Pursuing the Origin of the Gamma Rays in RX J1713.7-3946 Quantifying the Hadronic and Leptonic Components

Abstract

We analyzed the TeV gamma-ray image of a supernova remnant RX J1713.7−3946 (RX J1713) through a comparison with the interstellar medium (ISM) and nonthermal X-rays. The gamma-ray data sets at two energy bands of >2 TeV and >250–300 GeV were obtained with H.E.S.S. and utilized in the analysis. We employed a new methodology, which assumes that the gamma-ray counts can be expressed as a linear combination of two terms: one is proportional to the ISM column density and the other proportional to the X-ray count. We then assume that these represent the hadronic and leptonic components, respectively. By fitting the expression to the data pixels, we find that the gamma-ray counts are well represented by a flat plane in the 3D space formed by the gamma-ray counts, the ISM column density, and the X-ray counts. The results using the latest H.E.S.S. data at 4.′8 resolution show that the hadronic and leptonic components constitute (67 ± 8)% and (33 ± 8)% of the total gamma rays, respectively, where the two components have been quantified for the first time. The hadronic component is greater than the leptonic component, which reflects the massive ISM of ∼104 M ⊙ associated with the remnant, lending support for the acceleration of cosmic-ray protons. There is a marginal hint that the gamma rays are suppressed at high gamma-ray counts, which may be ascribed to second-order effects including the shock–cloud interaction and the effect of penetration depth.

Modelling the Gamma-Ray Morphology of HESS J1804-216 from Two Supernova Remnants in a Hadronic Scenario

“…Mature aged SNRs may also produce 𝛾-rays leptonically through the inverse-Compton effect (e.g. Araya & Frutos 2012;Devin et al 2018;Fukui et al 2021). To finally confirm the accelerator of HESS J1804−216, we need to explore the leptonic scenario, assuming the SNR is accelerating electrons which may contribute to the TeV 𝛾-ray emission as discussed by Ajello et al (2012); Liu et al (2019).…”

An Expanding Shell of Neutral Hydrogen Associated with SN 1006: Hints for the Single-Degenerate Origin and Faint Hadronic Gamma-Rays

“…The total interstellar proton column density of shock-associated clouds is ∼ 3×10 21 cm −2 for RX J0852.0−4622 (Fukui et al 2017;Maxted et al 2018). By contrast, young (∼1600 yr) TeV gamma-ray SNR RX J1713.7−3946 shows a strongly deformed X-ray shell owing to shock-interactions with dense clouds of ∼ 7 × 10 21 cm −2 as averaged column density (e.g., Fukui et al 2003Fukui et al , 2012Fukui et al , 2021Sano et al 2010Sano et al , 2013Sano et al , 2015. In the case of SN 1006, the column density of the shocked Hi cloud is ∼ 4 × 10 20 cm −2 (see Section 3.4).…”

“…Figure 4 shows the scatter plot between the SNR age and W p for 13 gamma-ray SNRs that are listed in Table 1. Note that the hadronic gamma-ray luminosity for deriving the W p value in each SNR was calculated by the SED modeling alone except for RX J1713.7−3946 (see also Fukui et al 2021). We find that SN 1006 lies on the regression line which was fitted using the data points with the ages of SNRs below 6 kyr, suggesting that the positive relation between the SNR age and W p is applicable to gamma-ray SNRs with ages at least ∼1-6 kyr.…”

Leptonic non-thermal emission from supernova remnants evolving in the circumstellar magnetic field

“…It is therefore tempting to assume that both emissions should be produced in the same regions and with proportional emissivity, hence the gamma-ray morphology would strongly correlate with the X-ray morphology. Fukui et al (2021) made this assumption to discriminate between the leptonic and hadronic scenario of the gamma-ray emission, likewise assuming that hadronic gamma-ray radiation should correlate with the gas distribution. The latter assumption is dubious because we measure column densities and not the gas density itself, that determines the hadronic emissivity.…”

“…10 and 11). Following Fukui et al (2021), we calculate the gamma-ray flux in two energy bands: above 250 GeV (solid lines) and above 1 TeV (dashed lines). The X-ray flux is calculated in the energy range of 1 − 5 keV.…”