Multiwavelength study of the galactic PeVatron candidate LHAASO J2108+5157

DOI: 
10.1051/0004-6361/202245086
Publication date: 
13/05/2023
Main author: 
Abe, S.
IAA authors: 
Agudo, I.;Bernardos, M. I.;Escudero, J.;López-Coto, R.
Authors: 
Abe, S.;Aguasca-Cabot, A.;Agudo, I.;Alvarez Crespo, N.;Antonelli, L. A.;Aramo, C.;Arbet-Engels, A.;Artero, M.;Asano, K.;Aubert, P.;Baktash, A.;Bamba, A.;Baquero Larriva, A.;Baroncelli, L.;Barres de Almeida, U.;Barrio, J. A.;Batkovic, I.;Baxter, J.;Becerra González, J.;Bernardini, E.;Bernardos, M. I.;Bernete Medrano, J.;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, J. L.;Cortina, J.;Costantini, H.;D'Amico, G.;Dalchenko, M.;De Angelis, A.;de Bony de Lavergne, M.;De Lotto, B.;de Menezes, R.;Deleglise, G.;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.;Dorner, D.;Doro, M.;Elsässer, D.;Emery, G.;Escudero, J.;Fallah Ramazani, V.;Ferrara, G.;Fiasson, A.;Freixas Coromina, L.;Fröse, S.;Fukami, S.;Fukazawa, Y.;Garcia, E.;Garcia López, R.;Gasparrini, D.;Geyer, D.;Giesbrecht Paiva, J.;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.;Herrera Llorente, J.;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.;Jimenez Martinez, I.;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, P. L.;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.;Mestre Guillen, E.;Micanovic, S.;Miceli, D.;Miener, T.;Miranda, J. M.;Mirzoyan, R.;Mizuno, T.;Molero Gonzalez, M.;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, F. R.;Paoletti, R.;Paredes, J. M.;Pavletić, 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.;Rodriguez Fernandez, G.;Saito, T.;Sakurai, S.;Sanchez, D. A.;Šarić, T.;Saturni, F. G.;Scherpenberg, J.;Schleicher, B.;Schmuckermaier, F.;Schubert, J. L.;Schussler, F.;Schweizer, T.;Seglar Arroyo, M.;Sitarek, J.;Sliusar, V.;Spolon, A.;Strišković, J.;Strzys, M.;Suda, Y.;Sunada, Y.;Tajima, H.;Takahashi, M.;Takahashi, H.;Takata, J.;Takeishi, R.;Tam, P. H. T.;Tanaka, S. J.;Tateishi, D.;Temnikov, P.;Terada, Y.;Terauchi, K.;Terzic, T.;Teshima, M.;Tluczykont, M.;Tokanai, F.;Torres, D. F.;Travnicek, P.;Truzzi, S.;Tutone, A.;Uhlrich, G.;Vacula, M.;Vázquez Acosta, M.;Verguilov, V.;Viale, I.;Vigliano, A.;Vigorito, C. F.;Vitale, V.;Voutsinas, G.;Vovk, I.;Vuillaume, T.;Walter, R.;Will, M.;Yamamoto, T.;Yamazaki, R.;Yoshida, T.;Yoshikoshi, T.;Zywucka (CTA-LST Project), N.;Balbo, M.;Eckert, D.;Tramacere, A.
Journal: 
Astronomy and Astrophysics
Publication type: 
Article
Volume: 
673
Pages: 
A75
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. <BR /> 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. <BR /> 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. <BR /> Results: We found an excess (3.7σ) in the LST-1 data at energies E &gt; 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. <BR /> 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<SUB>−30</SUB><SUP>+70</SUP> 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 π<SUP>0</SUP> 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.
Database: 
ADS
URL: 
https://ui.adsabs.harvard.edu/#abs/2023A&A...673A..75A/abstract
ADS Bibcode: 
2023A&A...673A..75A
Keywords: 
gamma rays: general;radiation mechanisms: non-thermal;pulsars: general;ISM: individual objects: LHAASO J2108+5157;Astrophysics - High Energy Astrophysical Phenomena