Multiwavelength study of the galactic PeVatron candidate LHAASO J2108+5157
- Autori: 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 Gonzalez 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 Lavergne M.D.B.; De Lotto B.; De Menezes R.; Deleglise G.; Delgado C.; Mengual J.D.; Volpe D.D.; Dellaiera M.; Di Piano A.; Di Pierro F.; Di Tria R.; Di Venere L.; Diaz C.; Dominik R.M.; Prester D.D.; Donini A.; Dorner D.; Doro M.; Elsasser D.; Emery G.; Escudero J.; Ramazani V.F.; Ferrara G.; Fiasson A.; Coromina L.F.; Frose S.; Fukami S.; Fukazawa Y.; Garcia E.; Lopez R.G.; Gasparrini D.; Geyer D.; Paiva J.G.; 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 J.H.; Hirotani K.; Hoffmann D.; Horns D.; Houles J.; Hrabovsky M.; Hrupec D.; Hui D.; Hutten M.; Imazawa R.; Inada T.; Inome Y.; Ioka K.; Iori M.; Ishio K.; Iwamura Y.; Jacquemont M.; Martinez I.J.; 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.; Lopez-Coto R.; Lopez-Moya M.; Lopez-Oramas A.; Loporchio S.; Lorini A.; Luque-Escamilla P.L.; Majumdar P.; Makariev M.; Mandat D.; Manganaro M.; Manico G.; Mannheim K.; Mariotti M.; Marquez P.; Marsella G.; Marti J.; Martinez O.; Martinez G.; Martinez M.; Marusevec P.; Mas-Aguilar A.; Maurin G.; Mazin D.; Guillen E.M.; Micanovic S.; Miceli D.; Miener T.; Miranda J.M.; Mirzoyan R.; Mizuno T.; Gonzalez M.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.; 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.; Ribo M.; Rizi V.; Fernandez G.R.; Saito T.; Sakurai S.; Sanchez D.A.; Saric T.; Saturni F.G.; Scherpenberg J.; Schleicher B.; Schmuckermaier F.; Schubert J.L.; Schussler F.; Schweizer T.; Arroyo M.S.; 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 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.; Acosta M.V.; 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 N.; Balbo M.; Eckert D.; Tramacere A.
- Anno di pubblicazione: 2023
- Tipologia: Articolo in rivista
- OA Link: http://hdl.handle.net/10447/615786
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 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.