Young Shell-type Supernova Remnant Research Articles

The Gamma-Ray Origin of RX J0852.0-4622 Quantifying the Hadronic and Leptonic Components: Further Evidence for the Cosmic-Ray Acceleration in Young Shell-type SNRs

Fukui et al. quantified the hadronic and leptonic gamma-rays in the young TeV gamma-ray shell-type supernova remnant (SNR) RX J1713.7-3946 (RX J1713), and demonstrated that gamma rays are a combination of hadronic and leptonic gamma-ray components with a ratio of ∼6: 4 in gamma-ray counts N g. This discovery, which adopted a new methodology of multi-linear gamma-ray decomposition, was the first quantification of the two gamma-ray components. In the present work, we applied the same methodology to another TeV gamma-ray shell-type SNR RX J0852.0-4622 (RXJ0852) in 3D space characterized by (the interstellar proton column density N p)-(the nonthermal X-ray count N x)-[N g], and quantified the hadronic and leptonic gamma-ray components as having a ratio of ∼5:5 in N g. The present work adopted the fitting of two/three flat planes in 3D space instead of a single flat plane, which allowed suppression of the fitting errors. This quantification indicates that hadronic and leptonic gamma-rays are of the same order of magnitude in these two core-collapse SNRs, verifying the significant hadronic gamma-ray components. We argue that the target interstellar protons, in particular their spatial distribution, are essential in any attempts to identify the type of particles responsible for gamma-ray emission. The present results confirm that cosmic-ray (CR) energy ≲100 TeV is compatible with a scheme in which SNRs are the dominant source of these Galactic CRs.

Numerically investigating the peculiar periphery of a supernova remnant in the medium with a density gradient: the case of RCW 103

The young shell-type supernova remnant RCW 103 has peculiar properties in the X-ray morphology obtained with Chandra. The southeastern shell is brighter in the X-rays, and the curved border of the shell in this region is flatter than the other part.We investigate the formation of the peculiar periphery of the supernova remnant RCW 103 using 3D hydrodynamical simulation. Assuming that the supernova ejecta has been evolved in the medium with a density gradient, the detected shape of the periphery can be generally reproduced. For RCW 103, with the ejecta mass of 3.0 M ⊙, the density of the background material of 2.0 cm−3, and a gradient of 3.3 − 4.0 cm−3 pc−1, the X-ray periphery can be generally reproduced. The simulation turned out that the asymmetry of the SNR RCW 103 is mainly due to the inhomogeneous medium with a density gradient.

Spatially resolved spectroscopy of non-thermal X-rays in RX J1713.7−3946 with Chandra

Abstract The young shell-type supernova remnant (SNR) RX J1713.7−3946 has been studied as a suitable target to test the SNR paradigm for the origin of Galactic cosmic rays. We present a spatially resolved spectroscopy of the non-thermal X-ray emission in RX J1713.7−3946 with Chandra. In order to obtain X-ray properties of the filamentary structures and their surrounding regions, we divide the southeastern (SE), southwestern (SW), and northwestern (NW) parts of the SNR into subregions on the typical order of several 10" and extract spectra from each subregion. Their photon indices are significantly different among the subregions, with a range of 1.8 < Γ < 3. In the SE part, the clear filaments are harder (Γ ∼ 2.0) than the surrounding regions. This is a common feature often observed in young SNRs and naturally interpreted as a consequence of synchrotron cooling. On the other hand, the bright filamentary regions do not necessarily coincide with the hardest regions in the SW and NW parts. We also find the SW filamentary region is relatively rather soft (Γ ∼ 2.7). In addition, we find that hard regions with photon indices of 2.0–2.2 exist around the bright emission although the hard regions lie in the downstream region and the bright emission does not appear to be the blast wave shock front. Both the aforementioned characteristic regions in SW are located close to peaks of the interstellar gas. We discuss possible origins of the spatial variation of the photon indices, paying particular attention to the shock–cloud interactions.

A Study of Fermi-LAT GeV γ-Ray Emission toward the Magnetar-harboring Supernova Remnant Kesteven 73 and Its Molecular Environment

Abstract We report our independent GeV γ-ray study of the young shell-type supernova remnant (SNR) Kes 73, which harbors a central magnetar, and CO-line millimeter observations toward the SNR. Using 7.6 years of Fermi-LAT observation data, we detected an extended γ-ray source (“source A”) with centroid on the west of the SNR, with a significance of 21σ in 0.1–300 GeV and an error circle of 5.′4 in angular radius. The γ-ray spectrum cannot be reproduced by a pure leptonic emission or a pure emission from the magnetar, and thus a hadronic emission component is needed. The CO-line observations reveal a molecular cloud (MC) at V LSR ∼ 90 km s−1, which demonstrates morphological correspondence with the western boundary of the SNR brightened in multiwavelength. The 12CO (J = 2 − 1)/12CO (J = 1 − 0) ratio in the left (blue) wing 85–88 km s−1 is prominently elevated to ∼1.1 along the northwestern boundary, providing kinematic evidence of the SNR-MC interaction. This SNR-MC association yields a kinematic distance 9 kpc to Kes 73. The MC is shown to be capable of accounting for the hadronic γ-ray emission component. The γ-ray spectrum can be interpreted with a pure hadronic emission or a magnetar+hadronic hybrid emission. In the case of pure hadronic emission, the spectral index of the protons is 2.4, very similar to that of the radio-emitting electrons, essentially consistent with the diffusive shock acceleration theory. In the case of magnetar+hadronic hybrid emission, a magnetic field decay rate ≳1036 erg s−1 is needed to power the magnetar’s curvature radiation.

Observations of supernova remnants and pulsar wind nebulae at gamma-ray energies

In the past few years, gamma-ray astronomy has entered a golden age thanks to two major breakthroughs: Cherenkov telescopes on the ground and the Large Area Telescope (LAT) onboard the Fermi satellite. The sample of supernova remnants (SNRs) detected at gamma-ray energies is now much larger: it goes from evolved supernova remnants interacting with molecular clouds up to young shell-type supernova remnants and historical supernova remnants. Studies of SNRs are of great interest, as these analyses are directly linked to the long standing issue of the origin of the Galactic cosmic rays. In this context, pulsar wind nebulae (PWNe) need also to be considered since they evolve in conjunction with SNRs. As a result, they frequently complicate interpretation of the gamma-ray emission seen from SNRs and they could also contribute directly to the local cosmic ray spectrum, particularly the leptonic component. This paper reviews the current results and thinking on SNRs and PWNe and their connection to cosmic ray production. Au cours des dernières années, l'astronomie gamma est entrée dans un âge d'or grâce à deux avancées majeures : les télescopes Tcherenkov au sol et le Large Area Telescope (LAT) à bord du satellite Fermi . L'échantillon des restes de supernova (SNR) détectés en rayons gamma de haute énergie est maintenant beaucoup plus vaste : il va des vestiges de supernovae évolués en interaction avec des nuages moléculaires jusqu'aux jeunes SNR en coquille et aux SNR historiques. Les études des SNR sont d'un grand intérêt, car ces analyses sont directement liées à la question de l'origine des rayons cosmiques galactiques. Dans ce contexte, les nébuleuses de pulsars (PWN) doivent également être prises en compte, car elles évoluent en conjonction avec les SNR. En conséquence, elles compliquent souvent l'interprétation de l'émission gamma en provenance des SNR et pourraient aussi contribuer directement au spectre local de rayons cosmiques, en particulier à sa composante leptonique. Cet article passe en revue les résultats et réflexions actuels concernant les SNR et les PWN, ainsi que leur connexion avec la production des rayons cosmiques.

TeV -ray observations of the young synchrotron-dominated SNRs G1.9+0.3 and G330.2+1.0 with H.E.S.S.

The non-thermal nature of the X-ray emission from the shell-type supernova remnants (SNRs) G1.9+0.3 and G330.2+1.0 is an indication of intense particle acceleration in the shock fronts of both objects. This suggests that the SNRs are prime candidates for very-high-energy (VHE; E $>$ 0.1 TeV) {\gamma}-ray observations. G1.9+0.3, recently established as the youngest known SNR in the Galaxy, also offers a unique opportunity to study the earliest stages of SNR evolution in the VHE domain. The purpose of this work is to probe the level of VHE {\gamma}-ray emission from both SNRs and use this to constrain their physical properties. Observations were conducted with the H.E.S.S. (High Energy Stereoscopic System) Cherenkov telescope array over a more than six-year period spanning 2004-2010. The obtained data have effective livetimes of 67 h for G1.9+0.3 and 16 h for G330.2+1.0. The data are analyzed in the context of the multi-wavelength observations currently available and in the framework of both leptonic and hadronic particle acceleration scenarios. No significant {\gamma}-ray signal from G1.9+0.3 or G330.2+1.0 was detected. Upper limits (99% confidence level) to the TeV flux from G1.9+0.3 and G330.2+1.0 for the assumed spectral index {\Gamma} = 2.5 were set at 5.6 $\times$ 10$^{-13}$ cm$^{-2}$ s$^{-1}$ above 0.26 TeV and 3.2 $\times$ 10$^{-12}$ cm$^{-2}$ s$^{-1}$ above 0.38 TeV, respectively. In a one-zone leptonic scenario, these upper limits imply lower limits on the interior magnetic field to B$_{\mathrm{G1.9}}$ $\gtrsim$ 11 {\mu}G for G1.9+0.3 and to B$_{\mathrm{G330}}$ $\gtrsim$ 8 {\mu}G for G330.2+1.0. In a hadronic scenario, the low ambient densities and the large distances to the SNRs result in very low predicted fluxes, for which the H.E.S.S. upper limits are not constraining.

Galactic sources of high energy neutrinos

The undisputed galactic origin of cosmic rays at energies below the so-called knee implies an existence of a nonthemal population of galactic objects which effectively accelerate protons and nuclei to TeV-PeV energies. The distinct signatures of these cosmic PeVatrons are high energy neutrinos and γ -rays produced through hadronic interactions. While γ -rays can be produced also by directly accelerated electrons, high energy neutrinos provide the most straightforward and unambiguous information about the nucleonic component of accelerated particles. The planned km 3 -volume class high energy neutrino detectors are expected to be sensitive enough to provide the first astrophysically meaningful probes of potential VHE neutrino sources. This optimistic prediction is based on the recent discovery of high energy γ -ray sources with hard energy spectra extending to 10 TeV and beyond. Amongst the best-bet candidates are two young shell-type supernova remnants – RXJ 1713.7-4946 and RXJ 0852.0-4622, and perhaps also two prominent plerions – the Crab Nebula and Vela X. Because of strong absorption of TeV γ -rays, one may expect detectable neutrino fluxes also from (somewhat fainter) compact TeV γ -ray emitters like the binary systems LS 5039 and LS I+61 303, and, hopefully, also from hypothetical “hidden” or “orphan” neutrino sources.

RADIO POLARIMETRY SIGNATURES OF STRONG MAGNETIC TURBULENCE IN SUPERNOVA REMNANTS

We discuss the emission and transport of polarized radio-band synchrotron radiation near the forward shocks of young shell-type supernova remnants, for which X-ray data indicate a strong amplification of turbulent magnetic field. Modeling the magnetic turbulence through the superposition of waves, we calculate the degree of polarization and the magnetic polarization direction which is at $90^\circ$ to the conventional electric polarization direction. We find that isotropic strong turbulence will produce weakly polarized radio emission even in the absence of internal Faraday rotation. If anisotropy is imposed on the magnetic-field structure, the degree of polarization can be significantly increased, provided internal Faraday rotation is inefficient. Both for shock compression and a mixture with a homogeneous field, the increase in polarization degree goes along with a fairly precise alignment of the magnetic-polarization angle with the direction of the dominant magnetic-field component, implying tangential magnetic polarization at the rims in the case of shock compression. We compare our model with high-resolution radio polarimetry data of Tycho's remnant. Using the absence of internal Faraday rotation we find a soft limit for the amplitude of magnetic turbulence, $\delta B \lesssim 200\ {\rm \mu G}$. The data are compatible with a turbulent magnetic field superimposed on a radial large-scale field of similar amplitude, $\delta B\simeq B_0$. An alternative viable scenario involves anisotropic turbulence with stronger amplitudes in the radial direction, as was observed in recent MHD simulations of shocks propagating through a medium with significant density fluctuations.

High-energy neutrino emission from shell-type supernova remnants

Based on a time-dependent model of particle production and non-thermal photon emission, we study high-energy neutrino emission from shell-type supernova remnants (SNRs). In such a model, particles are accelerated to relativistic energies through the shock acceleration mechanism and evolve with time in an SNR. For a given SNR, therefore, the temporal evolution of the particle energy distribution, the non-thermal spectrum of photons, and the spectrum of neutrinos can be calculated numerically. We apply the model to two young SNRs, G347.3−0.5 and G266.2−1.2, and two old ones, G8.7−0.1 and G23.3−0.3. For each SNR, we determine the parameters involved in the model by comparing the predicted non-thermal spectrum with the observed radio, X-ray and γ-ray data. We study the properties of the corresponding neutrino emission, including the neutrino spectrum and the event rates expected in the next-generation km 3 -scale neutrino telescope, KM3NeT. Our results indicate that the high-energy TeV γ-rays from the four SNRs are produced predominately via hadronic interaction and that young SNRs such as G266.2−1.2 and G347.3−0.5 are the potential neutrino sources whose neutrinos are most likely to be identified by next-generation km 3 neutrino telescopes.

Analytical solutions for energy spectra of electrons accelerated by nonrelativistic shock-waves in shell type supernova remnants

Context.Recent observations of hard X-rays and very high energy gamma-rays from a number of young shell type supernova remnants indicate the importance of detailed quantitative studies of energy spectra of relativistic electrons formed via diffusive shock acceleration accompanied by intense nonthermal emission through synchrotron radiation and inverse Compton scattering.

Galactic acceleration phenomena

AbstractI review the current status of our observational knowledge of prominent classes of particle accelerators in the Galaxy, namely shell-type supernova remnants (SNRs) and pulsar wind nebulae. I highlight in particular the contribution of the recent improvement in sensitivity of very-high-energy (VHE) γ-ray observations, which are currently the most direct probe of particle acceleration in the Galaxy up to energies of several hundreds of TeV.Shell-type SNRs have long been proposed as sources of the Galactic cosmic rays. In recent years, X-ray observations have revealed very thin, non-thermal rims in many young SNRs, and I discuss the implications of these observations for magnetic field amplification and the maximum particle energy attainable by acceleration at the blast wave. I then review the current status of the evidence for accelerated nuclei in these objects, and summarise current uncertainties.The most numerous class of identified Galactic VHE gamma-ray sources is currently that of pulsar wind nebulae (PWNe). The emission from these objects is generally assumed to be predominantly leptonic, and I outline the new information provided by VHE gamma-ray observations beyond what could be inferred from observations of synchrotron emission.

Discovery of a Radio Supernova Remnant and Nonthermal X-Rays Coincident with the TeV Source HESS J1813-178

We present the discovery of nonthermal radio and X-ray emission positionally coincident with the TeV gamma-ray source HESS J1813-178. We demonstrate that the nonthermal radio emission is due to a young shell-type supernova remnant (SNR), G12.8-0.0, and constrain its distance to be greater than 4 kpc. The X-ray emission is primarily nonthermal and is consistent with either an SNR shell or unidentified pulsar or pulsar wind nebula origin; pulsed emission is not detected in archival ASCA data. A simple synchrotron plus inverse Compton model for the broadband emission assuming that all of the emission arises from the SNR shell implies maximum energies of (30-450)[B/(10 μG)]-0.5 TeV. Further observations are needed in order to confirm that the broadband emission has a common origin and to better constrain the X-ray spectrum.