Multiwavelength study of the galactic PeVatron candidate LHAASO J2108 5157 S. Abe1A. Aguasca-Cabot2I. Agudo3N. Alvarez Crespo4L. A. Antonelli5

2025-05-02 0 0 2.97MB 26 页 10玖币
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Multiwavelength study of the galactic PeVatron candidate LHAASO
J2108+5157
S. Abe1A. Aguasca-Cabot2I. Agudo3N. Alvarez Crespo4L. A. Antonelli5
C. Aramo6A. Arbet-Engels7M. Artero8K. Asano1P. Aubert9A. Baktash10
A. Bamba11 A. Baquero Larriva12 L. Baroncelli13 U. Barres de Almeida14
J. A. Barrio12 I. Batkovic15 J. Baxter1J. Becerra Gonz´
alez16 E. Bernardini15
M. I. Bernardos3J. Bernete Medrano17 A. Berti7P. Bhattacharjee9
N. Biederbeck18 C. Bigongiari5E. Bissaldi19 O. Blanch8P. Bordas2
C. Buisson9A. Bulgarelli13 I. Burelli20 M. Buscemi21 M. Cardillo22
S. Caroff9A. Carosi5F. Cassol23 D. Cauz20 G. Ceribella1Y. Chai7
K. Cheng1A. Chiavassa24 M. Chikawa1L. Chytka25 A. Cifuentes17
J. L. Contreras12 J. Cortina17 H. Costantini23 G. D’Amico26 M. Dalchenko27
A. De Angelis15 M. de Bony de Lavergne9B. De Lotto20 R. de Menezes24
G. Deleglise9C. Delgado17 J. Delgado Mengual28 D. della Volpe27 M. Dellaiera9
A. Di Piano13 F. Di Pierro24 R. Di Tria29 L. Di Venere29 C. D´
ıaz17
R. M. Dominik18 D. Dominis Prester30 A. Donini8D. Dorner31 M. Doro15
D. Els¨
asser18 G. Emery27 J. Escudero3V. Fallah Ramazani32 G. Ferrara21
A. Fiasson9,33 L. Freixas Coromina17 S. Fr¨
ose18 S. Fukami1Y. Fukazawa34
E. Garcia9R. Garcia L´
opez16 D. Gasparrini35 D. Geyer18 J. Giesbrecht Paiva14
N. Giglietto19 F. Giordano29 E. Giro15 P. Gliwny36 N. Godinovic37 R. Grau8
D. Green7J. Green7S. Gunji38 J. Hackfeld32 D. Hadasch1A. Hahn7
K. Hashiyama1T. Hassan17 K. Hayashi39 L. Heckmann7M. Heller27
J. Herrera Llorente16 K. Hirotani1D. Hoffmann23 D. Horns10 J. Houles23
M. Hrabovsky25 D. Hrupec40 D. Hui1M. H¨
utten1R. Imazawa34 T. Inada1
Y. Inome1K. Ioka41 M. Iori42 K. Ishio36 Y. Iwamura1M. Jacquemont9
I. Jimenez Martinez17 J. Jurysek43*M. Kagaya1V. Karas44 H. Katagiri45
J. Kataoka46 D. Kerszberg8Y. Kobayashi1A. Kong1H. Kubo1J. Kushida47
M. Lainez12 G. Lamanna9A. Lamastra5T. Le Flour9M. Linhoff18
F. Longo48 R. L´
opez-Coto3M. L´
opez-Moya12 A. L´
opez-Oramas16
S. Loporchio29 A. Lorini49 P. L. Luque-Escamilla50 P. Majumdar1,51
M. Makariev52 D. Mandat53 M. Manganaro30 G. Manic`
o21 K. Mannheim31
M. Mariotti15 P. Marquez8G. Marsella21,54 J. Mart´
ı50 O. Martinez4
G. Mart´
ınez17 M. Mart´
ınez8P. Marusevec55 A. Mas-Aguilar12 G. Maurin9
D. Mazin1,7E. Mestre Guillen56 S. Micanovic30 D. Miceli15 T. Miener12
J. M. Miranda4R. Mirzoyan7T. Mizuno57 M. Molero Gonzalez16 E. Molina2
T. Montaruli27 I. Monteiro9A. Moralejo8D. Morcuende12 A. Morselli35
K. Mrakovcic30 K. Murase1A. Nagai27 T. Nakamori38 L. Nickel18
1
arXiv:2210.00775v4 [astro-ph.HE] 16 Mar 2023
M. Nievas16 K. Nishijima47 K. Noda1D. Nosek58 S. Nozaki7M. Ohishi1
Y. Ohtani1N. Okazaki1A. Okumura59,60 R. Orito61 J. Otero-Santos16
M. Palatiello20 D. Paneque7F. R. Pantaleo19 R. Paoletti49 J. M. Paredes2
L. Pavleti´
c30 M. Pech53 M. Pecimotika30 E. Pietropaolo62 G. Pirola7?
F. Podobnik49 V. Poireau9M. Polo17 E. Pons9E. Prandini15 J. Prast9
C. Priyadarshi8M. Prouza53 R. Rando15 W. Rhode18 M. Rib´
o2V. Rizi62
G. Rodriguez Fernandez35 T. Saito1S. Sakurai1D. A. Sanchez9T. ˇ
Sari´
c37
F. G. Saturni5J. Scherpenberg7B. Schleicher31 F. Schmuckermaier7
J. L. Schubert18 F. Schussler63 T. Schweizer7M. Seglar Arroyo9J. Sitarek36
V. Sliusar43 A. Spolon15 J. Striˇ
skovi´
c40 M. Strzys1Y. Suda34 Y. Sunada64
H. Tajima59 M. Takahashi1H. Takahashi34 J. Takata1R. Takeishi1
P. H. T. Tam1S. J. Tanaka65 D. Tateishi64 P. Temnikov52 Y. Terada64
K. Terauchi66 T. Terzic30 M. Teshima1,7M. Tluczykont10 F. Tokanai38
D. F. Torres56 P. Travnicek53 S. Truzzi49 A. Tutone5G. Uhlrich27
M. Vacula25 M. V´
azquez Acosta16 V. Verguilov52 I. Viale15 A. Vigliano20
C. F. Vigorito24,67 V. Vitale35 G. Voutsinas27 I. Vovk1T. Vuillaume9
R. Walter43?M. Will7T. Yamamoto68 R. Yamazaki65 T. Yoshida45
T. Yoshikoshi1N. Zywucka36 (CTA-LST Project) M. Balbo43?D. Eckert43?
A. Tramacere43?
1Institute for Cosmic Ray Research, University of Tokyo, 5-1-5, Kashiwa-no-ha, Kashiwa, Chiba
277-8582, Japan ; 2Departament de F´
ısica Qu`
antica i Astrof´
ısica, Institut de Ci`
encies del Cosmos,
Universitat de Barcelona, IEEC-UB, Mart´
ı i Franqu`
es, 1, 08028, Barcelona, Spain ; 3Instituto de
Astrof´
ısica de Andaluc´
ıa-CSIC, Glorieta de la Astronom´
ıa s/n, 18008, Granada, Spain ; 4Grupo de
Electronica, Universidad Complutense de Madrid, Av. Complutense s/n, 28040 Madrid, Spain ;
5INAF - Osservatorio Astronomico di Roma, Via di Frascati 33, 00040, Monteporzio Catone, Italy ;
6INFN Sezione di Napoli, Via Cintia, ed. G, 80126 Napoli, Italy ; 7Max-Planck-Institut f¨
ur Physik,
F¨
ohringer Ring 6, 80805 M¨
unchen, Germany ; 8Institut de Fisica d’Altes Energies (IFAE), The
Barcelona Institute of Science and Technology, Campus UAB, 08193 Bellaterra (Barcelona), Spain ;
9Univ. Savoie Mont Blanc, CNRS, Laboratoire d’Annecy de Physique des Particules - IN2P3, 74000
Annecy, France ; 10Universit¨
at Hamburg, Institut f¨
ur Experimentalphysik, Luruper Chaussee 149,
22761 Hamburg, Germany ; 11Graduate School of Science, University of Tokyo, 7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-0033, Japan ; 12EMFTEL department and IPARCOS, Universidad
Complutense de Madrid, 28040 Madrid, Spain ; 13INAF - Osservatorio di Astrofisica e Scienza dello
spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy ; 14Centro Brasileiro de Pesquisas
F´
ısicas, Rua Xavier Sigaud 150, RJ 22290-180, Rio de Janeiro, Brazil ; 15INFN Sezione di Padova
and Universit`
a degli Studi di Padova, Via Marzolo 8, 35131 Padova, Italy ; 16Instituto de Astrof´
ısica
de Canarias and Departamento de Astrof´
ısica, Universidad de La Laguna, La Laguna, Tenerife,
Spain ; 17CIEMAT, Avda. Complutense 40, 28040 Madrid, Spain ; 18Department of Physics, TU
Dortmund University, Otto-Hahn-Str. 4, 44227 Dortmund, Germany ; 19INFN Sezione di Bari and
Politecnico di Bari, via Orabona 4, 70124 Bari, Italy ; 20INFN Sezione di Trieste and Universit`
a
degli studi di Udine, via delle scienze 206, 33100 Udine, Italy. ; 21INFN Sezione di Catania, Via S.
Sofia 64, 95123 Catania, Italy ; 22INAF - Istituto di Astrofisica e Planetologia Spaziali (IAPS), Via
del Fosso del Cavaliere 100, 00133 Roma, Italy ; 23Aix Marseille Univ, CNRS/IN2P3, CPPM,
Marseille, France ; 24INFN Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy ; 25Palacky
2
University Olomouc, Faculty of Science, 17. listopadu 1192/12, 771 46 Olomouc, Czech Republic ;
26Department of Physics and Technology, University of Bergen, Museplass 1, 5007 Bergen, Norway
;27University of Geneva - D´
epartement de physique nucl´
eaire et corpusculaire, 24 Quai Ernest
Ansernet, 1211 Gen`
eve 4, Switzerland ; 28Port d’Informaci´
o Cient´
ıfica, Edifici D, Carrer de
l’Albareda, 08193 Bellaterrra (Cerdanyola del Vall`
es), Spain ; 29INFN Sezione di Bari and
Universit`
a di Bari, via Orabona 4, 70126 Bari, Italy ; 30University of Rijeka, Department of Physics,
Radmile Matejcic 2, 51000 Rijeka, Croatia ; 31Institute for Theoretical Physics and Astrophysics,
Universit¨
at W¨
urzburg, Campus Hubland Nord, Emil-Fischer-Str. 31, 97074 W¨
urzburg, Germany ;
32Institut f¨
ur Theoretische Physik, Lehrstuhl IV: Plasma-Astroteilchenphysik, Ruhr-Universit¨
at
Bochum, Universit¨
atsstraße 150, 44801 Bochum, Germany ; 33ILANCE, CNRS - University of
Tokyo International Research Laboratory, Kashiwa, Chiba 277-8582, Japan ; 34Physics Program,
Graduate School of Advanced Science and Engineering, Hiroshima University, 739-8526 Hiroshima,
Japan ; 35INFN Sezione di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy ;
36Faculty of Physics and Applied Informatics, University of Lodz, ul. Pomorska 149-153, 90-236
Lodz, Poland ; 37University of Split, FESB, R. Boˇ
skovi´
ca 32, 21000 Split, Croatia ; 38Department of
Physics, Yamagata University, Yamagata, Yamagata 990-8560, Japan ; 39Tohoku University,
Astronomical Institute, Aobaku, Sendai 980-8578, Japan ; 40Josip Juraj Strossmayer University of
Osijek, Department of Physics, Trg Ljudevita Gaja 6, 31000 Osijek, Croatia ; 41Kitashirakawa
Oiwakecho, Sakyo Ward, Kyoto, 606-8502, Japan ; 42INFN Sezione di Roma La Sapienza, P.le Aldo
Moro, 2 - 00185 Rome, Italy ; 43Department of Astronomy, University of Geneva, Chemin d’Ecogia
16, CH-1290 Versoix, Switzerland ; 44Astronomical Institute of the Czech Academy of Sciences,
Bocni II 1401 - 14100 Prague, Czech Republic ; 45Faculty of Science, Ibaraki University, Mito,
Ibaraki, 310-8512, Japan ; 46Faculty of Science and Engineering, Waseda University, Shinjuku,
Tokyo 169-8555, Japan ; 47Department of Physics, Tokai University, 4-1-1, Kita-Kaname, Hiratsuka,
Kanagawa 259-1292, Japan ; 48INFN Sezione di Trieste and Universit`
a degli Studi di Trieste, Via
Valerio 2 I, 34127 Trieste, Italy ; 49INFN and Universit`
a degli Studi di Siena, Dipartimento di
Scienze Fisiche, della Terra e dell’Ambiente (DSFTA), Sezione di Fisica, Via Roma 56, 53100
Siena, Italy ; 50Escuela Polit´
ecnica Superior de Ja´
en, Universidad de Ja´
en, Campus Las Lagunillas
s/n, Edif. A3, 23071 Ja´
en, Spain ; 51Saha Institute of Nuclear Physics, Bidhannagar, Kolkata-700
064, India ; 52Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences,
72 boul. Tsarigradsko chaussee, 1784 Sofia, Bulgaria ; 53FZU - Institute of Physics of the Czech
Academy of Sciences, Na Slovance 1999/2, 182 21 Praha 8, Czech Republic ; 54Dipartimento di
Fisica e Chimica ’E. Segr`
e’ Universit`
a degli Studi di Palermo, via delle Scienze, 90128 Palermo ;
55Department of Applied Physics, University of Zagreb, Horvatovac 102a, 10000 Zagreb, Croatia ;
56Institute of Space Sciences (ICE, CSIC), and Institut d’Estudis Espacials de Catalunya (IEEC), and
Instituci´
o Catalana de Recerca I Estudis Avanc¸ats (ICREA), Campus UAB, Carrer de Can Magrans,
s/n 08193 Bellatera, Spain ; 57Hiroshima Astrophysical Science Center, Hiroshima University,
Higashi-Hiroshima, Hiroshima 739-8526, Japan ; 58Charles University, Institute of Particle and
Nuclear Physics, V Holeˇ
soviˇ
ck´
ach 2, 180 00 Prague 8, Czech Republic ; 59Institute for Space-Earth
Environmental Research, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan ;
60Kobayashi-Maskawa Institute (KMI) for the Origin of Particles and the Universe, Nagoya
University, Chikusa-ku, Nagoya 464-8602, Japan ; 61Graduate School of Technology, Industrial and
Social Sciences, Tokushima University, Tokushima 770-8506, Japan ; 62INFN Dipartimento di
Scienze Fisiche e Chimiche - Universit`
a degli Studi dell’Aquila and Gran Sasso Science Institute,
Via Vetoio 1, Viale Crispi 7, 67100 L’Aquila, Italy ; 63IRFU, CEA, Universit´
e Paris-Saclay, Bˆ
at 141,
91191 Gif-sur-Yvette, France ; 64Graduate School of Science and Engineering, Saitama University,
255 Simo-Ohkubo, Sakura-ku, Saitama city, Saitama 338-8570, Japan ; 65Department of Physical
Sciences, Aoyama Gakuin University, Fuchinobe, Sagamihara, Kanagawa, 252-5258, Japan ;
66Division of Physics and Astronomy, Graduate School of Science, Kyoto University, Sakyo-ku,
Kyoto, 606-8502, Japan ; 67Dipartimento di Fisica - Universit´
a degli Studi di Torino, Via Pietro
Giuria 1 - 10125 Torino, Italy ; 68Department of Physics, Konan University, Kobe, Hyogo, 658-8501,
Japan; (March 17, 2023)
3
Abstract
Context: Several new ultrahigh-energy (UHE) gamma-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 gamma-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 4σand 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 cutoffenergy of 100+70
−30 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 gamma rays can
also be explained as π0decay-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 gamma-ray emission remains an open question.
Key words. radiation mechanisms: non-thermal /gamma rays: general /pulsars: general /ISM: individual
objects: LHAASO J2108+5157
1 Introduction
Cosmic rays (CRs) with energies up to the knee (∼1 PeV) are believed to be produced in hadronic PeVatrons,
cosmic accelerators located in our Galaxy (for a review see e.g., Gabici et al. 2019). Despite substantial observa-
tional efforts in the last decade, the origin of the highest-energy galactic CRs remains unknown, mainly because
of the difficulty in reconstructing the direction of their origin, as they are subject to deflection in the Galactic
magnetic field. When accelerated protons interact with ambient matter, they emit gamma rays through π0decay.
Similarly, electrons and positrons produce gamma rays via inverse Compton (IC) scattering on low-energy pho-
ton fields via bremsstrahlung when colliding with atomic nuclei of ambient matter, or via synchrotron radiation
when interacting with magnetic fields. Studying very high-energy (VHE, 0.1<E<100 TeV) and ultrahigh-
energy (UHE, E>0.1 PeV) cosmic gamma rays and disentangling the different origins of the radiation are
therefore essential in order to search for cosmic PeVatrons (CTA Consortium et al. 2019, CTA Consortium, in
prep.).
Diffusive shock acceleration (DSA; Bell (1978)) taking place in supernova remnants (SNRs) and pulsar
wind nebulae (PWNe) has been proposed as a possible mechanism to accelerate CRs (Bell 2013). In several
SNRs, a characteristic spectral feature known as a ”pion-decay bump” has been detected, providing evidence
that proton acceleration takes place in these sources (Ackermann et al. 2013; Jogler & Funk 2016; H. E. S. S.
*Corresponding authors; e-mail: lst-contact@cta-observatory.org
4
Collaboration et al. 2018b; Ambrogi et al. 2019; Abdollahi et al. 2022). However, none of the gamma-ray
spectra of the sources firmly identified as SNRs extend beyond 100 TeV (Aharonian et al. 2019; Zeng et al.
2019), which suggests that these sources are probably not capable of proton acceleration up to PeV energies.
The search for PeVatrons continues, and in the last few years several new candidates showing gamma-
ray emission above 100 TeV have been discovered by the Tibet Air Shower (AS) collaboration (Amenomori
et al. 2019; Tibet ASγCollaboration et al. 2021) and the High Altitude Water Cherenkov (HAWC) observatory
(Abeysekara et al. 2020). Recently, the Large High Altitude Air Shower Observatory (LHAASO) collabora-
tion, exploiting the unprecedented sensitivity of the LHAASO-KM2A instrument in the UHE range, reported
the discovery of 12 UHE gamma-ray sources reaching energies up to 1.4 PeV (Cao et al. 2021b). Among
these, there is only one unidentified source with an as-of-yet undetected TeV counterpart, namely LHAASO
J2108+5157.
LHAASO J2108+5157 is the first gamma-ray source directly discovered in the UHE band, and was detected
with a post-trial significance of 6.4σabove 100 TeV (Cao et al. 2021a). The position of the source is R.A.=
317.22◦±0.07◦,Dec =51.95◦±0.05◦. The source is reported to be point-like with a 95% confidence level
upper limit on its extension of 0.26◦with a two-dimensional symmetrical Gaussian shape assumption. The
spectrum of LHAASO J2108+5157 above 25 TeV can be described by a single power law (PL) with a photon
index of 2.83 ±0.18. There is no VHE or X-ray counterpart to the source, but Cao et al. (2021a) identified a
close high-energy (HE) point source, 4FGL J2108.0+5155 (Abdollahi et al. 2020), at an angular distance of
0.13◦. A dedicated analysis suggested that the HE source might be spatially extended (4FGL J2108.0+5155e)
with extension of 0.48◦. Its spectrum can be described with a single PL with a photon index of 2.3 between
1 GeV and 1 TeV. However, the physical connection between the spectral energy distributions (SEDs) of the
HE and UHE sources is not particularly clear because of the very different spectral indices. Cao et al. (2021a)
found the source to be coincident with the position of a molecular cloud [MML2017]4607 (Miville-Deschˆ
enes
et al. 2017), which would support the hypothesis that the emission has a hadronic origin, if CR protons collide
with the ambient gas. The authors suggested that the extended emission of 4FGL J2108.0+5155e could be
related to an old SNR, while the point-like UHE emission could be due to interaction of the escaping CRs
from the SNR with the molecular cloud. Alternatively, the authors proposed that the relativistic CRs could
be accelerated in one of the nearby open stellar clusters, but confirmation of these hypotheses is complicated
because of the unknown distance of the source. A lepto-hadronic emission scenario was also proposed by Kar
& Gupta (2022), whereby shock-accelerated electrons and protons were injected in the molecular cloud several
thousand years ago during an explosion.
TeV halos in the vicinity of pulsars were recently established as a class of extended VHE sources (Linden
et al. 2017; Abeysekara et al. 2017; L´
opez-Coto et al. 2022), featuring bright TeV emission and a hard spectrum
(Sudoh et al. 2019). Gamma-ray emission in such sources can be produced in IC scattering of ambient photons
by VHE electrons and positrons accelerated by the pulsar-wind termination shock (Sudoh et al. 2019). Even
though IC gamma-ray emission beyond 100 TeV is suppressed because of the Klein-Nishina effect, it has
been shown that IC can still dominate UHE emission in radiation-dominated environments (e.g., Vannoni et al.
2009; Breuhaus et al. 2021). This mechanism was used to explain UHE gamma-ray emission of extended
sources detected by HAWC, and three LHAASO sources associated with pulsars (Breuhaus et al. 2021, 2022).
In addition, the study of Albert et al. (2021) suggests that UHE gamma-ray emission may be a generic feature
in the vicinity of pulsars with high spin-down powers ˙
E>1036 ergs−1. The same limit on ˙
Ewas also derived
from first principles, showing that only very energetic pulsars can power PeV gamma-ray emission (de O˜
na
Wilhelmi et al. 2022).
According to the ATNF database1(Manchester et al. 2005) there is no detected pulsar within a 1◦radius
around LHAASO J2108+5157. This does not a priory exclude the PWN/TeV halo scenario, as the pulsar might
remain undetected if its beam is not pointing towards us. The spectral analysis of Cao et al. (2021a) showed that
a PWN scenario can also explain the observed UHE emission of LHAASO J2108+5157. With a lack of other
observational data, and especially the missing VHE counterpart, the nature of the source remains unknown.
In this paper, we present the results of a dedicated observation of the source region with the first Large-
Sized Telescope (LST-1) and XMM-Newton2, and results of a dedicated analysis of Fermi-LAT data, providing
strong constraints on LHAASO J2108+5157 gamma-ray and X-ray emission and the physical nature of the
1https://www.atnf.csiro.au/people/pulsar/psrcat/
2Proposed as Target of Opportunity observation, PI: R. Walter.
5
摘要：

MultiwavelengthstudyofthegalacticPeVatroncandidateLHAASOJ2108+5157S.Abe1A.Aguasca-Cabot2I.Agudo3N.AlvarezCrespo4L.A.Antonelli5C.Aramo6A.Arbet-Engels7M.Artero8K.Asano1P.Aubert9A.Baktash10A.Bamba11A.BaqueroLarriva12L.Baroncelli13U.BarresdeAlmeida14J.A.Barrio12I.Batkovic15J.Baxter1J.BecerraGonz´alez16E...

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Multiwavelength study of the galactic PeVatron candidate LHAASO J2108 5157 S. Abe1A. Aguasca-Cabot2I. Agudo3N. Alvarez Crespo4L. A. Antonelli5.pdf

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