L., Amato E., Ambrogi L., Ambrosi G., Ambrosio M., Ammendola R., Anderson J., Anduze M., Angüner E.O., Antonelli L.A., Antonuccio V., Antoranz P., Anutarawiramkul R., Aragunde Gutierrez J., Aramo C., Araudo A., Araya M., Arbet-Engels A., Arcaro C., Arendt V., Armand C., Armstrong T., Arqueros F., Arrabito L., Arsioli B., Artero M., Asano K., Ascasíbar Y., Aschersleben J., Ashley M., Attinà P., Aubert P., Singh C.B., Baack D., Babic A., Backes M., Baena V., Bajtlik S., Baktash A., Balazs C., Balbo M., Ballester O., Ballet J., Balmaverde B., Bamba A., Bandiera R., Baquero Larriva A., Barai P., Barbier C., Barbosa Martins V., Barcelo M., Barkov M., Barnard M., Baroncelli L., Barres de Almeida U., Barrio J.A., Bastieri D., Batista P.I., Batkovic I., Bauer C., Bautista-González R., Baxter J., Becciani U., Becerra González J., Becherini Y., Beck G., Becker Tjus J., Bednarek W., Belfiore A., Bellizzi L., Belmont R., Benbow W., Berge D., Bernardini E., Bernardos M.I., Bernlöhr K.

Proceedings of Science   Vol. 395   2022.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of Science  

The Cherenkov Telescope Array (CTA) will be the next-generation observatory in the field of very-high-energy (20 GeV to 300 TeV) gamma-ray astroparticle physics. Classically, data analysis in the field maximizes sensitivity by applying quality cuts on the data acquired. These cuts, optimized using Monte Carlo simulations, select higher quality events from the initial dataset. Subsequent steps of the analysis typically use the surviving events to calculate one set of instrument response functions (IRFs). An alternative approach is the use of event types, as implemented in experiments such as the Fermi-LAT. In this approach, events are divided into sub-samples based on their reconstruction quality, and a set of IRFs is calculated for each sub-sample. The sub-samples are then combined in a joint analysis, treating them as independent observations. This leads to an improvement in performance parameters such as sensitivity, angular and energy resolution. Data loss is reduced since lower quality events are included in the analysis as well, rather than discarded. In this study, machine learning methods will be used to classify events according to their expected angular reconstruction quality. We will report the impact on CTA high-level performance when applying such an event-type classification, compared to the classical procedure.

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