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- De La Fuente, Eduardo, et al.
(författare)
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Evidence for a gamma-ray molecular target in the enigmatic PeVatron candidate LHAASO J2108+5157
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 675
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Tidskriftsartikel (refereegranskat)abstract
- Context . Peta-eV (PeV) astronomy emerged in 2021 with the discovery of ultra-high-energy gamma-ray sources associated with powerful natural particle accelerators known as PeVatrons. In order to determine the nature of their emission, namely whether it has a hadronic or leptonic origin, it is essential to characterise the physical parameters of the environment where it originates. Aims . We unambiguously confirm the association of molecular gas with the PeVatron candidate LHAASO J2108+5157 using unprecedented high angular-resolution (17′) 12,13CO(J = 1 → 0) observations carried out with the Nobeyama 45m radio telescope. Methods . We characterised a molecular cloud in the vicinity of the PeVatron candidate LHAASO J2108+5157 by determining its physical parameters from our 12,13CO(J = 1 → 0) line observations. We used an updated estimation of the distance to the cloud, which provided a more reliable result. The molecular emission was compared with excess gamma-ray images obtained with Fermi-LAT at energies above 2 GeV to search for spatial correlations and test a possible hadronic (π0 decay) origin for the gamma-ray emission. Results . We find that the morphology of the spatial distribution of the CO emission is strikingly similar to that of the Fermi-LAT excess gamma ray. By combining our observations with archival 21 cm HI line data, the nucleons (HI + H2) number density of the target molecular cloud is found to be 133.0 ± 45.0 cm-3, for the measured angular size of 0.55 ± 0.02 at a distance of 1.6 ± 0.1 kpc. The resulting total mass of the cloud is M(HI + H2) = 7.5±2.9×103M⊙. Under a hadronic scenario, we obtain a total energy of protons of Wp = 4.3 ± 1.5 × 1046 erg with a cutoff of 700±300 TeV, which reproduces the sub-PeV gamma-ray emission. Conclusions . We identified a molecular cloud in the vicinity of LHAASO J2107+5157 as the main target where cosmic rays from an unknown PeVatron produce the observed gamma-ray emission via π0 decay.
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| 2. |
- De La Fuente, Eduardo, et al.
(författare)
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Detection of a new molecular cloud in the LHAASO J2108+5157 region supporting a hadronic PeVatron scenario
- 2023
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Ingår i: Publication of the Astronomical Society of Japan. - 2053-051X .- 0004-6264. ; 75:3, s. 546-566
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Tidskriftsartikel (refereegranskat)abstract
- PeVatrons are the most powerful naturally occurring particle accelerators in the Universe. The identification of counterparts associated to astrophysical objects such as dying massive stars, molecular gas, star-forming regions, and star clusters is essential to clarify the underlying nature of the PeV emission, i.e., hadronic or leptonic. We present 12,13CO (J = 2→1) observations made with the 1.85 m radio-Telescope of the Osaka Prefecture University toward the Cygnus OB7 molecular cloud, which contains the PeVatron candidate LHAASO J2108+5157. We investigate the nature of the sub-PeV (gamma-ray) emission by studying the nucleon density determined from the content of H i and H2, derived from the CO observations. In addition to MML[2017]4607, detected via the observations of the optically thick 12CO (J = 1→0) emission, we infer the presence of an optically thin molecular cloud, named [FKT-MC]2022, whose angular size is 1-1 ± 0.}^\circ}}2. We propose this cloud as a new candidate to produce the sub-PeV emission observed in LHAASO J2108+5157. Considering a distance of 1.7 kpc, we estimate a nucleon (H i + H2) density of 37 ± 14 cm-3, and a total nucleon mass(H i + H2) of 1.5 ± 0.6 × 104 M·. On the other hand, we confirm that Kronberger 82 is a molecular clump with an angular size of 0°1, a nucleon density ∼103 cm-3, and a mass ∼103 M·. Although Kronberger 82 hosts the physical conditions to produce the observed emission of LHAASO J2108+5157, [FKT-MC]2022 is located closer to it, suggesting that the latter could be the one associated to the sub-PeV emission. Under this scenario, our results favour a hadronic origin for the emission.
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