Nonthermal emission properties of the northwestern rim of supernova remnant RX J0852.0-4622

Abstract

The supernova remnant (SNR) RX J0852.0-4622 (Vela Jr., G266.6-1.2) is one of the most important SNRs for investigating the acceleration of multi-TeV particles and the origin of Galactic cosmic rays because of its strong synchrotron X-ray and TeV γ-ray emission, which show a shell-like morphology similar to each other. Using the XMM-Newton archival data consisting of multiple pointing observations of the northwestern rim of the remnant, we investigate the spatial properties of the nonthermal X-ray emission as a function of distance from an outer shock wave. All X-ray spectra are well reproduced by an absorbed power-law model above 2 keV. It is found that the spectra show gradual softening from a photon index Γ = 2.56 in the rim region to Γ = 2.96 in the interior region. We show that this radial profile can be interpreted as a gradual decrease of the cutoff energy of the electron spectrum due to synchrotron cooling. By using a simple spectral evolution model that includes continuous synchrotron losses, the spectral softening can be reproduced with the magnetic field strength in the post-shock flow to less than several tens of μG. If this is a typical magnetic field in the SNR shell, γ-ray emission would be accounted for by inverse Compton scattering of high-energy electrons that also produce the synchrotron X-ray emission. Future hard X-ray imaging observations with Nustar and ASTRO-H and TeV γ-ray observations with the Cherenkov Telescope Array (CTA) will allow us to explore other possible explanations of the systematic softening of the X-ray spectra.

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

“…At first sight, this kind of value is inconsistent with the simple interpretation for the observed time variability (Uchiyama et al 2007) and thin filamentary structures (Bamba et al 2005b;Parizot et al 2006) of synchrotron X-rays through a fast energy loss of high-energy electrons, which typically requires B100 μG. Recent X-ray observations of the SNR RXJ0852.0−4622, which show very similar features to RXJ1713.7−3946, have however recovered a shallow steepening of the synchrotron index behind the shock as a function of radius, suggesting an average magnetic field near the shock of only a fewμG (Kishishita et al 2013). This has been shown to be consistent with theoretical models (Lee et al 2013).…”

Magnetic field damping in the Vela Jr. SNR

“…X-ray radial profiles are calculated following the definition of the regions from Kishishita et al (2013) for direct comparison of our results with the observational data. Assuming a spherical symmetry we produce energy dependent 2D flux maps with a cell size of 0.67 , equal to the width of the regions defined for the X-ray spectral analysis in Kishishita et al (2013).…”

“…Assuming a spherical symmetry we produce energy dependent 2D flux maps with a cell size of 0.67 , equal to the width of the regions defined for the X-ray spectral analysis in Kishishita et al (2013). Then for the cells which correspond to the location of the regions we extract the flux and the specrum in the energy range between 2 keV and 10 keV.…”

“…This softening was interpret by the change in the cut-off energy due to synchrotron cooling. Using a simple spectral evolution model assuming that the downstream time evolution of the maximum electron energy is determined only by synchrotron losses, Kishishita et al (2013) showed that the softening of the spectrum can be explained by a rather low magnetic field of ∼ 5 − 20 µG. This would require however a quite high electron maximum energy of about ∼ 100 TeV which is in contradiction with H.E.S.S.…”

“…In this scenario strong magnetic turbulence formed upstream is damped downstream at typical length scales comparable to the width of the filaments. Recently a detailed analysis of the archival XMM-Newton data revealed a gradual softening of the spectrum (from a photon index of 2.56 to a photon idnex of 2.96) in the north western rim towards the interior of the remnant (Kishishita et al, 2013). This softening was interpret by the change in the cut-off energy due to synchrotron cooling.…”