A detailed spectral and morphological study of the gamma-ray supernova remnant RX J1713.7–3946 with HESS

Abstract

Aims. We present results from deep observations of the Galactic shell-type supernova remnant (SNR) RX J1713.7−3946 (also known as G347.3−0.5) conducted with the complete HESS array in 2004. Methods. Detailed morphological and spatially resolved spectral studies reveal the very-high-energy (VHE -Energies E > 100 GeV) gamma-ray aspects of this object with unprecedented precision. Since this is the first in-depth analysis of an extended VHE gamma-ray source, we present a thorough discussion of our methodology and investigations of possible sources of systematic errors. Results. Gamma rays are detected throughout the whole SNR. The emission is found to resemble a shell structure with increased fluxes from the western and northwestern parts. The differential gamma-ray spectrum of the whole SNR is measured over more than two orders of magnitude, from 190 GeV to 40 TeV, and is rather hard with indications for a deviation from a pure power law at high energies. Spectra have also been determined for spatially separated regions of RX J1713.7−3946. The flux values vary by more than a factor of two, but no significant change in spectral shape is found. There is a striking correlation between the X-ray and the gamma-ray image. Radial profiles in both wavelength regimes reveal the same shape almost everywhere in the region of the SNR. Conclusions. The VHE gamma-ray emission of RX J1713.7−3946 is phenomenologically discussed for two scenarios, one where the gamma rays are produced by VHE electrons via Inverse Compton scattering and one where the gamma rays are due to neutral pion decay from proton-proton interactions. In conjunction with multi-wavelength considerations, the latter case is favoured. However, no decisive conclusions can yet be drawn regarding the parent particle population dominantly responsible for the gamma-ray emission from RX J1713.7−3946.

Collisionless Shocks in Partly Ionized Plasma with Cosmic Rays: Microphysics of Non-thermal Components

“…The steep photon spectra has been found in the high energy gamma-ray spectra of some other remnants measured by, e.g., the CANGAROO (Enomoto et al 2002), H.E.S.S (Aharonian et al 2006) and MAGIC (Carmona 2011) atmospheric Cherenkov telescopes. Particles accelerated by DSA mechanism generally comprised two distinct populations -CRs confined in the accelerator and the CRs escaping the system and these two populations have very different spectral shapes.…”

Prospects for Cherenkov Telescope Array Observations of the Young Supernova Remnant RX J1713.7−3946

“…So far, VHE gamma-ray observations have revealed the existence of high-energy particles at the shock of young SNRs (e.g., Enomoto et al 2002;Aharonian et al 2004Aharonian et al , 2005Aharonian et al , 2006Aharonian et al , 2007aAharonian et al , 2007bAharonian et al , 2009Katagiri et al 2005;Albert et al 2007;Acero et al 2010;Abramowski et al 2011;Acciari et al 2011;see also Ferrand & Safi-Harb 2012). Although the gamma rays are suggested to originate from either leptonic (low-energy photons upscattered by high-energy electrons) or hadronic (π 0 -decay photons generated by accelerated protons colliding with surrounding gas) processes, it is generally a nontrivial task to distinguish these processes despite abundant multiwavelength studies.…”

“…RXJ1713.7−3946 (also known as a radio SNR G347.3 −0.5; Slane et al 1999), one of the brightest VHE gamma-ray sources ever detected (Muraishi et al 2000;Enomoto et al 2002;Aharonian et al 2004Aharonian et al , 2006Aharonian et al , 2007a, is an ideal target to study these unresolved mysteries. The distance and age of RXJ1713.7−3946 are estimated to be 0.9-1.3kpc and ∼1600yr, respectively (Fukui et al 2003;Moriguchi et al 2005), which is consistent with its connection with the guest star AD393 (e.g., Wang et al 1997).…”

“…was often suggested to be best explained by a hadronic model (Aharonian et al 2006(Aharonian et al , 2007a in which the gamma rays originate from the decay of π 0 mesons produced by CR protons interacting with the local gas. However, as Fermi/LAT measured the gamma-ray spectrum of RXJ1713.7−3946 in the 3-300GeV energy range, it turned out that the photon index (1.5 ± 0.1) is one more typically expected from leptonic (i.e., inverse Compton) emission from high-energy electrons with a spectral index of s=2.0 (Abdo et al 2011).…”

“…However, this scenario seems unlikely because of the apparently energy-independent gamma-ray morphology (Aharonian et al 2006). The smooth, single-peak spectral shape without any features would require fine-tuning of model parameters describing the two populations.…”