Observation of Gamma Rays up to 320 TeV from the Middle-aged TeV Pulsar Wind Nebula HESS J1849−000

Abstract

Gamma rays from HESS J1849−000, a middle-aged TeV pulsar wind nebula (PWN), are observed by the Tibet air shower array and the muon detector array. The detection significance of gamma rays reaches 4.0σ and 4.4σ levels above 25 TeV and 100 TeV, respectively, in units of the Gaussian standard deviation σ. The energy spectrum measured between 40 TeV < E < 320 TeV for the first time is described with a simple power-law function of dN / dE = ( 2.86 ± 1.44 ) × 10 − 16 ( E / 40 TeV ) − 2.24 ± 0.41 TeV − 1 cm − 2 s − 1 . The gamma-ray energy spectrum from the sub-TeV (E < 1 TeV) to sub-PeV (100 TeV < E < 1 PeV) ranges, including the results of previous studies, can be modeled with the leptonic scenario, i.e., inverse Compton scattering by high-energy electrons accelerated by the PWN of PSR J1849−0001. On the other hand, the gamma-ray energy spectrum can also be modeled with the hadronic scenario in which gamma rays are generated from the decay of neutral pions produced by collisions between accelerated cosmic-ray protons and the ambient molecular cloud found in the gamma-ray-emitting region. The cutoff energy of cosmic-ray protons E p,cut is estimated as log 10 ( E p , cut / TeV ) = 3.73 − 0.66 + 2.98 , suggesting that protons are accelerated up to the PeV energy range. Our study thus proposes that HESS J1849−000 should be further investigated as a new candidate as a Galactic PeV cosmic-ray accelerator, or “PeVatron.”

X-Ray Characterization of the Pulsar PSR J1849−0001 and Its Wind Nebula G32.64+0.53 Associated with TeV Sources Detected by H.E.S.S., HAWC, Tibet ASγ, and LHAASO

“…Our estimate of e,max g corresponds to a maximum electron energy of E e,max » 400 TeV, which is comparable to the 740 TeV inferred from modeling the TeV emission of G32.6 (Amenomori et al 2023). With the lack of measurements at >20 keV, our estimation of E e,max should be regarded as a lower limit.…”

“…-, and characteristic age τ c = 43 kyr, thus categorizing the point source as an energetic and middle-aged pulsar. Furthermore, this middle-aged pulsar and its PWN are of particular interest as their emission is significantly detected above 100 TeV by HAWC (Albert et al 2020), LHAASO (Cao et al 2023), and the Tibet air shower array (Tibet ASγ; Amenomori et al 2023) with a maximum photon energy of 350 TeV (Cao et al 2021). This indicates the presence of energetic particles within the PWN (G32.64+0.53, 8 hereafter G32.6).…”

Multiband Nonthermal Radiative Study of PeVatron Candidate Pulsar Wind Nebula HESS J1849-000

“…As for the observed multiband data, the X-ray data are taken from Gagnon et al (2023), Fermi-LAT upper limits are taken from Eagle (2022), TeV data are taken from H.E.S.S. Collaboration (2018b) and Amenomori et al (2023), and PeV data are taken from Cao et al (2024). Furthermore, the X-ray images have revealed the angular radius θ X−ray ∼150″ (Gotthelf et al 2011;Gagnon et al 2023;Kim et al 2024) and the corresponding radius R X−ray ∼5.0 pc for the distance of 7.0 kpc.…”

“…However, at energies above 100 TeV, the CMB radiation dominates the γ-ray photon production (for details, see 1 PeV e 0.77 (Cao et al 2021b). Amenomori et al (2023) measured the spectrum of HESS J1849-000 at TeV energies and found no evidence of cut-off up to 740 TeV, which implies the corresponding electron energy of E e ; 1.7 PeV. Furthermore, the LHAASO observation detects γ-ray photons up to 1.9 PeV (Cao et al 2024), and it implies the corresponding electron energy of E e ; 3.5 PeV.…”

“…Collaboration 2018b). Recently, Amenomori et al (2023) measured the spectrum of HESS J1849-000 at the TeV energy band and found no evidence of cut-off up to 740 TeV by the Tibet Air Shower Array (TASA), making the source a PeV candidate. Furthermore, LHAASO collaboration observation found also that the extended sources LHAASO J1848-0001 around PSR J 1849-0001, which can emit PeV γ-ray photons, and the best-fit size of the emission is less than 0°.09 (Cao et al 2024).…”