Historical Supernova Remnant Research Articles

Does or Did the Supernova Remnant Cassiopeia A Operate as a PeVatron?

For decades, supernova remnants (SNRs) have been considered the prime sources of Galactic cosmic rays (CRs). But whether SNRs can accelerate CR protons to PeV energies and thus dominate CR flux up to the knee is currently under intensive theoretical and phenomenological debate. The direct test of the ability of SNRs to operate as CR PeVatrons can be provided by ultrahigh-energy (UHE; E γ ≥ 100 TeV) γ-rays. In this context, the historical SNR Cassiopeia A (Cas A) is considered one of the most promising targets for UHE observations. This paper presents the observation of Cas A and its vicinity by the LHAASO KM2A detector. The exceptional sensitivity of LHAASO KM2A in the UHE band, combined with the young age of Cas A, enabled us to derive stringent model-independent limits on the energy budget of UHE protons and nuclei accelerated by Cas A at any epoch after the explosion. The results challenge the prevailing paradigm that Cas A–type SNRs are major suppliers of PeV CRs in the Milky Way.

Systematic Study of Acceleration Efficiency in Young Supernova Remnants with Nonthermal X-Ray Observations

Abstract Cutoff energy in a synchrotron radiation spectrum of a supernova remnant (SNR) contains a key parameter of ongoing particle acceleration. We systematically analyze 11 young SNRs, including all historical SNRs, to measure the cutoff energy, thus shedding light on the nature of particle acceleration at the early stage of SNR evolution. The nonthermal (synchrotron) dominated spectra in filament-like outer rims are selectively extracted and used for spectral fitting because our model assumes that accelerated electrons are concentrated in the vicinity of the shock front owing to synchrotron cooling. The cutoff energy parameter (ε 0) and shock speed (v sh) are related as ε 0 ∝ v sh 2 η − 1 with a Bohm factor of η. Five SNRs provide us with spatially resolved ε 0–v sh plots across the remnants, indicating a variety of particle acceleration. With all SNRs considered together, the systematic tendency of η clarifies a correlation between η and an age of t (or an expansion parameter of m) as η ∝ t −0.4 (η ∝ m 4). This might be interpreted as the magnetic field becomes more turbulent and self-generated, as particles are accelerated at a greater rate with time. The maximum energy achieved in SNRs can be higher if we consider the newly observed time dependence on η.

High-energy gamma-ray study of the dynamically young SNR G150.3+4.5

Aims. The supernova remnant (SNR) G150.3+4.5 was recently discovered in the radio band; it exhibits a shell-like morphology with an angular size of ~ 3°, suggesting either an old or a nearby SNR. Extended γ-ray emission spatially coincident with the SNR was reported in the Fermi Galactic Extended Source Catalog, with a power-law spectral index of Γ = 1.91 ± 0.09. Studying particle acceleration in SNRs through their γ-ray emission is of primary concern to assess the nature of accelerated particles and the maximum energy they can reach. Methods. Using more than ten years of Fermi-LAT data, we investigate the morphological and spectral properties of the SNR G150.3+4.5 from 300 MeV to 3 TeV. We use the latest releases of the Fermi-LAT catalog, the instrument response functions and the Galactic and isotropic diffuse emissions. We use ROSAT all-sky survey data to assess any thermal and nonthermal X-ray emission, and we derive minimum and maximum distance to G150.3+4.5. Results. We describe the γ-ray emission of G150.3+4.5 by an extended component which is found to be spatially coincident with the radio SNR. The spectrum is hard and the detection of photons up to hundreds of GeV points towards an emission from a dynamically young SNR. The lack of X-ray emission gives a tight constraint on the ambient density n0 ≤ 3.6 × 10−3 cm−3. Since G150.3+4.5 is not reported as a historical SNR, we impose a lower limit on its age of t = 1 kyr. We estimate its distance to be between 0.7 and 4.5 kpc. We find that G150.3+4.5 is spectrally similar to other dynamically young and shell-type SNRs, such as RX J1713.7−3946 or Vela Junior. The broadband nonthermal emission is explained with a leptonic scenario, implying a downstream magnetic field of B = 5 μG and acceleration of particles up to few TeV energies.

Emission Measures and Emission-measure-weighted Temperatures of Shocked Interstellar Medium and Ejecta in Supernova Remnants

Abstract A goal of supernova remnant (SNR) evolution models is to relate fundamental parameters of a supernova (SN) explosion and progenitor star to the current state of its SNR. The SNR hot plasma is characterized by its observed X-ray spectrum, which yields electron temperature, emission measure (EM), and abundances. Depending on their brightness, the properties of the plasmas heated by the SNR forward shock, reverse shock, or both can be measured. The current work uses models that are spherically symmetric. One-dimensional hydrodynamic simulations are carried out for SNR evolution prior to onset of radiative losses. From these, we derive dimensionless EMs and EM-weighted temperatures, and we present fitting formulae for these quantities as functions of scaled SNR time. These models allow one to infer SNR explosion energy, circumstellar medium density, age, ejecta mass, and ejecta density profile from SNR observations. The new results are incorporated into the SNR modeling code SNRPy. The code is demonstrated with application to three historical SNRs: Kepler, Tycho, and SN1006.

A cut-off in the TeV gamma-ray spectrum of the SNR Cassiopeia A

It is widely believed that the bulk of the Galactic cosmic rays are accelerated in supernova remnants (SNRs). However, no observational evidence of the presence of particles of PeV energies in SNRs has yet been found. The young historical SNR Cassiopeia A (Cas A) appears as one of the best candidates to study acceleration processes. Between December 2014 and October 2016 we observed Cas A with the MAGIC telescopes, accumulating 158 hours of good-quality data. We derived the spectrum of the source from 100 GeV to 10 TeV. We also analysed $\sim$8 years of $Fermi$-LAT to obtain the spectral shape between 60 MeV and 500 GeV. The spectra measured by the LAT and MAGIC telescopes are compatible within the errors and show a clear turn off (4.6 $\sigma$) at the highest energies, which can be described with an exponential cut-off at $E_c = 3.5\left(^{+1.6}_{-1.0}\right)_{\textit{stat}} \left(^{+0.8}_{-0.9}\right)_{\textit{sys}}$ TeV. The gamma-ray emission from 60 MeV to 10 TeV can be attributed to a population of high-energy protons with spectral index $\sim$2.2 and energy cut-off at $\sim$10 TeV. This result indicates that Cas A is not contributing to the high energy ($\sim$PeV) cosmic-ray sea in a significant manner at the present moment. A one-zone leptonic model fails to reproduce by itself the multi-wavelength spectral energy distribution. Besides, if a non-negligible fraction of the flux seen by MAGIC is produced by leptons, the radiation should be emitted in a region with a low magnetic field (B$\lessapprox$100$\mu$G) like in the reverse shock.)

Large-field CO (1–0) observations toward the Galactic historical supernova remnants: a large cavity aroundTycho’s supernova remnant

The investigation of the interaction between the supernova remnants (SNRs) and interstellar gas is not only necessary to improve our knowledge of SNRs, but also to understand the nature of the progenitor systems. As a part of the Milky Way Imaging Scroll Painting CO line survey (MWISP), we study the interstellar gas surrounding the Galactic historical SNRs, using the PMO 13.7-meter telescope. In this work, we present large-field (3$^\circ$$\times$2$^\circ$) and high-sensitivity CO(1-0) molecular line observations toward Tycho's SNR. The CO observations reveal, from the outside in, large molecular clouds, stream-like structures, and an inner rim around Tycho's SNR. We derived the basic properties (column density, mass, and kinematics) of these objects based on the CO observations. The large molecular clouds individually show an arc toward the remnant center, outlining a large cavity with radii of $\sim$0.3$^\circ$$\times$0.6$^\circ$ (or 13 pc $\times$27 pc at a distance of 2.5 kpc) around the remnant. The CO line broadenings and asymmetries detected in the surrounding clouds, the observed expansion of the cavity, in concert with enhanced $^{12}$CO(2-1)/(1-0) intensity ratio detected in previous studies, suggest the interaction of the large cavity with a wind in the region. After excluding the scenario of a large bubble produced by bright massive stars, we suggest that the large cavity could be explained by accretion wind from the progenitor system of Tycho's supernova. Nevertheless, the possibility of the random distribution of a large cavity around Tycho's SNR cannot be ruled out thus far. Further observations are needed to confirm the physical association of the large cavity with Tycho's SNR.

THE LIKELY FERMI DETECTION OF THE SUPERNOVA REMNANT SN 1006

ABSTRACT We report the likely detection of γ-ray emission from the northeast shell region of the historical supernova remnant (SNR) SN 1006. Having analyzed seven years of Fermi Large Area Telescope Pass 8 data for the region of SN 1006, we found a GeV gamma-ray source detected with significance. Both the position and spectrum of the source match those of HESS J1504−418, respectively, which is TeV emission from SN 1006. Considering the source as the GeV γ-ray counterpart to SN 1006, the broadband spectral energy distribution is found to be approximately consistent with the leptonic scenario that has been proposed for the TeV emission from the SNR. Our result has likely confirmed the previous study of the SNRs with TeV shell-like morphology: SN 1006 is one of them sharing very similar peak luminosity and spectral shape.

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.

Cosmic-ray acceleration and escape from supernova remnants

Galactic cosmic ray (CR) acceleration to the knee in the spectrum at a few PeV is only possible if the magnetic field ahead of a supernova remnant (SNR) shock is strongly amplified by CR escaping the SNR. A model formulated in terms of the electric charge carried by escaping CR predicts the maximum CR energy and the energy spectrum of CR released into the surrounding medium. We find that historical SNR such as Cas A, Tycho and Kepler may be expanding too slowly to accelerate CR to the knee at the present time.

Cosmic ray production in Historical Supernova Remnants

We present the results of observations of two types of Galactic supernova remnants with the SHALON mirror Cherenkov telescope of Tien-Shan high-mountain Observatory: the shell-type supernova remnants Tycho, Cas A and IC 443; plerions Crab Nebula, 3c58(SN1181) and Geminga (probably plerion). The experimental data have confirmed the prediction of the theory about the hadronic generation mechanism of very high energy (800 GeV − 100 TeV) gamma-rays in Tycho's supernova remnant. The data obtained suggest that the very high energy gamma-ray emission in the objects being discussed is different in origin.

Generation of Cosmic rays in Historical Supernova Remnants

Generation of Cosmic rays in Historical Supernova Remnants

Generation of Cosmic rays in Historical Supernova Remnants

We present the results of observations of two types of Galactic supernova remnants with the SHALON mirror Cherenkov telescope of Tien-Shan high-mountain Observatory: the shell-type supernova remnants Tycho, Cas A and IC 443; plerions Crab Nebula, 3c58(SN1181) and Geminga (probably plerion). The experimental data have confirmed the prediction of the theory about the hadronic generation mechanism of very high energy (800 GeV - 100 TeV) gamma-rays in Tycho's supernova remnant. The data obtainedsuggest that the very high energy gamma-ray emission in the objects being discussedis different in origin.

On the nature of the TeV emission from the supernova remnant SN 1006

We present a simple model for the non-thermal emission from the historical supernova remnant SN 1006. We constrain the synchrotron parameters of the model with archival radio and hard X-ray data. Our stationary emission model includes two populations of electrons, which is justified by multi-frequency images of the object. From the set of parameters that predict the correct synchrotron flux we select those which are able to account, either partly or entirely, for the gamma-ray emission of the source as seen by HESS. We use the results from this model as well as the latest constraints imposed by the Fermi observatory and conclude that the TeV emission cannot be accounted for by neutral pion decay produced by high-energy cosmic rays with a single "soft" power-law distribution (i.e., with a particle index greater than 2 or so).

TYCHO SN 1572: A NAKED Ia SUPERNOVA REMNANT WITHOUT AN ASSOCIATED AMBIENT MOLECULAR CLOUD

The historical supernova remnant (SNR) Tycho SN 1572 originates from the explosion of a normal Type Ia supernova which is believed to have originated from a carbon-oxygen white dwarf in a binary system. We analyze the 21cm continuum, HI and 12CO-line data from the Canadian Galactic Plane Survey in the direction of SN 1572 and surrounding region. We construct HI absorption spectra to SN 1572 and three nearby compact sources. We conclude that SN 1572 has no molecular cloud interaction, which argues against previous claims that a molecular cloud is interacting with the SNR. This new result does not support a recent claim that dust, newly detected by AKARI, originates from such a SNR-cloud interaction. We suggest that the SNR has a kinematic distance of 2.5 - 3.0 kpc based on a nonlinear rotational curve model. Very-high-energy Gamma-ray emission from the remnant has been detected by the VERITAS telescope, so our result shows that its origin should not be an SNR-cloud interaction. Both radio and X-ray observations support that SN 1572 is an isolated Type Ia SNR.

Diffusive Shock Acceleration with Magnetic Amplification by Nonresonant Streaming Instability in Supernova Remnants

We investigate the diffusive shock acceleration in the presence of the nonresonant streaming instability introduced by Bell. The numerical MHD simulations of the magnetic field amplification combined with the analytical treatment of cosmic-ray acceleration permit us to calculate the maximum energy of particles accelerated by high-velocity supernova shocks. The estimates for the Cas A, Kepler, SN 1006, and Tycho historical supernova remnants are given. We also found that the amplified magnetic field is preferentially oriented perpendicular to the shock front downstream of the fast shock. This explains the origin of the radial magnetic fields observed in young supernova remnants.

The gas density around SN 1006

The density of the ambient medium where the supernova remnant evolves is a relevant parameter for its hydrodynamical evolution, for the mechanism of particle acceleration, and for the emission at TeV energies. Using XMM-Newton X-ray observations, we present a study of the ambient medium density of the historical supernova remnant SN 1006. We modelled the post-shock thermal emission to constrain the ambient medium density. Our study is focused on the North-West and the South-East rims of the remnant, where the thermal emission dominates. We used a plane-parallel shock plasma model plus another component for the ejecta that are not negligible in the regions of our study. The importance of the synchrotron component is also studied. In order to improve statistics, we combined several observations of the remnant. The density found in the South-East rim is low, roughly 0.05 cm-3, and seems to be representative of the rest of the remnant. However, in the North-West rim (close to the bright optical filament), the density is significantly higher (about 0.15-0.25 cm-3). This confirms a picture of SN 1006 evolving in a tenuous ambient medium, except in the North-West where the remnant has recently encountered a denser region. A density this low is compatible with the non-detection of the remnant by the HESS gamma-ray observatory. The lower density in the South-East implies a higher shock speed of 4900 km/s, higher than that of 2890 km/s measured in the North-West. This new estimate of the velocity could increase the maximum energy that accelerated particles can reach to energies of about 1 PeV.

Small-scale structure of non-thermal X-rays in historical SNRs

The shock fronts of supernova remnants (SNRs) are the most probable acceleration sites of high energy electrons (up to ∼100 TeV) with diffusive shock acceleration (DSA). However, the evolution of the acceleration in SNRs is still unclear. Using the Chandra archival data, we resolve the spatial structure of the shocked region of five historical SNRs (Cas A, Kepler, Tycho, SN 1006, and RCW 86) in non-thermal X-rays. The non-thermal emission concentrates on very thin and filamentary regions (“filaments”) in all SNRs, as already reported in the SN 1006 case. We also report on the time evolution of the scale length of the filaments and roll-off frequency of their spectra.

A Spatial and Spectral Study of Nonthermal Filaments in Historical Supernova Remnants: Observational Results withChandra

The outer shells of young supernova remnants (SNRs) are the most plausible acceleration sites of high-energy electrons with the diffusive shock acceleration (DSA) mechanism. We studied spatial and spectral properties close to the shock fronts in four historical SNRs (Cas A, Kepler's remnant, Tycho's remnant, and RCW 86) with excellent spatial resolution of Chandra. In all of the SNRs, hard X-ray emissions were found on the rims of the SNRs, which concentrate in very narrow regions (so-called filaments); apparent scale widths on the upstream side are below or on the order of the point-spread function of Chandra, while they are 05-40'' (0.01-0.4 pc) on the downstream side with most reliable distances. The spectra of these filaments can be fitted with both thermal and nonthermal (power law and SRCUT) models. The former requires unrealistic high temperature (2 keV) and low abundances (1 solar) for emission from young SNRs and may be thus unlikely. The latter reproduces the spectra with best-fit photon indices of 2.1-3.8, or roll-off frequencies of (0.1-28) × 1017 Hz, which reminds us of the synchrotron emission from electrons accelerated via DSA. We consider various physical parameters as functions of the SNR age, including the previous results on SN 1006; the filament width on the downstream side increases with the SNR age, and the spectrum becomes softer, keeping a nonthermal feature. It was also found that a function, that is, the roll-off frequency divided by the square of the scale width on the downstream side, shows negative correlation with the age, which might provide us some information on the DSA theory.

THE ENVIRONMENT OF TYCHO: POSSIBLE INTERACTION WITH A MOLECULAR CLOUD

The Tycho supernova remnant (SNR), as one of the few historical SNRs, has been widely studied in various wavebands and previous observations have shown evidence that Tycho is interacting with a dense ambient medium toward the northeast direction, In this paper, we report our high-resolution (16`) observation of the remnant using the Nobeyama 45m radio telescope. The Nobeyama data shows that a large molecular cloud surrounds the SNR along the northeastern boundary. We suggest that the Tycho SNR and the molecular cloud are both located in the Perseus arm and that the dense medium interacting with the SNR is possibly the molecular cloud. We also discuss the possible connection between the molecular cloud and the Balmer-dominated optical filaments, and suggest that the preshock gas may be accelerated within the cosmic ray and/or fast neutral precursor.

The Environment of Tycho: Possible Interaction with the Molecular Cloud

Tycho's supernova remnant (SNR), as one of the few historical SNRs, has been widely studied in various wave bands. Observations show evidence that Tycho is expanding in a medium with density gradient and possibly interacting with a dense ambient medium toward the northeast direction. From the FCRAO CO survey of the outer Galaxy, we have identified a patch of molecular clouds in this area and have conducted a follow-up observation with the Nobeyama 45 m radio telescope. The high-resolution (16'') Nobeyama data show that a large molecular cloud surrounds the SNR along the northeastern boundary. We suggest that Tycho's SNR and the molecular cloud are located in the Perseus arm and that the dense medium interacting with the SNR is possibly the molecular cloud. We also discuss the possible connection between the molecular cloud and the Balmer-dominated optical filaments and suggest that the preshock gas may be accelerated within the cosmic-ray and/or fast neutral precursor.