The interaction of SNR Kes 17 with the interstellar medium: Fresh view from radio and γ-rays

Abstract

This paper presents a comprehensive analysis of the Galactic supernova remnant (SNR) Kes 17 (G304.6+0.1). The focus is on its radio synchrotron emission, its surroundings, and the factors contributing to the observed γ rays. The fitting to the first obtained integrated radio continuum spectrum spanning from 88 to 8800 MHz yields an index α = −0.488 ± 0.023 (Sν ∝ να), which is indicative of a linear particle acceleration process at the shock front of the remnant. Accounting for the SNR radio shell size, the distribution of atomic hydrogen (nH ~ 10 cm−3), and assuming that the SNR is in the Sedov-Taylor stage of its evolution, we estimate that the remnant age is roughly 11 kyr. This result falls at the lower end of the wide range (~2–64 kyr) derived from previous analyses of the diffuse X-ray emission interior to the remnant. Furthermore, we used 12CO and 13CO (J = 1–0) emission line data as a proxy for molecular hydrogen and provide the first evidence that the eastern shell of Kes 17 is engulfing a molecular enhancement in the surrounding gas, with an average mass 4.2 × 104 M⊙ and density n ~ 300 cm−3. Towards the western boundary of Kes 17, no signatures of carbon monoxide emissions are detected above 3σ, despite previously reported infrared observations that revealed shocked molecular gas at this location. This suggests the existence of a CO-dark interacting molecular gas, a phenomenon also recorded in other Galactic SNRs (e.g. CTB 37A and RX J1713.7–3946) that reveals itself both in the infrared and γ-ray domains. Additionally, by analysing ~14.5 yr of continuously collected data from the Large Area Telescope on board the satellite Fermi, we determined that the best-fit power-law photon index for the 0.3–300 GeV γ-ray emission from the Kes 17 region is Γ = 2.39 ± 0.04−0.114+0.063 (±stat ±syst), in agreement with prior studies. The energy flux is (2.98 ± 0.14) × 10−11 erg cm−2 s−1, implying a luminosity (2.22 ± 0.45) × 1035 erg s−1 at ~8 kpc. Finally, we successfully modelled the multiwavelength spectral energy distribution by incorporating the radio-synchrotron spectrum and the new measurements of GeV γ-rays. Our analysis indicates that the observed γ-ray flux most likely originates from the interaction of Kes 17 with a western dark CO zone with a proton density np ~ 400 cm−3.

Revisiting γ-Ray Emission of the Supernova Remnant RCW 103

“…α ; 2.4, and the spectrum is softer than the previously reported one (Γ ; 2.0 in Xing et al 2014). We note that this spectrum is very similar to that of the SNR Kes 17, which had Γ ; 2.39 (Supán et al 2023).…”

Energy-dependent Analyses of the Gamma-Ray Emission from HESS J1857+026 with Fermi-LAT

“…) erg is needed to explain the GeV gamma-ray emission, which is shown as the red solid line in the right panel of Figure 3. In addition, considering the fact that the cutoff energy of protons in the middle-aged SNRs is usually much lower than PeV (Gelfand et al 2013;Supán et al 2023), we decreased the cutoff energies of the protons to estimate the different hadronic models. The allowed minimum value of the cutoff energy is about 1 TeV for Src A and 4FGL J1857.9+0313e, with the total energies of the protons of )erg, respectively.…”

Energy-Dependent Morphological Study of HESS J1857+026 with Fermi-LAT

“…For 4FGL J1857.9+0313e, the spectral index of protons with γ ∼ 2.7 and total energy of W p ∼ 5.8×10 49 (n gas,B /50 cm −3 ) −2 (d/6.3 kpc) 2 erg or W p ∼ 6.4×10 47 (n gas,B /280 cm −3 ) −2 (d/3.7 kpc) 2 are needed to explain the GeV gamma-ray emission, which is shown as the red solid line in the right panel of Figure 3. In addition, considering the fact that the cut-off energy of protons in the middle-aged SNRs is usually much lower than PeV (Gelfand et al 2013;Supán et al 2023), we decreased the cutoff energies of protons to estimate the different hadronic models. And the allowed minimum value of cutoff energy is about 1 TeV for SrcA and 4FGL J1857.9+0313e, with the total energies of protons of ∼ 1.5 × 10 50 (n gas,A /27 cm −3 ) −2 (d/6.3 kpc) 2 erg and ∼ 5.7 × 10 49 (n gas,B /50 cm −3 ) −2 (d/6.3 kpc) 2 erg, respectively.…”